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Sample records for les colloides radioactifs

  1. Colloidal Phenomena.

    ERIC Educational Resources Information Center

    Russel, William B.; And Others

    1979-01-01

    Described is a graduate level engineering course offered at Princeton University in colloidal phenomena stressing the physical and dynamical side of colloid science. The course outline, reading list, and requirements are presented. (BT)

  2. Active colloids

    NASA Astrophysics Data System (ADS)

    Aranson, Igor S.

    2013-01-01

    A colloidal suspension is a heterogeneous fluid containing solid microscopic particles. Colloids play an important role in our everyday life, from food and pharmaceutical industries to medicine and nanotechnology. It is useful to distinguish two major classes of colloidal suspensions: equilibrium and active, i.e., maintained out of thermodynamic equilibrium by external electric or magnetic fields, light, chemical reactions, or hydrodynamic shear flow. While the properties of equilibrium colloidal suspensions are fairly well understood, active colloids pose a formidable challenge, and the research is in its early exploratory stage. One of the most remarkable properties of active colloids is the possibility of dynamic self-assembly, a natural tendency of simple building blocks to organize into complex functional architectures. Examples range from tunable, self-healing colloidal crystals and membranes to self-assembled microswimmers and robots. Active colloidal suspensions may exhibit material properties not present in their equilibrium counterparts, e.g., reduced viscosity and enhanced self-diffusivity, etc. This study surveys the most recent developments in the physics of active colloids, both in synthetic and living systems, with the aim of elucidation of the fundamental physical mechanisms governing self-assembly and collective behavior.

  3. Colloidal polypyrrole

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized aromatic heterocyclic monomer, a stabilizing effective amount of a vinyl pyridine-containing polymer and dopant anions and a method of preparing such polymer compositions are disclosed.

  4. Hexadecapolar colloids

    NASA Astrophysics Data System (ADS)

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of `colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

  5. Hexadecapolar colloids

    PubMed Central

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-01-01

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and f-orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms' displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. Here we describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and describe the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously. PMID:26864184

  6. Hexadecapolar Colloids

    DOE PAGES

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; ...

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Becausemore » of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.« less

  7. Hexadecapolar Colloids

    SciTech Connect

    Senyuk, Bohdan; Puls, Owen; Tovkach, Oleh M.; Chernyshuk, Stanislav B.; Smalyukh, Ivan I.

    2016-02-11

    Outermost occupied electron shells of chemical elements can have symmetries resembling that of monopoles, dipoles, quadrupoles and octupoles corresponding to filled s-, p-, d- and forbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known elements have filled g-orbitals. On the other hand, the research paradigm of ‘colloidal atoms’ displays complexity of particle behaviour exceeding that of atomic counterparts, which is driven by DNA functionalization, geometric shape and topology and weak external stimuli. We describe elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. Because of conically degenerate boundary conditions, the solid microspheres locally perturb the alignment of the nematic host, inducing hexadecapolar distortions that drive anisotropic colloidal interactions. We uncover physical underpinnings of formation of colloidal elastic hexadecapoles and report the ensuing bonding inaccessible to elastic dipoles, quadrupoles and other nematic colloids studied previously.

  8. Colloidal polyaniline

    DOEpatents

    Armes, Steven P.; Aldissi, Mahmoud

    1990-01-01

    Processable electrically conductive latex polymer compositions including colloidal particles of an oxidized, polymerized amino-substituted aromatic monomer, a stabilizing effective amount of a random copolymer containing amino-benzene type moieties as side chain constituents, and dopant anions, and a method of preparing such polymer compositions are provided.

  9. Soil colloidal behavior

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Recent understanding that organic and inorganic contaminants are often transported via colloidal particles has increased interest in colloid science. The primary importance of colloids in soil science stems from their surface reactivity and charge characteristics. Characterizations of size, shape,...

  10. EDITORIAL: Colloidal suspensions Colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Petukhov, Andrei; Kegel, Willem; van Duijneveldt, Jeroen

    2011-05-01

    Special issue in honour of Henk Lekkerkerker's 65th birthday Professor Henk N W Lekkerkerker is a world-leading authority in the field of experimental and theoretical soft condensed matter. On the occasion of his 65th birthday in the summer of 2011, this special issue celebrates his many contributions to science. Henk Lekkerkerker obtained his undergraduate degree in chemistry at the University of Utrecht (1968) and moved to Calgary where he received his PhD in 1971. He moved to Brussels as a NATO fellow at the Université Libre de Bruxelles and was appointed to an assistant professorship (1974), an associate professorship (1977) and a full professorship (1980) in physical chemistry at the Vrije Universiteit Brussel. In 1985 he returned to The Netherlands to take up a professorship at the Van 't Hoff Laboratory, where he has been ever since. He has received a series of awards during his career, including the Onsager Medal (1999) of the University of Trondheim, the Bakhuys Roozeboom Gold Medal (2003) of the Royal Dutch Academy of Arts and Sciences (KNAW), the ECIS-Rhodia European Colloid and Interface Prize (2003), and the Liquid Matter Prize of the European Physical Society (2008). He was elected a member of KNAW in 1996, was awarded an Academy Chair position in 2005, and has held several visiting lectureships. Henk's work focuses on phase transitions in soft condensed matter, and he has made seminal contributions to both the theoretical and experimental aspects of this field. Here we highlight three major themes running through his work, and a few selected publications. So-called depletion interactions may lead to phase separation in colloid-polymer mixtures, and Henk realised that the partitioning of polymer needs to be taken into account to describe the phase behaviour correctly [1]. Colloidal suspensions can be used as model fluids, with the time- and length-scales involved leading to novel opportunities, notably the direct observation of capillary waves at a

  11. What Is a Colloid?

    ERIC Educational Resources Information Center

    Lamb, William G.

    1985-01-01

    Describes the properties of colloids, listing those commonly encountered (such as whipped cream, mayonnaise, and fog). Also presents several experiments using colloids and discusses "Silly Putty," a colloid with viscoelastic properties whose counterintuitive properties result from its mixture of polymers. (DH)

  12. Electrohydrodynamically patterned colloidal crystals

    NASA Technical Reports Server (NTRS)

    Hayward, Ryan C. (Inventor); Poon, Hak F. (Inventor); Xiao, Yi (Inventor); Saville, Dudley A. (Inventor); Aksay, Ilhan A. (Inventor)

    2003-01-01

    A method for assembling patterned crystalline arrays of colloidal particles using ultraviolet illumination of an optically-sensitive semiconducting anode while using the anode to apply an electronic field to the colloidal particles. The ultraviolet illumination increases current density, and consequently, the flow of the colloidal particles. As a result, colloidal particles can be caused to migrate from non-illuminated areas of the anode to illuminated areas of the anode. Selective illumination of the anode can also be used to permanently affix colloidal crystals to illuminated areas of the anode while not affixing them to non-illuminated areas of the anode.

  13. Saturated Zone Colloid Transport

    SciTech Connect

    H. Viswanathan; P. Reimus

    2003-09-05

    Colloid retardation is influenced by the attachment and detachment of colloids from immobile surfaces. This analysis demonstrates the development of parameters necessary to estimate attachment and detachment of colloids and, hence, retardation in both fractured tuff and porous alluvium. Field and experimental data specific to fractured tuff are used for the analysis of colloid retardation in fractured tuff. Experimental data specific to colloid transport in alluvial material from Yucca Mountain as well as bacteriophage field studies in alluvial material, which are thought to be good analogs for colloid transport, are used to estimate attachment and detachment of colloids in the alluvial material. There are no alternative scientific approaches or technical methods for calculating these retardation factors.

  14. Microfluidic colloid filtration

    NASA Astrophysics Data System (ADS)

    Linkhorst, John; Beckmann, Torsten; Go, Dennis; Kuehne, Alexander J. C.; Wessling, Matthias

    2016-03-01

    Filtration of natural and colloidal matter is an essential process in today’s water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a “cake layer” – often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

  15. Saturated Zone Colloid Transport

    SciTech Connect

    H. S. Viswanathan

    2004-10-07

    This scientific analysis provides retardation factors for colloids transporting in the saturated zone (SZ) and the unsaturated zone (UZ). These retardation factors represent the reversible chemical and physical filtration of colloids in the SZ. The value of the colloid retardation factor, R{sub col} is dependent on several factors, such as colloid size, colloid type, and geochemical conditions (e.g., pH, Eh, and ionic strength). These factors are folded into the distributions of R{sub col} that have been developed from field and experimental data collected under varying geochemical conditions with different colloid types and sizes. Attachment rate constants, k{sub att}, and detachment rate constants, k{sub det}, of colloids to the fracture surface have been measured for the fractured volcanics, and separate R{sub col} uncertainty distributions have been developed for attachment and detachment to clastic material and mineral grains in the alluvium. Radionuclides such as plutonium and americium sorb mostly (90 to 99 percent) irreversibly to colloids (BSC 2004 [DIRS 170025], Section 6.3.3.2). The colloid retardation factors developed in this analysis are needed to simulate the transport of radionuclides that are irreversibly sorbed onto colloids; this transport is discussed in the model report ''Site-Scale Saturated Zone Transport'' (BSC 2004 [DIRS 170036]). Although it is not exclusive to any particular radionuclide release scenario, this scientific analysis especially addresses those scenarios pertaining to evidence from waste-degradation experiments, which indicate that plutonium and americium may be irreversibly attached to colloids for the time scales of interest. A section of this report will also discuss the validity of using microspheres as analogs to colloids in some of the lab and field experiments used to obtain the colloid retardation factors. In addition, a small fraction of colloids travels with the groundwater without any significant retardation

  16. Ring around the colloid

    NASA Astrophysics Data System (ADS)

    Cavallaro, Marcello, Jr.; Gharbi, Mohamed A.; Beller, Daniel A.; Čopar, Simon; Shi, Zheng; Kamien, Randall D.; Yang, Shu; Baumgart, Tobias; Stebe, Kathleen J.

    In this work, we show that Janus washers, genus-one colloids with hybrid anchoring conditions, form topologically required defects in nematic liquid crystals. Experiments under crossed polarizers reveal the defect structure to be a rigid disclination loop confined within the colloid, with an accompanying defect in the liquid crystal. When confined to a homeotropic cell, the resulting colloid-defect ring pair tilts relative to the far field director, in contrast to the behavior of toroidal colloids with purely homeotropic anchoring. We show that this tilting behavior can be reversibly suppressed by the introduction of a spherical colloid into the center of the toroid, creating a new kind of multi-shape colloidal assemblage.

  17. UZ Colloid Transport Model

    SciTech Connect

    M. McGraw

    2000-04-13

    The UZ Colloid Transport model development plan states that the objective of this Analysis/Model Report (AMR) is to document the development of a model for simulating unsaturated colloid transport. This objective includes the following: (1) use of a process level model to evaluate the potential mechanisms for colloid transport at Yucca Mountain; (2) Provide ranges of parameters for significant colloid transport processes to Performance Assessment (PA) for the unsaturated zone (UZ); (3) Provide a basis for development of an abstracted model for use in PA calculations.

  18. Pituitary Colloid Cyst

    PubMed Central

    Guduk, Mustafa; Sun, Halil Ibrahim; Sav, Murat Aydin; Berkman, Zafer

    2017-01-01

    Abstract Colloid cysts appear most commonly in the third ventricle, their occurrence in the sellar region is uncommon. The authors report a female patient with a pituitary colloid cyst. She was diagnosed incidentally with a sellar lesion by a routine paranasal computed tomography examination performed for planning of a dental implant surgery. Radiologic examinations revealed a pituitary lesion that was removed by transnasal transsphenoidal route. Her pathologic examination revealed that the lesion was a colloid cyst. Although rare, colloid cysts should be considered in the differential diagnosis of pituitary lesions PMID:27792102

  19. Analysis of colloid transport

    SciTech Connect

    Travis, B.J.; Nuttall, H.E.

    1985-12-31

    The population balance methodology is described and applied to the transport and capture of polydispersed colloids in packed columns. The transient model includes particle growth, capture, convective transport, and dispersion. We also follow the dynamic accumulation of captured colloids on the solids. The multidimensional parabolic partial differential equation was solved by a recently enhanced method of characteristics technique. This computational technique minimized numerical dispersion and is computationally very fast. The FORTRAN 77 code ran on a VAX-780 in less than a minute and also runs on an IBM-AT using the Professional FORTRAN compiler. The code was extensively tested against various simplified cases and against analytical models. The packed column experiments by Saltelli et al. were re-analyzed incorporating the experimentally reported size distribution of the colloid feed material. Colloid capture was modeled using a linear size dependent filtration function. The effects of a colloid size dependent filtration factor and various initial colloid size distributions on colloid migration and capture were investigated. Also, we followed the changing colloid size distribution as a function of position in the column. Some simple arguments are made to assess the likelihood of colloid migration at a potential NTS Yucca Mountain waste disposal site. 10 refs., 3 figs., 1 tab.

  20. Interface colloidal robotic manipulator

    DOEpatents

    Aronson, Igor; Snezhko, Oleksiy

    2015-08-04

    A magnetic colloidal system confined at the interface between two immiscible liquids and energized by an alternating magnetic field dynamically self-assembles into localized asters and arrays of asters. The colloidal system exhibits locomotion and shape change. By controlling a small external magnetic field applied parallel to the interface, structures can capture, transport, and position target particles.

  1. Driving magnetic colloidal polymers

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua; Olvera de La Cruz, Monica

    Magnetic colloids are of growing interest for applications such as drug delivery and in vitro tissue growth. Recent experiments have synthesized 1D chains of magnetic colloids into permanent colloidal polymers. We study magnetic colloidal polymers theoretically and computationally under the influence of time-varying external fields and find a rich set of controllable, dynamic conformations. By iterating through a sequence of conformations, these polymers can perform mechanical functions. We discuss possible roles for these polymers beyond those considered for single colloids. This work was supported as part of the Center for Bio-Inspired Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0000989.

  2. Lock and key colloids.

    PubMed

    Sacanna, S; Irvine, W T M; Chaikin, P M; Pine, D J

    2010-03-25

    New functional materials can in principle be created using colloids that self-assemble into a desired structure by means of a programmable recognition and binding scheme. This idea has been explored by attaching 'programmed' DNA strands to nanometre- and micrometre- sized particles and then using DNA hybridization to direct the placement of the particles in the final assembly. Here we demonstrate an alternative recognition mechanism for directing the assembly of composite structures, based on particles with complementary shapes. Our system, which uses Fischer's lock-and-key principle, employs colloidal spheres as keys and monodisperse colloidal particles with a spherical cavity as locks that bind spontaneously and reversibly via the depletion interaction. The lock-and-key binding is specific because it is controlled by how closely the size of a spherical colloidal key particle matches the radius of the spherical cavity of the lock particle. The strength of the binding can be further tuned by adjusting the solution composition or temperature. The composite assemblies have the unique feature of having flexible bonds, allowing us to produce flexible dimeric, trimeric and tetrameric colloidal molecules as well as more complex colloidal polymers. We expect that this lock-and-key recognition mechanism will find wider use as a means of programming and directing colloidal self-assembly.

  3. Sampling colloids and colloid-associated contaminants in ground water

    USGS Publications Warehouse

    Backhus, Debera A.; Ryan, Joseph N.; Groher, Daniel M.; MacFarlane, John K.; Gschwend, Philip M.

    1993-01-01

    It has recently been recognized that mobile colloids may affect the transport of contaminants in ground water. To determine the significance of this process, knowledge of both the total mobile load (dissolved + colloid-associated) and the dissolved concentration of a ground-water contaminant must be obtained. Additional information regarding mobile colloid characteristics and concentrations are required to predict accurately the fate and effects of contaminants at sites where significant quantities of colloids are found. To obtain this information, a sampling scheme has been designed and refined to collect mobile colloids while avoiding the inclusion of normally immobile subsurface and well-derived solids. The effectiveness of this sampling protocol was evaluated at a number of contaminated and pristine sites.The sampling results indicated that slow, prolonged pumping of ground water is much more effective at obtaining ground-water samples that represent in situ colloid populations than bailing. Bailed samples from a coal tar-contaminated site contained 10–100 times greater colloid concentrations and up to 750 times greater polycyclic aromatic hydrocarbon concentrations as were detected in slowly pumped samples. The sampling results also indicated that ground-water colloid concentrations should be monitored in the field to determine the adequacy of purging if colloid and colloid-associated contaminants are of interest. To avoid changes in the natural ground-water colloid population through precipitation or coagulation, in situ ground-water chemistry conditions must be preserved during sampling and storage. Samples collected for determination of the total mobile load of colloids and low-solubility contaminants must not be filtered because some mobile colloids are removed by this process. Finally, suggestions that mobile colloids are present in ground water at any particular site should be corroborated with auxiliary data, such as colloid levels in

  4. Spherical colloidal photonic crystals.

    PubMed

    Zhao, Yuanjin; Shang, Luoran; Cheng, Yao; Gu, Zhongze

    2014-12-16

    CONSPECTUS: Colloidal photonic crystals (PhCs), periodically arranged monodisperse nanoparticles, have emerged as one of the most promising materials for light manipulation because of their photonic band gaps (PBGs), which affect photons in a manner similar to the effect of semiconductor energy band gaps on electrons. The PBGs arise due to the periodic modulation of the refractive index between the building nanoparticles and the surrounding medium in space with subwavelength period. This leads to light with certain wavelengths or frequencies located in the PBG being prohibited from propagating. Because of this special property, the fabrication and application of colloidal PhCs have attracted increasing interest from researchers. The most simple and economical method for fabrication of colloidal PhCs is the bottom-up approach of nanoparticle self-assembly. Common colloidal PhCs from this approach in nature are gem opals, which are made from the ordered assembly and deposition of spherical silica nanoparticles after years of siliceous sedimentation and compression. Besides naturally occurring opals, a variety of manmade colloidal PhCs with thin film or bulk morphology have also been developed. In principle, because of the effect of Bragg diffraction, these PhC materials show different structural colors when observed from different angles, resulting in brilliant colors and important applications. However, this angle dependence is disadvantageous for the construction of some optical materials and devices in which wide viewing angles are desired. Recently, a series of colloidal PhC materials with spherical macroscopic morphology have been created. Because of their spherical symmetry, the PBGs of spherical colloidal PhCs are independent of rotation under illumination of the surface at a fixed incident angle of the light, broadening the perspective of their applications. Based on droplet templates containing colloidal nanoparticles, these spherical colloidal PhCs can be

  5. Les jeux de hasard chez les enfants et les adolescents

    PubMed Central

    Gupta, Rina; Pinzon, Jorge L

    2012-01-01

    RÉSUMÉ Même si, au Canada, les mineurs n’ont pas le droit de jouer à des jeux de hasard légalisés, les adolescents participent souvent à des jeux de hasard soit légalisés (produits de loterie, casino, terminaux de jeux vidéo), soit autonomes (jeux de cartes, paris sportifs, dés) à la maison et en milieu scolaire. Chez les adultes, le taux de prévalence de dépendance aux jeux de hasard au cours de la vie se situe entre 1 % et 2 %. D’après les données existantes, la prévalence chez les adolescents serait de deux à quatre fois plus élevée. On ne sait pas grand-chose des facteurs de risque d’apparition et de perpétuation d’une dépendance pathologique aux jeux de hasard. Le présent document de principes vise à informer les pédiatres, les médecins de famille et les autres professionnels de la santé des connaissances émergentes sur les jeux de hasard pendant l’enfance et l’adolescence et du risque de conséquences graves qui s’y rattachent. On y exhorte également les gouvernements fédéral, provinciaux et territoriaux à inclure cette question dans leur programme et à tenir compte des facteurs sociopolitiques associés aux jeux de hasard.

  6. Cadarache LOR (liquides organiques radioactifs) treatment by a solidification process using NOCHAR polymers

    SciTech Connect

    Vaudey, Claire-Emilie; Renou, Sebastien; Kelley, Dennis; Cochaud, Chantal; Serrano, Roger

    2013-07-01

    In France, two options can be considered to handle the Very Low Level Waste (VLLW) and the Low Level Waste (LLW). The first one is the incineration at CENTRACO facility and the second one is the disposal at ANDRA sites. The waste acceptance in these two channels is dependent upon the adequacy between the waste characteristics (physical chemistry and radiological) and the channel specifications. If the waste characteristics and the channel specifications (presence of significant quantities of halogens, complexing agents, organic components... or/and high activity limits) are incompatible, an alternative solution have to be identify. It consists of a waste pre-treatment process. For Cadarache LOR (Liquides Organiques Radioactifs) waste streams, two radioactive scintillation cocktails have to be treated. They are composed of a mix of organic liquids and water: for the first one, 19 % of organic compounds (xylene, mesitylene, diphenyloxazole, TBP...) and 86.9 % of water, and for the second one, 23 % of organic compounds (TBP...) and 77 % of water. They contain halogens (chlorine and fluorine), complexants agents (nitrate, sulphate, oxalate and formate) and have got αβγ spectra with mass activities equal to some 100 Bq/g. Therefore, tritium is also present. As a consequence, in order for storage acceptance at the ANDRA site, it is necessary to pre-treat the waste. An adequate solution seems to be a solidification process using NOCHAR polymers. Indeed, NOCHAR polymers correspond to an important variety of products applied to the treatment of radioactive aqueous and organic liquids (solvent, oil, solvent/oil mixing ...) and sludge through a mechanical and chemical solidification process. For Cadarache LOR, N910 and N960 respectively dedicated to the organic and aqueous liquids solidification are considered. With the N910, the organic waste solidification occurs in two steps. As the organic liquid travels moves through the polymer strands, the strands swell and

  7. Viscosity of colloidal suspensions

    SciTech Connect

    Cohen, E.G.D.; Schepper, I.M. de

    1995-12-31

    Simple expressions are given for the effective Newtonian viscosity as a function of concentration as well as for the effective visco-elastic response as a function of concentration and imposed frequency, of monodisperse neutral colloidal suspensions over the entire fluid range. The basic physical mechanisms underlying these formulae are discussed. The agreement with existing experiments is very good.

  8. Nucleation in food colloids

    NASA Astrophysics Data System (ADS)

    Povey, Malcolm J. W.

    2016-12-01

    Nucleation in food colloids has been studied in detail using ultrasound spectroscopy. Our data show that classical nucleation theory (CNT) remains a sound basis from which to understand nucleation in food colloids and analogous model systems using n-alkanes. Various interpretations and modifications of CNT are discussed with regard to their relevance to food colloids. Much of the evidence presented is based on the ultrasound velocity spectrometry measurements which has many advantages for the study of nucleating systems compared to light scattering and NMR due to its sensitivity at low solid contents and its ability to measure true solid contents in the nucleation and early crystal growth stages. Ultrasound attenuation spectroscopy also responds to critical fluctuations in the induction region. We show, however, that a periodic pressure fluctuation such as a quasi-continuous (as opposed to a pulse comprising only a few pressure cycles) ultrasound field can alter the nucleation process, even at very low acoustic intensity. Thus care must be taken when using ultrasound techniques that the measurements do not alter the studied processes. Quasi-continuous ultrasound fields may enhance or suppress nucleation and the criteria to determine such effects are derived. The conclusions of this paper are relevant to colloidal systems in foods, pharmaceuticals, agro-chemicals, cosmetics, and personal products.

  9. COLLOIDS. Colloidal matter: Packing, geometry, and entropy.

    PubMed

    Manoharan, Vinothan N

    2015-08-28

    Colloidal particles with well-controlled shapes and interactions are an ideal experimental system for exploring how matter organizes itself. Like atoms and molecules, these particles form bulk phases such as liquids and crystals. But they are more than just crude analogs of atoms; they are a form of matter in their own right, with complex and interesting collective behavior not seen at the atomic scale. Their behavior is affected by geometrical or topological constraints, such as curved surfaces or the shapes of the particles. Because the interactions between the particles are often short-ranged, we can understand the effects of these constraints using geometrical concepts such as packing. The geometrical viewpoint gives us a window into how entropy affects not only the structure of matter, but also the dynamics of how it forms.

  10. Colloidal Double Quantum Dots

    PubMed Central

    2016-01-01

    Conspectus Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole–dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single

  11. Colloidal Double Quantum Dots.

    PubMed

    Teitelboim, Ayelet; Meir, Noga; Kazes, Miri; Oron, Dan

    2016-05-17

    Pairs of coupled quantum dots with controlled coupling between the two potential wells serve as an extremely rich system, exhibiting a plethora of optical phenomena that do not exist in each of the isolated constituent dots. Over the past decade, coupled quantum systems have been under extensive study in the context of epitaxially grown quantum dots (QDs), but only a handful of examples have been reported with colloidal QDs. This is mostly due to the difficulties in controllably growing nanoparticles that encapsulate within them two dots separated by an energetic barrier via colloidal synthesis methods. Recent advances in colloidal synthesis methods have enabled the first clear demonstrations of colloidal double quantum dots and allowed for the first exploratory studies into their optical properties. Nevertheless, colloidal double QDs can offer an extended level of structural manipulation that allows not only for a broader range of materials to be used as compared with epitaxially grown counterparts but also for more complex control over the coupling mechanisms and coupling strength between two spatially separated quantum dots. The photophysics of these nanostructures is governed by the balance between two coupling mechanisms. The first is via dipole-dipole interactions between the two constituent components, leading to energy transfer between them. The second is associated with overlap of excited carrier wave functions, leading to charge transfer and multicarrier interactions between the two components. The magnitude of the coupling between the two subcomponents is determined by the detailed potential landscape within the nanocrystals (NCs). One of the hallmarks of double QDs is the observation of dual-color emission from a single nanoparticle, which allows for detailed spectroscopy of their properties down to the single particle level. Furthermore, rational design of the two coupled subsystems enables one to tune the emission statistics from single photon

  12. Fractal nematic colloids

    PubMed Central

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter. PMID:28117325

  13. Fractal nematic colloids

    NASA Astrophysics Data System (ADS)

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter.

  14. Fractal nematic colloids.

    PubMed

    Hashemi, S M; Jagodič, U; Mozaffari, M R; Ejtehadi, M R; Muševič, I; Ravnik, M

    2017-01-24

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter.

  15. Colloidal Covalent Organic Frameworks

    PubMed Central

    2017-01-01

    Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material’s morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications. PMID:28149954

  16. Flocking ferromagnetic colloids

    PubMed Central

    Kaiser, Andreas; Snezhko, Alexey; Aranson, Igor S.

    2017-01-01

    Assemblages of microscopic colloidal particles exhibit fascinating collective motion when energized by electric or magnetic fields. The behaviors range from coherent vortical motion to phase separation and dynamic self-assembly. Although colloidal systems are relatively simple, understanding their collective response, especially under out-of-equilibrium conditions, remains elusive. We report on the emergence of flocking and global rotation in the system of rolling ferromagnetic microparticles energized by a vertical alternating magnetic field. By combing experiments and discrete particle simulations, we have identified primary physical mechanisms, leading to the emergence of large-scale collective motion: spontaneous symmetry breaking of the clockwise/counterclockwise particle rotation, collisional alignment of particle velocities, and random particle reorientations due to shape imperfections. We have also shown that hydrodynamic interactions between the particles do not have a qualitative effect on the collective dynamics. Our findings shed light on the onset of spatial and temporal coherence in a large class of active systems, both synthetic (colloids, swarms of robots, and biopolymers) and living (suspensions of bacteria, cell colonies, and bird flocks). PMID:28246633

  17. Increasing entropy for colloidal stabilization

    PubMed Central

    Mo, Songping; Shao, Xuefeng; Chen, Ying; Cheng, Zhengdong

    2016-01-01

    Stability is of paramount importance in colloidal applications. Attraction between colloidal particles is believed to lead to particle aggregation and phase separation; hence, stability improvement can be achieved through either increasing repulsion or reducing attraction by modifying the fluid medium or by using additives. Two traditional mechanisms for colloidal stability are electrostatic stabilization and steric stabilization. However, stability improvement by mixing attractive and unstable particles has rarely been considered. Here, we emphasize the function of mixing entropy in colloidal stabilization. Dispersion stability improvement is demonstrated by mixing suspensions of attractive nanosized titania spheres and platelets. A three-dimensional phase diagram is proposed to illustrate the collaborative effects of particle mixing and particle attraction on colloidal stability. This discovery provides a novel method for enhancing colloidal stability and opens a novel opportunity for engineering applications. PMID:27872473

  18. Equilibrium Shape of Colloidal Crystals.

    PubMed

    Sehgal, Ray M; Maroudas, Dimitrios

    2015-10-27

    Assembling colloidal particles into highly ordered configurations, such as photonic crystals, has significant potential for enabling a broad range of new technologies. Facilitating the nucleation of colloidal crystals and developing successful crystal growth strategies require a fundamental understanding of the equilibrium structure and morphology of small colloidal assemblies. Here, we report the results of a novel computational approach to determine the equilibrium shape of assemblies of colloidal particles that interact via an experimentally validated pair potential. While the well-known Wulff construction can accurately capture the equilibrium shape of large colloidal assemblies, containing O(10(4)) or more particles, determining the equilibrium shape of small colloidal assemblies of O(10) particles requires a generalized Wulff construction technique which we have developed for a proper description of equilibrium structure and morphology of small crystals. We identify and characterize fully several "magic" clusters which are significantly more stable than other similarly sized clusters.

  19. Increasing entropy for colloidal stabilization

    NASA Astrophysics Data System (ADS)

    Mo, Songping; Shao, Xuefeng; Chen, Ying; Cheng, Zhengdong

    2016-11-01

    Stability is of paramount importance in colloidal applications. Attraction between colloidal particles is believed to lead to particle aggregation and phase separation; hence, stability improvement can be achieved through either increasing repulsion or reducing attraction by modifying the fluid medium or by using additives. Two traditional mechanisms for colloidal stability are electrostatic stabilization and steric stabilization. However, stability improvement by mixing attractive and unstable particles has rarely been considered. Here, we emphasize the function of mixing entropy in colloidal stabilization. Dispersion stability improvement is demonstrated by mixing suspensions of attractive nanosized titania spheres and platelets. A three-dimensional phase diagram is proposed to illustrate the collaborative effects of particle mixing and particle attraction on colloidal stability. This discovery provides a novel method for enhancing colloidal stability and opens a novel opportunity for engineering applications.

  20. Colloidal Metamaterials at Optical Frequencies

    DTIC Science & Technology

    2014-07-18

    AFRL-OSR-VA-TR-2014-0184 Colloidal Metamaterials at Optical Frequencies Jennifer Dionne LELAND STANFORD JUNIOR UNIV CA Final Report 07/18/2014...Prescribed by ANSI Std. Z39.18 Colloidal Metamaterials at Optical Frequencies Annual Report, June 30, 2014 A. Investigators PI: Jennifer Dionne...team has combined theoretical and experimental methods to produce a colloidally -synthesized metamaterial fluid, or “metafluid,” exhibiting strong

  1. Physics of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Huang, Jiping

    Colloidal suspensions are complex fluids that consist of mesoscopic particles suspended in a solvent, e.g. water, oil, etc. In this thesis, the objective is to investigate the four aspects of colloidal suspensions: electrorotation, dielectrophoresis, dielectric dispersion spectrum, and nonlinear alternating current (AC) response. The traditional theories failed to fit the recent experimental data, and hence, for the purpose of a better fitting, we aim to develop new theories. In addition, our theories also predicted some new phenomena which are expected to be verified in experiments. Electrorotation has been increasingly employed as a sensitive tool for non-invasive studies of a broad variety of microparticles, ranging from living cells to spores and seeds, as well as synthetic materials. In order to analyze the abundant experimental data, we extend here the existing theory by taking into account crucial elements, such as inhomogeneities, multipolar interactions, nonspherical shapes as well as many-body (local-field) effects. Good agreement is shown between our theoretical results and the experimental data. Dielectrophoresis is typically used for micromanipulation and separation of biological cellular size particles, and it has recently been successfully applied to submicron size particles as well. Specific applications include diverse problems in medicine, colloidal science and nanotechnology. To analyze the recent experimental observations, we present a theory which includes the effects of both charging and multipolar interactions. Our theoretical results are favorably compared with the recent experimental observations. Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. However, the existing theory does not fit the experimental data. Hence, we here put

  2. Light-structured colloidal assemblies

    NASA Astrophysics Data System (ADS)

    Aubret, Antoine; Mena, Youssef; Ramananarivo, Sophie; Sacanna, Stefano; Palacci, Jeremie; Palacci lab Team; Sacanna lab Team

    2016-11-01

    Self-propelled particles (SPP) are a key tool since they are of relative simplicity as compared to biological micro-entities and provide a higher level of control. They can convert an energy source into motion and work, and exhibit surprising non-equilibrium behavior. In our work, we focus on the manipulation of colloids using light. We exploit osmotic and phoretic effects to act on single and ensemble of colloids. The key mechanism relies on the photocatalytic decomposition of hydrogen peroxide using hematite, which triggers the motion of colloids around it when illuminated. We use hematite particles and particles with photocatalytic inclusions (i.e. SPP). We first show that the interactions between hematite and colloidal tracers can be tuned by adjusting the chemical environment. Furthermore, we report a phototaxic behavior (migration in light gradient) of the particles. From this, we explore the effect of spatio-temporal modulation of the light to control the motion of colloids at the single particle level, and to generate self-assembled colloidal structures through time and space. The so-formed structures are maintained by phoretic and hydrodynamic forces resulting from the motion of each particles. Ultimately, a dynamic light modulation may be a route for the creation of active colloidal motion on a collective scale through the synchronization of the individual motions of SPP. This work is supported by NSF CAREER DMR 1554724.

  3. Clathrate colloidal crystals

    NASA Astrophysics Data System (ADS)

    Lin, Haixin; Lee, Sangmin; Sun, Lin; Spellings, Matthew; Engel, Michael; Glotzer, Sharon C.; Mirkin, Chad A.

    2017-03-01

    DNA-programmable assembly has been used to deliberately synthesize hundreds of different colloidal crystals spanning dozens of symmetries, but the complexity of the achieved structures has so far been limited to small unit cells. We assembled DNA-modified triangular bipyramids (~250-nanometer long edge, 177-nanometer short edge) into clathrate architectures. Electron microscopy images revealed that at least three different structures form as large single-domain architectures or as multidomain materials. Ordered assemblies, isostructural to clathrates, were identified with the help of molecular simulations and geometric analysis. These structures are the most sophisticated architectures made via programmable assembly, and their formation can be understood based on the shape of the nanoparticle building blocks and mode of DNA functionalization.

  4. Microfluidic control using colloidal devices.

    PubMed

    Terray, Alex; Oakey, John; Marr, David W M

    2002-06-07

    By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.

  5. Microfluidic Control Using Colloidal Devices

    NASA Astrophysics Data System (ADS)

    Terray, Alex; Oakey, John; Marr, David W. M.

    2002-06-01

    By manipulating colloidal microspheres within customized channels, we have created micrometer-scale fluid pumps and particulate valves. We describe two positive-displacement designs, a gear and a peristaltic pump, both of which are about the size of a human red blood cell. Two colloidal valve designs are also demonstrated, one actuated and one passive, for the direction of cells or small particles. The use of colloids as both valves and pumps will allow device integration at a density far beyond what is currently achievable by other approaches and may provide a link between fluid manipulation at the macro- and nanoscale.

  6. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, R.W.; Hines, J.J.

    1990-11-13

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints. No Drawings

  7. Method of making colloid labeled with radionuclide

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1991-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  8. Colloid labelled with radionuclide and method

    DOEpatents

    Atcher, Robert W.; Hines, John J.

    1990-01-01

    A ferric hydroxide colloid having an alpha-emitting radionuclide essentially on the outer surfaces and a method of forming same. The method includes oxidizing a ferrous hydroxide to ferric hydroxide in the presence of a preselected radionuclide to form a colloid having the radionuclide on the outer surface thereof, and thereafter washing the colloid, and suspending the washed colloid in a suitable solution. The labelled colloid is useful in cancer therapy and for the treatment of inflamed joints.

  9. Colloidal nanomaterial-based immunoassay.

    PubMed

    Teste, Bruno; Descroix, Stephanie

    2012-06-01

    Nanomaterials have been widely developed for their use in nanomedicine, especially for immunoassay-based diagnosis. In this review we focus on the use of nanomaterials as a nanoplatform for colloidal immunoassays. While conventional heterogeneous immunoassays suffer from mass transfer limitations and consequently long assay time, colloidal immunosupports allow target capture in the entire volume, thus speeding up reaction kinetics and shortening assay time. Owing to their wide range of chemical and physical properties, nanomaterials are an interesting candidate for immunoassay development. The most popular colloidal nanomaterials for colloidal immunoassays will be discussed, as well as their influence on immune reactions. Recent advances in nanomaterial applications for different formats of immunoassays will be reported, such as nanomaterial-based indirect immunoassays, optical-based agglutination immunoassays, resonance energy transfer-based immunoassays and magnetic relaxation-based immunoassays. Finally, the future of using nanomaterials for homogeneous immunoassays dedicated to clinical diagnosis will be discussed.

  10. Mechanical Failure in Colloidal Gels

    NASA Astrophysics Data System (ADS)

    Kodger, Thomas Edward

    When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form

  11. Aggregation of Heterogeneously Charged Colloids.

    PubMed

    Dempster, Joshua M; Olvera de la Cruz, Monica

    2016-06-28

    Patchy colloids are attractive as programmable building blocks for metamaterials. Inverse patchy colloids, in which a charged surface is decorated with patches of the opposite charge, are additionally noteworthy as models for heterogeneously charged biological materials such as proteins. We study the phases and aggregation behavior of a single charged patch in an oppositely charged colloid with a single-site model. This single-patch inverse patchy colloid model shows a large number of phases when varying patch size. For large patch sizes we find ferroelectric crystals, while small patch sizes produce cross-linked gels. Intermediate values produce monodisperse clusters and unusual worm structures that preserve finite ratios of area to volume. The polarization observed at large patch sizes is robust under extreme disorder in patch size and shape. We examine phase-temperature dependence and coexistence curves and find that large patch sizes produce polarized liquids, in contrast to mean-field predictions. Finally, we introduce small numbers of unpatched charged colloids. These can either suppress or encourage aggregation depending on their concentration and the size of the patches on the patched colloids. These effects can be exploited to control aggregation and to measure effective patch size.

  12. Les hommes regardent le ciel.

    NASA Astrophysics Data System (ADS)

    Jaschek, C.

    Contents: 1. Le ciel nocturne. 2. Le mouvement du soleil. 3. La lune et ses mouvements. 4. L'orientation des bâtiments. 5. Les étoiles et les constellations. 6. Les planètes. 7. Les comètes, météores et météorites. 8. Les phénomènes météorologico-astronomiques. 9. Les éclipses. 10. Le temps et les calendriers. 11. Astres et destinée humaine - l'astrologie. 12. Les mythes de la création du monde. 13. Les mythes de la fin du monde. 14. Astronomie et société.

  13. Colloids in the vicinity of landfills

    NASA Astrophysics Data System (ADS)

    Baumann, T.; Fruhstorfer, P.; Klein, T.; Niessner, R.

    2003-04-01

    Waste disposals without adequate landfill liner system are a source of contaminants and colloids. In order to assess the effects of the presence of colloids on the transport of heavy metal ions, the colloids at three landfill sites were characterized with regard to their chemical and mineralogical composition, their size distribution, and the concentration of heavy metal ions associated to the colloids. It can be shown that the pattern of the colloids inside and outside of the landfill is different in all examined parameters, e.g. inside of the disposal we find organic colloids and salt particles, whereas the groundwater downstream of the disposal contains mainly iron-colloids and carbonatic particles. Therefore a direct transfer of colloids from the landfill to the aquifer seems unlikely. Changes of the hydrochemical (mainly redox) and hydrodynamic conditions contribute to this behaviour. The association of heavy metal ions to colloids shows an interesting pattern: High concentrations are present in solution and associated to smaller (< 10 nm) and larger (> 1 μm) colloids, whereas the colloids in between show only small concentrations. This finding has some impact on the assessment of colloidal transport processes, since it suggests, that the more mobile colloids do not carry high concentrations of heavy metal ions.

  14. PREFACE: Colloidal and molecular electro-optics Colloidal and molecular electro-optics

    NASA Astrophysics Data System (ADS)

    Palberg, Thomas; Löwen, Hartmut

    2010-12-01

    exciting trends and earn the interest of a good fraction of contemporary soft matter scientists. Note1 http://www.elopto2010.fb08.uni-mainz.de Note2 http://www.sfb-tr6.de References [1] Weinberger P 2008 John Kerr and his effects found in 1877 and 1878 Phil. Mag. Lett. 88 897-907 [2] Benoit H 1948 Calcul de l'écart quadratique moyen entre les extrémités de diverses chaînes moléculaires de type usuel J. Polym. Sci. 3 376-87 [3] Benoit H 1949 Sur un dispositif de mesure de l'effet Kerr par impulsions electriques isoles Comptes Rendus 228 1716-8 [4] Benoit H 1951 Contribution a l'etude de l'effet Kerr presente par les solutions diluees de macromolecules rigide Ann. Phys. 6 561-609 Colloidal and molecular electro-optics contents Electric dichroism transients of aqueous solutions of DNA J A Bertolotto, G M Corral, E M Farias de La Torre and G B Roston The role of effective charges in the electrophoresis of highly charged colloids Apratim Chatterji and Jürgen Horbach Nonlinear response of the electric birefringence of polyelectrolyte solutions J L Déjardin and J M Martinez Kerr constant of multi-subunit particles and semiflexible, wormlike chains J García de la Torre, F G Díaz Baños and H E Pérez Sánchez Self-assembling electroactive hydrogels for flexible display technology Scott L Jones, Kok Hou Wong, Pall Thordarson and François Ladouceur Electrooptical effects in colloid systems subjected to short pulses of strong electric field S A Klemeshev, M P Petrov, A A Trusov and A V Voitylov The effect of ionic strength on electrical properties of polyelectrolyte multilayers on colloidal particles V Milkova and Ts Radeva Charge transport and current in non-polar liquids Kristiaan Neyts, Filip Beunis, Filip Strubbe, Matthias Marescaux, Bart Verboven, Masoumeh Karvar and Alwin Verschueren Ionic concentration- and pH-dependent electrophoretic mobility as studied by single colloid electrophoresis I Semenov, P Papadopoulos, G Stober and F Kremer Effect of magnesium ions and

  15. Colloids and Nucleation

    NASA Technical Reports Server (NTRS)

    Ackerson, Bruce

    1997-01-01

    The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range

  16. Colloid characterization and quantification in groundwater samples

    SciTech Connect

    K. Stephen Kung

    2000-06-01

    This report describes the work conducted at Los Alamos National Laboratory for studying the groundwater colloids for the Yucca Mountain Project in conjunction with the Hydrologic Resources Management Program (HRMP) and the Underground Test Area (UGTA) Project. Colloidal particle size distributions and total particle concentration in groundwater samples are quantified and characterized. Colloid materials from cavity waters collected near underground nuclear explosion sites by HRMP field sampling personnel at the Nevada Test Site (NTS) were quantified. Selected colloid samples were further characterized by electron microscope to evaluate the colloid shapes, elemental compositions, and mineral phases. The authors have evaluated the colloid size and concentration in the natural groundwater sample that was collected from the ER-20-5 well and stored in a 50-gallon (about 200-liter) barrel for several months. This groundwater sample was studied because HRMP personnel have identified trace levels of radionuclides in the water sample. Colloid results show that even though the water sample had filtered through a series of Millipore filters, high-colloid concentrations were identified in all unfiltered and filtered samples. They had studied the samples that were diluted with distilled water and found that diluted samples contained more colloids than the undiluted ones. These results imply that colloids are probably not stable during the storage conditions. Furthermore, results demonstrate that undesired colloids have been introduced into the samples during the storage, filtration, and dilution processes. They have evaluated possible sources of colloid contamination associated with sample collection, filtrating, storage, and analyses of natural groundwaters. The effects of container types and sample storage time on colloid size distribution and total concentration were studied to evaluate colloid stability by using J13 groundwater. The data suggests that groundwater samples

  17. Solid colloidal optical wavelength filter

    DOEpatents

    Alvarez, Joseph L.

    1992-01-01

    A solid colloidal optical wavelength filter includes a suspension of spheal particles dispersed in a coagulable medium such as a setting plastic. The filter is formed by suspending spherical particles in a coagulable medium; agitating the particles and coagulable medium to produce an emulsion of particles suspended in the coagulable medium; and allowing the coagulable medium and suspended emulsion of particles to cool.

  18. Dynamics of evaporative colloidal patterning

    NASA Astrophysics Data System (ADS)

    Kaplan, C. Nadir; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna; Mahadevan, L.

    2015-09-01

    Drying suspensions often leave behind complex patterns of particulates, as might be seen in the coffee stains on a table. Here, we consider the dynamics of periodic band or uniform solid film formation on a vertical plate suspended partially in a drying colloidal solution. Direct observations allow us to visualize the dynamics of band and film deposition, where both are made of multiple layers of close packed particles. We further see that there is a transition between banding and filming when the colloidal concentration is varied. A minimal theory of the liquid meniscus motion along the plate reveals the dynamics of the banding and its transition to the filming as a function of the ratio of deposition and evaporation rates. We also provide a complementary multiphase model of colloids dissolved in the liquid, which couples the inhomogeneous evaporation at the evolving meniscus to the fluid and particulate flows and the transition from a dilute suspension to a porous plug. This allows us to determine the concentration dependence of the bandwidth and the deposition rate. Together, our findings allow for the control of drying-induced patterning as a function of the colloidal concentration and evaporation rate.

  19. Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

    Weitz, Dave; Weeks, Eric; Gasser, Urs; Dinsmore, Tony; Mawley, Suliana; Segre, Phil; Cipelletti, Lucia

    2000-01-01

    This talk will present recent results from ground-based research to support the "Physics of Colloids in Space" project which is scheduled to fly in the ISS approximately one year from now. In addition, results supporting future planned flights will be discussed.

  20. Microbial effects on colloidal agglomeration

    SciTech Connect

    Hersman, L.

    1995-11-01

    Colloidal particles are known to enhance the transport of radioactive metals through soil and rock systems. This study was performed to determine if a soil microorganism, isolated from the surface samples collected at Yucca Mountain, NV, could affect the colloidal properties of day particles. The agglomeration of a Wyoming bentonite clay in a sterile uninoculated microbial growth medium was compared to the agglomeration in the medium inoculated with a Pseudomonas sp. In a second experiment, microorganisms were cultured in the succinate medium for 50 h and removed by centrifugation. The agglomeration of the clay in this spent was compared to sterile uninoculated medium. In both experiments, the agglomeration of the clay was greater than that of the sterile, uninoculated control. Based on these results, which indicate that this microorganism enhanced the agglomeration of the bentonite clay, it is possible to say that in the presence of microorganisms colloidal movement through a rock matrix could be reduced because of an overall increase in the size of colloidal particle agglomerates. 32 refs.

  1. Enhanced colloidal stability of hydroxyapatite

    NASA Astrophysics Data System (ADS)

    Borum, La Rhonda Terese

    Hydroxyapatite, Ca10(PO4)6(OH) 2 is the most thermodynamically stable calcium phosphate in physiological environments. Hence, it is the main inorganic mineral found in bone and teeth. Its colloidal stability, however, is poor because hydroxyapatite (HAp) particles exhibit sediment formation upon standing at short time periods, where agglomerates form and lead to non-homogeneous suspensions. Surface modification is a promising method to tailor the colloidal stability of hydroxyapatite for biomaterial applications. Three techniques to modify the HAp surface and enhance the colloidal stability of HAp were investigated. Modified particles were characterized by methods sensitive to surface chemistry changes, such as sedimentation studies, diffuse reflectance Fourier transform infrared spectroscopy (DRIFT), Brunauer-Emmett-Teller (BET) surface area, and electrophoresis. Sedimentation studies demonstrated how effective each technique was in improving the colloidal stability of hydroxyapatite particles. Electrophoresis provided information on electrostatic interactions within each system. The first technique entailed an esterification reaction of the HAp surface with dodecyl alcohol at elevated temperatures. DRIFT results showed that dodecyl groups from the alcohol replaced acidic hydroxyl and phosphate sites on the HAp surface, giving rise to enhanced colloidal stability through steric interactions in ethanol suspensions. TGA curves gave insight to the degree of esterification for the esterified particles. Higher reaction temperatures give rise to a higher degree of esterification resulting in better colloidal stability. The second technique applied a silica coating on the HAp surface by the hydrolysis of tetraethyl orthosilicate in ethanol. Silica was coated onto the HAp surface at 5--75 wt% loading amounts. A combination of acid dissolution and x-ray diffraction (XRD), along with BET showed that the silica coating is complete at 50 wt% silica loading. The silica coating

  2. Effective Forces Between Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Tehver, Riina; Banavar, Jayanth R.; Koplik, Joel

    1999-01-01

    Colloidal suspensions have proven to be excellent model systems for the study of condensed matter and its phase behavior. Many of the properties of colloidal suspensions can be investigated with a systematic variation of the characteristics of the systems and, in addition, the energy, length and time scales associated with them allow for experimental probing of otherwise inaccessible regimes. The latter property also makes colloidal systems vulnerable to external influences such as gravity. Experiments performed in micro-ravity by Chaikin and Russell have been invaluable in extracting the true behavior of the systems without an external field. Weitz and Pusey intend to use mixtures of colloidal particles with additives such as polymers to induce aggregation and form weak, tenuous, highly disordered fractal structures that would be stable in the absence of gravitational forces. When dispersed in a polarizable medium, colloidal particles can ionize, emitting counterions into the solution. The standard interaction potential in these charged colloidal suspensions was first obtained by Derjaguin, Landau, Verwey and Overbeek. The DLVO potential is obtained in the mean-field linearized Poisson-Boltzmann approximation and thus has limited applicability. For more precise calculations, we have used ab initio density functional theory. In our model, colloidal particles are charged hard spheres, the counterions are described by a continuum density field and the solvent is treated as a homogeneous medium with a specified dielectric constant. We calculate the effective forces between charged colloidal particles by integrating over the solvent and counterion degrees of freedom, taking into account the direct interactions between the particles as well as particle-counterion, counterion-counterion Coulomb, counterion entropic and correlation contributions. We obtain the effective interaction potential between charged colloidal particles in different configurations. We evaluate two

  3. Colloid particle size-dependent dispersivity

    NASA Astrophysics Data System (ADS)

    Chrysikopoulos, C. V.; Katzourakis, V. E.

    2014-12-01

    Laboratory and field studies have demonstrated that dispersion coefficients evaluated by fitting advection-dispersion transport models to nonreactive tracer breakthrough curves do not adequately describe colloid transport under the same flow field conditions. Here an extensive laboratory study was undertaken to assess whether the dispersivity, which traditionally has been considered to be a property of the porous medium, is dependent on colloid particle size and interstitial velocity. A total of 49 colloid transport experiments were performed in columns packed with glass beads under chemically unfavorable colloid attachment conditions. Nine different colloid diameters, and various flow velocities were examined. The breakthrough curves were successfully simulated with a mathematical model describing colloid transport in homogeneous, water saturated porous media. The results demonstrated that the dispersivity is positively correlated with colloid particle size, and increases with increasing velocity.

  4. Nonequilibrium interfaces in colloidal fluids

    NASA Astrophysics Data System (ADS)

    Bier, Markus; Arnold, Daniel

    2013-12-01

    The time-dependent structure, interfacial tension, and evaporation of an oversaturated colloid-rich (liquid) phase in contact with an undersaturated colloid-poor (vapor) phase of a colloidal dispersion is investigated theoretically during the early-stage relaxation, where the interface is relaxing towards a local equilibrium state while the bulk phases are still out of equilibrium. Since systems of this type exhibit a clear separation of colloidal and solvent relaxation time scales with typical times of interfacial tension measurements in between, they can be expected to be suitable for analogous experimental studies, too. The major finding is that, irrespective of how much the bulk phases differ from two-phase coexistence, the interfacial structure and the interfacial tension approach those at two-phase coexistence during the early-stage relaxation process. This is a surprising observation since it implies that the relaxation towards global equilibrium of the interface is not following but preceding that of the bulk phases. Scaling forms for the local chemical potential, the flux, and the dissipation rate exhibit qualitatively different leading order contributions depending on whether an equilibrium or a nonequilibrium system is considered. The degree of nonquilibrium between the bulk phases is found to not influence the qualitative relaxation behavior (i.e., the values of power-law exponents), but to determine the quantitative deviation of the observed quantities from their values at two-phase coexistence. Whereas the underlying dynamics differs between colloidal and molecular fluids, the behavior of quantities such as the interfacial tension approaching the equilibrium values during the early-stage relaxation process, during which nonequilibrium conditions of the bulk phases are not changed, can be expected to occur for both types of systems.

  5. Les urgences infectieuses ORL

    PubMed Central

    Sereme, Moustapha; Tarnagda, Souleymane; Guiguimde, Patrice; Gyebre, Yvette Marie Chantal; Ouedraogo, Bertin; Céline, Bambara; Ouattara, Maimouna; Ouoba, Kampadilemba

    2016-01-01

    Affections gravissimes à pronostic très réservé particulièrement dans notre contexte de sous médicalisation et de pauvreté. Notre but en initiant ce travail est de déterminer les étiologies de ces urgences et discuter de leur prise en charge thérapeutique. Étude de type rétrospective et descriptive sur 05 ans, au total 52 dossiers cliniques ont été inclus. Ces infections ont représenté 0,33% de nos consultations. La moyenne d'âge de nos patients a été 23 ans. Le jeune âge, les traitements inappropriés et certaines affections ORL ont été retrouvés comme facteurs favorisants. Les motifs de consultation ont été variés en fonction du siège de l'infection, cependant deux signes cliniques ont été constants: la douleur et la fièvre. L'adénophlegmon, le phlegmon péri-amygdalien, les cellulites ont été nos principales étiologies avec le streptocoque et le staphylocoque comme principaux germes en cause. L'antibiothérapie probabiliste a été utilisée en première intention notamment l'association céphalosporine de 3ème génération + aminoside + imidazolé. L'évolution clinique de nos patients a été marquée par la survenue de complications locales et générales. Urgence diagnostic et thérapeutique leur évolution reste encore émaillée de complication en raison de la consultation tardive de nos patients. PMID:28154719

  6. Magnetic Assisted Colloidal Pattern Formation

    NASA Astrophysics Data System (ADS)

    Yang, Ye

    Pattern formation is a mysterious phenomenon occurring at all scales in nature. The beauty of the resulting structures and myriad of resulting properties occurring in naturally forming patterns have attracted great interest from scientists and engineers. One of the most convenient experimental models for studying pattern formation are colloidal particle suspensions, which can be used both to explore condensed matter phenomena and as a powerful fabrication technique for forming advanced materials. In my thesis, I have focused on the study of colloidal patterns, which can be conveniently tracked in an optical microscope yet can also be thermally equilibrated on experimentally relevant time scales, allowing for ground states and transitions between them to be studied with optical tracking algorithms. In particular, I have focused on systems that spontaneously organize due to particle-surface and particle-particle interactions, paying close attention to systems that can be dynamically adjusted with an externally applied magnetic or acoustic field. In the early stages of my doctoral studies, I developed a magnetic field manipulation technique to quantify the adhesion force between particles and surfaces. This manipulation technique is based on the magnetic dipolar interactions between colloidal particles and their "image dipoles" that appear within planar substrate. Since the particles interact with their own images, this system enables massively parallel surface force measurements (>100 measurements) in a single experiment, and allows statistical properties of particle-surface adhesion energies to be extracted as a function of loading rate. With this approach, I was able to probe sub-picoNewton surface interactions between colloidal particles and several substrates at the lowest force loading rates ever achieved. In the later stages of my doctoral studies, I focused on studying patterns formed from particle-particle interaction, which serve as an experimental model of

  7. Colloid Straining within Saturated Heterogeneous Porous Media

    NASA Astrophysics Data System (ADS)

    Porubcan, A.; Walczak, J.; Xu, S.

    2008-12-01

    A thorough understanding of colloid movement in the subsurface system is critical to the assessment of groundwater pollution by pathogenic bacteria and colloid-bound contaminants. It is increasingly recognized that straining, a process that occurs when the pore space is too small to allow for a particle's passage, represents an important process in colloid immobilization within groundwater systems. Previously published studies have focused on the kinetics of colloid straining within sand packs composed of uniform mineral grains. Natural aquifers, however, are usually characterized by physically heterogeneous sediments. In this study, we conducted column transport experiments with carboxylated latex particles and quartz sand to investigate the impact of sediment texture (i.e., the size distribution of mineral grains) on colloid straining kinetics. The quartz sands used in the experiment were thoroughly cleaned and the strong repulsive interactions between colloid particles and quartz sands resulted in minimal physicochemical deposition so the straining kinetics can be quantified unambiguously. Sand packs of different textures were prepared by mixing sands of various sizes (mesh sizes of 20-25, 35-40 and 60-70). Our results suggested that the ratio of colloid size and the median sand grain size was insufficient to predict colloid straining within heterogeneous sediments. Soil texture, which was related to the size distribution of the sand grains, must be considered. A relationship between colloid straining kinetics and the heterogeneity of porous media that can be useful for the prediction of colloid transport within heterogeneous sediments was presented.

  8. What happens when pharmaceuticals meet colloids.

    PubMed

    Xing, Yingna; Chen, Xijuan; Zhuang, Jie; Chen, Xin

    2015-12-01

    Pharmaceuticals (PCs) have been widely detected in natural environment due to agricultural application of reclaimed water, sludge and animal wastes. Their potential risks to various ecosystems and even to human health have caused great concern; however, little was known about their environmental behaviors. Colloids (such as clays, metal oxides, and particulate organics) are kind of substances that are active and widespread in the environment. When PCs meet colloids, their interaction may influence the fate, transport, and toxicity of PCs. This review summarizes the progress of studies on the role of colloids in mediating the environmental behaviors of PCs. Synthesized results showed that colloids can adsorb PCs mainly through ion exchange, complexation and non-electrostatic interactions. During this process the structure of colloids and the stability of PCs may be changed. The adsorbed PCs may have higher risks to induce antibiotic resistance; besides, their transport may also be altered considering they have great chance to move with colloids. Solution conditions (such as pH, ionic strength, and cations) could influence these interactions between PCs and colloids, as they can change the forms of PCs and alter the primary forces between PCs and colloids in the solution. It could be concluded that PCs in natural soils could bind with colloids and then co-transport during the processes of irrigation, leaching, and erosion. Therefore, colloid-PC interactions need to be understood for risk assessment of PCs and the best management practices of various ecosystems (such as agricultural and wetland systems).

  9. Stable colloids in molten inorganic salts

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Dasbiswas, Kinjal; Ludwig, Nicholas B.; Han, Gang; Lee, Byeongdu; Vaikuntanathan, Suri; Talapin, Dmitri V.

    2017-02-01

    A colloidal solution is a homogeneous dispersion of particles or droplets of one phase (solute) in a second, typically liquid, phase (solvent). Colloids are ubiquitous in biological, chemical and technological processes, homogenizing highly dissimilar constituents. To stabilize a colloidal system against coalescence and aggregation, the surface of each solute particle is engineered to impose repulsive forces strong enough to overpower van der Waals attraction and keep the particles separated from each other. Electrostatic stabilization of charged solutes works well in solvents with high dielectric constants, such as water (dielectric constant of 80). In contrast, colloidal stabilization in solvents with low polarity, such as hexane (dielectric constant of about 2), can be achieved by decorating the surface of each particle of the solute with molecules (surfactants) containing flexible, brush-like chains. Here we report a class of colloidal systems in which solute particles (including metals, semiconductors and magnetic materials) form stable colloids in various molten inorganic salts. The stability of such colloids cannot be explained by traditional electrostatic and steric mechanisms. Screening of many solute–solvent combinations shows that colloidal stability can be traced to the strength of chemical bonding at the solute–solvent interface. Theoretical analysis and molecular dynamics modelling suggest that a layer of surface-bound solvent ions produces long-ranged charge-density oscillations in the molten salt around solute particles, preventing their aggregation. Colloids composed of inorganic particles in inorganic melts offer opportunities for introducing colloidal techniques to solid-state science and engineering applications.

  10. Analytic studies of colloid transport in fractured porous media

    SciTech Connect

    Hwang, Y.; Chambre, P.L.; Lee, W.W.L.; Pigford, T.H.

    1989-11-01

    We analyze the interactive migration of radioactive colloids and solute in fractured rock. Two possible interactions between radionuclides as colloids and as solute are considered: solute sorption on nonradioactive colloids to form pseudocolloids, and dissolution of radioactive colloids. Previous studies have discussed the formation and transport of colloids in porous media, including removal of colloids by filtration and sedimentation. Colloids can migrate faster than solute because of weaker sorption on stationary solids and because of hydrochromatography of colloid particles in flow channels. However, the migration of colloids and pseudocolloids can be retarded by the interaction of colloids with solute, and the migration of solute in local equilibrium with colloids can be more rapid than if colloids were not present. Here we present a new quantative analysis to predict the interactive migration of colloids and solute in porous and fractured media. 4 figs.

  11. Chancellor Water Colloids: Characterization and Radionuclide Association

    SciTech Connect

    Abdel-Fattah, Amr I.

    2012-06-18

    Concluding remarks about this paper are: (1) Gravitational settling, zeta potential, and ultrafiltration data indicate the existence of a colloidal phase of both the alpha and beta emitters in the Chancellor water; (2) The low activity combined with high dispersion homogeneity of the Chancellor water indicate that both alpha and beta emitters are not intrinsic colloids; (3) Radionuclides in the Chancellor water, particularly Pu, coexist as dissolved aqueous and sorbed phases - in other words the radionuclides are partitioned between the aqueous phase and the colloidal phase; (4) The presence of Pu as a dissolved species in the aqueous phase, suggests the possibility of Pu in the (V) oxidation state - this conclusion is supported by the similarity of the k{sub d} value of Pu determined in the current study to that determined for Pu(V) sorbed onto smectite colloids, and the similar electrokinetic behavior of the Chancellor water colloids to smectite colloids; (5) About 50% of the Pu(V) is in the aqueous phase and 50% is sorbed on colloids (mass concentration of colloids in the Chancellor water is 0.12 g/L); (6) The k{sub d} of the Pu and the beta emitters (fission products) between aqueous and colloidal phases in the Chancellor water is {approx}8.0 x 10{sup 3} mL/g using two different activity measurement techniques (LSC and alpha spectroscopy); (7) The gravitational settling and size distributions of the association colloids indicate that the properties (at least the physical ones) of the colloids to which the alpha emitters are associated with seem to be different that the properties of the colloids to which the beta emitters are associated with - the beta emitters are associated with very small particles ({approx}50 - 120 nm), while the alpha emitters are associated with relatively larger particles; and (8) The Chancellor water colloids are extremely stable under the natural pH and ionic strength conditions, indicating high potential for transport in the

  12. Designing Colloidal Molecules with Microfluidics

    PubMed Central

    Shen, Bingqing; Ricouvier, Joshua; Malloggi, Florent

    2016-01-01

    The creation of new colloidal materials involves the design of functional building blocks. Here, a microfluidic method for designing building blocks one by one, at high throughput, with a broad range of shapes is introduced. The method exploits a coupling between hydrodynamic interactions and depletion forces that controls the configurational dynamics of droplet clusters traveling in microfluidic channels. Droplet clusters can be solidified in situ with UV. By varying the flow parameters, clusters are prescribed a given size, geometry, chemical and/or magnetic heterogeneities enabling local bonding. Compact structures (chains, triangles, diamonds, tetrahedrons,...) and noncompact structures, such as crosses and T, difficult to obtain with current techniques are produced. Size dispersions are small (2%) and throughputs are high (30 000 h−1). The work opens a new pathway, based on microfluidics, for designing colloidal building blocks with a potential to enable the creation of new materials. PMID:27840804

  13. Biaxial ferromagnetic liquid crystal colloids

    PubMed Central

    Liu, Qingkun; Ackerman, Paul J.; Lubensky, Tom C.; Smalyukh, Ivan I.

    2016-01-01

    The design and practical realization of composite materials that combine fluidity and different forms of ordering at the mesoscopic scale are among the grand fundamental science challenges. These composites also hold a great potential for technological applications, ranging from information displays to metamaterials. Here we introduce a fluid with coexisting polar and biaxial ordering of organic molecular and magnetic colloidal building blocks exhibiting the lowest symmetry orientational order. Guided by interactions at different length scales, rod-like organic molecules of this fluid spontaneously orient along a direction dubbed “director,” whereas magnetic colloidal nanoplates order with their dipole moments parallel to each other but pointing at an angle to the director, yielding macroscopic magnetization at no external fields. Facile magnetic switching of such fluids is consistent with predictions of a model based on competing actions of elastic and magnetic torques, enabling previously inaccessible control of light. PMID:27601668

  14. Predicting crystals of Janus colloids

    NASA Astrophysics Data System (ADS)

    Vissers, Teun; Preisler, Zdeněk; Smallenburg, Frank; Dijkstra, Marjolein; Sciortino, Francesco

    2013-04-01

    We present a numerical study on the phase diagram for a simple model of Janus colloids, including ordered and disordered structures. Using a range of techniques, we generate a set of crystal structures and investigate their relative stability field in the pressure-temperature and temperature-density planes by means of free-energy calculations and thermodynamic integration schemes. We find that despite the Janus colloids' simple architecture, they form stable crystal structures with complicated bond-topologies on an underlying face-centered-cubic or hexagonal-close-packed lattice. In addition, we find a phase consisting of wrinkled bilayer sheets, competing with both the fluid and the crystal phases. We detect a metastable gas-liquid coexistence which displays a micellization-driven re-entrant behavior.

  15. Electrokinetic properties of polymer colloids

    NASA Technical Reports Server (NTRS)

    Micale, F. J.; Fuenmayor, D. Y.

    1986-01-01

    The surface of polymer colloids, especially polystyrene latexes, were modified for the purpose of controlling the electrokinetic properties of the resulting colloids. Achievement required a knowledge of electrical double layer charging mechanism, as a function of the electrolyte conditions, at the polymer/water interface. The experimental approach is to control the recipe formulation in the emulsion polymerization process so as to systematically vary the strong acid group concentration on the surface of the polymer particles. The electrophoretic mobility of these model particles will then be measured as a function of surface group concentration and as a function of electrolyte concentration and type. An effort was also made to evaluate the electrophoretic mobility of polystyrene latexes made in space and to compare the results with latexes made on the ground.

  16. Colloids at Curved Fluid Interfaces

    NASA Astrophysics Data System (ADS)

    Stebe, Kathleen

    2016-11-01

    Fluid interfaces are remarkable sites for colloidal assembly. When a colloid attaches to a fluid interface, it distorts a region around it; this distortion has an associated capillary energy, the product of its area and interfacial tension. The particle's capillary energy depends on the local interface curvature. By molding the interface, we can define curvature fields that drive microparticles along pre-determined paths. This example captures the emergent nature of the interactions. We discuss curvature fields as analogues to external electro-magnetic fields, and define curvatures that drive particles to well-defined locations, and to equilibrium sites far from boundaries. Particle-particle and particle-curvature interactions can guide particles into structures via interaction among many particles. This work demonstrates the potential importance of curvature capillary interactions in schemes to make reconfigurable materials, since interfaces and their associated capillary energy landscapes can be readily reconfigured. Analogies in other soft systems will be described. Support acknowledged from NSF DMR 1607878.

  17. Les noyaux actifs de galaxies

    NASA Astrophysics Data System (ADS)

    Camenzind, Max; Boucher, A.

    Découverts il y a plus de 30 ans, les quasars et les radiogalaxies sont des galaxies particulières qui manifestent en leur centre une activité intense. Cet ouvrage se consacre aux principales questions de la physique des noyaux actifs en les illustrant par de récentes données. Y sont traités les domaines suivants: les noyaux des galaxies actives, la théorie des trous noirs en rotation et de leurs disques d'accrétion, l'origine des raies d'émission et les jets des galaxies actives. Fournissant une introduction génerale à la terminologie, cet ouvrage s'adresse aussi bien aux étudiants en astronomie qu'aux astrophysiciens.

  18. Thermophoresis of charged colloidal particles.

    PubMed

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-04-01

    Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  19. Dynamics of evaporative colloidal patterning

    NASA Astrophysics Data System (ADS)

    Mahadevan, L.; Kaplan, C. Nadir; Wu, Ning; Mandre, Shreyas; Aizenberg, Joanna

    2014-11-01

    Evaporating suspensions of colloidal particles lead to the formation of a variety of patterns, ranging from rings left behind a coffee drop to periodic bands or uniform solid films deposited on a substrate suspended vertically in a container of the colloidal solution. To characterize the transition between different types of patterns, we develop minimal models of the liquid meniscus deformation due to the evaporation and colloidal deposition. A complementary multiphase model allows us to investigate the detailed dynamics of patterning in a drying solvent. This approach couples the inhomogeneous evaporation at the evolving liquid-air interface to the dynamics inside the suspension, i.e. the liquid flow, local variations of the particle concentration, and the propagation of the deposition front where the solute forms a wet, incompressible porous medium at high concentrations. The results of our theory are in good agreement with direct observations. This research was supported by the Air Force Office of Scientific Research (AFOSR) under Award FA9550-09-1-0669-DOD35CAP and the Kavli Institute for Bionano Science and Technology at Harvard University.

  20. Three-dimensional colloidal lithography.

    PubMed

    Nagai, Hironori; Poteet, Austen; Zhang, Xu A; Chang, Chih-Hao

    2017-03-24

    Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle-light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd's mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

  1. Three-dimensional colloidal lithography

    NASA Astrophysics Data System (ADS)

    Nagai, Hironori; Poteet, Austen; Zhang, Xu A.; Chang, Chih-Hao

    2017-03-01

    Light interactions with colloidal particles can generate a variety of complex three-dimensional (3D) intensity patterns, which can be utilized for nanolithography. The study of particle–light interactions can add more types of intensity patterns by manipulating key factors. Here we investigate a novel 3D nanolithography technique using colloidal particles under two-beam coherent illuminations. The fabricated 3D nanostructures are hollow, nested within periodic structures, and possess multiple chamber geometry. The effects of incident angles and particle size on the fabricated nanostructures were examined. The relative phase shift between particle position and interference pattern is identified as another significant parameter influencing the resultant nanostructures. A numerical model has been developed to show the evolution of nanostructure geometry with phase shifts, and experimental studies confirm the simulation results. Through the introduction of single colloidal particles, the fabrication capability of Lloyd’s mirror interference can now be extended to fabrication of 3D nanostructure with complex shell geometry. The fabricated hollow nanostructures with grating background could find potential applications in the area of photonics, drug delivery, and nanofluidics.

  2. Crystallization of DNA-coated colloids

    PubMed Central

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

    2015-01-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids. PMID:26078020

  3. Nanostructured colloidal crystals from forced hydrolysis methods.

    PubMed

    Otal, Eugenio H; Granada, Mara; Troiani, Horacio E; Cánepa, Horacio; Walsöe de Reca, Noemí E

    2009-08-18

    In this work, an original route for ZnO nanostructured spherical colloids and their assembly into colloidal crystals are presented. The temporal evolution of crystal size and shape was followed by X-ray diffraction and the colloids size distribution by scanning electron microscopy. These spherical colloids showed a change in their size dispersion with aging time. Early stage suspensions, with a narrow size distribution, were settled to the bottom and dried with a slow evaporation rate to obtain colloidal crystals. This original route provides a new material for future applications in opalline photonic crystals, with a dielectric constant higher than that of classical materials (silica and latex). Moreover, this route means an improvement of previously reported data from the literature since it involves a one-pot strategy and room-temperature colloid assembly.

  4. Crystallization of DNA-coated colloids

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Wang, Yufeng; Zheng, Xiaolong; Ducrot, Étienne; Yodh, Jeremy S.; Weck, Marcus; Pine, David J.

    2015-06-01

    DNA-coated colloids hold great promise for self-assembly of programmed heterogeneous microstructures, provided they not only bind when cooled below their melting temperature, but also rearrange so that aggregated particles can anneal into the structure that minimizes the free energy. Unfortunately, DNA-coated colloids generally collide and stick forming kinetically arrested random aggregates when the thickness of the DNA coating is much smaller than the particles. Here we report DNA-coated colloids that can rearrange and anneal, thus enabling the growth of large colloidal crystals from a wide range of micrometre-sized DNA-coated colloids for the first time. The kinetics of aggregation, crystallization and defect formation are followed in real time. The crystallization rate exhibits the familiar maximum for intermediate temperature quenches observed in metallic alloys, but over a temperature range smaller by two orders of magnitude, owing to the highly temperature-sensitive diffusion between aggregated DNA-coated colloids.

  5. Does colloid shape affect detachment of colloids by a moving air-water interface?

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L; Davis, Howard P

    2013-05-14

    Air-water interfaces interact strongly with colloidal particles by capillary forces. The magnitude of the interaction force depends on, among other things, the particle shape. Here, we investigate the effects of particle shape on colloid detachment by a moving air-water interface. We used hydrophilic polystyrene colloids with four different shapes (spheres, barrels, rods, and oblong disks), but otherwise identical surface properties. The nonspherical shapes were created by stretching spherical microspheres on a film of polyvinyl alcohol (PVA). The colloids were then deposited onto the inner surface of a glass channel. An air bubble was introduced into the channel and passed through, thereby generating a receding followed by an advancing air-water interface. The detachment of colloids by the air-water interfaces was visualized with a confocal microscope, quantified by image analysis, and analyzed statistically to determine significant differences. For all colloid shapes, the advancing air-water interface caused pronounced colloid detachment (>63%), whereas the receding interface was ineffective in colloid detachment (<1.5%). Among the different colloid shapes, the barrels were most readily removed (94%) by the advancing interface, followed by the spheres and oblong disks (80%) and the rods (63%). Colloid detachment was significantly affected by colloid shape. The presence of an edge, as it occurs in a barrel-shaped colloid, promoted colloid detachment because the air-water interface is being pinned at the edge of the colloid. This suggests that the magnitude of colloid mobilization and transport in porous media is underestimated for edged particles and overestimated for rodlike particles when a sphere is used as a model colloid.

  6. Dynamic Colloidal Stabilization by Nanoparticle Halos

    NASA Astrophysics Data System (ADS)

    Karanikas, S.; Louis, A. A.

    2004-12-01

    We explore the conditions under which colloids can be stabilized by the addition of smaller particles. The largest repulsive barriers between colloids occur when the added particles repel each other with soft interactions, leading to an accumulation near the colloid surfaces. At lower densities these layers of mobile particles (nanoparticle halos) result in stabilization, but when too many are added, the interactions become attractive again. We systematically study these effects—accumulation repulsion, reentrant attraction, and bridging—by accurate integral equation techniques.

  7. Transformative Colloidal Nanomaterials for Mid- Infrared Devices

    DTIC Science & Technology

    2015-06-11

    SECURITY CLASSIFICATION OF: The grant focused on the Photoluminescence efficiency of HgTe colloidal quantum dots. The photoluminescence quantum yield...of HgTe colloidal quantum dots was measured from 1800 to 6500 cm-1 . There is a steep drop at low energy consistent with the generic gap law...Distribution Unlimited Final Report: Transformative Colloidal Nanomaterials for Mid- Infrared Devices The views, opinions and/or findings contained in this

  8. Binodal Colloidal Aggregation Test - 4: Polydispersion

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.

    2008-01-01

    Binodal Colloidal Aggregation Test - 4: Polydispersion (BCAT-4-Poly) will use model hard-spheres to explore seeded colloidal crystal nucleation and the effects of polydispersity, providing insight into how nature brings order out of disorder. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  9. Thermophoresis of colloids by mesoscale simulations.

    PubMed

    Lüsebrink, Daniel; Yang, Mingcheng; Ripoll, Marisol

    2012-07-18

    The motion of a colloid induced by a temperature gradient is simulated by means of multiparticle collision dynamics, a mesoscale simulation technique. Two algorithms to quantify the thermophoretic behavior are employed and contrasted. The validity of the methods is verified as a function of the temperature gradient, system size, and algorithm parameters. The variation of the solvent-colloid interaction from attractive to purely repulsive interestingly results in the change of the colloid behavior from thermophobic to thermophilic.

  10. Binary Colloidal Alloy Test Conducted on Mir

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica I.; Ansari, Rafat R.

    1999-01-01

    Colloids are tiny (submicron) particles suspended in fluid. Paint, ink, and milk are examples of colloids found in everyday life. The Binary Colloidal Alloy Test (BCAT) is part of an extensive series of experiments planned to investigate the fundamental properties of colloids so that scientists can make colloids more useful for technological applications. Some of the colloids studied in BCAT are made of two different sized particles (binary colloidal alloys) that are very tiny, uniform plastic spheres. Under the proper conditions, these colloids can arrange themselves in a pattern to form crystals. These crystals may form the basis of new classes of light switches, displays, and optical devices. Windows made of liquid crystals are already in the marketplace. These windows change their appearance from transparent to opaque when a weak electric current is applied. In the future, if the colloidal crystals can be made to control the passage of light through them, such products could be made much more cheaply. These experiments require the microgravity environment of space because good quality crystals are difficult to produce on Earth because of sedimentation and convection in the fluid. The BCAT experiment hardware included two separate modules for two different experiments. The "Slow Growth" hardware consisted of a 35-mm camera with a 250- exposure photo film cartridge. The camera was aimed toward the sample module, which contained 10 separate colloid samples. A rack of small lights provided backlighting for the photographs. The BCAT hardware was launched on the shuttle and was operated aboard the Russian space station Mir by American astronauts John Blaha and David Wolf (launched September 1996 and returned January 1997; reflown September 1997 and returned January 1998). To begin the experiment, one of these astronauts would mix the samples to disperse the colloidal particles and break up any crystals that might have already formed. Once the samples were mixed and

  11. Colloid Titration--A Rapid Method for the Determination of Charged Colloid.

    ERIC Educational Resources Information Center

    Ueno, Keihei; Kina, Ken'yu

    1985-01-01

    "Colloid titration" is a volumetric method for determining charged polyelectrolytes in aqueous solutions. The principle of colloid titration, reagents used in the procedure, methods of endpoint detection, preparation of reagent solutions, general procedure used, results obtained, and pH profile of colloid titration are considered. (JN)

  12. Collective motion in populations of colloidal bots

    NASA Astrophysics Data System (ADS)

    Bartolo, Denis

    One of the origins of active matter physics was the idea that flocks, herds, swarms and shoals could be quantitatively described as emergent ordered phases in self-driven materials. From a somehow dual perspective, I will show how to engineer active materials our of colloidal flocks. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors and how to handle them in microfluidic chips. These populations of colloidal bots display a non-equilibrium transition toward collective motion. A special attention will be paid to the robustness of the resulting colloidal flocks with respect to geometrical frustration and to quenched disorder.

  13. Colloid Coalescence with Focused X Rays

    SciTech Connect

    Weon, B. M.; Kim, J. T.; Je, J. H.; Yi, J. M.; Wang, S.; Lee, W.-K.

    2011-07-01

    We show direct evidence that focused x rays enable us to merge polymer colloidal particles at room temperature. This phenomenon is ascribed to the photochemical scission of colloids with x rays, reducing the molecular weight, glass transition temperature, surface tension, and viscosity of colloids. The observation of the neck bridge growth with time shows that the x-ray-induced colloid coalescence is analogous to viscoelastic coalescence. This finding suggests a feasible protocol of photonic nanofabrication by sintering or welding of polymers, without thermal damage, using x-ray photonics.

  14. Les Abondances Chimiques dans les Galaxies Spirales de Type Precoce

    NASA Astrophysics Data System (ADS)

    Dutil, Yvan

    1998-09-01

    Les galaxies spriales presentent une distribution continue de formes et de proprietes physiques. A l'heure actuelle, il existe deux ecoles de pensee au sujet de la nature de ces proprietes morphologiques des galaxies. Pour certains elles sont innees, pour d'autres elles sont acquises. Les gradients d'abondance nebulaires, de par leur sensibilite aux mouvements a grande echelle du gaz et au taux de formation stellaire, offrent une possibilite de trancher dans ce debat. Toutefois, jusqu'ici, on a surtout observe les gradients d'abondance dans les galaxies de type tardif. Le premier objectif de cette these est d'enrichir l'echantillon de galaxies de type precoce observees. Le second objectif est de demontrer qu'il y a deja eu une barre dans les galaxies de type precoce et, si possible, de chercher des traces d'interactions dans ces galaxies. Dans le cadre de cette these, j'ai observe huit galaxies de type precoce. Mes observations indiquent que ces galaxies presentent des profils d'abondance dont les caracteristiques se rapprochent des galaxies barrees, meme si certaines ne presentent pas de barres. Ce resultat renforce l'hypothese selon laquelle les galaxies changent de type morphologique au cours du temps sous l'effet d'instabilites comme les barres.

  15. Colloid transport in dual-permeability media.

    PubMed

    Leij, Feike J; Bradford, Scott A

    2013-07-01

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the increased risks for disease caused by microorganisms and colloid-associated contaminants. This study presents a model for colloid transport in dual-permeability media that includes reversible and irreversible retention of colloids and first-order exchange between the aqueous phases of the two regions. The model may also be used to describe transport of other reactive solutes in dual-permeability media. Analytical solutions for colloid concentrations in aqueous and solid phases were obtained using Laplace transformation and matrix decomposition. The solutions proved convenient to assess the effect of model parameters on the colloid distribution. The analytical model was used to describe effluent concentrations for a bromide tracer and 3.2- or 1-μm-colloids that were observed after transport through a composite 10-cm long porous medium made up of a cylindrical lens or core of sand and a surrounding matrix with sand of a different grain size. The tracer data were described very well and realistic estimates were obtained for the pore-water velocity in the two flow domains. An accurate description was also achieved for most colloid breakthrough curves. Dispersivity and retention parameters were typically greater for the larger 3.2-μm-colloids while both reversible and irreversible retention rates tended to be higher for the finer sands than the coarser sand. The relatively small sample size and the complex flow pattern in the composite medium made it difficult to reach definitive conclusions regarding transport parameters for colloid transport.

  16. The hydrodynamics of colloidal gelation.

    PubMed

    Varga, Zsigmond; Wang, Gang; Swan, James

    2015-12-14

    Colloidal gels are formed during arrested phase separation. Sub-micron, mutually attractive particles aggregate to form a system spanning network with high interfacial area, far from equilibrium. Models for microstructural evolution during colloidal gelation have often struggled to match experimental results with long standing questions regarding the role of hydrodynamic interactions. In nearly all models, these interactions are neglected entirely. In the present work, we report simulations of gelation with and without hydrodynamic interactions between the suspended particles executed in HOOMD-blue. The disparities between these simulations are striking and mirror the experimental-theoretical mismatch in the literature. The hydrodynamic simulations agree with experimental observations, however. We explore a simple model of the competing transport processes in gelation that anticipates these disparities, and conclude that hydrodynamic forces are essential. Near the gel boundary, there exists a competition between compaction of individual aggregates which suppresses gelation and coagulation of aggregates which enhances it. The time scale for compaction is mildly slowed by hydrodynamic interactions, while the time scale for coagulation is greatly accelerated. This enhancement to coagulation leads to a shift in the gel boundary to lower strengths of attraction and lower particle concentrations when compared to models that neglect hydrodynamic interactions. Away from the gel boundary, differences in the nearest neighbor distribution and fractal dimension persist within gels produced by both simulation methods. This result necessitates a fundamental rethinking of how dynamic, discrete element models for gelation kinetics are developed as well as how collective hydrodynamic interactions influence the arrest of attractive colloidal dispersions.

  17. Patchy particles using colloidal caps

    NASA Astrophysics Data System (ADS)

    Middleton, Christine; Pine, David

    2015-03-01

    We present a method for making patchy particles functionalized with single stranded sticky end DNA only on their patches. This is done by adding ``spherical cap'' particles as patches to spherical colloids using the depletion interaction. The caps are then functionalized with single stranded DNA using copper-free click chemistry. Due to being attached only by depletion, the patches diffuse on the surface of the particle. The patchy particles can then interact with each other in a specific, directional way through the mobile, DNA functionalized patches.

  18. Corralled Colloids in Four Dimensions

    NASA Astrophysics Data System (ADS)

    Anthony, Stephen; Kim, Minsu; Granick, Steve

    2008-03-01

    Three colloidal particles were placed in small corrals and the strong correlations between their translation and rotation were quantified using the optical anisotropy of MOON (Modulated Optical Nanoprobes) particles to simultaneously measure their translation and rotation in an optical microscope. This system represents the simplest system which can capture one of the relevant components of multi-body interactions, the fact that while two particles can freely rotate together (like gears), once a third particle (or gear) is added there is no universally favorable set of rotations. This simple multi-body system provides a paradigm of how rotation influences translation and vice-versa.

  19. Colloidal Electrolytes and the Critical Micelle Concentration

    ERIC Educational Resources Information Center

    Knowlton, L. G.

    1970-01-01

    Describes methods for determining the Critical Micelle Concentration of Colloidal Electrolytes; methods described are: (1) methods based on Colligative Properties, (2) methods based on the Electrical Conductivity of Colloidal Electrolytic Solutions, (3) Dye Method, (4) Dye Solubilization Method, and (5) Surface Tension Method. (BR)

  20. Binary Colloidal Alloy Test-5: Aspheres

    NASA Technical Reports Server (NTRS)

    Chaikin, Paul M.; Hollingsworth, Andrew D.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Aspheres (BCAT-5-Aspheres) experiment photographs initially randomized colloidal samples (tiny nanoscale spheres suspended in liquid) in microgravity to determine their resulting structure over time. BCAT-5-Aspheres will study the properties of concentrated systems of small particles when they are identical, but not spherical in microgravity..

  1. Colloid transport in dual-permeability media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    It has been widely reported that colloids can travel faster and over longer distances in natural structured porous media than in uniform structureless media used in laboratory studies. The presence of preferential pathways for colloids in the subsurface environment is of concern because of the incre...

  2. Structural transitions in condensed colloidal virus phases

    NASA Astrophysics Data System (ADS)

    Schmidt, Nathan; Barr, Steve; Udit, Andrew; Gutierrez, Leonardo; Nguyen, Thanh; Finn, M. G.; Luijten, Erik; Wong, Gerard

    2010-03-01

    Analogous to monatomic systems colloidal phase behavior is entirely determined by the interaction potential between particles. This potential can be tuned using solutes such as multivalent salts and polymers with varying affinity for the colloids to create a hierarchy of attractions. Bacteriophage viruses are a naturally occurring type of colloidal particle with characteristics difficult to achieve by laboratory synthesis. They are monodisperse, nanometers in size, and have heterogeneous surface charge distributions. We use the MS2 and Qbeta bacteriophages (diameters 27-28nm) to understand the interplay between different attraction mechanisms on nanometer-sized colloids. Small Angle X-ray Scattering (SAXS) is used to characterize the inter-particle interaction between colloidal viruses using several polymer species and different salt types.

  3. Optical effects of charges in colloidal solutions

    NASA Astrophysics Data System (ADS)

    Chang, Railing; Chung, Hung-Yi; Chen, Chih-Wei; Chiang, Hai-Pang; Leung, P. T.

    2017-04-01

    The optical response of charged polymeric and metallic colloids is investigated using effective medium theories for composite systems of nanoparticles. Based on the Bohren-Hunt theory for generalized Mie scattering from charged particles, an effective quasi-static dielectric function previously obtained is applied to the present study to characterize the response from the various colloidal particles. It is found that such effects are more prominent for polymeric and nonmetallic colloidal solutions in general. In addition, the effects of clustering among the colloidal particles are also studied via a fractal model available from the literature. Detailed numerical studies of the dependence of these effects on the amount of extraneous charge, as well as on the geometry and volume fraction of the colloidal particles are presented.

  4. Colloid Transport and Retention in Fractured Media

    SciTech Connect

    McCarthy, J.F.

    2001-02-01

    The goal of this project was to identify the chemical and physical factors that control the transport of colloids in fractured materials, and develop a generalized capability to predict colloid attachment and detachment based on hydraulic factors (head, flow rate), physical processes and structure (fracture aperture, matrix porosity), and chemical properties (surface properties of colloids, solution chemistry, and mineralogy of fracture surfaces). Both aqueous chemistry and physical structure of geologic formations influenced transport. Results of studies at all spatial scales reached consensus on the importance of several key controlling variables: (1) colloid retention is dominated by chemical conditions favoring colloid-wall interactions; (2) even in the presence of conditions favorable to colloid collection, deposited colloids are remobilized over long times and this process contributes substantially to the overall extent of transport; (3) diffusive exchange between water-conducting fractures and finer fractures and pores acts to ''buffer'' the effects of the major fracture network structure, and reduces predictive uncertainties. Predictive tools were developed that account for fundamental mechanisms of colloid dynamics in fracture geometry, and linked to larger-scale processes in networks of fractures. The results of our study highlight the key role of physical and hydrologic factors, and processes of colloid remobilization that are potentially of even greater importance to colloid transport in the vadose zone than in saturated conditions. We propose that this work be extended to focus on understanding vadose zone transport processes so that they can eventually be linked to the understanding and tools developed in our previous project on transport in saturated groundwater systems.

  5. Gel trapping of dense colloids.

    PubMed

    Laxton, Peter B; Berg, John C

    2005-05-01

    Phase density differences in sols, foams, or emulsions often lead to sedimentation or creaming, causing problems for materials where spatial uniformity over extended periods of time is essential. The problem may be addressed through the use of rheology modifiers in the continuous phase. Weak polymer gels have found use for this purpose in the food industry where they appear to be capable of trapping dispersoid particles in a three-dimensional matrix while displaying water-like viscosities at low shear. Attempts to predict sedimentation stability in terms of particle properties (size, shape, density difference) and gel yield stress have led to qualitative success for suspensions of large particles. The effect of particle size, however, in particular the case in which colloidal dimensions are approached, has not been investigated. The present work seeks to determine useful stability criteria for colloidal dispersions in terms of readily accessible viscoelastic descriptors. Results are reported for systems consisting of 12 microm poly(methyl methacrylate) (PMMA) spheres dispersed in aqueous gellan gum. Monovalent salt concentration is varied to control rheological properties, and sedimentation/centrifugation experiments are performed to determine dispersion stability. Necessary conditions for stability consist of a minimum yield stress together with a value of tan delta less than unity.

  6. Synthesis of substantially monodispersed colloids

    NASA Technical Reports Server (NTRS)

    Klabunde, Kenneth J. (Inventor); Stoeva, Savka (Inventor); Sorensen, Christopher (Inventor)

    2003-01-01

    A method of forming ligated nanoparticles of the formula Y(Z).sub.x where Y is a nanoparticle selected from the group consisting of elemental metals having atomic numbers ranging from 21-34, 39-52, 57-83 and 89-102, all inclusive, the halides, oxides and sulfides of such metals, and the alkali metal and alkaline earth metal halides, and Z represents ligand moieties such as the alkyl thiols. In the method, a first colloidal dispersion is formed made up of nanoparticles solvated in a molar excess of a first solvent (preferably a ketone such as acetone), a second solvent different than the first solvent (preferably an organic aryl solvent such as toluene) and a quantity of ligand moieties; the first solvent is then removed under vacuum and the ligand moieties ligate to the nanoparticles to give a second colloidal dispersion of the ligated nanoparticles solvated in the second solvent. If substantially monodispersed nanoparticles are desired, the second dispersion is subjected to a digestive ripening process. Upon drying, the ligated nanoparticles may form a three-dimensional superlattice structure.

  7. Kinetically guided colloidal structure formation

    PubMed Central

    Hecht, Fabian M.; Bausch, Andreas R.

    2016-01-01

    The self-organization of colloidal particles is a promising approach to create novel structures and materials, with applications spanning from smart materials to optoelectronics to quantum computation. However, designing and producing mesoscale-sized structures remains a major challenge because at length scales of 10–100 μm equilibration times already become prohibitively long. Here, we extend the principle of rapid diffusion-limited cluster aggregation (DLCA) to a multicomponent system of spherical colloidal particles to enable the rational design and production of finite-sized anisotropic structures on the mesoscale. In stark contrast to equilibrium self-assembly techniques, kinetic traps are not avoided but exploited to control and guide mesoscopic structure formation. To this end the affinities, size, and stoichiometry of up to five different types of DNA-coated microspheres are adjusted to kinetically control a higher-order hierarchical aggregation process in time. We show that the aggregation process can be fully rationalized by considering an extended analytical DLCA model, allowing us to produce mesoscopic structures of up to 26 µm in diameter. This scale-free approach can easily be extended to any multicomponent system that allows for multiple orthogonal interactions, thus yielding a high potential of facilitating novel materials with tailored plasmonic excitation bands, scattering, biochemical, or mechanical behavior. PMID:27444018

  8. Plutonium and Cesium Colloid Mediated Transport

    NASA Astrophysics Data System (ADS)

    Boukhalfa, H.; Dittrich, T.; Reimus, P. W.; Ware, D.; Erdmann, B.; Wasserman, N. L.; Abdel-Fattah, A. I.

    2013-12-01

    Plutonium and cesium have been released to the environment at many different locations worldwide and are present in spent fuel at significant levels. Accurate understanding of the mechanisms that control their fate and transport in the environment is important for the management of contaminated sites, for forensic applications, and for the development of robust repositories for the disposal of spent nuclear fuel and nuclear waste. Plutonium, which can be present in the environment in multiple oxidations states and various chemical forms including amorphous oxy(hydr)oxide phases, adsorbs/adheres very strongly to geological materials and is usually immobile in all its chemical forms. However, when associated with natural colloids, it has the potential to migrate significant distances from its point of release. Like plutonium, cesium is not very mobile and tends to remain adhered to geological materials near its release point, although its transport can be enhanced by natural colloids. However, the reactivity of plutonium and cesium are very different, so their colloid-mediated transport might be significantly different in subsurface environments. In this study, we performed controlled experiments in two identically-prepared columns; one dedicated to Pu and natural colloid transport experiments, and the other to Cs and colloid experiments. Multiple flow-through experiments were conducted in each column, with the effluent solutions being collected and re-injected into the same column two times to examine the persistence and scaling behavior of the natural colloids, Pu and Cs. The data show that that a significant fraction of colloids were retained in the first elution through each column, but the eluted colloids collected from the first run transported almost conservatively in subsequent runs. Plutonium transport tracked natural colloids in the first run but deviated from the transport of natural colloids in the second and third runs. Cesium transport tracked natural

  9. A generalized description of aquatic colloidal interactions: The three-colloidal component approach

    SciTech Connect

    Buffle, J.; Wilkinson, K.J.; Stoll, S.; Filella, M.; Zhang, J.

    1998-10-01

    This paper describes several possible interactions among the different types of organic and inorganic aquatic colloids, based on present knowledge of their size, electric charge, and conformation. The physico-chemical properties of the different groups of colloids are described. Emphasis is placed on the various types of organic components, including fulvic compounds. Subsequently, the role of each colloid class is discussed with respect to homoaggregation (aggregation within a given colloid class) and heteroaggregation (aggregation among different colloid types). On the basis of a synthesis of literature reports, microscopic observations of natural colloids, experimental results obtained with model systems, and numerical simulations, it is concluded that the formation of aggregates in aquatic systems can be understood by mainly considering the roles of three types of colloids: (1) compact inorganic colloids; (2) large, rigid biopolymers; and (3) either the soil-derived fulvic compounds or their equivalent in pelagic waters, aquagenic refractory organic matter. In most natural aquatic systems, the small fulvic compounds will stabilize the inorganic colloids whereas the rigid biopolymers will destabilize them. The concentration of stable colloids in a particular aquatic system will depend on the relative proportions of these three components.

  10. Fluid-fluid demixing curves for colloid-polymer mixtures in a random colloidal matrix

    NASA Astrophysics Data System (ADS)

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2011-12-01

    We study fluid-fluid phase separation in a colloid-polymer mixture adsorbed in a colloidal porous matrix close to the θ point. For this purpose we consider the Asakura-Oosawa model in the presence of a quenched matrix of colloidal hard spheres. We study the dependence of the demixing curve on the parameters that characterize the quenched matrix, fixing the polymer-to-colloid size ratio to 0.8. We find that, to a large extent, demixing curves depend only on a single parameter f, which represents the volume fraction which is unavailable to the colloids. We perform Monte Carlo simulations for volume fractions f equal to 40% and 70%, finding that the binodal curves in the polymer and colloid packing-fraction plane have a small dependence on disorder. The critical point instead changes significantly: for instance, the colloid packing fraction at criticality increases with increasing f. Finally, we observe for some values of the parameters capillary condensation of the colloids: a bulk colloid-poor phase is in chemical equilibrium with a colloid-rich phase in the matrix.

  11. Colloid Transport in Saturated Porous Media: Elimination of Attachment Efficiency in a New Colloid Transport Model

    SciTech Connect

    Landkamer, Lee L.; Harvey, Ronald W.; Scheibe, Timothy D.; Ryan, Joseph N.

    2013-05-11

    A new colloid transport model is introduced that is conceptually simple but captures the essential features of complicated attachment and detachment behavior of colloids when conditions of secondary minimum attachment exist. This model eliminates the empirical concept of collision efficiency; the attachment rate is computed directly from colloid filtration theory. Also, a new paradigm for colloid detachment based on colloid population heterogeneity is introduced. Assuming the dispersion coefficient can be estimated from tracer behavior, this model has only two fitting parameters: (1) the fraction of colloids that attach irreversibly and (2) the rate at which reversibly attached colloids leave the surface. These two parameters were correlated to physical parameters that control colloid transport such as the depth of the secondary minimum and pore water velocity. Given this correlation, the model serves as a heuristic tool for exploring the influence of physical parameters such as surface potential and fluid velocity on colloid transport. This model can be extended to heterogeneous systems characterized by both primary and secondary minimum deposition by simply increasing the fraction of colloids that attach irreversibly.

  12. Colloid transport and retention in unsaturated porous media: effect of colloid input concentration.

    PubMed

    Zhang, Wei; Morales, Verónica L; Cakmak, M Ekrem; Salvucci, Anthony E; Geohring, Larry D; Hay, Anthony G; Parlange, Jean-Yves; Steenhuis, Tammo S

    2010-07-01

    Colloids play an important role in facilitating transport of adsorbed contaminants in soils. Recent studies showed that under saturated conditions colloid retention was a function of its concentration. It is unknown if this is the case under unsaturated conditions. In this study, the effect of colloid concentration on colloid retention was investigated in unsaturated columns by increasing concentrations of colloid influents with varying ionic strength. Colloid retention was observed in situ by bright field microscopy and quantified by measuring colloid breakthrough curves. In our unsaturated experiments, greater input concentrations resulted in increased colloid retention at ionic strength above 0.1 mM, but not in deionized water (i.e., 0 mM ionic strength). Bright field microscope images showed that colloid retention mainly occurred at the solid-water interface and wedge-shaped air-water-solid interfaces, whereas the retention at the grain-grain contacts was minor. Some colloids at the air-water-solid interfaces were rotating and oscillating and thus trapped. Computational hydrodynamic simulation confirmed that the wedge-shaped air-water-solid interface could form a "hydrodynamic trap" by retaining colloids in its low velocity vortices. Direct visualization also revealed that colloids once retained acted as new retention sites for other suspended colloids at ionic strength greater than 0.1 mM and thereby could explain the greater retention with increased input concentrations. Derjaguin-Landau-Verwey-Overbeek (DLVO) energy calculations support this concept. Finally, the results of unsaturated experiments were in agreement with limited saturated experiments under otherwise the same conditions.

  13. Polymer-Induced Depletion Interaction and Its Effect on Colloidal Sedimentation in Colloid-Polymer Mixtures

    NASA Technical Reports Server (NTRS)

    Tong, Penger

    1996-01-01

    In this paper we focus on the polymer-induced depletion attraction and its effect on colloidal sedimentation in colloid-polymer mixtures. We first report a small angle neutron scattering (SANS) study of the depletion effect in a mixture of hard-sphere-like colloid and non-adsorbing polymer. Then we present results of our recent sedimentation measurements in the same colloid-polymer mixture. A key parameter in controlling the sedimentation of heavy colloidal particles is the interparticle potential U(tau), which is the work required to bring two colloidal particles from infinity to a distance tau under a give solvent condition. This potential is known to affect the average settling velocity of the particles and experimentally one needs to have a way to continuously vary U(tau) in order to test the theory. The interaction potential U(tau) can be altered by adding polymer molecules into the colloidal suspension. In a mixture of colloid and non-adsorbing polymer, the potential U(tau) can develop an attractive well because of the depletion effect, in that the polymer chains are expelled from the region between two colloidal particles when their surface separation becomes smaller than the size of the polymer chains. The exclusion of polymer molecules from the space between the colloidal particles leads to an unbalanced osmotic pressure difference pushing the colloidal particles together, which results in an effective attraction between the two colloidal particles. The polymer-induced depletion attraction controls the phase stability of many colloid-polymer mixtures, which are directly of interest to industry.

  14. Photochemical manipulation of colloidal structures in liquid-crystal colloids

    NASA Astrophysics Data System (ADS)

    Yamamoto, T.; Tabe, Y.; Yokoyama, H.

    2007-05-01

    We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

  15. Quantification of hydrophobic interaction affinity of colloids

    NASA Astrophysics Data System (ADS)

    Saini, G.; Nasholm, N.; Wood, B. D.

    2009-12-01

    Colloids play an important role in a wide variety of disciplines, including water and wastewater treatment, subsurface transport of metals and organic contaminants, migration of fines in oil reservoirs, biocolloid (virus and bacteria) transport in subsurface, and are integral to laboratory transport studies. Although the role of hydrophobicity in adhesion and transport of colloids, particularly bacteria, is well known; there is scarcity of literature regarding hydrophobicity measurement of non-bacterial colloids and other micron-sized particles. Here we detail an experimental approach based on differential partitioning of colloids between two liquid phases (hydrocarbon and buffer) as a measure of the hydrophobic interaction affinity of colloids. This assay, known as Microbial adhesion to hydrocarbons or MATH, is frequently used in microbiology and bacteriology for quantifying the hydrophobicity of microbes. Monodispersed colloids and particles, with sizes ranging from 1 micron to 33 micron, were used for the experiments. A range of hydrophobicity values were observed for different particles. The hydrophobicity results are also verified against water contact angle measurements of these particles. This liquid-liquid partitioning assay is quick, easy-to-perform and requires minimal instrumentation. Estimation of the hydrophobic interaction affinity of colloids would lead to a better understanding of their adhesion to different surfaces and subsequent transport in porous media.

  16. Structural evolution of Colloidal Gels under Flow

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao; Jamali, Safa

    Colloidal suspensions are ubiquitous in different industrial applications ranging from cosmetic and food industries to soft robotics and aerospace. Owing to the fact that mechanical properties of colloidal gels are controlled by its microstructure and network topology, we trace the particles in the networks formed under different attraction potentials and try to find a universal behavior in yielding of colloidal gels. Many authors have implemented different simulation techniques such as molecular dynamics (MD) and Brownian dynamics (BD) to capture better picture during phase separation and yielding mechanism in colloidal system with short-ranged attractive force. However, BD neglects multi-body hydrodynamic interactions (HI) which are believed to be responsible for the second yielding of colloidal gels. We envision using dissipative particle dynamics (DPD) with modified depletion potential and hydrodynamic interactions, as a coarse-grain model, can provide a robust simulation package to address the gel formation process and yielding in short ranged-attractive colloidal systems. The behavior of colloidal gels with different attraction potentials under flow is examined and structural fingerprints of yielding in these systems will be discussed.

  17. Les violences conjugales à Dakar

    PubMed Central

    Soumah, Mohamed Maniboliot; Issa, Abdoul Wahab; Ndiaye, Mor; Ndoye, El Hadj Oumar; Sow, Mamadou Lamine

    2015-01-01

    L'objectif était d’évaluer les aspects épidémiologiques des violences conjugales, identifier les facteurs de risques et les différents types de violences conjugales, évaluer les conséquences des violences conjugales sur la santé des victimes, afin d'améliorer la prise en charge des victimes et la prévention du phénomène. Il s'est agit d'une étude transversale effectuée de décembre 2012 à janvier 2013 à Dakar. Les données ont été recueillies, après consentement, sur fiche d'enquête anonyme soumise à toute personne volontaire vivant en couple et résidant à Dakar. L'analyse statistique a été effectuée avec le logiciel SPSS 13.0. Le nombre de personnes victimes de violences conjugales était de 60 soit 37,30% dont 31 femmes (51,70%) et 29 hommes (48,30%). Le sex-ratio était de 0,93. Parmi les victimes, 53 étaient scolarisées soit 88,30%. Le régime matrimonial était de type monogame dans 39 cas (65%) et polygame dans 21 cas (35%). La vie en couple durait depuis moins de 11 ans dans 60% des cas et durait de 11 ans à 20 ans au plus dans 26,6% des cas. L’étude des types de violences montrait la fréquence des agressions physiques. Les armes utilisées étaient surtout les armes naturelles. Les principaux facteurs de risque de violence conjugale sont les facteurs sociodémographiques, culturels et économiques comme le jeune âge, l'inégalité du genre, les jeunes couples, la précarité, le niveau d'instruction élevé. La prise en charge des victimes et la prévention du phénomène restent insuffisantes dans nos pays. PMID:26918077

  18. [The colloid milium: An observation associated with trichinosis].

    PubMed

    Okhremchuk, Ilona; Abed, Safia; Nguyen, Anh Tuan; Brandone, Nicolas; Morand, Jean-Jacques

    2016-04-01

    The colloid milium has four clinical forms: adult colloid milium, juvenile colloid milium, paracolloid (or nodular colloid degeneration) and pigmented colloid milium. We report the case of an adult colloid milium in a man of 56, who presented episodes of diffuse pruritus associated with myalgia and digestive disorders, indicative of trichinosis. He also developed gradually over the past 10 years, yellowish injuries in the mandibles and neck for whom histology objectified a colloid milium. Etiology and treatment are still unknown; association with a trichinosis is probably coincidental.

  19. Colloidal Synthesis of Gold Semishells

    PubMed Central

    Rodríguez-Fernández, Denis; Pérez-Juste, Jorge; Pastoriza-Santos, Isabel; Liz-Marzán, Luis M

    2012-01-01

    This work describes a novel and scalable colloid chemistry strategy to fabricate gold semishells based on the selective growth of gold on Janus silica particles (500 nm in diameter) partly functionalized with amino groups. The modulation of the geometry of the Janus silica particles allows us to tune the final morphology of the gold semishells. This method also provides a route to fabricating hollow gold semishells through etching of the silica cores with hydrofluoric acid. The optical properties were characterized by visible near-infrared (vis-NIR) spectroscopy and compared with simulations performed using the boundary element method (BEM). These revealed that the main optical features are located beyond the NIR region because of the large core size. PMID:24551496

  20. Diffusiophoretic Focusing of Suspended Colloids

    NASA Astrophysics Data System (ADS)

    Shi, Nan; Nery-Azevedo, Rodrigo; Abdel-Fattah, Amr I.; Squires, Todd M.

    2016-12-01

    Using a microfluidic system to impose and maintain controlled, steady-state multicomponent p H and electrolyte gradients, we present systems where the diffusiophoretic migration of suspended colloids leads them to focus at a particular position, even in steady-state gradients. We show that naively superpositing effects of each gradient may seem conceptually and qualitatively reasonable, yet is invalid due to the coupled transport of these multicomponent electrolytes. In fact, reformulating the classic theories in terms of the flux of each species (rather than local gradients) reveals rather stringent conditions that are necessary for diffusiophoretic focusing in steady gradients. Either particle surface properties must change as a function of local composition in solution (akin to isoelectric focusing in electrophoresis), or chemical reactions must occur between electrolyte species, for such focusing to be possible. The generality of these findings provides a conceptual picture for understanding, predicting, or designing diffusiophoretic systems.

  1. Oxyhydroxy Silicate Colloids: A New Type of Waterborne Actinide(IV) Colloids

    PubMed Central

    Weiss, Stephan; Hennig, Christoph; Brendler, Vinzenz; Ikeda‐Ohno, Atsushi

    2016-01-01

    Abstract At the near‐neutral and reducing aquatic conditions expected in undisturbed ore deposits or in closed nuclear waste repositories, the actinides Th, U, Np, and Pu are primarily tetravalent. These tetravalent actinides (AnIV) are sparingly soluble in aquatic systems and, hence, are often assumed to be immobile. However, AnIV could become mobile if they occur as colloids. This review focuses on a new type of AnIV colloids, oxyhydroxy silicate colloids. We herein discuss the chemical characteristics of these colloids and the potential implication for their environmental behavior. The binary oxyhydroxy silicate colloids of AnIV could be potentially more mobile as a waterborne species than the well‐known mono‐component oxyhydroxide colloids. PMID:27957406

  2. Three-dimensional ultrasonic colloidal crystals

    NASA Astrophysics Data System (ADS)

    Caleap, Mihai; Drinkwater, Bruce W.

    2016-05-01

    Colloidal assembly represents a powerful method for the fabrication of functional materials. In this article, we describe how acoustic radiation forces can guide the assembly of colloidal particles into structures that serve as microscopic elements in novel acoustic metadevices or act as phononic crystals. Using a simple three-dimensional orthogonal system, we show that a diversity of colloidal structures with orthorhombic symmetry can be assembled with megahertz-frequency (MHz) standing pressure waves. These structures allow rapid tuning of acoustic properties and provide a new platform for dynamic metamaterial applications.

  3. Transport in charged colloids driven by thermoelectricity.

    PubMed

    Würger, Alois

    2008-09-05

    We study the thermal diffusion coefficient D{T} of a charged colloid in a temperature gradient, and find that it is to a large extent determined by the thermoelectric response of the electrolyte solution. The thermally induced salinity gradient leads in general to a strong increase with temperature. The difference of the heat of transport of coions and counterions gives rise to a thermoelectric field that drives the colloid to the cold or to the warm, depending on the sign of its charge. Our results provide an explanation for recent experimental findings on thermophoresis in colloidal suspensions.

  4. Linear colloidal crystal arrays by electrohydrodynamic printing

    NASA Astrophysics Data System (ADS)

    Poon, H. F.; Saville, D. A.; Aksay, I. A.

    2008-09-01

    We use electrohydrodynamic jets of colloidal suspensions to produce arrays of colloidal crystalline stripes on surfaces. A critical factor in maintaining a stable jet is the distance of separation between the nozzle and the surface. Colloidal crystalline stripes are produced as two wetting lines of the deployed suspension merge during drying. To ensure that the two wetting lines merge, the "deployed-line-width" to "particle size" ratio is kept below a critical value so that the capillary forces overcome the frictional forces between the particles and the substrate.

  5. Food colloids research: historical perspective and outlook.

    PubMed

    Dickinson, Eric

    2011-06-09

    Trends and past achievements in the field of food colloids are reviewed. Specific mention is made of advances in knowledge and understanding in the areas of (i) structure and rheology of protein gels, (ii) properties of adsorbed protein layers, (iii) functionality derived from protein-polysaccharide interactions, and (iv) oral processing of food colloids. Amongst ongoing experimental developments, the technique of particle tracking for monitoring local dynamics and microrheology of food colloids is highlighted. The future outlook offers exciting challenges with expected continued growth in research into digestion processes, encapsulation, controlled delivery, and nanoscience.

  6. Aggregation and Gelation of Anisometric Colloidal Particles

    NASA Astrophysics Data System (ADS)

    Mohraz, Ali; Solomon, Michael J.

    2002-11-01

    The quiescent and flow-induced structure and dynamics of colloidal aggregates and gels of anisometric particles are studied by means of static and dynamic light scattering. Ground-based studies of weak gels are possible due to the submicron size of the boehmite rod suspensions investigated; however, microgravity conditions would be required for more general studies. The properties of colloidal rod suspensions are compared to typical properties of spherical particle gels to understand the role of anisotropic excluded volume on gel structure and dynamics. The structure and dynamics of colloidal aggregates and gels have long been of scientific and technological interest; however, most research has focused on suspensions of spherical particles. Yet, aggregates and gels of anisometric particles - colloidal rods and platelets - may exhibit structure and dynamics that are quite different from spherical colloids. For example, suspensions of colloidal rods gel at extremely low volume fractions and form birefringent sediments. The rheology of solutions and gels of colloidal rods and platelets differs dramatically from that of colloidal spheres. Scientifically, studies with anisometric particles offer the opportunity to assess the role of anisotropic excluded volume and particle orientation in aggregates and gels. Technologically, anisometric colloids find use in a wide range of materials such as ceramics, polymer nanocomposites, well-bore drilling fluids and magnetic storage media. Model colloidal boehmite rods of approximately monodisperse dimension and aspect ratio have been synthesized according to the method of Philipse and coworkers. In aqueous solution, these materials undergo gelation upon the addition of divalent salt. By means of a novel grafting reaction and procedure for solvent refractive index matching, the rods have also been dispersed in mixed organic solvents. In this case, gelation is induced by means of depletion interaction. We report the effect of

  7. A colloidal quantum dot spectrometer

    NASA Astrophysics Data System (ADS)

    Bao, Jie; Bawendi, Moungi G.

    2015-07-01

    Spectroscopy is carried out in almost every field of science, whenever light interacts with matter. Although sophisticated instruments with impressive performance characteristics are available, much effort continues to be invested in the development of miniaturized, cheap and easy-to-use systems. Current microspectrometer designs mostly use interference filters and interferometric optics that limit their photon efficiency, resolution and spectral range. Here we show that many of these limitations can be overcome by replacing interferometric optics with a two-dimensional absorptive filter array composed of colloidal quantum dots. Instead of measuring different bands of a spectrum individually after introducing temporal or spatial separations with gratings or interference-based narrowband filters, a colloidal quantum dot spectrometer measures a light spectrum based on the wavelength multiplexing principle: multiple spectral bands are encoded and detected simultaneously with one filter and one detector, respectively, with the array format allowing the process to be efficiently repeated many times using different filters with different encoding so that sufficient information is obtained to enable computational reconstruction of the target spectrum. We illustrate the performance of such a quantum dot microspectrometer, made from 195 different types of quantum dots with absorption features that cover a spectral range of 300 nanometres, by measuring shifts in spectral peak positions as small as one nanometre. Given this performance, demonstrable avenues for further improvement, the ease with which quantum dots can be processed and integrated, and their numerous finely tuneable bandgaps that cover a broad spectral range, we expect that quantum dot microspectrometers will be useful in applications where minimizing size, weight, cost and complexity of the spectrometer are critical.

  8. Colloid-Facilitated Transport of Radionuclides through the Vadose Zone

    SciTech Connect

    Flury, Markus; Harsh, James B.; Zachara, John M.; McCarthy, John F.; Lichtner, Peter C.

    2006-05-31

    This project seeks to improve the basic understanding of the role of colloids in facilitating the transport of contaminants in the vadose zone. We focus on three major thrusts: (1) thermodynamic stability and mobility of colloids formed by reactions of sediments with highly alkaline tank waste solutions, (2) colloid-contaminant interactions, and (3) in-situ colloid mobilization and colloid facilitated contaminant transport occurring in both contaminated and uncontaminated Hanford sediments.

  9. Polarity inversion of ζ-potential in concentrated colloidal dispersions.

    PubMed

    Manzanilla-Granados, Héctor M; Jiménez-Ángeles, Felipe; Lozada-Cassou, Marcelo

    2011-10-27

    A concentrated colloidal dispersion is studied by applying an integral equations theory to the colloidal primitive model fluid. Important effects, attributed to large size and charge and to the finite concentration of colloidal particles, are found. We observe a polarity inversion of ζ-potential for concentrated colloidal dispersions, while it is not present for a single colloidal particle at infinite dilution. An excellent qualitative agreement between our theoretical predictions and our computer simulations is observed.

  10. Quantum oscillations in magnetically doped colloidal nanocrystals.

    PubMed

    Ochsenbein, Stefan T; Gamelin, Daniel R

    2011-02-01

    Progress in the synthesis of colloidal quantum dots has recently provided access to entirely new forms of diluted magnetic semiconductors, some of which may find use in quantum computation. The usefulness of a spin qubit is defined by its Rabi frequency, which determines the operation time, and its coherence time, which sets the error correction window. However, the spin dynamics of magnetic impurity ions in colloidal doped quantum dots remain entirely unexplored. Here, we use pulsed electron paramagnetic resonance spectroscopy to demonstrate long spin coherence times of ∼0.9 µs in colloidal ZnO quantum dots containing the paramagnetic dopant Mn(2+), as well as Rabi oscillations with frequencies ranging between 2 and 20 MHz depending on microwave power. We also observe electron spin echo envelope modulations of the Mn(2+) signal due to hyperfine coupling with protons outside the quantum dots, a situation unique to the colloidal form of quantum dots, and not observed to date.

  11. Luminol chemiluminescence catalysed by colloidal platinum nanoparticles.

    PubMed

    Xu, Sheng-Liang; Cui, Hua

    2007-01-01

    Platinum colloids prepared by the reduction of hexachloroplatinic acid with citrate in the presence of different stabilizers were found to enhance the chemiluminescence (CL) of the luminol-H(2)O(2) system, and the most intensive CL signals were obtained with citrate-protected Pt colloids synthesized with citrate as both a reductant and a stabilizer. Light emission was intense and reproducible. Transmission electron microscopy and X-ray photoelectron spectroscopy studies were conducted before and after the CL reaction to investigate the possible CL enhancement mechanism. It is suggested that this CL enhancement is attributed to the catalysis of platinum nanoparticles, which could accelerate the electron-transfer process and facilitate the CL radical generation in aqueous solution. The effects of Pt colloids prepared by the hydroborate reduction were also investigated. The application of the luminol-H(2)O(2)-Pt colloids system was exploited for the determination of compounds such as uric acid, ascorbic acid, phenols and amino acids.

  12. Computer simulations of charged colloids in confinement.

    PubMed

    Puertas, Antonio M; de las Nieves, F Javier; Cuetos, Alejandro

    2015-02-15

    We study by computer simulations the interaction between two similarly charged colloidal particles confined between parallel planes, in salt free conditions. Both the colloids and ions are simulated explicitly, in a fine-mesh lattice, and the electrostatic interaction is calculated using Ewald summation in two dimensions. The internal energy is measured by setting the colloidal particles at a given position and equilibrating the ions, whereas the free energy is obtained introducing a bias (attractive) potential between the colloids. Our results show that upon confining the system, the internal energy decreases, resulting in an attractive contribution to the interaction potential for large charges and strong confinement. However, the loss of entropy of the ions is the dominant mechanism in the interaction, irrespective of the confinement of the system. The interaction potential is therefore repulsive in all cases, and is well described by the DLVO functional form, but effective values have to be used for the interaction strength and Debye length.

  13. A Course in Colloid and Surface Science.

    ERIC Educational Resources Information Center

    Scamehorn, John F.

    1984-01-01

    Describes a course for chemical engineers, chemists, and petroleum engineers that focuses on colloid and surface science. Major topic areas in the course include capillarity, surface thermodynamics, adsorption contact angle, micelle formation, solubilization in micelles, emulsions, foams, and applications. (JN)

  14. Self-similarity in active colloid motion

    NASA Astrophysics Data System (ADS)

    Constant, Colin; Sukhov, Sergey; Dogariu, Aristide

    The self-similarity of displacements among randomly evolving systems has been used to describe the foraging patterns of animals and predict the growth of financial systems. At micron scales, the motion of colloidal particles can be analyzed by sampling their spatial displacement in time. For self-similar systems in equilibrium, the mean squared displacement increases linearly in time. However, external forces can take the system out of equilibrium, creating active colloidal systems, and making this evolution more complex. A moment scaling spectrum of the distribution of particle displacements quantifies the degree of self-similarity in the colloid motion. We will demonstrate that, by varying the temporal and spatial characteristics of the external forces, one can control the degree of self-similarity in active colloid motion.

  15. Thin film interference of colloidal thin films.

    PubMed

    Cong, Hailin; Cao, Weixiao

    2004-09-14

    A stairlike colloidal crystal thin film composed of poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) monodispersed colloids was fabricated on an inclined silicon substrate. Different bright colors were observed on the various parts of the film with different layers as white light irradiated perpendicularly on it. The relationship between the colors and layers of the film was investigated and discussed according to the principle of thin film interference. On the basis of the phenomenon of thin film interference, a one-layer colloidal film having uniform color was researched and it would display diverse colors before and after swollen by styrene (St). A circular stairlike colloidal film was achieved to mimic the colors of the peacock tail feather.

  16. Hemorrhagic Colloid Cyst Presenting with Acute Hydrocephaly

    PubMed Central

    Akhavan, Reza; Zandi, Behrouz; Pezeshki-Rad, Masoud; Farrokh, Donya

    2017-01-01

    Colloid cysts are benign slow-growing cystic lesions located on the roof of the third ventricle that usually present with symptoms related to gradual rise of intracranial pressure. They mostly remain asymptomatic and sometimes grow progressively and cause diverse symptoms associated with increased intracranial pressure such as headache, diplopia, and sixth cranial nerve palsy. Here we report a 47-year-old female who presented to the emergency department with acute severe headache and nausea/vomiting. On MRI examination acute hydrocephaly due to hemorrhagic colloid cyst was detected. Acute hemorrhage in colloid cysts is extremely rare and may present with symptoms of acute increase in the intracranial pressure. Intracystic hemorrhage is very rarely reported as a complication of colloid cyst presenting with paroxysmal symptoms of acute hydrocephaly. PMID:28210514

  17. Sulfonated nanoporous colloidal films and membranes

    NASA Astrophysics Data System (ADS)

    Smith, Joanna Jane

    The objective of this thesis is to describe the preparation and investigation of a new class of proton-conducting membrane materials, namely, nanoporous colloidal membranes whose proton conductivity results from the nanopore surface modification with organic molecules carrying acid functionalities. Both the proton transport and ion transport were studied in nanoporous silica colloidal crystals that were surface modified with sulfonic groups. First, the transport of ions was studied through sulfonated silica colloidal films that were supported on platinum electrodes using cyclic voltammetry. The surface of self-assembled nanoporous silica colloidal crystalline films was sulfonated using 1,3-propanesultone. We found that the flux of anions through the sulfonated colloidal films is reduced, while the flux of cations is increased, compared to the unmodified colloidal films. Second, the proton transport in free-standing assemblies of surface-sulfonated silica nanospheres, either randomly packed or self-assembled into a close-packed arrangement, were studied. It was demonstrated that colloidal assemblies prepared using surface-sulfonated silica nanospheres posses proton conductivity that depends on the ordering of the material, temperature and relative humidity. Based on the comparison between the close-packed and disordered assemblies made of the same spheres, we conclude that the increase in structural organization of the self-assembled colloidal materials leads to increased proton conductivity and better water retention. Next free-standing colloidal membranes with a relatively large area and no mechanical defects were prepared by sintering silica colloidal films. The sintered membranes were then surface rehydroxylated, which restores the surface silanol groups, and then can be chemically modified. Finally, sintered self-assembled nanoporous silica colloidal crystals were modified with poly(sulfopropyl-methacrylate) (pSPM) and poly(stryrenesulfonic acid) (pSSA) brushes

  18. Colloid Thrusters, Physics, Fabrication and Performance

    DTIC Science & Technology

    2005-11-17

    Murray, Paulo Lozano and Manuel Martinez-Sanchez, "Mass Spectrometric Analysis of Colloid Thruster Ion Emission from Selected Propellants", JOURNAL...OF PROPULSION AND POWER Vol. 21, No. 3, May-June 2005. 21. Paulo Lozano and Manuel Martinez-Sanchez, "Ionic liquid ion sources: characterization of...externally wetted emitters", Journal of Colloid and Interface Science 282 (2005) 415-421. 22. Paulo Lozano and Manuel Martinez-Sanchez, "Efficiency

  19. Colloid milium: a rare cutaneous deposition disease.

    PubMed

    Rahman, Simeen Ber; Arfan Ul Bari; Mumtaz, Nadeem

    2008-04-01

    Colloid milium is a rare degenerative skin disorder known by the development of small translucent, yellowish brown pappular nodules or plaques, generally located in sun exposed areas. Clinically they are of two types, adult and juvenile type. We present a case of adult type Colloid milium in a 60 years old female patient with clinical and histological findings unmistakable of the condition. She was treated with IPL. (Intense Pulsed Light) laser following unsatisfactory response with dermabrasion.

  20. Linked topological colloids in a nematic host.

    PubMed

    Martinez, Angel; Hermosillo, Leonardo; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-04-14

    Geometric shape and topology of constituent particles can alter many colloidal properties such as Brownian motion, self-assembly, and phase behavior. Thus far, only single-component building blocks of colloids with connected surfaces have been studied, although topological colloids, with constituent particles shaped as freestanding knots and handlebodies of different genus, have been recently introduced. Here we develop a topological class of colloids shaped as multicomponent links. Using two-photon photopolymerization, we fabricate colloidal microparticle analogs of the classic examples of links studied in the field of topology, the Hopf and Solomon links, which we disperse in nematic fluids that possess orientational ordering of anisotropic rod-like molecules. The surfaces of these particles are treated to impose tangential or perpendicular boundary conditions for the alignment of liquid crystal molecules, so that they generate a host of topologically nontrivial field and defect structures in the dispersing nematic medium, resulting in an elastic coupling between the linked constituents. The interplay between the topologies of surfaces of linked colloids and the molecular alignment field of the nematic host reveals that linking of particle rings with perpendicular boundary conditions is commonly accompanied by linking of closed singular defect loops, laying the foundations for fabricating complex composite materials with interlinking-based structural organization.

  1. Tunable Time-Dependent Colloidal Interactions

    NASA Astrophysics Data System (ADS)

    Bergman, Andrew M.; Rogers, W. Benjamin; Manoharan, Vinothan N.

    Self-assembly of colloidal particles can be driven by changes in temperature, density, or the concentration of solutes, and it is even possible to program the thermal response and equilibrium phase transitions of such systems. It is still difficult, however, to tune how the self-assembly process varies in time. We demonstrate control over the time-dependence of colloidal interactions, using DNA-functionalized colloidal particles with binding energies that are set by the concentration of a free linker strand in solution. We control the rate at which this free strand is consumed using a catalytic DNA reaction, whose rate is governed by the concentration of a catalyst strand. Varying the concentration of the linker, its competitor, and the catalyst at a fixed temperature, we can tune the rate and degree of the formation of colloidal aggregates and their following disassembly. Close to the colloidal melting point, the timescales of these out-of-equilibrium assembly and disassembly processes are determined by the rate of the catalytic reaction. Far below the colloidal melting point, however, the effects from varying our linker and competitor concentrations dominate.

  2. Self-replication with magnetic dipolar colloids.

    PubMed

    Dempster, Joshua M; Zhang, Rui; Olvera de la Cruz, Monica

    2015-10-01

    Colloidal self-replication represents an exciting research frontier in soft matter physics. Currently, all reported self-replication schemes involve coating colloidal particles with stimuli-responsive molecules to allow switchable interactions. In this paper, we introduce a scheme using ferromagnetic dipolar colloids and preprogrammed external magnetic fields to create an autonomous self-replication system. Interparticle dipole-dipole forces and periodically varying weak-strong magnetic fields cooperate to drive colloid monomers from the solute onto templates, bind them into replicas, and dissolve template complexes. We present three general design principles for autonomous linear replicators, derived from a focused study of a minimalist sphere-dimer magnetic system in which single binding sites allow formation of dimeric templates. We show via statistical models and computer simulations that our system exhibits nonlinear growth of templates and produces nearly exponential growth (low error rate) upon adding an optimized competing electrostatic potential. We devise experimental strategies for constructing the required magnetic colloids based on documented laboratory techniques. We also present qualitative ideas about building more complex self-replicating structures utilizing magnetic colloids.

  3. Inventions Utilizing Microfluidics and Colloidal Particles

    NASA Technical Reports Server (NTRS)

    Marr, David W.; Gong, Tieying; Oakey, John; Terray, Alexander V.; Wu, David T.

    2009-01-01

    Several related inventions pertain to families of devices that utilize microfluidics and/or colloidal particles to obtain useful physical effects. The families of devices can be summarized as follows: (1) Microfluidic pumps and/or valves wherein colloidal-size particles driven by electrical, magnetic, or optical fields serve as the principal moving parts that propel and/or direct the affected flows. (2) Devices that are similar to the aforementioned pumps and/or valves except that they are used to manipulate light instead of fluids. The colloidal particles in these devices are substantially constrained to move in a plane and are driven to spatially order them into arrays that function, variously, as waveguides, filters, or switches for optical signals. (3) Devices wherein the ultra-laminar nature of microfluidic flows is exploited to effect separation, sorting, or filtering of colloidal particles or biological cells in suspension. (4) Devices wherein a combination of confinement and applied electrical and/or optical fields forces the colloidal particles to become arranged into three-dimensional crystal lattices. Control of the colloidal crystalline structures could be exploited to control diffraction of light. (5) Microfluidic devices, incorporating fluid waveguides, wherein switching of flows among different paths would be accompanied by switching of optical signals.

  4. Colloids with high-definition surface structures.

    PubMed

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-07-03

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of approximately 10(7) to 10(8) particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors.

  5. Colloids with high-definition surface structures

    PubMed Central

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-01-01

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of ≈107 to 108 particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors. PMID:17592149

  6. Une vie active saine pour les enfants et les adolescents

    PubMed Central

    2002-01-01

    De mauvais modes de vie, comme une alimentation malsaine et l’inactivité physique, sont d'importants facteurs contributifs à une augmentation de la morbidité et de la mortalité secondaires à des maladies chroniques à l’âge adulte. Depuis dix ans, on remarque une augmentation du mode de vie sédentaire et de l’obésité chez les enfants et les adolescents, tant en Amérique du Nord qu’ailleurs dans le monde. Les médecins doivent être conscients de l’importance du problème, fournir des conseils de prévention aux familles et promouvoir une vie active saine dans leur pratique.

  7. Estuarine mixing behavior of colloidal organic carbon and colloidal mercury in Galveston Bay, Texas.

    PubMed

    Lee, Seyong; Han, Seunghee; Gill, Gary A

    2011-06-01

    Mercury (Hg) in estuarine water is distributed among different physical phases (i.e. particulate, colloidal, and truly dissolved). This phase speciation influences the fate and cycling of Hg in estuarine systems. However, limited information exists on the estuarine distribution of colloidal phase Hg, mainly due to the technical difficulties involved in measuring it. In the present study, we determined Hg and organic carbon levels from unfiltered, filtered (<0.45 μm), colloidal (10 kDa-0.45 μm), and truly dissolved (<10 kDa) fractions of Galveston Bay surface water in order to understand the estuarine mixing behavior of Hg species as well as interactions of Hg with colloidal organic matter. For the riverine end-member, the colloidal fraction comprised 43 ± 11% of the total dissolved Hg pool and decreased to 17 ± 8% in brackish water. In the estuarine mixing zone, dissolved Hg and colloidal organic carbon showed non-conservative removal behavior, particularly in the low salinity (<15 ppt) region. This removal may be caused by salt-induced coagulation of colloidal matter and consequent removal of dissolved Hg. The particle-water interaction, K(d) ([particulate Hg (mol kg(-1))]/[dissolved Hg (mol L(-1))]) of Hg decreased as particle concentration increased, while the particle-water partition coefficient based on colloidal Hg and the truly dissolved Hg fraction, K(c) ([colloidal Hg (mol kg(-1))]/[truly dissolved Hg (mol L(-1))]) of Hg remained constant as particle concentration increased. This suggests that the particle concentration effect is associated with the amount of colloidal Hg, increasing in proportion to the amount of suspended particulate matter. This work demonstrates that, colloidal organic matter plays an important role in the transport, particle-water partitioning, and removal of dissolved Hg in estuarine waters.

  8. ["Les Impatients": expression through art].

    PubMed

    Lamontagne, Céline; Palardy, Lorraine

    2015-01-01

    The organization called "Les Impatients" was founded in 1992. Using a unique model, Les Impatients welcomes those with mental health issues who would like to express themselves through art. Les Impatients offers free creative workshops and encourages exchanges with the community through the sharing of its participants' creations. The name Les Impatients reinforces the idea that the organization does not consider those attending its workshops as patients, but rather creators who are eager to heal, develop their craft and find their place in society. The participants contribute to the collective objective of breaking down the stigma that surrounds mental illness.Les Impatients collaborates with various mental health organizations in Quebec, such as the Institut universitaire en santé mentale de Montréal (IUSMM) affiliated to the Université de Montréal, Douglas Mental Health University Institute (DMHUI), the Centre de santé et services sociaux Drummond (CSSS Drummond) and the Centre de santé et services sociaux Pierre-Boucher (CSSS Pierre-Boucher). Les Impatients offers more than 48 workshops in eight different locations to around 450 participants each week.Dissemination activities, remarkable events, original projects: Les Impatients stands out through its realizations. Examples are exhibitions, collections of love letters, comic books, CD, concerts, and reading nights. The organization's originality resides in the exploration of the links between the work of the participants and that of professional artists. An illustration of this interest is the annual Parle-moi d'amour auction-exhibition, which has been one of Les Impatients' major events since 1999.As part of its mission, Les Impatients conserves the works of art created by the participants during the workshops. Its collection includes more than 15,000 works of art from Les Impatients as well as pieces donated by collectors of unconventional art, commonly known as "art brut" or "outsider art". The

  9. Colloid's influences on microalgae growth as a potential environmental factor

    NASA Astrophysics Data System (ADS)

    Zhao, Xinhuai; Zhang, Zhengbin; Liu, Liansheng

    2003-09-01

    The role of colloid as “colloid pump” in the ocean is well known. The important influence of colloid in seawater on the growth of microalga was found in our 1999 2000 study. Colloid concentrates were obtained by employing a cross-flow filtration system to ultrafilter seawater (which had been pre-filtrated by 0.45 μm acetate cellulose membrane) successively with different membranes. Ultrafiltration retentions (we called them colloid concentrates) together with control sample (seawater without colloid) were then inoculated with two species of microalgae and cultivated in selected conditions. Monitoring of microalgae growth during cultivation showed that all colloid concentrates had obvious influence on the growth of the microalgae studied. Addition of Fe(OH)3 colloid or organic colloid (protein or carbohydrate) to the control sample enhanced the microalgae’s growth.

  10. Statistical thermodynamics of charge-stabilized colloids

    NASA Astrophysics Data System (ADS)

    Torres Valderrama, A.

    2008-06-01

    This thesis is a theoretical study of equilibrium statistical thermodynamic properties of colloidal systems in which electrostatic interactions play a dominant role, namely, charge-stabilized colloidal suspensions. Such systems are fluids consisting of a mixture of a large number of mesoscopic particles and microscopic ions which interact via the Coulomb force, suspended in a molecular fluid. Quantum statistical mechanics is essential to fully understand the properties and stability of such systems. A less fundamental but for many purposes, sufficient description, is provided by classical statistical mechanics. In such approximation the system is considered as composed of a great number of charged classical particles with additional hard-core repulsions. The kinetic energy or momentum integrals become independent Gaussians, and hence their contribution to the free energy can be trivially evaluated. The contribution of the potential energy to the free energy on the other hand, depends upon the configuration of all the particles and becomes highly non-trivial due to the long-range character of the Coulomb force and the extremely different length scales involved in the problem. Using the microscopic model described above, we focus on the calculation of equilibrium thermodynamic properties (response functions), correlations (structure factors), and mechanical properties (forces and stresses), which can be measured in experiments and computed by Monte Carlo simulations. This thesis is divided into three parts. In part I, comprising chapters 2 and 3, we focus on finite-thickness effects in colloidal platelets and rigid planar membranes. In chapter 2 we study electrolyte-mediated interactions between two of such colloidal objects. Several aspects of these interactions are considered including the nature (attractive or repulsive) of the force between the objects, the osmotic properties for different types of surfaces and image charge effects. In part II, which includes

  11. Colloids and polymers in random colloidal matrices: Demixing under good-solvent conditions

    NASA Astrophysics Data System (ADS)

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2012-10-01

    We consider a simplified coarse-grained model for colloid-polymer mixtures, in which polymers are represented as monoatomic molecules interacting by means of pair potentials. We use it to study polymer-colloid segregation in the presence of a quenched matrix of colloidal hard spheres. We fix the polymer-to-colloid size ratio to 0.8 and consider matrices such that the fraction f of the volume that is not accessible to the colloids due to the matrix is equal to 40%. As in the Asakura-Oosawa-Vrij (AOV) case, we find that binodal curves in the polymer and colloid volume-fraction plane have a small dependence on disorder. As for the position of the critical point, the behavior differs from that observed in the AOV case: While the critical colloid volume fraction is essentially the same in the bulk and in the presence of the matrix, the polymer volume fraction at criticality increases as f increases. At variance with the AOV case, no capillary colloid condensation or evaporation is generically observed.

  12. Colloids and polymers in random colloidal matrices: demixing under good-solvent conditions.

    PubMed

    Annunziata, Mario Alberto; Pelissetto, Andrea

    2012-10-01

    We consider a simplified coarse-grained model for colloid-polymer mixtures, in which polymers are represented as monoatomic molecules interacting by means of pair potentials. We use it to study polymer-colloid segregation in the presence of a quenched matrix of colloidal hard spheres. We fix the polymer-to-colloid size ratio to 0.8 and consider matrices such that the fraction f of the volume that is not accessible to the colloids due to the matrix is equal to 40%. As in the Asakura-Oosawa-Vrij (AOV) case, we find that binodal curves in the polymer and colloid volume-fraction plane have a small dependence on disorder. As for the position of the critical point, the behavior differs from that observed in the AOV case: While the critical colloid volume fraction is essentially the same in the bulk and in the presence of the matrix, the polymer volume fraction at criticality increases as f increases. At variance with the AOV case, no capillary colloid condensation or evaporation is generically observed.

  13. Colloidal Gelation-2 and Colloidal Disorder-Order Transition-2 Investigations Conducted on STS-95

    NASA Technical Reports Server (NTRS)

    Hoffmann, Monica T.

    2000-01-01

    The Colloidal Gelation-2 (CGEL 2) and Colloidal Disorder-Order Transition-2 (CDOT 2) investigations flew on Space Shuttle Discovery mission STS-95 (also known as the John Glenn Mission). These investigations were part of a series of colloid experiments designed to help scientists answer fundamental science questions and reduce the trial and error involved in developing new and better materials. Industries dealing with semiconductors, electro-optics, ceramics, and composites are just a few that may benefit from this knowledge. The goal of the CGEL 2 investigation was to study the fundamental properties of colloids to help scientists better understand their nature and make them more useful for technology. Colloids consist of very small (submicron) particles suspended in a fluid. They play a critical role in the technology of this country, finding uses in materials ranging from paints and coatings to drugs, cosmetics, food, and drink. Although these products are routinely produced and used, there are still many aspects of their behavior about which scientists know little. Understanding their structures may allow scientists to manipulate the physical properties of colloids (a process called "colloidal engineering") to produce new materials and products. Colloid research may even improve the processing of known products to enhance their desirable properties.

  14. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Baumann, Thomas

    2014-05-01

    In the light of an increasing number of technical applications using nanoparticles and reports of adverse effects of engineered nanoparticles, research on the occurrence and stability of particles in all compartments has to be intensified. Colloids in river water represent the geologic setting, environmental conditions, and the anthropogenic use in its catchment. The river not only acts as a sink for nanoparticles but also as the source term due to exchange in the hyporheic zone and in bank filtration setups. The concentration, size distribution and elemental composition of particles in the River Inn were studied from the source in the Swiss Alps to the river mouth at Passau. Samples were collected after each tributary from a sub-catchment and filtered on-site. The elemental composition was determined after acid digestion with ICP/MS. SEM/EDX analyses provided morphological and elemental information for single particles. A complementary chemical analysis of the river water was performed to assess the geochemical stability of indvidual particles. Particles in the upper, rural parts mainly reveal changes in the geological setting of the tributary catchments. Not unexpectedly, particles originating from crystalline rocks, were more stable than particles originating from calcareous rocks. Anthropogenic and industrial influences increase in the lower parts. This went together with a change of the size distribution, an increase of the number of organic particles, and a decrease of the microfauna. Interestingly, specific leisure activities in a sub-catchment, like extensive downhill skiing, manifest itself in the particle composition.

  15. Drying of thin colloidal films

    NASA Astrophysics Data System (ADS)

    Routh, Alexander F.

    2013-04-01

    When thin films of colloidal fluids are dried, a range of transitions are observed and the final film profile is found to depend on the processes that occur during the drying step. This article describes the drying process, initially concentrating on the various transitions. Particles are seen to initially consolidate at the edge of a drying droplet, the so-called coffee-ring effect. Flow is seen to be from the centre of the drop towards the edge and a front of close-packed particles passes horizontally across the film. Just behind the particle front the now solid film often displays cracks and finally the film is observed to de-wet. These various transitions are explained, with particular reference to the capillary pressure which forms in the solidified region of the film. The reasons for cracking in thin films is explored as well as various methods to minimize its effect. Methods to obtain stratified coatings through a single application are considered for a one-dimensional drying problem and this is then extended to two-dimensional films. Different evaporative models are described, including the physical reason for enhanced evaporation at the edge of droplets. The various scenarios when evaporation is found to be uniform across a drying film are then explained. Finally different experimental techniques for examining the drying step are mentioned and the article ends with suggested areas that warrant further study.

  16. Self-Pinning by Colloids Confined at a Contact Line

    NASA Astrophysics Data System (ADS)

    Weon, Byung Mook; Je, Jung Ho

    2013-01-01

    Colloidal particles suspended in a fluid usually inhibit complete wetting of the fluid on a solid surface and cause pinning of the contact line, known as self-pinning. We show differences in spreading and drying behaviors of pure and colloidal droplets using optical and confocal imaging methods. These differences come from spreading inhibition by colloids confined at a contact line. We propose a self-pinning mechanism based on spreading inhibition by colloids. We find a good agreement between the mechanism and the experimental result taken by directly tracking individual colloids near the contact lines of evaporating colloidal droplets.

  17. Seismic stress mobilization of natural colloids in a porous rock

    SciTech Connect

    Roberts, Peter M; Abdel-fattah, Amr I

    2008-01-01

    Stress oscillations at 26 Hz enhanced the release of natural micro-particles (colloids) in a porous rock sample. Micron-scale effects were induced by meter-scale wavelengths. The results are attributed to altering the release rate coefficient for colloids trapped in pores. The rate change did not depend on colloid size and thus is not due to altering colloid-pore-wall interactions. Enhanced colloid detachment from pore walls and flushing from dead-end pores are likely mechanisms. This phenomenon could impact a broad range of physical sciences involving colloid dynamics and porous transport.

  18. Les plaies du tendon patellaire

    PubMed Central

    Mechchat, Atif; Elidrissi, Mohammed; Mardy, Abdelhak; Elayoubi, Abdelghni; Shimi, Mohammed; Elibrahimi, Abdelhalim; Elmrini, Abdelmajid

    2014-01-01

    Les plaies du tendon patellaire sont peu fréquentes et sont peu rapportés dans la littérature, contrairement aux ruptures sous cutanées. Les sections du tendon patellaire nécessitent une réparation immédiate afin de rétablir l'appareil extenseur et de permettre une récupération fonctionnelle précoce. A travers ce travail rétrospectif sur 13 cas, nous analysons les aspects épidémiologiques, thérapeutiques et pronostiques de ce type de pathologie en comparant différents scores. L’âge moyen est de 25 ans avec une prédominance masculine. Les étiologies sont dominées par les accidents de la voie publique (68%) et les agressions par agent tranchant (26%) et contendant (6 %). Tous nos patients ont bénéficié d'un parage chirurgical avec suture tendineuse direct protégée par un laçage au fils d'aciers en légère flexion. La rééducation est débutée après sédation des phénomènes inflammatoires. Au dernier recul les résultats sont excellents et bon à 92%. Nous n'avons pas noté de différence de force musculaire et d'amplitude articulaire entre le genou sain et le genou lésé. Les lésions ouvertes du tendon patellaire est relativement rare. La prise en charge chirurgicale rapide donne des résultats assez satisfaisants. La réparation est généralement renforcée par un semi-tendineux, synthétique ou métallique en forme de cadre de renfort pour faciliter la réadaptation et réduire le risque de récidive après la fin de l'immobilisation. PMID:25170379

  19. Rheological properties of Cubic colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Boromand, Arman; Maia, Joao

    2016-11-01

    Colloidal and non-colloidal suspensions are ubiquitous in many industrial application. There are numerous studies on these systems to understand and relate their complex rheological properties to their microstructural evolution under deformation. Although most of the experimental and simulation studies are centered on spherical particles, in most of the industrial applications the geometry of the colloidal particles deviate from the simple hard sphere and more complex geometries exist. Recent advances in microfabrication paved the way to fabricate colloidal particles with complex geometries for applications in different areas such as drug delivery where the fundamental understanding of their dynamics has remained unexplored. In this study, using dissipative particle dynamics, we investigate the rheological properties of cubic (superball) particles which are modeled as the cluster of core-modified DPD particles. Explicit representation of solvent particles in the DPD scheme will conserve the full hydrodynamic interactions between colloidal particles. Rheological properties of these cubic suspensions are investigated in the dilute and semi-dilute regimes. The Einstein and Huggins coefficients for these particles with different superball exponent will be calculate which represent the effect of single particle's geometry and multibody interactions on viscosity, respectively. The response of these suspensions is investigated under simple shear and oscillatory shear where it is shown that under oscillation these particles tend to form crystalline structure giving rise to stronger shear-thinning behavior recently measured experimentally.

  20. Quasicrystalline tilings with nematic colloidal platelets

    PubMed Central

    Dontabhaktuni, Jayasri; Ravnik, Miha; Žumer, Slobodan

    2014-01-01

    Complex nematic fluids have the remarkable capability for self-assembling regular colloidal structures of various symmetries and dimensionality according to their micromolecular orientational order. Colloidal chains, clusters, and crystals were demonstrated recently, exhibiting soft-matter functionalities of robust binding, spontaneous chiral symmetry breaking, entanglement, shape-driven and topological driven assembly, and even memory imprinting. However, no quasicrystalline structures were found. Here, we show with numerical modeling that quasicrystalline colloidal lattices can be achieved in the form of original Penrose P1 tiling by using pentagonal colloidal platelets in layers of nematic liquid crystals. The tilings are energetically stabilized with binding energies up to 2500 kBT for micrometer-sized platelets and further allow for hierarchical substitution tiling, i.e., hierarchical pentagulation. Quasicrystalline structures are constructed bottom-up by assembling the boat, rhombus, and star maximum density clusters, thus avoiding other (nonquasicrystalline) stable or metastable configurations of platelets. Central to our design of the quasicrystalline tilings is the symmetry breaking imposed by the platelet shape and the surface anchoring conditions at the colloidal platelets, which are misaligning and asymmetric over two perpendicular mirror planes. Finally, the design of the quasicrystalline tilings as platelets in nematic liquid crystals is inherently capable of a continuous variety of length scales of the tiling, ranging over three orders of magnitude in the typical length (from to ), which could allow for the design of quasicrystalline photonics at multiple frequency ranges. PMID:24550269

  1. Colloid-polymer mixtures under slit confinement.

    PubMed

    Pérez-Ramírez, Allan; Figueroa-Gerstenmaier, Susana; Odriozola, Gerardo

    2017-03-14

    We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1⩾q⩾0.4 and the confinement distance, H, in 10σc⩾H⩾3σc, σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H-σc)(-1) for H≳4σc. The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H-σc)(-1), from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.

  2. Colloids with continuously tunable surface charge.

    PubMed

    van Ravensteijn, Bas G P; Kegel, Willem K

    2014-09-09

    In this paper, we present a robust way to tune the surface potential of polystyrene colloids without changing the pH, ionic strength, etc. The colloids are composed of a cross-linked polystyrene core and a cross-linked vinylbenzyl chloride layer. Besides the chlorine groups, the particle surface contains sulfate/sulfonate groups (arising from the polymerization initiators) that provide a negative surface potential. Performing a Menschutkin reaction on the surface chlorine groups with tertiary amines allows us to introduce quaternary, positively charged amines. The overall charge on the particles is then determined by the ratio between the sulfate/sulfonate moieties and the quaternary amines. Using this process, we were able to invert the charge in a continuous manner without losing colloidal stability upon passing the isoelectric point. The straightforward reaction mechanism together with the fact that the reaction could be quenched rapidly resulted in a colloidal system in which the ζ potential can be tuned between -80 and 45 mV. As proof of principle, the positively charged particles were used in heterocoagulation experiments with nanometer- and micrometer-sized negatively charged silica particles to create geometrically well-defined colloidal (nano) clusters.

  3. Colloid-polymer mixtures under slit confinement

    NASA Astrophysics Data System (ADS)

    Pérez-Ramírez, Allan; Figueroa-Gerstenmaier, Susana; Odriozola, Gerardo

    2017-03-01

    We report a NVT molecular dynamic study of colloid-polymer mixtures under slit confinement. For this purpose, we are employing the Asakura-Oosawa model for studying colloidal particles, polymer coils, and hard walls as the external confining field. The colloid-polymer size ratio, q, is varied in the range 1 ⩾q ⩾0.4 and the confinement distance, H, in 10 σc ⩾H ⩾3 σc , σc being the colloidal diameter. Vapor-liquid coexistence properties are assessed, from which phase diagrams are built. The obtained data fulfill the corresponding states law for a constant H when q is varied. The shift of the polymer and colloidal chemical potentials of coexistence follows a linear relationship with (H-σc ) -1 for H ≳4 σc . The confined vapor-liquid interfaces can be fitted with a semicircular line of curvature (H-σc ) -1, from which the contact angle can be obtained. We observe complete wetting of the confining walls for reservoir polymer concentrations above and close to the critical value, and partial wetting for reservoir polymer concentrations above and far from it.

  4. Interparticle interactions and polarization effects in colloids

    SciTech Connect

    Hayter, J.B.

    1987-01-01

    The physics of simple colloidal systems is usually dominated by three independent length scales: the particle size, the average interparticle distance, and the range of the interparticle potential. The dispersed particles typically have characteristic dimensions in the range 5 to 100 nm, often with spherical or cylindrical symmetry. Dispersion densities vary over volume fractions ranging from 0.5 to 10/sup -4/, with the corresponding mean interparticle distances ranging from about 1 to 10 diameters (in spherical systems). The interaction potential may be very short ranged (hard sphere), very long ranged (Coulomb or dipolar), or anywhere in between (screened Coulomb), and the correlations exhibited in the dispersion may be gas-like, liquid-like or crystalline, depending on the range of the potential relative to the interparticle distance. This rich phase behavior is responsible for the remarkable importance of colloidal studies in many areas of condensed matter physics and biophysics, but it poses often intractable problems in developing the statistical mechanical descriptions necessary for an understanding of scattering data from colloids. This paper will review the considerable recent progress in this field, in the context of SANS experiments on colloids in which the potentials are dominated by either screened Coulomb or magnetic dipolar interactions; in the case of magnetic colloids (ferrofluids), the use of polarization analysis will also be discussed. 32 refs., 4 figs.

  5. Method for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

    Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

    1999-01-01

    A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

  6. Apparatus for electrohydrodynamically assembling patterned colloidal structures

    NASA Technical Reports Server (NTRS)

    Trau, Mathias (Inventor); Aksay, Ilhan A. (Inventor); Saville, Dudley A. (Inventor)

    2000-01-01

    A method apparatus is provided for electrophoretically depositing particles onto an electrode, and electrohydrodynamically assembling the particles into crystalline structures. Specifically, the present method and apparatus creates a current flowing through a solution to cause identically charged electrophoretically deposited colloidal particles to attract each other over very large distances (<5 particle diameters) on the surface of electrodes to form two-dimensional colloidal crystals. The attractive force can be created with both DC and AC fields and can modulated by adjusting either the field strength or frequency of the current. Modulating this lateral attraction between the particles causes the reversible formation of two-dimensional fluid and crystalline colloidal states on the electrode surface. Further manipulation allows for the formation of two or three-dimensional colloidal crystals, as well as more complex designed structures. Once the required structures are formed, these three-dimension colloidal crystals can be permanently frozen or glued by controlled coagulation induced by to the applied field to form a stable crystalline structure.

  7. Validating LES for Jet Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Bridges, James

    2011-01-01

    Engineers charged with making jet aircraft quieter have long dreamed of being able to see exactly how turbulent eddies produce sound and this dream is now coming true with the advent of large eddy simulation (LES). Two obvious challenges remain: validating the LES codes at the resolution required to see the fluid-acoustic coupling, and the interpretation of the massive datasets that result in having dreams come true. This paper primarily addresses the former, the use of advanced experimental techniques such as particle image velocimetry (PIV) and Raman and Rayleigh scattering, to validate the computer codes and procedures used to create LES solutions. It also addresses the latter problem in discussing what are relevant measures critical for aeroacoustics that should be used in validating LES codes. These new diagnostic techniques deliver measurements and flow statistics of increasing sophistication and capability, but what of their accuracy? And what are the measures to be used in validation? This paper argues that the issue of accuracy be addressed by cross-facility and cross-disciplinary examination of modern datasets along with increased reporting of internal quality checks in PIV analysis. Further, it is argued that the appropriate validation metrics for aeroacoustic applications are increasingly complicated statistics that have been shown in aeroacoustic theory to be critical to flow-generated sound.

  8. Validating LES for Jet Aeroacoustics

    NASA Technical Reports Server (NTRS)

    Bridges, James; Wernet, Mark P.

    2011-01-01

    Engineers charged with making jet aircraft quieter have long dreamed of being able to see exactly how turbulent eddies produce sound and this dream is now coming true with the advent of large eddy simulation (LES). Two obvious challenges remain: validating the LES codes at the resolution required to see the fluid-acoustic coupling, and the interpretation of the massive datasets that are produced. This paper addresses the former, the use of advanced experimental techniques such as particle image velocimetry (PIV) and Raman and Rayleigh scattering, to validate the computer codes and procedures used to create LES solutions. This paper argues that the issue of accuracy of the experimental measurements be addressed by cross-facility and cross-disciplinary examination of modern datasets along with increased reporting of internal quality checks in PIV analysis. Further, it argues that the appropriate validation metrics for aeroacoustic applications are increasingly complicated statistics that have been shown in aeroacoustic theory to be critical to flow-generated sound, such as two-point space-time velocity correlations. A brief review of data sources available is presented along with examples illustrating cross-facility and internal quality checks required of the data before it should be accepted for validation of LES.

  9. Influence of heteroaggregation processes between intrinsic colloids and carrier colloids on cerium(III) mobility through fractured carbonate rocks.

    PubMed

    Tran, Emily; Klein Ben-David, Ofra; Teutch, Nadya; Weisbrod, Noam

    2016-09-01

    Colloid facilitated transport of radionuclides has been implicated as a major transport vector for leaked nuclear waste in the subsurface. Sorption of radionuclides onto mobile carrier colloids such as bentonite and humic acid often accelerates their transport through saturated rock fractures. Here, we employ column studies to investigate the impact of intrinsic, bentonite and humic acid colloids on the transport and recovery of Ce(III) through a fractured chalk core. Ce(III) recovery where either bentonite or humic colloids were added was 7.7-26.9% Ce for all experiments. Greater Ce(III) recovery was observed when both types of carrier colloids were present (25.4-37.4%). When only bentonite colloids were present, Ce(III) appeared to be fractionated between chemical sorption to the bentonite colloid surfaces and heteroaggregation of bentonite colloids with intrinsic carbonate colloids, precipitated naturally in solution. However, scanning electron microscope (SEM) images and colloid stability experiments reveal that in suspensions of humic acid colloids, colloid-facilitated Ce(III) migration results only from the latter attachment mechanism rather than from chemical sorption. This observed heteroaggregation of different colloid types may be an important factor to consider when predicting potential mobility of leaked radionuclides from geological repositories for spent fuel located in carbonate rocks.

  10. Colloidal crystallization of colloidal silica modified with ferrocenyl group-contained polymers in organic solvents.

    PubMed

    Yoshinaga, Kohji; Shigeta, Maki; Komune, Seishu; Mouri, Emiko; Nakai, Akemi

    2007-01-15

    Surface modification of colloidal silica with ferrocenyl-grafted polymer and colloidal crystallization of the particles in organic solvent were studied. Poly(methyl methacrylate-co-vinylferrocene)-grafted silica never formed colloidal crystals in polar solvent, such as acetone, acetonitrile, ethanol and N,N-dimethylformamide (DMF), while poly(methyl methacrylate-co-ferrocenyl acrylate)-grafted silica gave colloidal crystallization in DMF. The particles prepared by grafting of poly(N,N-dimethylacrylamide-co-vinylferrocene), with vinylferrocene (Vfc) mole fraction of 1/13 and 1/23, were observed to give the crystallization in ethanol and DMF over particle volume fraction of 0.058. Further, silica modified with copolymer of Vfc and N-vinyl-2-pyrrolidone, N-vinylcarbazole or N-isopropylacrylamide formed colloidal crystals in ethanol and DMF. Especially, poly(N-isopropylacrylamide-co-Vfc)-grafted silica, which was composed of the highest mole fraction of vinylferrocene, 1/3, afforded colloidal crystallization in ethanol over particle volume fraction of 0.053. Relatively high polar vinylferrocene copolymer grafting of silica resulted in colloidal polymerization in organic solvents.

  11. Electrochemical reduction of chlorophyll in colloidal solutions

    SciTech Connect

    Suponeva, E.P.; Kadoshnikova, I.G.; Kazakova, A.A.; Kiselev, B.A.

    1986-02-01

    This paper discusses determining the energy yield of the photochemical reaction. The authors investigated the peculiarities of the electrochemical reduction of Chl in the colloidal state, where the elements of the molecular organization of the pigments in the reaction centers of photosynthesis are simulated and, as a result, the lifetime of Chl.- is substantially increased. Polarograms of a colloidal solution of Chl ''a'' in aqueous buffer solution contining less than 5% acetone are presented. The adsorption spectra were measured on a spectrophotometer and the fluorescence spectra were recorded on a setup assembled on the basis of RM-w and FEU-30 monochromators. The results obtained are evidence of the ability of Chl for spontaneous formation of molecular associates in aqueous medium, which are characterized by hindrance of the protonation of Chl.- in comparison with monomeric Chl at a high rate of exchange of an electron between the eletrode and the colloidal particle and between molecules in the volume of the particle.

  12. Spin Dynamics of Charged Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Stern, N. P.

    2005-03-01

    Colloidal semiconductor quantum dots are promising structures for controlling spin phenomena because of their highly size- tunable physical properties, ease of manufacture, and nanosecond-scale spin lifetimes at room temperature. Recent experiments have succeeded in controlling the charging of the lowest electronic state of colloidal quantum dots ootnotetextC. Wang, B. L. Wehrenberg, C. Y. Woo, and P. Guyot-Sionnest, J. Phys. Chem B 108, 9027 (2004).. Here we use time-resolved Faraday rotation measurements in the Voigt geometry to investigate the spin dynamics of colloidal CdSe quantum dot films in both a charged and uncharged state at room temperature. The charging of the film is controlled by applying a voltage in an electrochemical cell and is confirmed by absorbance measurements. Significant changes in the spin precession are observed upon charging, reflecting the voltage- controlled electron occupation of the quantum dot states and filling of surface states.

  13. Targeted delivery of colloids by swimming bacteria

    NASA Astrophysics Data System (ADS)

    Koumakis, N.; Lepore, A.; Maggi, C.; di Leonardo, R.

    2013-10-01

    The possibility of exploiting motile microorganisms as tiny propellers represents a fascinating strategy for the transport of colloidal cargoes. However, delivery on target sites usually requires external control fields to steer propellers and trigger cargo release. The need for a constant feedback mechanism prevents the design of compact devices where biopropellers could perform their tasks autonomously. Here we show that properly designed three-dimensional (3D) microstructures can define accumulation areas where bacteria spontaneously and efficiently store colloidal beads. The process is stochastic in nature and results from the rectifying action of an asymmetric energy landscape over the fluctuating forces arising from collisions with swimming bacteria. As a result, the concentration of colloids over target areas can be strongly increased or depleted according to the topography of the underlying structures. Besides the significance to technological applications, our experiments pose some important questions regarding the structure of stationary probability distributions in non-equilibrium systems.

  14. Colloidal Disorder-Order Transition (CDOT-2)

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This is an image of a colloidal crystal from the CDOT-2 investigation flown on STS-95. There are so many colloidal particles in this sample that it behaves like a glass. In the laboratory on Earth, the sample remained in an amorphous state, showing no sign of crystal growth. In microgravity the sample crystallized in 3 days, as did the other glassy colloidal samples examined in the CDOT-2 experiment. During the investigation, crystallization occurred in samples that had a volume fraction (number of particles per total volume) larger than the formerly reported glass transition of 0.58. This has great implications for theories of the structural glass transition. These crystals were strong enough to survive space shuttle re-entry and landing.

  15. Manipulating semiconductor colloidal stability through doping.

    PubMed

    Fleharty, Mark E; van Swol, Frank; Petsev, Dimiter N

    2014-10-10

    The interface between a doped semiconductor material and electrolyte solution is of considerable fundamental interest, and is relevant to systems of practical importance. Both adjacent domains contain mobile charges, which respond to potential variations. This is exploited to design electronic and optoelectronic sensors, and other enabling semiconductor colloidal materials. We show that the charge mobility in both phases leads to a new type of interaction between semiconductor colloids suspended in aqueous electrolyte solutions. This interaction is due to the electrostatic response of the semiconductor interior to disturbances in the external field upon the approach of two particles. The electrostatic repulsion between two charged colloids is reduced from the one governed by the charged groups present at the particles surfaces. This type of interaction is unique to semiconductor particles and may have a substantial effect on the suspension dynamics and stability.

  16. Shape-shifting colloids via stimulated dewetting

    PubMed Central

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-01-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly. PMID:27426418

  17. Manipulating colloidal assemblies with active dopants

    NASA Astrophysics Data System (ADS)

    Ramananarivo, Sophie; Palacci, Jeremie

    2016-11-01

    The dynamics of a densely packed 2D layer of colloids can be significantly altered upon introducing a small amount of active microparticles. Those motile intruders drive the system out-of-equilibrium, which produces a variety of new complex phenomena such as the accentuation of density heterogeneities or the reorganization of crystalline colloidal structures. We investigate the altered dynamics of the passive spheres, as well as the behavior of micro-swimmers propelling in such crowded environment where interactions with passive obstacles or other active units become important. Ultimately, understanding and controlling such mixed systems could open new routes toward activity-assisted manipulation of colloids, potentially guiding the design of materials able to self-anneal their defects.

  18. Convection of a stratified colloidal suspension

    SciTech Connect

    Cherepanov, I. N.; Smorodin, B. L.

    2013-11-15

    The convection of a colloidal suspension, which is a binary mixture of a carrier medium with an admixture of nanoparticles having a large positive thermal diffusion parameter, has been studied for the case of the heating of a horizontal cell from below and periodic conditions at the vertical boundaries corresponding to the experimental situation of ring channels. Bifurcation diagrams have been constructed for vibrational and monotonic regimes of the convection of the colloidal mixture. The time dependences of the maximum stream function and the stream function at a fixed point of the cell, as well as the spatial distributions of the concentration field of the colloid admixture, have been obtained. It has been shown that a stable regime of traveling waves exists in a certain region of the parameters of the problem (Boltzmann and Rayleigh numbers characterizing the gravitational stratification and intensity of the thermal effect, respectively)

  19. Colloids in food: ingredients, structure, and stability.

    PubMed

    Dickinson, Eric

    2015-01-01

    This article reviews progress in the field of food colloids with particular emphasis on advances in novel functional ingredients and nanoscale structuring. Specific aspects of ingredient development described here are the stabilization of bubbles and foams by the protein hydrophobin, the emulsifying characteristics of Maillard-type protein-polysaccharide conjugates, the structural and functional properties of protein fibrils, and the Pickering stabilization of dispersed droplets by food-grade nanoparticles and microparticles. Building on advances in the nanoscience of biological materials, the application of structural design principles to the fabrication of edible colloids is leading to progress in the fabrication of functional dispersed systems-multilayer interfaces, multiple emulsions, and gel-like emulsions. The associated physicochemical insight is contributing to our mechanistic understanding of oral processing and textural perception of food systems and to the development of colloid-based strategies to control delivery of nutrients during food digestion within the human gastrointestinal tract.

  20. Plasmonic films based on colloidal lithography.

    PubMed

    Ai, Bin; Yu, Ye; Möhwald, Helmuth; Zhang, Gang; Yang, Bai

    2014-04-01

    This paper reviews recent advances in the field of plasmonic films fabricated by colloidal lithography. Compared with conventional lithography techniques such as electron beam lithography and focused ion beam lithography, the unconventional colloidal lithography technique with advantages of low-cost and high-throughput has made the fabrication process more efficient, and moreover brought out novel films that show remarkable surface plasmon features. These plasmonic films include those with nanohole arrays, nanovoid arrays and nanoshell arrays with precisely controlled shapes, sizes, and spacing. Based on these novel nanostructures, optical and sensing performances can be greatly enhanced. The introduction of colloidal lithography provides not only efficient fabrication processes but also plasmonic films with unique nanostructures, which are difficult to be fabricated by conventional lithography techniques.

  1. Dynamic Assembly of Magnetic Colloidal Vortices

    SciTech Connect

    Mohorič, Tomaž; Kokot, Gašper; Osterman, Natan; Snezhko, Alexey; Vilfan, Andrej; Babič, Dušan; Dobnikar, Jure

    2016-04-29

    Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications.

  2. Energy transport velocity in bidispersed magnetic colloids

    NASA Astrophysics Data System (ADS)

    Bhatt, Hem; Patel, Rajesh; Mehta, R. V.

    2012-07-01

    Study of energy transport velocity of light is an effective background for slow, fast, and diffuse light and exhibits the photonic property of the material. We report a theoretical analysis of magnetic field dependent resonant behavior in forward-backward anisotropy factor, light diffusion constant, and energy transport velocity for bidispersed magnetic colloids. A bidispersed magnetic colloid is composed of micrometer size magnetic spheres dispersed in a magnetic nanofluid consisting of magnetic nanoparticles in a nonmagnetic liquid carrier. Magnetic Mie resonances and reduction in energy transport velocity accounts for the possible delay (longer dwell time) by field dependent resonant light transport. This resonant behavior of light in bidispersed magnetic colloids suggests a novel magnetophotonic material.

  3. Shape-shifting colloids via stimulated dewetting

    NASA Astrophysics Data System (ADS)

    Youssef, Mena; Hueckel, Theodore; Yi, Gi-Ra; Sacanna, Stefano

    2016-07-01

    The ability to reconfigure elementary building blocks from one structure to another is key to many biological systems. Bringing the intrinsic adaptability of biological systems to traditional synthetic materials is currently one of the biggest scientific challenges in material engineering. Here we introduce a new design concept for the experimental realization of self-assembling systems with built-in shape-shifting elements. We demonstrate that dewetting forces between an oil phase and solid colloidal substrates can be exploited to engineer shape-shifting particles whose geometry can be changed on demand by a chemical or optical signal. We find this approach to be quite general and applicable to a broad spectrum of materials, including polymers, semiconductors and magnetic materials. This synthetic methodology can be further adopted as a new experimental platform for designing and rapidly prototyping functional colloids, such as reconfigurable micro swimmers, colloidal surfactants and switchable building blocks for self-assembly.

  4. Phosphate binding by natural iron-rich colloids in streams.

    PubMed

    Baken, Stijn; Moens, Claudia; van der Grift, Bas; Smolders, Erik

    2016-07-01

    Phosphorus (P) in natural waters may be bound to iron (Fe) bearing colloids. However, the natural variation in composition and P binding strength of these colloids remain unclear. We related the composition of "coarse colloids" (colloids in the 0.1-1.2 μm size range) in 47 Belgian streams to the chemical properties of the streamwater. On average, 29% of the P in filtered (<1.2 μm) samples of these streams is present in coarse colloids. The concentration of Fe-rich colloids in streams decreases with increasing water hardness and pH. The P bearing colloids in these streams mostly consist of Fe hydroxyphosphates and of Fe oxyhydroxides with surface adsorbed P, which is underpinned by geochemical speciation calculations. In waters with molar P:Fe ratios above 0.5, only a minor part of the P is bound to coarse colloids. In such waters, the colloids have molar P:Fe ratios between 0.2 and 1 and are, therefore, nearly saturated with P. Conversely, in streams with molar P:Fe ratios below 0.1, most of the P is bound to Fe-rich colloids. Equilibration of synthetic and natural Fe and P bearing colloids with a zero sink reveals that colloids with low molar P:Fe ratios contain mostly nonlabile P, whereas P-saturated colloids contain mostly labile P which can be released within 7 days. Equilibration at a fixed free orthophosphate activity shows that the Fe-rich colloids may bind only limited P through surface adsorption, in the range of 0.02-0.04 mol P (mol Fe)(-1). The P:Fe ratios measured in naturally occurring Fe and P bearing colloids is clearly higher (between 0.05 and 1). These colloids are therefore likely formed by coprecipitation of P during oxidation of Fe(II), which leads to the formation of Fe hydroxyphosphate minerals.

  5. Highly Elastic and Self-Healing Composite Colloidal Gels.

    PubMed

    Diba, Mani; Wang, Huanan; Kodger, Thomas E; Parsa, Shima; Leeuwenburgh, Sander C G

    2017-03-01

    Composite colloidal gels are formed by the pH-induced electrostatic assembly of silica and gelatin nanoparticles. These injectable and moldable colloidal gels are able to withstand substantial compressive and tensile loads, and exhibit a remarkable self-healing efficiency. This study provides new, critical insight into the structural and mechanical properties of composite colloidal gels and opens up new avenues for practical application of colloidal gels.

  6. Colloid straining within saturated heterogeneous porous media.

    PubMed

    Porubcan, Alexis A; Xu, Shangping

    2011-02-01

    The transport of 0.46 μm, 2.94 μm, 5.1 μm and 6.06 μm latex particles in heterogeneous porous media prepared from the mixing of 0.78 mm, 0.46 mm and 0.23 mm quartz sands was investigated through column transport experiments. It was observed that the 0.46 μm particles traveled conservatively within the heterogeneous porous media, suggesting that under the experimental conditions employed in this research the strong repulsive interactions between the negatively charged latex particles and the clean quartz sands led to minimal colloid immobilization due to physicochemical filtration. The immobilization of the 2.94 μm, 5.1 μm and 6.06 μm latex particles was thus attributed to colloid straining. Experimental results showed that the straining of colloidal particles within heterogeneous sand mixtures increased when the fraction of finer sands increased. The mathematical model that was developed and tested based on results obtained using uniform sands (Xu et al., 2006) was found to be able to describe colloid straining within heterogeneous porous media. Examination of the relationship between the best-fit values of the clean-bed straining rate coefficients (k(0)) and the ratio of colloid diameter (d(p)) and sand grain size (d(g)) indicated that when number-average sizes were used to represent the size of the heterogeneous porous media, there existed a consistent relationship for both uniform sands and heterogeneous sand mixtures. Similarly, the use of the number-averaged sizes for the heterogeneous porous media produced a uniform relationship between the colloid straining capacity term (λ) and the ratio of d(p)/d(g) for all the sand treatments.

  7. Pair Potential of Charged Colloidal Stars

    NASA Astrophysics Data System (ADS)

    Huang, F.; Addas, K.; Ward, A.; Flynn, N. T.; Velasco, E.; Hagan, M. F.; Dogic, Z.; Fraden, S.

    2009-03-01

    We report on the construction of colloidal stars: 1μm polystyrene beads grafted with a dense brush of 1μm long and 10 nm wide charged semiflexible filamentous viruses. The pair interaction potentials of colloidal stars are measured using an experimental implementation of umbrella sampling, a technique originally developed in computer simulations in order to probe rare events. The influence of ionic strength and grafting density on the interaction is measured. Good agreements are found between the measured interactions and theoretical predictions based upon the osmotic pressure of counterions.

  8. Fabrication of anisotropic multifunctional colloidal carriers

    NASA Astrophysics Data System (ADS)

    Jerri, Huda A.

    The field of colloidal assembly has grown tremendously in recent years, although the direct or template-assisted methods used to fabricate complex colloidal constructions from monodisperse micro- and nanoparticles have been generally demonstrated on model materials. In this work, novel core particle syntheses, particle functionalizations and bottom-up assembly techniques are presented to create functional colloidal devices. Using particle lithography, high-information colloidal vectors have been developed and modified with imaging and targeting agents. Localized nanoscale patches have been reliably positioned on microparticles to serve as foundations for further chemical or physical modifications. Site-specific placement of RGD targeting ligands has been achieved in these lithographed patches. Preferential uptake of these targeted vectors by RGD-specific 3T3 fibroblasts was verified using confocal laser scanning microscopy. A transition was made from the functionalization of model imaging core particles to the lithography of colloidal cartridges, in an effort to construct colloidal syringes with specialized, programmable release profiles. A variety of functional, pH-sensitive fluorescent cores were engineered to respond to solution conditions. When triggered, the diverse composite core microparticles and reservoir microcapsules released embedded fluorescent moieties such as dye molecules, and fluorophore-conjugated nanoparticles. The microcapsules, created using layer-by-layer polyelectrolyte deposition on sacrificial templates, were selectively modified with a robust coating. The pH-responsive anisotropic reservoir microcapsules were extremely stable in solution, and exhibited a "Lazarus" functionality of rehydrating to their original state following desiccation. A snapshot of focused-release of core constituents through the lone opening in colloidal monotremes has been obtained by anisotropically-functionalizing degradable cores with barrier shells. Additionally

  9. Colloidal-gold electrosensor measuring device

    DOEpatents

    Wegner, S.; Harpold, M.A.; McCaffrey, T.M.; Morris, S.E.; Wojciechowski, M.; Zhao, J.; Henkens, R.W.; Naser, N.; O`Daly, J.P.

    1995-11-21

    The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 {micro}g/dL in blood samples as small as 10 {micro}L. 9 figs.

  10. Dynamics of Colloidal Disorder-Order Transition

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Experiments with colloidal solutions of plastic microspheres suspended in a liquid serve as models of how molecules interact and form crystals. For the Dynamics of Colloidal Disorder-Order Transition (CDOT) experiment, Paul Chaikin of Princeton University has identified effects that are attributable to Earth's gravity and demonstrated that experiments are needed in the microgravity of orbit. Space experiments have produced unexpected dendritic (snowflake-like) structures. To date, the largest hard sphere crystal grown is a 3 mm single crystal grown at the cool end of a ground sample. At least two more additional flight experiments are plarned aboard the International Space Station. This image is from a video downlink.

  11. Colloidal-gold electrosensor measuring device

    DOEpatents

    Wegner, Steven; Harpold, Michael A.; McCaffrey, Terence M.; Morris, Susan E.; Wojciechowski, Marek; Zhao, Junguo; Henkens, Robert W.; Naser, Najih; O'Daly, John P.

    1995-01-01

    The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 .mu.g/dL in blood samples as small as 10 .mu.L.

  12. Anisotropic elasticity of experimental colloidal Wigner crystals.

    PubMed

    Russell, Emily R; Spaepen, Frans; Weitz, David A

    2015-03-01

    Colloidal particles interacting via a long-range repulsion can, in contrast to hard-sphere systems, exhibit crystalline ordering at low volume fraction. Here we experimentally investigate the structure and properties of such "colloidal Wigner crystals." We find a body-centered-cubic crystalline phase at volume fractions of ϕ≳15%, which exhibits large fluctuations of individual particles from their average positions. We determine the three independent crystalline elastic constants and find that these crystals are very compliant and highly anisotropic.

  13. Collective sliding states for colloidal molecular crystals

    SciTech Connect

    Reichhardt, Charles; Reichhardt, Cynthia

    2008-01-01

    We study the driving of colloidal molecular crystals over periodic substrates such as those created with optical traps. The n-merization that occurs in the colloidal molecular crystal states produces a remarkably rich variety of distinct dynamical behaviors, including polarization effects within the pinned phase and the formation of both ordered and disordered sliding phases. Using computer simulations, we map the dynamic phase diagrams as a function of substrate strength for dimers and trimers on a triangular substrate, and correlate features on the phase diagram with transport signatures.

  14. Self-assembly of colloidal surfactants

    NASA Astrophysics Data System (ADS)

    Kegel, Willem

    2012-02-01

    We developed colloidal dumbbells with a rough and a smooth part, based on a method reported in Ref. [1]. Specific attraction between the smooth parts occurs upon addition of non-adsorbing polymers of appropriate size. We present the first results in terms of the assemblies that emerge in these systems. [4pt] [1] D.J. Kraft, W.S. Vlug, C.M. van Kats, A. van Blaaderen, A. Imhof and W.K. Kegel, Self-assembly of colloids with liquid protrusions, J. Am. Chem. Soc. 131, 1182, (2009)

  15. Binary Colloidal Alloy Test-5: Phase Separation

    NASA Technical Reports Server (NTRS)

    Lynch, Matthew; Weitz, David A.; Lu, Peter J.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Phase Separation (BCAT-5-PhaseSep) experiment will photograph initially randomized colloidal samples onboard the ISS to determine their resulting structure over time. This allows the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-PhaseSep studies collapse (phase separation rates that impact product shelf-life); in microgravity the physics of collapse is not masked by being reduced to a simple top and bottom phase as it is on Earth.

  16. Binary Colloidal Alloy Test-5: Compete

    NASA Technical Reports Server (NTRS)

    Frisken, Barbara J.; Bailey, Arthur E.; Weitz, David A.

    2008-01-01

    The Binary Colloidal Alloy Test - 5: Compete (BCAT-5-Compete) investigation will photograph andomized colloidal samples onboard the International Space Station (ISS) to determine their resulting structure over time. The use of EarthKAM software and hardware will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-Compete will utilize samples 6 - 8 in the BCAT-5 hardware to study the competition between phase separation and crystallization, which is important in the manufacture of plastics and other materials.

  17. Colloid mobilization and transport during capillary fringe fluctuations.

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L

    2014-07-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead-filled column. We studied four specific conditions: (1) colloids suspended in the aqueous phase, (2) colloids attached to the glass beads in an initially wet porous medium, (3) colloids attached to the glass beads in an initially dry porous medium, and (4) colloids suspended in the aqueous phase with the presence of a static air bubble. Confocal images confirmed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively charged colloids did not attach to static air-bubbles, but hydrophobic negatively charged and hydrophilic positively charged colloids did. Our results demonstrate that capillary fringe fluctuations are an effective means for colloid mobilization.

  18. Novel Colloidal and Dynamic Interfacial Phenomena in Liquid Crystalline Systems

    DTIC Science & Technology

    2014-09-13

    investigation supported by this grant moved beyond past studies of interfacial and colloidal phenomena involving isotropic liquids to explore and understand a...2010 20-May-2014 Approved for Public Release; Distribution Unlimited Final Report: Novel Colloidal and Dynamic Interfacial Phenomena in Liquid...Army Research Office P.O. Box 12211 Research Triangle Park, NC 27709-2211 liquid crystals, interfacial phenomena, colloids , amphiphiles

  19. Colloids in the River Inn

    NASA Astrophysics Data System (ADS)

    Ueckert, Martina; Niessner, Reinhard; Baumann, Thomas

    2015-04-01

    In the light of an increasing number of technical applications using nanoparticles and reports of adverse effects of engineered nanoparticles, research on the occurrence and stability of particles in all compartments has to be intensified. Colloids in river water represent the geologic setting, environmental conditions, and the anthropogenic use in its catchment. The river not only acts as a sink for nanoparticles but also as the source term due to exchange in the hyporheic zone and in bank filtration setups. The concentration, size distribution and elemental composition of particles in the River Inn were studied from the source in the Swiss Alps to the river mouth at Passau from 2008 to 2014. Samples were collected after each tributary from a sub-catchment and filtered on site using a new filtration device for gentle filtration. The elemental composition was determined after acid digestion with ICP/MS. SEM/EDX analysis provided morphological and elemental information for single particles. A complementary chemical analysis of the river water was performed to assess the geochemical stability of individual particles. As presented at EGU 2014, particles in the upper, rural parts mainly reveal changes in the geological setting of the tributary catchments. Not unexpectedly, particles originating from crystalline rocks, were more stable than particles originating from calcareous rocks. Anthropogenic and industrial influences increase in the lower parts. This went together with a change of the size distribution, an increase of the number of organic particles, and a decrease of the microfauna. Interestingly, specific leisure activities in a sub-catchment, like extensive downhill skiing, manifest itself in the particle composition. This general setting was validated in last year's sampling campaigns. An interesting change in on site parameters and hydrochemical composition was seen during all sampling campaigns at an inflow from the valley Kaunertal, Austria. Therefore

  20. Pore water colloid properties in argillaceous sedimentary rocks.

    PubMed

    Degueldre, Claude; Cloet, Veerle

    2016-11-01

    The focus of this work is to evaluate the colloid nature, concentration and size distribution in the pore water of Opalinus Clay and other sedimentary host rocks identified for a potential radioactive waste repository in Switzerland. Because colloids could not be measured in representative undisturbed porewater of these host rocks, predictive modelling based on data from field and laboratory studies is applied. This approach allowed estimating the nature, concentration and size distributions of the colloids in the pore water of these host rocks. As a result of field campaigns, groundwater colloid concentrations are investigated on the basis of their size distribution quantified experimentally using single particle counting techniques. The colloid properties are estimated considering data gained from analogue hydrogeochemical systems ranging from mylonite features in crystalline fissures to sedimentary formations. The colloid concentrations were analysed as a function of the alkaline and alkaline earth element concentrations. Laboratory batch results on clay colloid generation from compacted pellets in quasi-stagnant water are also reported. Experiments with colloids in batch containers indicate that the size distribution of a colloidal suspension evolves toward a common particle size distribution independently of initial conditions. The final suspension size distribution was found to be a function of the attachment factor of the colloids. Finally, calculations were performed using a novel colloid distribution model based on colloid generation, aggregation and sedimentation rates to predict under in-situ conditions what makes colloid concentrations and size distributions batch- or fracture-size dependent. The data presented so far are compared with the field and laboratory data. The colloid occurrence, stability and mobility have been evaluated for the water of the considered potential host rocks. In the pore water of the considered sedimentary host rocks, the clay

  1. Colloid Transport in Porous Medium: Impact of High Salinity Solutions

    NASA Astrophysics Data System (ADS)

    Weisbrod, N.; Magal, E.; Yechieli, Y.; Yakirevich, A.

    2009-12-01

    We explored the transport of colloids suspended in natural saline solutions with a wide range of ionic strengths, up to Dead Sea brines. Migration of latex microspheres through saturated sand columns of different sizes was studied in lab experiments, and colloid transport was simulated with a mathematical model. We have found that latex microspheres were mobile even in the extremely saline brines of the Dead Sea (ionic strength = 100.9 M). At this high ionic strength, according to the common colloid transport theories, no energetic barrier to colloid attachment exists and colloid adsorption was expected to be a favorable process. Apparently, even in that high salinity, colloids adsorption is not complete and ~20% colloids are allowed to transport (through 30-cm long column). Colloid transport was found to be related to the solution salinity, as expected. After 2-3 pore volumes (PV) the relative concentration of colloids at the outlet of 30-cm long columns decreased as the solution ionic strength increased until some critical value (ionic strength greater than 10-1.8 M) and then remained constant as the solution salinity increased. To further explore the sorption of colloids on sand surfaces in Dead Sea brines, breakthrough curves (BTCs) were studied using 7-cm long columns, through which hundreds of PV were introduced. The observed BTCs exhibited a bi-modal shape that suggests different rates of colloid attachment. After initial breakthrough the relative concentration of colloids at the outlet rose to a value of 0.8 (after 1.5 PV), and it remained relatively constant until approximately 17 PV were flushed through the column. After a total flow of about 20 PV, the relative concentration reached a value of one. The colloid migration process was successfully modeled using the limited entrapment model (Pachepsky et al., 2006), assuming the colloid attachment rate is dependent on the concentration of attached colloids.

  2. Measuring colloidal osmotic compressibility of a polymer-crowded colloidal suspension by optical trapping

    NASA Astrophysics Data System (ADS)

    Fu, Jinxin; Kara, Vural; Ou-Yang, H. Daniel

    2013-03-01

    Particle interactions determine the stability of nanoparticle suspensions and the phase separation of particle-polymer mixtures. However, due to the small sizes of the dispersed nanoparticles, it is not easy to directly measure interaction forces between particles in a colloidal suspension. In this paper, we propose an ``Optical Bottle'' approach to quantify these particle interactions in a suspension by measuring the colloidal osmotic compressibility of the nanoparticles. Virial expansion of the colloidal osmotic compressibility yields virial coefficients of different orders. The second order virial coefficient of aqueous suspensions of colloidal polystyrene nanospheres in the presence of high-salt (KCl) and polyethylene glycol (PEG) is found to decrease with increasing PEG concentration, suggesting an attractive depletion interaction between the PEG-crowed polystyrene particles.

  3. SUSY Les Houches Accord 2

    SciTech Connect

    Allanach, B.; Balazs, C.; Belanger, G.; Bernhardt, M.; Boudjema, F.; Choudhury, D.; Desch, K.; Ellwanger, U.; Gambino, P.; Godbole, R.; Goto, T.; /Cambridge U., DAMTP /Monash U. /Annecy, LAPTH /Bonn U. /Harish-Chandra Res. Inst. /Orsay, LPT /Turin U. /INFN, Turin /Bangalore, Indian Inst. Sci. /KEK, Tsukuba /Barcelona U.

    2007-11-08

    The Supersymmetry Les Houches Accord (SLHA) [1] provides a universal set of conventions for conveying spectral and decay information for supersymmetry analysis problems in high energy physics. Here, we propose extensions of the conventions of the first SLHA to include various generalizations: the minimal supersymmetric standard model with violation of CP, R-parity, and flavor, as well as the simplest next-to-minimal model.

  4. SUSY Les Houches Accord 2

    SciTech Connect

    Allanach, B.; Balazs, C.; Belanger, G.; Bernhardt, M.; Boudjema, F.; Choudhury, D.; Desch, K.; Ellwanger, U.; Gambino, P.; Godbole, R.; Goto, T.; Guasch, J.; Guchait, M.; Hahn, T.; Heinemeyer, S.; Hugonie, C.; Hurth, T.; Kraml, S.; Kreiss, S.; Lykken, J.; Moortgat, F.; /Cambridge U., DAMTP /Monash U. /Annecy, LAPTH /Bonn U. /Harish-Chandra Res. Inst. /Orsay, LPT /Turin U. /INFN, Turin /Bangalore, Indian Inst. Sci. /KEK, Tsukuba /Barcelona U. /Tata Inst. /Munich, Max Planck Inst. /Cantabria Inst. of Phys. /Montpellier U. /CERN /SLAC /Edinburgh U. /Fermilab /Zurich, ETH /Southampton U.

    2007-11-08

    The Supersymmetry Les Houches Accord (SLHA) provides a universal set of conventions for conveying spectral and decay information for supersymmetry analysis problems in high energy physics. Here, we propose extensions of the conventions of the first SLHA to include various generalizations: the minimal supersymmetric standard model with violation of CP, R-parity, and flavor, as well as the simplest next-to-minimal model.

  5. Size determinations of plutonium colloids using autocorrelation photon spectroscopy

    SciTech Connect

    Triay, I.R.; Rundberg, R.S.; Mitchell, A.J.; Ott, M.A.; Hobart, D.E.; Palmer, P.D.; Newton, T.W.; Thompson, J.L.

    1989-12-01

    Autocorrelation Photon Spectroscopy (APS) is a light-scattering technique utilized to determine the size distribution of colloidal suspensions. The capabilities of the APS methodology have been assessed by analyzing colloids of known sizes. Plutonium(IV) colloid samples were prepared by a variety of methods including: dilution; peptization; and alpha-induced auto-oxidation of Pu(III). The size of theses Pu colloids was analyzed using APS. The sizes determined for the Pu colloids studied varied from 1 to 370 nanometers. 7 refs., 5 figs., 3 tabs.

  6. Preparation of iridescent colloidal crystal coatings with variable structural colors.

    PubMed

    Cong, Hailin; Yu, Bing; Wang, Shaopeng; Qi, Limin; Wang, Jilei; Ma, Yurong

    2013-07-29

    Iridescent colloidal crystal coatings with variable structural colors were fabricated by incorporating carbon black nanoparticles (CB-NPs) into the voids of polystyrene (PS) colloidal crystals. The structural color of the colloid crystal coatings was not only greatly enhanced after the composition but also varied with observation angles. By changing the diameter of monodisperse PS colloids in the composites, colloidal crystal coatings with three primary colors for additive or subtractive combination were obtained. After incorporation of the PS/CB-NPs hybrid coatings into polydimethylsiloxane (PDMS) matrix, manmade opal jewelry with variable iridescent colors was made facilely.

  7. Photoelectrochromism in Tungsten Trioxide Colloidal Solutions

    ERIC Educational Resources Information Center

    Chenthamarakshan, C. R.; Tacconi, N. R. de; Xu, Lucy; Rajeshwar, Krishnan

    2004-01-01

    Photophysical and photochemical properties of semiconductor metal oxide colloids are studied in the context of photoelectrochemical conversion and storage of solar energy. The experiment teaches the instrumental principles of UV-visible spectrophotometry, spectral acquisition and background subtraction strategies and diode array spectrometers.

  8. Aggregation kinetics of coalescing polymer colloids.

    PubMed

    Gauer, Cornelius; Jia, Zichen; Wu, Hua; Morbidelli, Massimo

    2009-09-01

    The aggregation behavior of a soft, rubbery colloidal system with a relatively low glass transition temperature, T(g) approximately -20 degrees C, has been investigated. It is found that the average gyration and hydrodynamic radii, R(g) and R(h), measured by light scattering techniques, evolve in time in parallel, without exhibiting the crossover typical of rigid particle aggregation. Cryogenic scanning electron microscopy (cryo-SEM) images reveal sphere-like clusters, indicating that complete coalescence between particles occurs during aggregation. Since coalescence leads to a reduction in the total colloidal surface area, the surfactant adsorption equilibrium, and thus the colloidal stability, change in the course of aggregation. It is found that to simulate the observed kinetic behavior based on the population balance equations, it is necessary to assume that all the clusters are spherical and to account for variations in the colloidal stability of each aggregating particle pair with time. This indicates that, for the given system, the coalescence is very fast, i.e., its time scale is much smaller than that of the aggregation.

  9. Colloid Formation at Waste Plume Fronts

    SciTech Connect

    Wan, Jiamin; Tokunaga, Tetsu K.; Saiz, Eduardo; Larsen, Joern T.; Zheng, Zuoping; Couture, Rex A.

    2004-05-22

    Highly saline and caustic tank waste solutions containing radionuclides and toxic metals have leaked into sediments at U. S. Department of Energy (DOE) facilities such as the Hanford Site (Washington State). Colloid transport is frequently invoked to explain migration of radionuclides and metals in the subsurface. To understand colloid formation during interactions between highly reactive fluids and sediments and its impact on contaminant transport, we simulated tank waste solution (TWS) leakage processes in laboratory columns at ambient and elevated (70 C) temperatures. We found that maximum formation of mobile colloids occurred at the plume fronts (hundreds to thousands times higher than within the plume bodies or during later leaching). Concentrations of suspended solids were as high as 3 mass%, and their particle-sizes ranged from tens of nm to a few {micro}m. Colloid chemical composition and mineralogy depended on temperature. During infiltration of the leaked high Na{sup +} waste solution, rapid and completed Na{sup +} replacement of exchangeable Ca{sup 2+} and Mg{sup 2+} from the sediment caused accumulation of these divalent cations at the moving plume front. Precipitation of supersaturated Ca{sup 2+}/Mg{sup 2+}-bearing minerals caused dramatic pH reduction at the plume front. In turn, the reduced pH caused precipitation of other minerals. This understanding can help predict the behavior of contaminant trace elements carried by the tank waste solutions, and could not have been obtained through conventional batch studies.

  10. Motile Fluids: Granular, Colloidal and Living

    NASA Astrophysics Data System (ADS)

    Ramaswamy, Sriram

    2014-03-01

    My talk will present our recent results from theory, simulation and experiment on flocking, swarming and instabilities in diverse realizations of active systems. The findings I will report include: flocking at a distance in vibrated granular monolayers; the active hydrodynamics of self-propelled solids; clusters, asters and oscillations in colloidal chemotaxis. Supported by a J C Bose Fellowship.

  11. Cobalt-doped cadmium selenide colloidal nanowires.

    PubMed

    Li, Zhen; Du, Ai Jun; Sun, Qiao; Aljada, Muhsen; Cheng, Li Na; Riley, Mark J; Zhu, Zhong Hua; Cheng, Zhen Xiang; Wang, Xiao Lin; Hall, Jeremy; Krausz, Elmars; Qiao, Shi Zhang; Smith, Sean C; Lu, Gao Qing Max

    2011-11-21

    Co(2+)-doped CdSe colloidal nanowires with tunable size and dopant concentration have been prepared by a solution-liquid-solid (SLS) approach for the first time. These doped nanowires exhibit anomalous photoluminescence temperature dependence in comparison with undoped nanowires.

  12. Electroneutrality and phase behavior of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Denton, A. R.

    2007-11-01

    Several statistical mechanical theories predict that colloidal suspensions of highly charged macroions and monovalent microions can exhibit unusual thermodynamic phase behavior when strongly deionized. Density-functional, extended Debye-Hückel, and response theories, within mean-field and linearization approximations, predict a spinodal phase instability of charged colloids below a critical salt concentration. Poisson-Boltzmann cell model studies of suspensions in Donnan equilibrium with a salt reservoir demonstrate that effective interactions and osmotic pressures predicted by such theories can be sensitive to the choice of reference system, e.g., whether the microion density profiles are expanded about the average potential of the suspension or about the reservoir potential. By unifying Poisson-Boltzmann and response theories within a common perturbative framework, it is shown here that the choice of reference system is dictated by the constraint of global electroneutrality. On this basis, bulk suspensions are best modeled by density-dependent effective interactions derived from a closed reference system in which the counterions are confined to the same volume as the macroions. Lower-dimensional systems (e.g., monolayers, clusters), depending on the strength of macroion-counterion correlations, may be governed instead by density-independent effective interactions tied to an open reference system with counterions dispersed throughout the reservoir, possibly explaining the observed structural crossover in colloidal monolayers and anomalous metastability of colloidal crystallites.

  13. Practical colloidal processing of multication ceramics

    DOE PAGES

    Bell, Nelson S.; Monson, Todd C.; Diantonio, Christopher; ...

    2015-09-07

    The use of colloidal processing principles in the formation of ceramic materials is well appreciated for developing homogeneous material properties in sintered products, enabling novel forming techniques for porous ceramics or 3D printing, and controlling microstructure to enable optimized material properties. The solution processing of electronic ceramic materials often involves multiple cationic elements or dopants to affect microstructure and properties. Material stability must be considered through the steps of colloidal processing to optimize desired component properties. This review provides strategies for preventing material degradation in particle synthesis, milling processes, and dispersion, with case studies of consolidation using spark plasma sinteringmore » of these systems. The prevention of multication corrosion in colloidal dispersions can be achieved by utilizing conditions similar to the synthesis environment or by the development of surface passivation layers. The choice of dispersing surfactants can be related to these surface states, which are of special importance for nanoparticle systems. A survey of dispersant chemistries related to some common synthesis conditions is provided for perovskite systems as an example. Furthermore, these principles can be applied to many colloidal systems related to electronic and optical applications.« less

  14. Practical colloidal processing of multication ceramics

    SciTech Connect

    Bell, Nelson S.; Monson, Todd C.; Diantonio, Christopher; Wu, Yiquan

    2015-09-07

    The use of colloidal processing principles in the formation of ceramic materials is well appreciated for developing homogeneous material properties in sintered products, enabling novel forming techniques for porous ceramics or 3D printing, and controlling microstructure to enable optimized material properties. The solution processing of electronic ceramic materials often involves multiple cationic elements or dopants to affect microstructure and properties. Material stability must be considered through the steps of colloidal processing to optimize desired component properties. This review provides strategies for preventing material degradation in particle synthesis, milling processes, and dispersion, with case studies of consolidation using spark plasma sintering of these systems. The prevention of multication corrosion in colloidal dispersions can be achieved by utilizing conditions similar to the synthesis environment or by the development of surface passivation layers. The choice of dispersing surfactants can be related to these surface states, which are of special importance for nanoparticle systems. A survey of dispersant chemistries related to some common synthesis conditions is provided for perovskite systems as an example. Furthermore, these principles can be applied to many colloidal systems related to electronic and optical applications.

  15. Model colloid system for interfacial sorption kinetics

    NASA Astrophysics Data System (ADS)

    Salipante, Paul; Hudson, Steven

    2014-11-01

    Adsorption kinetics of nanometer scale molecules, such as proteins at interfaces, is usually determined through measurements of surface coverage. Their small size limits the ability to directly observe individual molecule behavior. To better understand the behavior of nanometer size molecules and the effect on interfacial kinetics, we use micron size colloids with a weak interfacial interaction potential as a model system. Thus, the interaction strength is comparable to many nanoscale systems (less than 10 kBT). The colloid-interface interaction potential is tuned using a combination of depletion, electrostatic, and gravitational forces. The colloids transition between an entropically trapped adsorbed state and a desorbed state through Brownian motion. Observations are made using an LED-based Total Internal Reflection Microscopy (TIRM) setup. The observed adsorption and desorption rates are compared theoretical predictions based on the measured interaction potential and near wall particle diffusivity. This experimental system also allows for the study of more complex dynamics such as nonspherical colloids and collective effects at higher concentrations.

  16. Stratification dynamics in drying colloidal mixtures.

    PubMed

    Howard, Michael P; Nikoubashman, Arash; Panagiotopoulos, Athanassios Z

    2017-03-28

    Stratification in binary colloidal mixtures was investigated using implicit-solvent molecular dynamics simulations. For large particle size ratios and film Péclet numbers greater than unity, smaller colloids migrated to the top of the film, while big colloids were pushed to the bottom, creating an "inverted" stratification. This peculiar behavior was observed in recent simulations and experiments conducted by Fortini et al. (Phys. Rev. Lett. 2016, 116, 118301). To rationalize this behavior, particle size ratios and drying rates spanning qualitatively different Péclet number regimes were systematically studied, and the dynamics of the inverted stratification were quantified in detail. The stratified layer of small colloids was found to grow faster and to larger thicknesses for larger size ratios. Interestingly, inverted stratification was observed even at moderate drying rates where the film Péclet numbers were comparable to unity, but the thickness of the stratified layer decreased. A model based on dynamical density functional theory is proposed to explain the observed phenomena.

  17. Forces between colloid particles in natural waters.

    PubMed

    Mosley, Luke M; Hunter, Keith A; Ducker, William A

    2003-08-01

    The origin and nature of interparticle forces acting on colloid surfaces in natural waters has been examined using an atomic force microscope. Natural colloids were represented by a surface film of iron oxide precipitated onto spherical SiO2 particles, and the effects of adsorbed natural organic matter (NOM), solution pH, and ionic composition on the force-separation curves were investigated. NOM from both riverine and marine environments was strongly adsorbed to the iron oxide surface. Under conditions of low ionic strength, the interparticle forces were dominated by electrostatic repulsion arising from negative functional groups on the NOM, except at very small separations (<10 nm) where repulsive forces arising from steric interference of the NOM molecules were also present. At high ionic strength (e.g., seawater) or low pH, the electrostatic forces were largely absent, allowing steric repulsion forces to dominate. In addition, adhesive bridging between surfaces by adsorbed NOM was observed, creating a strong energy barrier to spontaneous disaggregation of colloid aggregates. Our results demonstrate that adsorbed NOM dominates the surface forces and thus stability with respect to aggregation of natural water colloids.

  18. Colloidal nanophotonics: the emerging technology platform.

    PubMed

    Gaponenko, Sergey; Demir, Hilmi Volkan; Seassal, Christian; Woggon, Ulrike

    2016-01-25

    Dating back to decades or even centuries ago, colloidal nanophotonics during the last ten years rapidly extends towards light emitting devices, lasers, sensors and photonic circuitry to manifest itself as an emerging technology platform rather than an entirely academic research field.

  19. From crystal chemistry to colloid stability

    NASA Astrophysics Data System (ADS)

    Gilbert, B.; Burrows, N.; Penn, R. L.

    2008-12-01

    Aqueous suspensions of ferrihydrite nanoparticles form a colloid with properties that can be understood using classical theories but which additionally exhibit the distinctive phenomenon of nanocluster formation. While use of in situ light and x-ray scattering methods permit the quantitative determination of colloid stability, interparticle interactions, and cluster or aggregate geometry, there are currently few approaches to predict the colloidal behavior of mineral nanoparticles. A longstanding goal of aqueous geochemistry is the rationalization and prediction of the chemical properties of hydrated mineral interfaces from knowledge of interface structure at the molecular scale. Because interfacial acid-base reactions typically lead to the formation of a net electrostatic charge at the surfaces of oxide, hydroxide, and oxyhydroxide mineral surfaces, quantitative descriptions of this behavior have the potential to permit the prediction of long-range interactions between mineral particles. We will evaluate the feasibility of this effort by constructing a model for surface charge formation for ferrihydrite that combines recent insights into the crystal structure of this phase and proposed methods for estimating the pKa of acidic surface groups. We will test the ability of this model to predict the colloidal stability of ferrihydrite suspensions as a function of solution chemistry.

  20. Advanced Colloids Experiment (ACE-T1)

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ron; Brown, Dan; Eustace, John

    2015-01-01

    Increment 45 - 46 Science Symposium presentation of Advanced Colloids Experiment (ACE-T1) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  1. Advanced Colloids Experiment (ACE-H-2)

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ron; Chmiel, Alan J.; Eustace, John; LaBarbera, Melissa

    2015-01-01

    Increment 43 - 44 Science Symposium presentation of Advanced Colloids Experiment (ACE-H-2) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  2. Rheology and dynamics of colloidal superballs.

    PubMed

    Royer, John R; Burton, George L; Blair, Daniel L; Hudson, Steven D

    2015-07-28

    Recent advances in colloidal synthesis make it possible to generate a wide array of precisely controlled, non-spherical particles. This provides a unique opportunity to probe the role that particle shape plays in the dynamics of colloidal suspensions, particularly at higher volume fractions, where particle interactions are important. We examine the role of particle shape by characterizing both the bulk rheology and micro-scale diffusion in a suspension of pseudo-cubic silica superballs. Working with these well-characterized shaped colloids, we can disentangle shape effects in the hydrodynamics of isolated particles from shape-mediated particle interactions. We find that the hydrodynamic properties of isolated superballs are marginally different from comparably sized hard spheres. However, shape-mediated interactions modify the suspension microstructure, leading to significant differences in the self-diffusion of the superballs. While this excluded volume interaction can be captured with a rescaling of the superball volume fraction, we observe qualitative differences in the shear thickening behavior of moderately concentrated superball suspensions that defy simple rescaling onto hard sphere results. This study helps to define the unknowns associated with the effects of shape on the rheology and dynamics of colloidal solutions.

  3. Continuous separation of colloidal particles using dielectrophoresis.

    PubMed

    Yunus, Nurul Amziah Md; Nili, Hossein; Green, Nicolas G

    2013-04-01

    Dielectrophoresis is the movement of particles in nonuniform electric fields and has been of interest for application to manipulation and separation at and below the microscale. This technique has the advantages of being noninvasive, nondestructive, and noncontact, with the movement of particle achieved by means of electric fields generated by miniaturized electrodes and microfluidic systems. Although the majority of applications have been above the microscale, there is increasing interest in application to colloidal particles around a micron and smaller. This paper begins with a review of colloidal and nanoscale dielectrophoresis with specific attention paid to separation applications. An innovative design of integrated microelectrode array and its application to flow-through, continuous separation of colloidal particles is then presented. The details of the angled chevron microelectrode array and the test microfluidic system are then discussed. The variation in device operation with applied signal voltage is presented and discussed in terms of separation efficiency, demonstrating 99.9% separation of a mixture of colloidal latex spheres.

  4. Preparation and properties of uniform size colloids

    SciTech Connect

    Matijevic, E. )

    1993-04-01

    The achievements and problems in the preparation of uniform colloids by precipitation from homogeneous electrolyte solutions are reviewed. Specifically, the syntheses of [open quotes]monodispersed[close quotes] particles of simple and mixed compositions as well as of coated and hollow particles of different shapes are described, and the physical and chemical mechanisms of their formation are discussed. 126 refs., 25 figs., 1 tab.

  5. The colloidal chemistry of ceramic clays

    NASA Technical Reports Server (NTRS)

    Phelps, G. W.

    1984-01-01

    The colloidal chemistry and mineralogy of two argil minerals were studied. Deposits of kaolin and of ceramic clays in the United States and England are discussed for the probable mechanism of formation. The structural modifications of the bed, original material associated with the clays and the proper use of flocculants are discussed.

  6. Appendicite chronique chez les enfants

    PubMed Central

    Kim, David; Butterworth, Sonia A.; Goldman, Ran D.

    2016-01-01

    Résumé Question Alors que le diagnostic d’appendicite aigu est relativement simple à poser, celui d’appendicite chronique peut être controversé et souvent mal posé. De quelle manière et à quel moment les cliniciens devraient-ils investiguer l’appendicite chronique comme la cause de douleurs abdominales chroniques et récidivantes dans la population pédiatrique? Réponse L’appendicite chronique est une inflammation ou fibrose de longue date de l’appendice dont le tableau clinique est une douleur abdominale prolongée ou intermittente. Son diagnostic est souvent difficile à poser et elle peut entraîner des complications telles que des infections intra-abdominales, ou l’occlusion ou la perforation de l’intestin. Le tableau clinique, de même que les études d’imagerie, peuvent aider le clinicien à écarter d’autres affections, et chez les patients qui reçoivent un diagnostic, dont de nombreux enfants, l’appendicectomie soulage partiellement ou complètement la douleur.

  7. Assembly of Colloidal Materials Using Bioadhesive Interactions

    NASA Technical Reports Server (NTRS)

    Hammer, Daniel A.; Hiddessen, Amy L.; Tohver, Valeria; Crocker, John C.; Weitz, David A.

    2002-01-01

    We have pursued the use of biological crosslinking molecules of several types to make colloidal materials at relatively low volume fraction of colloidal particles. The objective is to make binary alloys of colloidal particles, made of two different colloidal particles coated with complementary biological lock-and-key binding molecules, which assemble due to the biological specificity. The long-term goal is to use low affinity lock-and-key biological interactions, so that the can anneal to form crystalline states. We have used a variety of different surface chemistries in order to make colloidal materials. Our first system involved using selectin-carbohydrate (sialyl-Lewis) interactions; this chemistry is derived from immune system. This chemical interaction is of relatively low affinity, with timescales for dissociation of several seconds. Furthermore, the adhesion mediated by these molecules can be reversed by the chelation of calcium atoms; thus assembled structures can be disassembled reversibly. Our second system employed avidin-biotin chemistry. This well-studied system is of high affinity, and is generally irreversible on a laboratory time-scale. Thus, we would expect selectin-carbohydrate interactions at high molecular density and avidin-biotin interactions to give kinetically-trapped structures; however, at low densities, we would expect significant differences in the structure and dynamics of the two materials, owing to their very different release rates. We have also begun to use a third chemistry - DNA hybridization. By attaching single stranded DNA oligonucleotide chains to beads, we can drive the assembly of colloidal materials by hybridization of complementary DNA chains. It is well known that DNA adenosine-thymine (A-T) and guanine-cytosine (G-C) bases hybridize pairwise with a Gibbs free energy change of 1.7 kcal/mol per base; thus, the energy of the assembly can be modulated by altering the number of complementary bases in the DNA chains. Using

  8. Colloid suspension stability and transport through unsaturated porous media

    SciTech Connect

    McGraw, M.A.; Kaplan, D.I.

    1997-04-01

    Contaminant transport is traditionally modeled in a two-phase system: a mobile aqueous phase and an immobile solid phase. Over the last 15 years, there has been an increasing awareness of a third, mobile solid phase. This mobile solid phase, or mobile colloids, are organic or inorganic submicron-sized particles that move with groundwater flow. When colloids are present, the net effect on radionuclide transport is that radionuclides can move faster through the system. It is not known whether mobile colloids exist in the subsurface environment of the Hanford Site. Furthermore, it is not known if mobile colloids would likely exist in a plume emanating from a Low Level Waste (LLW) disposal site. No attempt was made in this study to ascertain whether colloids would form. Instead, experiments and calculations were conducted to evaluate the likelihood that colloids, if formed, would remain in suspension and move through saturated and unsaturated sediments. The objectives of this study were to evaluate three aspects of colloid-facilitated transport of radionuclides as they specifically relate to the LLW Performance Assessment. These objectives were: (1) determine if the chemical conditions likely to exist in the near and far field of the proposed disposal site are prone to induce flocculation (settling of colloids from suspension) or dispersion of naturally occurring Hanford colloids, (2) identify the important mechanisms likely involved in the removal of colloids from a Hanford sediment, and (3) determine if colloids can move through unsaturated porous media.

  9. Colloid Mobilization and Transport during Capillary Fringe Fluctuations

    NASA Astrophysics Data System (ADS)

    Aramrak, Surachet; Flury, Markus

    2016-04-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead filled column. Confocal images showed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively-charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively-charged colloids did not attach to static air-bubbles, but hydrophobic negatively-charged and hydrophilic positively-charged colloids did.

  10. Tracking liquid in drying colloidal fluids with polarized light microscopy

    NASA Astrophysics Data System (ADS)

    Cho, Kun; Park, Jung Soo; Kim, Joon Heon; Weon, Byung Mook

    2014-11-01

    When colloidal fluids dry, tracking liquid surfaces around colloids is difficult with conventional imaging techniques. Here we show that polarized light microscopy (PM) is very useful in tracking liquid surfaces during drying processes of colloidal fluids. In particular, the PM mode is not a new or difficult way but is able to visualize liquid films above colloids in real time. We demonstrate that when liquid films above colloidal particles are broken, the PM patterns appear clearly: this feature is useful to identify the moment of liquid film rupture above colloids in drying colloidal fluids. This result is helpful to improve relevant processes such as inkjet printing, painting, and nanoparticle patterning (K.C. and J.S.P. equally contributed). This work (NRF-2013R1A22A04008115) was supported by Mid-career Researcher Program through NRF grant funded by the MEST.

  11. Active structuring of colloidal armour on liquid drops

    PubMed Central

    Dommersnes, Paul; Rozynek, Zbigniew; Mikkelsen, Alexander; Castberg, Rene; Kjerstad, Knut; Hersvik, Kjetil; Otto Fossum, Jon

    2013-01-01

    Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal ‘ribbons’, electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of ‘pupil’-like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for ‘smart armoured’ droplets. PMID:23811716

  12. [Preliminary study of colloid osmotic pressure for cardiopulmonary bypass].

    PubMed

    Wang, D; Xiang, L; Luo, J

    1996-12-01

    The ideal colloid osmotic pressure is beneficial to decrease the fluid accumulated in the pulmonary and other tissue during cardiopulmonary bypass. Schupbach reported the proper colloidosmotic pressure for cardiopulmonary bypass was 2.1 kPa (16 mmHg). Colloid osmotic pressures of blood and priming fluid during cardiopulmonary bypass were measured in 28 patients with heart disease by using colloid osmotic pressure detection apparatus. The value of colloid osmotic pressure suitable for the designed standard was apparently different among the Gelofusine group and other groups. P value was 0.005. Priming fluid for cardiopulmonary bypass needs to satisfy the quality and the quantity of colloid osmotic pressure. Using Albumin isn't economical. Whole blood and plazma are not suitable for increasing colloid osmotic pressure. Hydroxyethyl starch or Gelofusine is best choice in priming to get designed standard of colloid osmotic pressure. The ratio of hydroxyethyl starch or Gelofusine in priming fluid should beyond 1/2.

  13. Introduction to special section on Colloid Transport in Subsurface Environments

    NASA Astrophysics Data System (ADS)

    Saiers, James E.; Ryan, Joseph N.

    2006-12-01

    The Water Resources Research special section on Colloid Transport in Subsurface Environments presents new knowledge that is critical to solving problems related to groundwater pollution by microbial pathogens and hazardous chemicals. This introduction to the special section surveys fourteen manuscripts that advance current understanding of the transport of biocolloids (e.g., bacteria, viruses, and protozoa), mineral colloids, and colloid-associated contaminants in the vadose zone and in groundwater. These papers present new techniques for elucidating mechanisms that govern colloid mobility, propose mathematical models appropriate for quantifying colloid and colloid-associated contaminant transport, and report pore-scale and column-scale observations requisite for evaluating these models. Together, the papers of this special section illuminate the complexity of the colloid transport problem and describe progress toward understanding this complexity.

  14. Scattering from correlations in colloidal systems

    SciTech Connect

    Hayter, J.B.

    1984-01-01

    Colloidal suspensions typically exhibit spatial correlations over distances of order 10-10/sup 4/ A, corresponding either to the size of individual particles (e.g., polymer chains, surfactant micelles) or to the range of interaction between particles (e.g., charged polymer lattices at low ionic strength). Apart from having fundamental intrinsic interest, such systems are also extremely useful as model systems with which to study, for example, non-Newtonian hydrodynamics, since temporal correlations are generally much longer lived (10/sup -8/-10/sup -3/ sec) than those found in simple atomic or small molecular systems (10/sup -13/-10/sup -10/ sec). Colloids have long been the subject of macroscopic phenomenological research (on rheological properties, for example), but it is only recently that microscopic light, x-ray and neutron scattering techniques have been applied to their study, in large part because of theoretical difficulties in understanding the scattering from dense liquid-like systems of interacting particles. For spherical colloids, such theoretical problems have now been largely overcome, and for anisotropic colloids experimental techniques are being developed which circumvent the intractable theoretical areas. This paper will first review some static light and small-angle neutron scattering (SANS) results on colloidal suspensions, both at equilibrium and in steady-state non-equilibrium situations, and will then discuss some dynamic measurements on polymer solutions and melts made using the neutron spin-echo (NSE) technique. Emphasis is placed on experiments which have a possible counterpart in synchrotron radiation studies. In particular, NSE extends the results of photon correlation spectroscopy (PCS) to larger momentum transfers and shorter time-scales than are available with visible light, and the extension of PCS to short wavelength on a synchrotron source would be of similar fundamental interest.

  15. Les torsions sur testicules cryptorchides

    PubMed Central

    Gharbi, Mohamed; Amri, Najmeddine; Chambeh, Wahib; Braiek, Salem; Kamel, Rafik El

    2010-01-01

    Résumé But : La cryptorchidie est une pathologie assez fréquente en urologie. Elle est associée à un risque élevé d’infertilité et de dégénérescence. Elle semble aussi être associée à un risque important de torsion. Cette entité est très peu abordée dans la littérature. Nous rapportons tous les cas de torsion sur testicule cryptorchide observés à notre service dans le but de mieux caractériser cette pathologie et de réduire ainsi le taux d’orchidectomies. Méthodologie : Il s’agit d’une étude rétrospective portant sur tous les cas de torsion sur testicule cryptorchide opérés dans notre service d’urologie entre 1999 et 2007. Les patients ont fait l’objet d’une description basée sur le résumé de leurs observations. Résultats : Les patients étaient âgés de 7 mois à 39 ans. La torsion touchait le testicule droit dans 53 % des cas. Le tableau clinique comportait une douleur au niveau de la région inguinale d’apparition soudaine avec une masse sous-cutanée inflammatoire et douloureuse à ce niveau et surtout un hémiscrotum homolatéral vide. Dans 60 % des cas, le diagnostic était tardif et une orchidectomie a été réalisée. Dans les autre cas, un abaissement du testicule a été réalisé avec orchidopexie controlatéral dans le même temps opératoire. Conclusion : Bien qu’il s’agisse d’une pathologie peu courante, la torsion sur testicule cryptorchide doit être étudiée davantage. Le diagnostic précoce permettra de sauver et d’abaisser le testicule et faciliter ainsi le dépistage d’une éventuelle dégénérescence. PMID:21191497

  16. LONG-TERM COLLOID MOBILIZATION AND COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES IN A SEMI-ARID VADOSE ZONE

    SciTech Connect

    Markus Flury; James B. Harsh; Fred Zhang; Glendon W. Gee; Earl D. Mattson; Peter C. L

    2012-08-01

    The main purpose of this project was to improve the fundamental mechanistic understanding and quantification of long-term colloid mobilization and colloid-facilitated transport of radionuclides in the vadose zone, with special emphasis on the semi-arid Hanford site. While we focused some of the experiments on hydrogeological and geochemical conditions of the Hanford site, many of our results apply to colloid and colloid-facilitated transport in general. Specific objectives were (1) to determine the mechanisms of colloid mobilization and colloid-facilitated radionuclide transport in undisturbed Hanford sediments under unsaturated flow, (2) to quantify in situ colloid mobilization and colloid-facilitated radionuclidetransport from Hanford sediments under field conditions, and (3) to develop a field-scale conceptual and numerical model for colloid mobilization and transport at the Hanford vadose zone, and use that model to predict long-term colloid and colloid- facilitated radionuclide transport. To achieve these goals and objectives, we have used a combination of experimental, theoretical, and numerical methods at different spatial scales, ranging from microscopic investigationsof single particle attachment and detachment to larger-scale field experiments using outdoor lysimeters at the Hanford site. Microscopic and single particle investigations provided fundamental insight into mechanisms of colloid interactions with the air-water interface. We could show that a moving air water interface (such as a moving water front during infiltration and drainage) is very effective in removing and mobilizing particles from a stationary surface. We further demonstrated that it is particularly the advancing air-water interface which is mainly responsible for colloid mobilization. Forces acting on the colloids calculated from theory corroborated our experimental results, and confirm that the detachment forces (surface tension forces) during the advancing air-water interface

  17. EDITORIAL: Colloidal dispersions in external fields Colloidal dispersions in external fields

    NASA Astrophysics Data System (ADS)

    Löwen, Hartmut

    2012-11-01

    Colloidal dispersions have long been proven as pivotal model systems for equilibrium phase transition such as crystallization, melting and liquid-gas phase transition. The last decades have revealed that this is also true for nonequilibrium phenomena. In fact, the fascinating possibility to track the individual trajectories of colloidal particles has greatly advanced our understanding of collective behaviour in classical many-body systems and has helped to reveal the underlying physical principles of glass transition, crystal nucleation, and interfacial dynamics (to name just a few typical nonequilibrium effects). External fields can be used to bring colloids out of equilibrium in a controlled way. Different kinds of external fields can be applied to colloidal dispersions, namely shear flow, electric, magnetic and laser-optical fields, and confinement. Typical research areas can be sketched with the by now traditional complexity diagram (figure 1). The complexity of the colloidal system itself as embodied in statistical degrees of freedom is shown on the x-axis while the complexity of the problem posed, namely bulk, an inhomogeneity in equilibrium, steady state nonequilibrium and full time-dependent nonequilibrium are shown on the y-axis. The different external fields which can be imposed are indicated by the different hatched areas. figure1 Figure 1. Diagram of complexity for colloidal dispersions in external fields: while the x-axis shows the complexity of the system, the y-axis shows the complexity of the problem. Regions which can be accessed by different kinds of external fields are indicated. The arrows indicate recent research directions. Active particles are also indicated with a special complexity of internal degrees of freedom [1]. This collection of papers reflects the scientific programme of the International Conference on Colloidal Dispersions in External Fields III (CODEF III) which took place in Bonn-Bad Godesberg from 20-23 March 2012. This was the

  18. Approaches to separations using silica colloidal membranes

    NASA Astrophysics Data System (ADS)

    Ignacio-de Leon, Patricia Anne Argana

    This thesis describes the synthesis and properties of free-standing nanoporous silica colloidal membranes where the molecular transport is controlled on the basis of size, charge, and chiral selectivity. To achieve this, free-standing membranes were prepared from colloidal solutions of silica nanospheres and the nanopore size and surface functionality were varied. First, Au-coated membranes were prepared and the transport of neutral and charged small molecules through Au-coated silica colloidal membranes modified with poly(methacrylic acid) was studied. Polymer length was controlled by polymerization time to produce pH- and ion-responsive brushes inside the nanopores. By monitoring the flux of a diffusing species, it was demonstrated that the polyelectrolyte brush undergoes swelling and collapse when the pH is increased and decreased, respectively. We also observed an expansion and contraction in the absence and presence of counterions, respectively. We also studied the transport of enantiomers of a chiral dye molecule through silica colloidal membranes with attached chiral moieties. We used small molecules and polymers of amino acid derivatives and chiral calixarenes capable of chiral recognition as a result of stereochemically dependent noncovalent interactions with the diffusing molecule. We found that the selectivity remains approximately the same for membranes modified with small molecules and with polymers. This suggests that enantiopermselectivity depends primarily on the strength of noncovalent interactions rather than the availability of recognition sites. Next, the transport of various generations of dendrimers through silica colloidal membranes was studied in a proof-of-concept experiment to demonstrate the size-selectivity of our materials. Smaller dendrimers were found to diffuse faster and selectivity is improved by using smaller nanopores. Finally, the transport of proteins through silica colloidal membranes was studied as a function of nanopore size

  19. Advanced Colloids Experiment (ACE) Science Overview

    NASA Technical Reports Server (NTRS)

    Meyer, William V.; Sicker, Ronald J.; Chiaramonte, Francis P.; Luna, Unique J.; Chaiken, Paul M.; Hollingsworth, Andrew; Secanna, Stefano; Weitz, David; Lu, Peter; Yodh, Arjun; Yunker, Peter; Lohr, Matthew; Gratale, Matthew; Lynch, Matthew; Kodger, Thomas; Piazza, Roberto; Buzzaccaro, Stefano; Cipelletti, Luca; Schall, Peter; Veen, Sandra; Wegdam, Gerhard; Lee, Chand-Soo; Choi, Chang-Hyung; Paul, Anna-Lisa; Ferl, Robert J.; Cohen, Jacob

    2013-01-01

    The Advanced Colloids Experiment is being conducted on the International Space Station (ISS) using the Light Microscopy Module (LMM) in the Fluids Integrated Rack (FIR). Work to date will be discussed and future plans and opportunities will be highlighted. The LMM is a microscope facility designed to allow scientists to process, manipulate, and characterize colloidal samples in micro-gravity where the absence of gravitational settling and particle jamming enables scientists to study such things as:a.The role that disordered and ordered-packing of spheres play in the phase diagram and equation of state of hard sphere systems,b.crystal nucleation and growth, growth instabilities, and the glass transition, c.gelation and phase separation of colloid polymer mixtures,d.crystallization of colloidal binary alloys,e.competition between crystallization and phase separation,f.effects of anisotropy and specific interactions on packing, aggregation, frustration and crystallization,g.effects of specific reversible and irreversible interactions mediated in the first case by hybridization of complementary DNA strands attached to separate colloidal particles,h.Lock and key interactions between colloids with dimples and spheres which match the size and shape of the dimples,i.finding the phase diagrams of isotropic and interacting particles,j.new techniques for complex self-assembly including scenarios for self-replication, k.critical Casimir forces,l.biology (real and model systems) in microgravity,m.etc. By adding additional microscopy capabilities to the existing LMM, NASA will increase the tools available for scientists that fly experiments on the ISS enabling scientists to observe directly what is happening at the particle level. Presently, theories are needed to bridge the gap between what is being observed (at a macroscopic level when photographing samples) with what is happening at a particle (or microscopic) level. What is happening at a microscopic level will be directly

  20. Colloid Mobilization in Two Atlantic Coastal Plain Aquifers: Field Studies

    NASA Astrophysics Data System (ADS)

    Ryan, Joseph N.; Gschwend, Philip M.

    1990-02-01

    The geochemical mechanisms leading to the mobilization of colloids in groundwater were investigated in the Pine Barrens of New Jersey and in rural central Delaware by sampling pairs of wells screened in oxic and anoxic groundwaters in the same geologic formations. Samples were carefully taken at very low flow rates (˜100 mL min-1) to avoid suspending immobilized particles. The colloidal matter was characterized by light-scattering photometry, scanning electron microscopy, energy-dispersive X ray analysis, microelectrophoresis, and Fe, Al, Si, and organic carbon analyses. The colloids, composed primarily of clays, were observed at high concentrations (up to 60 mg colloids/L) in the anoxic groundwaters, while the oxic groundwaters exhibited ≤1 mg colloids/L. Colloidal organic carbon was present in all groundwaters; but under anoxic conditions, one-third to one-half of the total organic carbon was associated with the inorganic colloids. The field evidence indicates that anoxic conditions cause the mobilization of soil colloids by dissolving the ferric oxyhydroxide coatings cementing the clay particles to the aquifer solids. The depletion of oxidized iron on the surfaces of immobile particles and the addition of organic carbon coatings on the soil particles and colloids apparently stabilizes the colloidal suspension in the anoxic groundwaters.

  1. Quantifying colloid retention in partially saturated porous media

    NASA Astrophysics Data System (ADS)

    Zevi, Yuniati; Dathe, Annette; Gao, Bin; Richards, Brian K.; Steenhuis, Tammo S.

    2006-12-01

    The transport of colloid-contaminant complexes and colloid-sized pathogens through soil to groundwater is of concern. Visualization and quantification of pore-scale colloid behavior will enable better description and simulation of retention mechanisms at individual surfaces, in contrast to breakthrough curves which only provide an integrated signal. We tested two procedures for quantifying colloid movement and retention as observed in pore-scale image sequences. After initial testing with static images, three series of images of synthetic microbead suspensions passing through unsaturated sand were examined. The region procedure (implemented in ImageJ) and the Boolean procedure (implemented in KS400) yielded nearly identical results for initial test images and for total colloid-covered areas in three image series. Because of electronic noise resulting in pixel-level brightness fluctuations the Boolean procedure tended to underestimate attached colloid counts and conversely overestimate mobile colloid counts. The region procedure had a smaller overestimation error of attached colloids. Reliable quantification of colloid retention at pore scale can be used to improve current understanding on the transport mechanisms of colloids in unsaturated porous media. For example, attachment counts at individual air/water meniscus/solid interface were well described by Langmuir isotherms.

  2. Sorption of selected endocrine disrupting chemicals to different aquatic colloids.

    PubMed

    Zhou, J L; Liu, R; Wilding, A; Hibberd, A

    2007-01-01

    The sorption of seven endocrine disrupting chemicals (EDCs) to aquatic colloids was determined by cross-flow ultrafiltration (CFUF) followed by gas chromatography-mass spectrometry (GC-MS). Results show that the colloidal organic carbon normalized sorption coefficient (Kcoc) of EDCs to different aquatic colloids varies by a factor of 6-12 because such colloids are of different origin. Through characterization of colloidal samples, a significant relationship was established between Kcoc values and the molar extinction coefficient of colloids at 280 nm, whereas no other colloidal properties such as elemental ratios were correlated with Kcoc values. The results are consistent with other reports of the importance of the quality of sorbents such as their aromatic carbon content in sorbing various organic pollutants. The presence of a surfactant was found to increase Kcoc values for estrone (El) and 17alpha-ethynylestradiol (EE2). The method was subsequently applied for determining EDC concentrations in field samples, where both conventional and truly dissolved EDCs showed higher concentrations close to sewage outfalls than either upstream or downstream, confirming the sourceconcentration relationship. In addition, the truly dissolved EDC concentrations were lower than the conventional dissolved concentrations, confirming that there were interactions between aquatic colloids and EDCs. It is estimated that between 10 and 29% of EDCs are associated with aquatic colloids. As colloids are highly abundant in rivers and ocean, they will therefore play a significant role in the environmental behavior and fate of EDCs.

  3. Shape recognition of microbial cells by colloidal cell imprints

    NASA Astrophysics Data System (ADS)

    Borovička, Josef; Stoyanov, Simeon D.; Paunov, Vesselin N.

    2013-08-01

    We have engineered a class of colloids which can recognize the shape and size of targeted microbial cells and selectively bind to their surfaces. These imprinted colloid particles, which we called ``colloid antibodies'', were fabricated by partial fragmentation of silica shells obtained by templating the targeted microbial cells. We successfully demonstrated the shape and size recognition between such colloidal imprints and matching microbial cells. High percentage of binding events of colloidal imprints with the size matching target particles was achieved. We demonstrated selective binding of colloidal imprints to target microbial cells in a binary mixture of cells of different shapes and sizes, which also resulted in high binding selectivity. We explored the role of the electrostatic interactions between the target cells and their colloid imprints by pre-coating both of them with polyelectrolytes. Selective binding occurred predominantly in the case of opposite surface charges of the colloid cell imprint and the targeted cells. The mechanism of the recognition is based on the amplification of the surface adhesion in the case of shape and size match due to the increased contact area between the target cell and the colloidal imprint. We also tested the selective binding for colloid imprints of particles of fixed shape and varying sizes. The concept of cell recognition by colloid imprints could be used for development of colloid antibodies for shape-selective binding of microbes. Such colloid antibodies could be additionally functionalized with surface groups to enhance their binding efficiency to cells of specific shape and deliver a drug payload directly to their surface or allow them to be manipulated using external fields. They could benefit the pharmaceutical industry in developing selective antimicrobial therapies and formulations.

  4. Cotransport of bismerthiazol and montmorillonite colloids in saturated porous media

    NASA Astrophysics Data System (ADS)

    Shen, Chongyang; Wang, Hong; Lazouskaya, Volha; Du, Yichun; Lu, Weilan; Wu, Junxue; Zhang, Hongyan; Huang, Yuanfang

    2015-06-01

    While bismerthiazol [N,N‧-methylene-bis-(2-amino-5-mercapto-1,3,4-thiadiazole)] is one of the most widely used bactericides, the transport of bismerthiazol in subsurface environments is unclear to date. Moreover, natural colloids are ubiquitous in the subsurface environments. The cotransport of bismerthiazol and natural colloids has not been investigated. This study conducted laboratory column experiments to examine the transport of bismerthiazol in saturated sand porous media both in the absence and presence of montmorillonite colloids. Results show that a fraction of bismerthiazol was retained in sand and the retention was higher at pH 7 than at pH 4 and 10. The retention did not change with ionic strength. The retention was attributed to the complex of bismerthiazol with metals/metal oxides on sand surfaces through ligand exchange. The transport of bismerthiazol was enhanced with montmorillonite colloids copresent in the solutions and, concurrently, the transport of montmorillonite colloids was facilitated by the bismerthiazol. The transport of montmorillonite colloids was enhanced likely because the bismerthiazol and the colloids competed for the attachment/adsorption sites on collector surfaces and the presence of bismerthiazol changed the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies between colloids and collectors. The transport of bismerthiazol was inhibited if montmorillonite colloids were pre-deposited in sand because bismerthiazol could adsorb onto the colloid surfaces. The adsorbed bismerthiazol could be co-remobilized with the colloids from primary minima by decreasing ionic strength. Whereas colloid-facilitated transport of pesticides has been emphasized, our study implies that transport of colloids could also be facilitated by the presence of pesticides.

  5. Cotransport of bismerthiazol and montmorillonite colloids in saturated porous media.

    PubMed

    Shen, Chongyang; Wang, Hong; Lazouskaya, Volha; Du, Yichun; Lu, Weilan; Wu, Junxue; Zhang, Hongyan; Huang, Yuanfang

    2015-01-01

    While bismerthiazol [N,N'-methylene-bis-(2-amino-5-mercapto-1,3,4-thiadiazole)] is one of the most widely used bactericides, the transport of bismerthiazol in subsurface environments is unclear to date. Moreover, natural colloids are ubiquitous in the subsurface environments. The cotransport of bismerthiazol and natural colloids has not been investigated. This study conducted laboratory column experiments to examine the transport of bismerthiazol in saturated sand porous media both in the absence and presence of montmorillonite colloids. Results show that a fraction of bismerthiazol was retained in sand and the retention was higher at pH7 than at pH 4 and 10. The retention did not change with ionic strength. The retention was attributed to the complex of bismerthiazol with metals/metal oxides on sand surfaces through ligand exchange. The transport of bismerthiazol was enhanced with montmorillonite colloids copresent in the solutions and, concurrently, the transport of montmorillonite colloids was facilitated by the bismerthiazol. The transport of montmorillonite colloids was enhanced likely because the bismerthiazol and the colloids competed for the attachment/adsorption sites on collector surfaces and the presence of bismerthiazol changed the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energies between colloids and collectors. The transport of bismerthiazol was inhibited if montmorillonite colloids were pre-deposited in sand because bismerthiazol could adsorb onto the colloid surfaces. The adsorbed bismerthiazol could be co-remobilized with the colloids from primary minima by decreasing ionic strength. Whereas colloid-facilitated transport of pesticides has been emphasized, our study implies that transport of colloids could also be facilitated by the presence of pesticides.

  6. Colloidal Dancers: Designing networks of DNA-functionalized colloids for non-random walks

    NASA Astrophysics Data System (ADS)

    Gehrels, Emily W.; Rogers, W. Benjamin; Zeravcic, Zorana; Manoharan, Vinothan N.

    2014-03-01

    We present experimental developments of a system of DNA-functionalized colloidal particles with the goal of creating directed motion (`dancing') along patterned substrates in response to temperature cycling. We take advantage of toehold exchange in the design of the DNA sequences that mediate the colloidal interactions to produce broadened, flat, or even re-entrant binding and unbinding transitions between the particles and substrate. Using this new freedom of design, we devise systems where, by thermal ratcheting, we can externally control the direction of motion and sequence of steps of the colloidal dancer. In comparison to DNA-based walkers, which move autonomously and whose motion is controlled by the substrate, our colloidal dancers respond to external driving, and their motion can be controlled in situ. Our use of DNA-functionalized colloidal particles instead of pure DNA systems also enables walking on the mesoscale in contrast to the molecular length scales previously demonstrated, allowing for the future prospect of directed transport over larger distances.

  7. Tunable Assembly of Heterogeneously Charged Colloids

    PubMed Central

    2014-01-01

    The self-assembly of colloidal particles is a route to designed materials production that combines high flexibility, cost effectiveness, and the opportunity to create ordered structures at length scales ranging from nano- to micrometers. For many practical applications in electronics, photovoltaics, and biomimetic material synthesis, ordered mono- and bilayers are often needed. Here we present a novel and simple way to tune via external parameters the ordering of heterogeneously charged colloids into quasi two-dimensional structures. Depending on the charges of the underlying substrate and of the particles, a rich and versatile assembly scenario takes place, resulting from the complex interplay between directional attractive and repulsive particle–particle and particle–substrate interactions. Upon subtle variations of the relative charge of the system components, emerging via pH modification, reversible changes either from extended aggregates to a monomeric phase or from triangular to square domains are observed. PMID:24842542

  8. Renormalized jellium model for colloidal mixtures

    NASA Astrophysics Data System (ADS)

    García de Soria, María Isabel; Álvarez, Carlos E.; Trizac, Emmanuel

    2016-10-01

    In an attempt to quantify the role of polydispersity in colloidal suspensions, we present an efficient implementation of the renormalized jellium model for a mixture of spherical charged colloids. The different species may have different size, charge, and density. Advantage is taken from the fact that the electric potential pertaining to a given species obeys a Poisson's equation that is species independent; only boundary conditions do change from one species to the next. All species are coupled through the renormalized background (jellium) density, that is determined self-consistently. The corresponding predictions are compared to the results of Monte Carlo simulations of binary mixtures, where Coulombic interactions are accounted for exactly, at the primitive model level (structureless solvent with fixed dielectric permittivity). An excellent agreement is found.

  9. Structure and hydrodynamics of colloidal systems

    SciTech Connect

    Hayter, J.B.

    1985-07-01

    Colloidal phases (for example, micellar solutions, latex suspensions, ferrofluids and microemulsions) provide excellent model systems with which to test structural and hydrodynamic theories of the liquid state. Interparticle potentials may be attractive or repulsive, and the experimentalist is often free to control the strength, range and symmetry of the interactions. Small-angle neutron scattering (SANS) and small-angle neutron spin-echo (SANSE) provide excellent complementary tools for studying the structure and time-dependence of these systems, where correlation lengths typically vary from about one to several tens of nm. Correlation times are usually in the nsec to ..mu..sec range, but may be of order minutes in certain systems. This paper will review some of the current theories and their recent experimental tests, using colloidal systems in which the direct interaction potentials may have spherical, dipolar or cylindrical symmetry and the hydrodynamic interactions may be weak or strong.

  10. Correlated Clusters in Aging Colloidal Glass

    NASA Astrophysics Data System (ADS)

    Robe, Dominic; Boettcher, Stefan; Yunker, Peter

    A numerical model of correlated domains in glassy colloids is recreated, following its development by Becker, et. al.. The model is a course grained representation of 2D colloidal systems inspired by record dynamics, and produces emergent dynamic heterogeneity and aging. Results from the original development are reproduced, and compared to the same observables in an experimental system of bidisperse microgel spheres studied by Yunker, et. al.. Basic observables such as particle persistence and mean square displacement are measured at different waiting times to observe aging. Four-point correlation lengths are also examined for signs of dynamic heterogeneity. Results from both the numerical and experimental systems are consistent with the predictions of record dynamics, that aging systems evolve on a logarithmic time scale. This work is supported by NSF Grant DMR-1207431.

  11. Hybrid colloidal plasmonic-photonic crystals.

    PubMed

    Romanov, Sergei G; Korovin, Alexander V; Regensburger, Alois; Peschel, Ulf

    2011-06-17

    We review the recently emerged class of hybrid metal-dielectric colloidal photonic crystals. The hybrid approach is understood as the combination of a dielectric photonic crystal with a continuous metal film. It allows to achieve a strong modification of the optical properties of photonic crystals by involving the light scattering at electronic excitations in the metal component into moulding of the light flow in series to the diffraction resonances occurring in the body of the photonic crystal. We consider different realizations of hybrid plasmonic-photonic crystals based on two- and three-dimensional colloidal photonic crystals in association with flat and corrugated metal films. In agreement with model calculations, different resonance phenomena determine the optical response of hybrid crystals leading to a broadly tuneable functionality of these crystals.

  12. Knot theory realizations in nematic colloids

    PubMed Central

    Čopar, Simon; Tkalec, Uroš; Muševič, Igor; Žumer, Slobodan

    2015-01-01

    Nematic braids are reconfigurable knots and links formed by the disclination loops that entangle colloidal particles dispersed in a nematic liquid crystal. We focus on entangled nematic disclinations in thin twisted nematic layers stabilized by 2D arrays of colloidal particles that can be controlled with laser tweezers. We take the experimentally assembled structures and demonstrate the correspondence of the knot invariants, constructed graphs, and surfaces associated with the disclination loop to the physically observable features specific to the geometry at hand. The nematic nature of the medium adds additional topological parameters to the conventional results of knot theory, which couple with the knot topology and introduce order into the phase diagram of possible structures. The crystalline order allows the simplified construction of the Jones polynomial and medial graphs, and the steps in the construction algorithm are mirrored in the physics of liquid crystals. PMID:25624467

  13. Colloidal cholesteric liquid crystal in spherical confinement

    PubMed Central

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-01-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter. PMID:27561545

  14. Collective motion in populations of colloidal robots

    NASA Astrophysics Data System (ADS)

    Bartolo, Denis; Bricard, Antoine; Caussin, Jean-Baptiste; Dauchot, Olivier; Desreumaux, Nicolas

    2014-03-01

    Could the behavior of bacteria swarms, fish schools, and bird flocks be understood within a unified framework? Can one ignore the very details of the interaction mechanisms at the individual level to elucidate how strikingly similar collective motion emerges at the group level in this broad range of motile systems? These seemingly provocative questions have triggered significant advance in the physics and the biology, communities over the last decade. In the physics language these systems, made of motile individuals, can all be though as different realizations of ``active matter.'' In this talk, I will show how to gain more insight into this vivid field using self-propelled colloids as a proxy for motile organism. I will show how to motorize colloidal particles capable of sensing the orientation of their neighbors. Then, I will demonstrate that these archetypal populations display spontaneous transitions to swarming motion, and to global directed motion with very few density and orientation fluctuations.

  15. Slab photonic crystals with dimer colloid bases

    SciTech Connect

    Riley, Erin K.; Liddell Watson, Chekesha M.

    2014-06-14

    The photonic band gap properties for centered rectangular monolayers of asymmetric dimers are reported. Colloids in suspension have been organized into the phase under confinement. The theoretical model is inspired by the range of asymmetric dimers synthesized via seeded emulsion polymerization and explores, in particular, the band structures as a function of degree of lobe symmetry and degree of lobe fusion. These parameters are varied incrementally from spheres to lobe-tangent dimers over morphologies yielding physically realizable particles. The work addresses the relative scarcity of theoretical studies on photonic crystal slabs with vertical variation that is consistent with colloidal self-assembly. Odd, even and polarization independent gaps in the guided modes are determined for direct slab structures. A wide range of lobe symmetry and degree of lobe fusion combinations having Brillouin zones with moderate to high isotropy support gaps between odd mode band indices 3-4 and even mode band indices 1-2 and 2-3.

  16. The NASA GSFC MEMS Colloidal Thruster

    NASA Technical Reports Server (NTRS)

    Cardiff, Eric H.; Jamieson, Brian G.; Norgaard, Peter C.; Chepko, Ariane B.

    2004-01-01

    A number of upcoming missions require different thrust levels on the same spacecraft. A highly scaleable and efficient propulsion system would allow substantial mass savings. One type of thruster that can throttle from high to low thrust while maintaining a high specific impulse is a Micro-Electro-Mechanical System (MEMS) colloidal thruster. The NASA GSFC MEMS colloidal thruster has solved the problem of electrical breakdown to permit the integration of the electrode on top of the emitter by a novel MEMS fabrication technique. Devices have been successfully fabricated and the insulation properties have been tested to show they can support the required electric field. A computational finite element model was created and used to verify the voltage required to successfully operate the thruster. An experimental setup has been prepared to test the devices with both optical and Time-Of-Flight diagnostics.

  17. Forging Colloidal Nanostructures via Cation Exchange Reactions

    PubMed Central

    2016-01-01

    Among the various postsynthesis treatments of colloidal nanocrystals that have been developed to date, transformations by cation exchange have recently emerged as an extremely versatile tool that has given access to a wide variety of materials and nanostructures. One notable example in this direction is represented by partial cation exchange, by which preformed nanocrystals can be either transformed to alloy nanocrystals or to various types of nanoheterostructures possessing core/shell, segmented, or striped architectures. In this review, we provide an up to date overview of the complex colloidal nanostructures that could be prepared so far by cation exchange. At the same time, the review gives an account of the fundamental thermodynamic and kinetic parameters governing these types of reactions, as they are currently understood, and outlines the main open issues and possible future developments in the field. PMID:26891471

  18. Restricted Defect Dynamics in Colloidal Peanut Crystals

    NASA Astrophysics Data System (ADS)

    Gerbode, Sharon; Lee, Stephanie; John, Bettina; Wolfgang, Angie; Liddell, Chekesha; Escobedo, Fernando; Cohen, Itai

    2008-03-01

    We report that monolayers of hard peanut-shaped colloidal particles consisting of two connected spherical lobes order into a crystalline phase at high area fractions. In this ``lobe-close-packed'' (LCP) crystal, the peanut particle lobes occupy triangular lattice sites, much like close-packed spheres, while the connections between lobe pairs are randomly oriented, uniformly populating the three crystalline directions of the underlying lattice. Using optical microscopy, we directly observe defect nucleation and dynamics in sheared LCP crystals. We find that many particle configurations form obstacles blocking dislocation glide. Consequently, in stark contrast to colloidal monolayers of close-packed spheres, single dislocation pair nucleation is not the only significant energetic barrier to relieving an imposed shear strain. Dislocation propagation beyond such obstructions can proceed only through additional mechanisms such as dislocation reactions. We discuss the implications of such restricted defect mobility for the plasticity of LCP crystals.

  19. Restricted Defect Dynamics in Colloidal Peanut Crystals

    NASA Astrophysics Data System (ADS)

    Gerbode, Sharon; Lee, Stephanie; John, Bettina; Wolfgang, Angie; Liddell, Chakesha; Escobedo, Fernando; Cohen, Itai

    2008-03-01

    We report that monolayers of hard peanut-shaped colloidal particles consisting of two connected spherical lobes order into a crystalline phase at high area fractions. In this ``lobe- close-packed'' (LCP) crystal, the peanut particle lobes occupy triangular lattice sites, much like close-packed spheres, while the connections between lobe pairs are randomly oriented, uniformly populating the three crystalline directions of the underlying lattice. Using optical microscopy, we directly observe defect nucleation and dynamics in sheared LCP crystals. We find that many particle configurations form obstacles blocking dislocation glide. Consequently, in stark contrast to colloidal monolayers of close-packed spheres, single dislocation pair nucleation is not the only significant energetic barrier to relieving an imposed shear strain. Dislocation propagation beyond such obstructions can proceed only through additional mechanisms such as dislocation reactions. We discuss the implications of such restricted defect mobility for the plasticity of LCP crystals.

  20. Colloidal cholesteric liquid crystal in spherical confinement

    NASA Astrophysics Data System (ADS)

    Li, Yunfeng; Jun-Yan Suen, Jeffrey; Prince, Elisabeth; Larin, Egor M.; Klinkova, Anna; Thérien-Aubin, Héloïse; Zhu, Shoujun; Yang, Bai; Helmy, Amr S.; Lavrentovich, Oleg D.; Kumacheva, Eugenia

    2016-08-01

    The organization of nanoparticles in constrained geometries is an area of fundamental and practical importance. Spherical confinement of nanocolloids leads to new modes of packing, self-assembly, phase separation and relaxation of colloidal liquids; however, it remains an unexplored area of research for colloidal liquid crystals. Here we report the organization of cholesteric liquid crystal formed by nanorods in spherical droplets. For cholesteric suspensions of cellulose nanocrystals, with progressive confinement, we observe phase separation into a micrometer-size isotropic droplet core and a cholesteric shell formed by concentric nanocrystal layers. Further confinement results in a transition to a bipolar planar cholesteric morphology. The distribution of polymer, metal, carbon or metal oxide nanoparticles in the droplets is governed by the nanoparticle size and yields cholesteric droplets exhibiting fluorescence, plasmonic properties and magnetic actuation. This work advances our understanding of how the interplay of order, confinement and topological defects affects the morphology of soft matter.

  1. Renormalized jellium model for colloidal mixtures.

    PubMed

    García de Soria, María Isabel; Álvarez, Carlos E; Trizac, Emmanuel

    2016-10-01

    In an attempt to quantify the role of polydispersity in colloidal suspensions, we present an efficient implementation of the renormalized jellium model for a mixture of spherical charged colloids. The different species may have different size, charge, and density. Advantage is taken from the fact that the electric potential pertaining to a given species obeys a Poisson's equation that is species independent; only boundary conditions do change from one species to the next. All species are coupled through the renormalized background (jellium) density, that is determined self-consistently. The corresponding predictions are compared to the results of Monte Carlo simulations of binary mixtures, where Coulombic interactions are accounted for exactly, at the primitive model level (structureless solvent with fixed dielectric permittivity). An excellent agreement is found.

  2. Colloidal Nanocrystals Fluoresced by Surface Coordination Complexes

    PubMed Central

    Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

    2014-01-01

    Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications. PMID:24970242

  3. Colloidal nanocrystals fluoresced by surface coordination complexes.

    PubMed

    Wang, Guan; Ji, Jianwei; Zhang, Xinwen; Zhang, Yan; Wang, Qiangbin; You, Xiaozeng; Xu, Xiangxing

    2014-06-27

    Colloidal Nanocrystals (NCs) with fluorescence originating from surface complexes are successfully prepared. The components of these NCs range from insulator, semiconductor to metal, with either pure phase, doped or core/shell structures. The photoluminescence of these NCs can be reversibly tuned across the visible to infrared spectrum, and even allow multi-color emission. A light emitting device is fabricated and a new in vivo cell imaging method is performed to demonstrate the power of this technology for emerging applications.

  4. Toward Multispectral Imaging with Colloidal Metasurface Pixels.

    PubMed

    Stewart, Jon W; Akselrod, Gleb M; Smith, David R; Mikkelsen, Maiken H

    2017-02-01

    Multispectral colloidal metasurfaces are fabricated that exhibit greater than 85% absorption and ≈100 nm linewidths by patterning film-coupled nanocubes in pixels using a fusion of bottom-up and top-down fabrication techniques over wafer-scale areas. With this technique, the authors realize a multispectral pixel array consisting of six resonances between 580 and 1125 nm and reconstruct an RGB image with 9261 color combinations.

  5. CGEL-2: Structural Studies of Colloidal Suspensions

    NASA Technical Reports Server (NTRS)

    2004-01-01

    These are images of CGEL-2 samples taken during STS-95. They show binary colloidal suspensions that have formed ordered crystalline structures in microgravity. In sample 5, there are more particles therefore, many, many crystallites (small crystals) form. In sample 6, there are less particles therefore, the particles are far apart and few, much larger crystallites form. The white object in the right corner of sample 5 is the stir bar used to mix the sample at the begirning of the mission.

  6. Stabilization of Colloidal Silica Using Small Polyols

    SciTech Connect

    GULLEY, GERALD L.; MARTIN, JAMES E.

    1999-09-07

    We have discovered that small polyols are reasonably effective at stabilizing colloidal silica against aggregation, even under the conditions of high pH and salt concentration. Both quasielastic and elastic light scattering were used to show that these polyols dramatically decrease the aggregation rate of the suspension, changing the growth kinetics from diffusion-limited cluster-cluster aggregation to reaction-limited cluster-cluster aggregation. These polyols maybe useful in the treatment of tank wastes at the Hanford site.

  7. Columnar self-assembly of colloidal nanodisks.

    PubMed

    Saunders, Aaron E; Ghezelbash, Ali; Smilgies, Detlef-M; Sigman, Michael B; Korgel, Brian A

    2006-12-01

    The self-assembly of sterically stabilized colloidal copper sulfide nanodisks, 14-20 nm in diameter and 5-7 nm thick, was studied. The nanodisks were observed by electron microscopy and small-angle X-ray scattering to form columnar arrays when evaporated as thin films from concentrated dispersions. These superstructured nanomaterials might give rise to technologically useful properties, such as anisotropic electrical transport and electrorheological and optical properties.

  8. Influence of biofilms on the movement of colloids in porous media. Implications for colloid facilitated transport in subsurface environments.

    PubMed

    Leon Morales, Carlos Felipe; Strathmann, Martin; Flemming, Hans-Curt

    2007-05-01

    Colloid transport through porous media can be influenced by the presence of biofilms. Sterile and non-sterile sand columns were investigated using Laponite RD as model colloid and a highly mucoid strain of Pseudomonas aeruginosa as model biofilm former. Laponite RD was marked specifically by fluorescent complexes with rhodamine 6G. Breakthrough curves (BTCs) were used as parameters for determination of colloid transport characteristics. In the sterile columns, the colloid was mobile (collision efficiencies from 0.05 to 0.08) both after the presence of Na(+) and Ca(2+) ions followed by deionised water influent. In the biofilm-grown column, the same treatment did not result in colloid retention in the case of Na(+) exposure, but in altered or enhanced colloid transport. In the case of Ca(2+) ions exposure, colloid retention increased with biofilm age. After 3 weeks, almost complete retention was observed. Similar observations were made in columns packed with material from slow sand filtration units. These data reveal the complex interactions between biofilms, cations and colloid transport. Changes in the electrolyte composition of water percolating the subsurface can frequently occur and will result in different colloid transport characteristics with regard to the dominating species of ions and the relative abundance of microbial biofilms. This has to be considered when modelling colloid transport through the subsurface.

  9. Transport of Intrinsic Plutonium Colloids in Saturated Porous Media

    NASA Astrophysics Data System (ADS)

    Zhou, D.; Abdel-Fattah, A.; Boukhalfa, H.; Ware, S. D.; Tarimala, S.; Keller, A. A.

    2011-12-01

    Actinide contaminants were introduced to the subsurface environment as a result of nuclear weapons development and testing, as well as for nuclear power generation and related research activities for defense and civilian applications. Even though most actinide species were believed to be fairly immobile once in the subsurface, recent studies have shown the transport of actinides kilometers away from their disposal sites. For example, the treated liquid wastes released into Mortandad Canyon at the Los Alamos National Laboratory were predicted to travel less than a few meters; however, plutonium and americium have been detected 3.4 km away from the waste outfall. A colloid-facilitated mechanism has been suggested to account for this unexpected transport of these radioactive wastes. Clays, oxides, organic matters, and actinide hydroxides have all been proposed as the possible mobile phase. Pu ions associated with natural colloids are often referred to as pseudo-Pu colloids, in contrast with the intrinsic Pu colloids that consist of Pu oxides. Significant efforts have been made to investigate the role of pseudo-Pu colloids, while few studies have evaluated the environmental behavior of the intrinsic Pu colloids. Given the fact that Pu (IV) has extremely low solubility product constant, it can be inferred that the transport of Pu in the intrinsic form is highly likely at suitable environmental conditions. This study investigates the transport of intrinsic Pu colloids in a saturated alluvium material packed in a cylindrical column (2.5-cm Dia. x 30-cm high) and compares the results to previous data on the transport of pseudo Pu colloids in the same material. A procedure to prepare a stable intrinsic Pu colloid suspension that produced consistent and reproducible electrokinetic and stability data was developed. Electrokinetic properties and aggregation stability were characterized. The Pu colloids, together with trillium as a conservative tracer, were injected into the

  10. General nonequilibrium theory of colloid dynamics.

    PubMed

    Ramírez-González, Pedro; Medina-Noyola, Magdaleno

    2010-12-01

    A nonequilibrium extension of Onsager's canonical theory of thermal fluctuations is employed to derive a self-consistent theory for the description of the statistical properties of the instantaneous local concentration profile n(r,t) of a colloidal liquid in terms of the coupled time-evolution equations of its mean value n(r,t) and of the covariance [Formula in text] of its fluctuations δn(r,t)=n(r,t)-n(r,t). These two coarse-grained equations involve a local mobility function b(r,t) which, in its turn, is written in terms of the memory function of the two-time correlation function [Formula in text]. For given effective interactions between colloidal particles and applied external fields, the resulting self-consistent theory is aimed at describing the evolution of a strongly correlated colloidal liquid from an initial state with arbitrary mean and covariance n(0)(r) and σ(0)(r,r') toward its equilibrium state characterized by the equilibrium local concentration profile n(eq)(r) and equilibrium covariance σ(eq)(r,r'). This theory also provides a general theoretical framework to describe irreversible processes associated with dynamic arrest transitions, such as aging, and the effects of spatial heterogeneities.

  11. Dynamics of Polymers in Colloidal Flows

    NASA Astrophysics Data System (ADS)

    Chen, Hsieh; Alexander-Katz, Alfredo

    2011-03-01

    This research is motivated by recent studies on the von Willebrand factor (vWF), a large multimeric protein that plays an essential role in the initial stages of blood clotting in blood vessels. Recent experiments substantiated the hypothesis that the vWF is activated by shear stress in blood flow that causes its shape to transform from a compact globule to an extended state, and biological function is obtained only in the extended state. Simple simulations (which only consider a single polymer in bulk shear flow) have successfully reproduced the observed dynamics of the vWF. However, a more refined model is still demanding for the better understanding of the behaviors of this biomolecule in the physiological environments. Here we refine the existing model by adding the drifting colloids into the flows to mimic the presence of the blood cells in the bloodstream. Preliminary result shows that colloids greatly influence the dynamics of the polymers. It is observed that the average extensions of polymers along and perpendicular to the shear flow direction are both increased with the presence of the colloids.

  12. Armoring confined bubbles in concentrated colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Yu, Yingxian; Khodaparast, Sepideh; Stone, Howard

    2016-11-01

    Encapsulation of a bubble with microparticles is known to significantly improve the stability of the bubble. This phenomenon has recently gained increasing attention due to its application in a variety of technologies such as foam stabilization, drug encapsulation and colloidosomes. Nevertheless, the production of such colloidal armored bubble with controlled size and particle coverage ratio is still a great challenge industrially. We study the coating process of a long air bubble by microparticles in a circular tube filled with a concentrated microparticles colloidal suspension. As the bubble proceeds in the suspension of particles, a monolayer of micro-particles forms on the interface of the bubble, which eventually results in a fully armored bubble. We investigate the phenomenon that triggers and controls the evolution of the particle accumulation on the bubble interface. Moreover, we examine the effects of the mean flow velocity, the size of the colloids and concentration of the suspension on the dynamics of the armored bubble. The results of this study can potentially be applied to production of particle-encapsulated bubbles, surface-cleaning techniques, and gas-assisted injection molding.

  13. Composition of estuarine colloidal material: organic components

    USGS Publications Warehouse

    Sigleo, A.C.; Hoering, T.C.; Helz, G.R.

    1982-01-01

    Colloidal material in the size range 1.2 nm to 0.4 ??m was isolated by ultrafiltration from Chesapeake Bay and Patuxent River waters (U.S.A.). Temperature controlled, stepwise pyrolysis of the freeze-dried material, followed by gas chromatographic-mass spectrometric analyses of the volatile products indicates that the primary organic components of this polymer are carbohydrates and peptides. The major pyrolysis products at the 450??C step are acetic acid, furaldehydes, furoic acid, furanmethanol, diones and lactones characteristic of carbohydrate thermal decomposition. Pyrroles, pyridines, amides and indole (protein derivatives) become more prevalent and dominate the product yield at the 600??C pyrolysis step. Olefins and saturated hydrocarbons, originating from fatty acids, are present only in minor amounts. These results are consistent with the composition of Chesapeake phytoplankton (approximately 50% protein, 30% carbohydrate, 10% lipid and 10% nucleotides by dry weight). The pyrolysis of a cultured phytoplankton and natural particulate samples produced similar oxygen and nitrogencontaining compounds, although the proportions of some components differ relative to the colloidal fraction. There were no lignin derivatives indicative of terrestrial plant detritus in any of these samples. The data suggest that aquatic microorganisms, rather than terrestrial plants, are the dominant source of colloidal organic material in these river and estuarine surface waters. ?? 1982.

  14. Colloidal solitary waves with temperature dependent compressibility

    NASA Astrophysics Data System (ADS)

    Azmi, A.; Marchant, T. R.

    2014-05-01

    Spatial solitary waves which form in colloidal suspensions of dielectric nanoparticles are considered. The interactions, or compressibility, of the colloidal particles, is modelled using a series in the particle density, or packing fraction, where the virial, or series, coefficients depend on the type of particle interaction model. Both the theoretical hard disk and sphere repulsive models, and a model with temperature dependent compressibility, are considered. Experimental results show that particle interactions can be temperature dependent and either repulsive or attractive in nature, so we model the second virial coefficient using a physically realistic temperature power law. One- and two-dimensional semi-analytical colloidal solitary wave solutions are found. Trial functions, based on the form of the nonlinear Schrödinger equation soliton, are used, together with averaging, to develop the semi-analytical solutions. When the background packing fraction is low, the one-dimensional solitary waves have three solutions branches (with a bistable regime) while the two-dimensional solitary waves have two solution branches, with a single stable branch. The temperature dependent second virial coefficient results in changes to the solitary wave properties and the parameter space, in which multiple solutions branches occur. An excellent comparison is found between the semi-analytical and numerical solutions.

  15. Colloidal competences of any polyethyleneglycol conjugates.

    PubMed

    Jianu, C; Cocan, Ileana; Rujescu, Cristina; Jianu, I

    2008-01-01

    The present paper presents research rely on the knowledge of basic colloidal competences (surface tension, critical micelar concentration, HLB value) of certain new structured lipids by accessing "homogeneous" polyoxyethylene chains (n=3-18) (PEGn) monoderivatized R(NF; EH) during processing by cyanoethylation, hydrolysis, and esterification together with fatty acids (R') isolated and characterized from grape seeds (Vitis vinifera) (S), wild chestnut (Aesculus hyppocastanum) (Ca), wild rose (Rosa Canina) (mn), coriander (Coriandri fructus) (Co) in the architecture of the conjugates about foaming and wetting competences. Basic colloidal characterisation aimed at directing future research to optimagrape seed technological directions for agroalimentary and horticultural processing (and not only) among which these structures through synergic cumulus of defining competences of the polyunsaturated fatty acids (1 delta; 2delta; 3delta), of "homogeneous" derivatised polyethyleneoxy chains (PEO) with monitored degree of oligomerization (n=3-18). We thought it useful to access oligomeric chains PEO processed through adapted Williamson synthesis to clearly quantify its role in the global "colloidal fingerprint" of the studied conjugate. On the other hand, polyunsaturated plant lipid residues we selected constitute a variant of valorification by-products from horticultural and/or agroalimentary processing accessible over worldwide geographical areas with differences due to soil and climate conditions and to the cultivars specific to spontaneous and cultivated flora.

  16. Patchy polymer colloids with tunable anisotropy dimensions.

    PubMed

    Kraft, Daniela J; Hilhorst, Jan; Heinen, Maria A P; Hoogenraad, Mathijs J; Luigjes, Bob; Kegel, Willem K

    2011-06-09

    We present the synthesis of polymer colloids with continuously tunable anisotropy dimensions: patchiness, roughness, and branching. Our method makes use of controlled fusion of multiple protrusions on highly cross-linked polymer particles produced by seeded emulsion polymerization. Carefully changing the synthesis conditions, we can tune the number of protrusions, or branching, of the obtained particles from spheres with one to three patches to raspberry-like particles with multiple protrusions. In addition to that, roughness is generated on the seed particles by adsorption of secondary nucleated particles during synthesis. The size of the roughness relative to the smooth patches can be continuously tuned by the initiator, surfactant, and styrene concentrations. Seed colloids chemically different from the protrusions induce patches of different chemical nature. The underlying generality of the synthesis procedure allows for application to a variety of seed particle sizes and materials. We demonstrate the use of differently sized polyNIPAM (poly-N-isopropylacrylamide), as well as polystyrene and magnetite filled polyNIPAM seed particles, the latter giving rise to magnetically anisotropic colloids. The high yield together with the uniform, anisotropic shape make them interesting candidates for use as smart building blocks in self-assembling systems.

  17. Dense colloidal fluids form denser amorphous sediments

    PubMed Central

    Liber, Shir R.; Borohovich, Shai; Butenko, Alexander V.; Schofield, Andrew B.; Sloutskin, Eli

    2013-01-01

    We relate, by simple analytical centrifugation experiments, the density of colloidal fluids with the nature of their randomly packed solid sediments. We demonstrate that the most dilute fluids of colloidal hard spheres form loosely packed sediments, where the volume fraction of the particles approaches in frictional systems the random loose packing limit, φRLP = 0.55. The dense fluids of the same spheres form denser sediments, approaching the so-called random close packing limit, φRCP = 0.64. Our experiments, where particle sedimentation in a centrifuge is sufficiently rapid to avoid crystallization, demonstrate that the density of the sediments varies monotonically with the volume fraction of the initial suspension. We reproduce our experimental data by simple computer simulations, where structural reorganizations are prohibited, such that the rate of sedimentation is irrelevant. This suggests that in colloidal systems, where viscous forces dominate, the structure of randomly close-packed and randomly loose-packed sediments is determined by the well-known structure of the initial fluids of simple hard spheres, provided that the crystallization is fully suppressed. PMID:23530198

  18. Light-activated self-propelled colloids

    PubMed Central

    Palacci, J.; Sacanna, S.; Kim, S.-H.; Yi, G.-R.; Pine, D. J.; Chaikin, P. M.

    2014-01-01

    Light-activated self-propelled colloids are synthesized and their active motion is studied using optical microscopy. We propose a versatile route using different photoactive materials, and demonstrate a multiwavelength activation and propulsion. Thanks to the photoelectrochemical properties of two semiconductor materials (α-Fe2O3 and TiO2), a light with an energy higher than the bandgap triggers the reaction of decomposition of hydrogen peroxide and produces a chemical cloud around the particle. It induces a phoretic attraction with neighbouring colloids as well as an osmotic self-propulsion of the particle on the substrate. We use these mechanisms to form colloidal cargos as well as self-propelled particles where the light-activated component is embedded into a dielectric sphere. The particles are self-propelled along a direction otherwise randomized by thermal fluctuations, and exhibit a persistent random walk. For sufficient surface density, the particles spontaneously form ‘living crystals’ which are mobile, break apart and reform. Steering the particle with an external magnetic field, we show that the formation of the dense phase results from the collisions heads-on of the particles. This effect is intrinsically non-equilibrium and a novel principle of organization for systems without detailed balance. Engineering families of particles self-propelled by different wavelength demonstrate a good understanding of both the physics and the chemistry behind the system and points to a general route for designing new families of self-propelled particles. PMID:25332383

  19. Improving feed slurry rheology by colloidal techniques

    SciTech Connect

    Heath, W.O.; Ternes, R.L.

    1984-06-01

    Pacific Northwest Laboratory (PSN) has investigated three colloidal techniques in the laboratory to improve the sedimentation and flowability of Hanford simulated (nonradioactive) current acid waste (CAW) melter feed slurry: polymer-induced bridging flocculation; manipulating glass former (raw SiO/sub 2/ or frit) particle size; and alteration of nitric acid content. All three methods proved successful in improving the rheology of the simulated CAW feed. This initially had exhibited nearly worst-case flow and clogging properties, but was transformed into a flowable, resuspendable (nonclogging) feed. While each has advantages and disadvantages, the following three specific alternatives proved successful: addition of a polyelectrolyte in 2000 ppM concentration to feed slurry; substitution of a 49 wt % SiO/sub 2/ colloidal suspension (approx. 10-micron particle size) for the -325 mesh (less than or equal to 44-micron particle size) raw-chemical SiO/sub 2/; and increase of nitric acid content from the reference 1.06 M to optimum 1.35 M. The first method, polymer-induced bridging flocculation, results in a high sediment volume, nonclogging CAW feed. The second method, involving the use of colloidal silica particles results in a nonsedimenting feed that when left unagitated forms a gel. The third method, increase in feed acidity, results in a highly resuspendable (nonclogging) melter feed. Further research is therefore required to determine which of the three alternatives is the preferred method of achieving rheological control of CAW melter feeds.

  20. Theory of dynamic arrest in colloidal mixtures

    NASA Astrophysics Data System (ADS)

    Juárez-Maldonado, R.; Medina-Noyola, M.

    2008-05-01

    We present a first-principles theory of dynamic arrest in colloidal mixtures based on the multicomponent self-consistent generalized Langevin equation theory of colloid dynamics [M. A. Chávez-Rojo and M. Medina-Noyola, Phys. Rev. E 72, 031107 (2005); M. A. Chávez-Rojo and M. Medina-Noyola, Phys. Rev. E76, 039902 (2007)]. We illustrate its application with a description of dynamic arrest in two simple model colloidal mixtures: namely, hard-sphere and repulsive Yukawa binary mixtures. Our results include observation of the two patterns of dynamic arrest, one in which both species become simultaneously arrested and the other involving the sequential arrest of the two species. The latter case gives rise to mixed states in which one species is arrested while the other species remains mobile. We also derive the (”bifurcation” or fixed-point”) equations for the nonergodic parameters of the system, which takes the surprisingly simple form of a system of coupled equations for the localization length of the particles of each species. The solution of this system of equations indicates unambiguously which species is arrested (finite localization length) and which species remains ergodic (infinite localization length). As a result, we are able to draw the entire ergodic-nonergodic phase diagram of the binary hard-sphere mixture.

  1. Dissipative Particle Dynamics simulation of colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Jamali, Safa; Boromand, Arman; Maia, Joao

    2014-03-01

    DPD as a mesoscale method was firstly proposed to study dynamics of suspensions under flow condition. However the proposed method failed to capture shear properties of suspensions because it lacked: first a potential to reproduce lubrication forces and second a clear definition for the colloid surface. Recently we reported a modified DPD method which defines colloidal particles as particles with hard core and a dissipative coat. An additional lubrication force was introduced to include the short-range hydrodynamics that are not captured in original DPD. The model was found to be able to reproduce shear properties of suspensions for a wide range of different systems, from monodisperse to bimodal with different volume fractions, compositions and size ratios. In present work our modified DPD method is employed to study both equilibrium and flow properties of colloidal suspension. Zero shear viscosity of suspension is measured using Green-Kubo expressions and the results are compared to theoretical predictions. Furthermore, structure formation in suspensions is studied in respect to energy landscape of the fluid both at rest and under flow.

  2. Design and elaboration of colloidal molecules: an overview.

    PubMed

    Duguet, Etienne; Désert, Anthony; Perro, Adeline; Ravaine, Serge

    2011-02-01

    The concept of colloidal molecules was first evoked by van Blaaderen in 2003 for describing small non-spherical colloids made of the aggregation of a small number of particles. He predicted original properties to the complex assemblies of such colloids, in particular in optics. This critical review deals with the different strategies reported for creating robust clusters of spherical particles which could mimic the space-filling models of simple conventional molecules. These routes concern either the controlled clustering of preformed colloids directed by coalescence, physical routes, chemical routes, or 2-D/3-D geometrical confinement, or strategies starting from a single colloid which is decorated by satellite colloids by taking advantage of controlled phase separation or nucleation and growth phenomena. These routes are compared from the viewpoint of the accessible shapes, their tunability and scalability (146 references).

  3. Local elastic response measured near the colloidal glass transition

    NASA Astrophysics Data System (ADS)

    Anderson, D.; Schaar, D.; Hentschel, H. G. E.; Hay, J.; Habdas, Piotr; Weeks, Eric R.

    2013-03-01

    We examine the response of a dense colloidal suspension to a local force applied by a small magnetic bead. For small forces, we find a linear relationship between the force and the displacement, suggesting the medium is elastic, even though our colloidal samples macroscopically behave as fluids. We interpret this as a measure of the strength of colloidal caging, reflecting the proximity of the samples' volume fractions to the colloidal glass transition. The strain field of the colloidal particles surrounding the magnetic probe appears similar to that of an isotropic homogeneous elastic medium. When the applied force is removed, the strain relaxes as a stretched exponential in time. We introduce a model that suggests this behavior is due to the diffusive relaxation of strain in the colloidal sample.

  4. Self-pinning by colloids confined at a contact line

    NASA Astrophysics Data System (ADS)

    Weon, Byung; Je, Jung

    2013-03-01

    Colloidal particles suspended in a fluid usually inhibit complete wetting of the fluid on a solid surface and cause pinning of the contact line, known as self-pinning. We show differences in spreading and drying behaviors of pure and colloidal droplets using optical and confocal imaging methods. These differences come from spreading inhibition by colloids confined at a contact line. We propose a self-pinning mechanism based on spreading inhibition by colloids. We find a good agreement between the mechanism and the experimental result taken by directly tracking individual colloids near the contact lines of evaporating colloidal droplets. This research was supported by the Creative Research Initiatives (Functional X-ray Imaging) of MEST/NRF.

  5. Evanescent wave excited luminescence from levitated quantum dot modified colloids.

    PubMed

    Everett, W Neil; Beckham, Richard E; Meissner, Kenith; Bevan, Michael A

    2007-08-14

    Evanescent wave excited luminescence of quantum dot modified polystyrene (QDPS) colloids is investigated to measure potential energy profiles of QDPS colloids electrostatically levitated above a planar glass surface. Luminescence is characterized for three different-sized PS colloids modified with three different-sized QDs using confocal microscopy, emission spectra, flow cytometry, and temporal measurements of levitated and deposited colloids. Colloid-surface potential energy profiles constructed from scattering and luminescence intensity data display excellent agreement with each other, theoretical predictions, and independently measured parameters. QDPS luminescence intensity is indirectly confirmed to have an exponential dependence on height similar to conventional colloidal evanescent wave scattering. Our findings indicate that evanescent wave excited QDPS luminescence could enable total internal reflection microscopy measurements of index-matched hard spheres, multiple specific biomolecular interactions via spectral multiplexing, enhanced morphology-dependent resonance modes, and integrated evanescent wave-video-confocal microscopy experiments not possible with scattering.

  6. Inertial and viscoelastic forces on rigid colloids in microfluidic channels.

    PubMed

    Howard, Michael P; Panagiotopoulos, Athanassios Z; Nikoubashman, Arash

    2015-06-14

    We perform hybrid molecular dynamics simulations to study the flow behavior of rigid colloids dispersed in a dilute polymer solution. The underlying Newtonian solvent and the ensuing hydrodynamic interactions are incorporated through multiparticle collision dynamics, while the constituent polymers are modeled as bead-spring chains, maintaining a description consistent with the colloidal nature of our system. We study the cross-stream migration of the solute particles in slit-like channels for various polymer lengths and colloid sizes and find a distinct focusing onto the channel center under specific solvent and flow conditions. To better understand this phenomenon, we systematically measure the effective forces exerted on the colloids. We find that the migration originates from a competition between viscoelastic forces from the polymer solution and hydrodynamically induced inertial forces. Our simulations reveal a significantly stronger fluctuation of the lateral colloid position than expected from thermal motion alone, which originates from the complex interplay between the colloid and polymer chains.

  7. Remotely Controlled Mixers for Light Microscopy Module (LMM) Colloid Samples

    NASA Technical Reports Server (NTRS)

    Kurk, Michael A. (Andy)

    2015-01-01

    Developed by NASA Glenn Research Center, the LMM aboard the International Space Station (ISS) is enabling multiple biomedical science experiments. Techshot, Inc., has developed a series of colloid specialty cell systems (C-SPECS) for use in the colloid science experiment module on the LMM. These low-volume mixing devices will enable uniform particle density and remotely controlled repetition of LMM colloid experiments. By automating the experiment process, C-SPECS allow colloid samples to be processed more quickly. In addition, C-SPECS will minimize the time the crew will need to spend on colloid experiments as well as eliminate the need for multiple and costly colloid samples, which are expended after a single examination. This high-throughput capability will lead to more efficient and productive use of the LMM. As commercial launch vehicles begin routine visits to the ISS, C-SPECS could become a significant means to process larger quantities of high-value materials for commercial customers.

  8. A colloidal singularity reveals the crucial role of colloidal stability for nanomaterials in-vitro toxicity testing: nZVI-microalgae colloidal system as a case study.

    PubMed

    Gonzalo, Soledad; Llaneza, Veronica; Pulido-Reyes, Gerardo; Fernández-Piñas, Francisca; Bonzongo, Jean Claude; Leganes, Francisco; Rosal, Roberto; García-Calvo, Eloy; Rodea-Palomares, Ismael

    2014-01-01

    Aggregation raises attention in Nanotoxicology due to its methodological implications. Aggregation is a physical symptom of a more general physicochemical condition of colloidal particles, namely, colloidal stability. Colloidal stability is a global indicator of the tendency of a system to reduce its net surface energy, which may be achieved by homo-aggregation or hetero-aggregation, including location at bio-interfaces. However, the role of colloidal stability as a driver of ENM bioactivity has received little consideration thus far. In the present work, which focuses on the toxicity of nanoscaled Fe° nanoparticles (nZVI) towards a model microalga, we demonstrate that colloidal stability is a fundamental driver of ENM bioactivity, comprehensively accounting for otherwise inexplicable differential biological effects. The present work throws light on basic aspects of Nanotoxicology, and reveals a key factor which may reconcile contradictory results on the influence of aggregation in bioactivity of ENMs.

  9. A Colloidal Singularity Reveals the Crucial Role of Colloidal Stability for Nanomaterials In-Vitro Toxicity Testing: nZVI-Microalgae Colloidal System as a Case Study

    PubMed Central

    Fernández-Piñas, Francisca; Bonzongo, Jean Claude; Leganes, Francisco; Rosal, Roberto; García-Calvo, Eloy; Rodea-Palomares, Ismael

    2014-01-01

    Aggregation raises attention in Nanotoxicology due to its methodological implications. Aggregation is a physical symptom of a more general physicochemical condition of colloidal particles, namely, colloidal stability. Colloidal stability is a global indicator of the tendency of a system to reduce its net surface energy, which may be achieved by homo-aggregation or hetero-aggregation, including location at bio-interfaces. However, the role of colloidal stability as a driver of ENM bioactivity has received little consideration thus far. In the present work, which focuses on the toxicity of nanoscaled Fe° nanoparticles (nZVI) towards a model microalga, we demonstrate that colloidal stability is a fundamental driver of ENM bioactivity, comprehensively accounting for otherwise inexplicable differential biological effects. The present work throws light on basic aspects of Nanotoxicology, and reveals a key factor which may reconcile contradictory results on the influence of aggregation in bioactivity of ENMs. PMID:25340509

  10. Colloidal Surfaces with Boundaries, Apex Boojums, and Nested Elastic Self-Assembly of Nematic Colloids

    NASA Astrophysics Data System (ADS)

    Park, Sungoh; Liu, Qingkun; Smalyukh, Ivan I.

    2016-12-01

    Self-assembly of colloidal particles is poised to become a powerful composite material fabrication technique, but remains challenged by a limited control over the ensuing structures. We develop a new breed of nematic colloids that are physical analogs of a mathematical surface with boundary, interacting with the molecular alignment field without inducing defects when flat. However, made from a thin nanofoil, they can be shaped to prompt formation of self-compensating defects that drive preprogramed elastic interactions mediated by the nematic host. To show this, we wrap the nanofoil on all triangular side faces of a pyramid, except its square base. The ensuing pyramidal cones induce point defects with fractional hedgehog charges of opposite signs, spontaneously align with respect to the far-field director to form elastic dipoles and nested assemblies with tunable spacing. Nanofoils shaped into octahedrons interact as elastic quadrupoles. Our findings may drive realization of low-symmetry colloidal phases.

  11. [Bactericidal activity of colloidal silver against grampositive and gramnegative bacteria].

    PubMed

    Afonina, I A; Kraeva, L A; Tseneva, G Ia

    2010-01-01

    It was shown that colloidal silver solution prepared in cooperation with the A. F. Ioffe Physical Technical Institute of the Russian Academy of Sciences, had significant bactericidal activity. Stable bactericidal effect on gramnegative microorganisms was observed after their 2-hour exposition in the solution of colloidal silver at a concentration of 10 ppm. Grampositive capsule-forming microorganisms were less susceptible to the colloidal silver solution: their death was observed after the 4-hour exposition in the solution.

  12. Influence of Nanoscale Surface Roughness on Colloidal Force Measurements.

    PubMed

    Zou, Yi; Jayasuriya, Sunil; Manke, Charles W; Mao, Guangzhao

    2015-09-29

    Forces between colloidal particles determine the performances of many industrial processes and products. Colloidal force measurements conducted between a colloidal particle AFM probe and particles immobilized on a flat substrate are valuable in selecting appropriate surfactants for colloidal stabilization. One of the features of inorganic fillers and extenders is the prevalence of rough surfaces-even the polymer latex particles, often used as model colloidal systems including the current study, have rough surfaces albeit at a much smaller scale. Surface roughness is frequently cited as the reason for disparity between experimental observations and theoretical treatment but seldom verified by direct evidence. This work reports the effect of nanoscale surface roughness on colloidal force measurements carried out in the presence of surfactants. We applied a heating method to reduce the mean surface roughness of commercial latex particles from 30 to 1 nm. We conducted force measurements using the two types of particles at various salt and surfactant concentrations. The surfactants used were pentaethylene glycol monododecyl ether, Pluronic F108, and a styrene/acrylic copolymer, Joncryl 60. In the absence of the surfactant, nanometer surface roughness affects colloidal forces only in high salt conditions when the Debye length becomes smaller than the surface roughness. The adhesion is stronger between colloids with higher surface roughness and requires a higher surfactant concentration to be eliminated. The effect of surface roughness on colloidal forces was also investigated as a function of the adsorbed surfactant layer structure characterized by AFM indentation and dynamic light scattering. We found that when the layer thickness exceeds the surface roughness, the colloidal adhesion is less influenced by surfactant concentration variation. This study demonstrates that surface roughness at the nanoscale can influence colloidal forces significantly and should be taken

  13. The Colloidal Stability of Magnetic Nanoparticles in Ionic Liquids

    DTIC Science & Technology

    2014-09-01

    SEP 2014 2. REPORT TYPE Final 3. DATES COVERED 06-03-2013 to 05-06-2014 4. TITLE AND SUBTITLE The Colloidal Stability of Magnetic...DATES COVERED (From - To) 6 Mar 2013 – 5 June 2014 4. TITLE AND SUBTITLE The Colloidal Stability of Magnetic Nanoparticles in Ionic Liquids...Polymers and Colloids , Chemistry F11, The University of Sydney, NSW 2006, Australia. - Phone : +61 2 9351 6973 - Fax : +61 2 9351 851 Period of

  14. Computational Study of Colloidal Droplet Interactions with Three Dimensional Structures

    DTIC Science & Technology

    2015-05-18

    SECURITY CLASSIFICATION OF: The colloidal droplet spreading on and sorption into a porous medium is important to 3D printing technology. In this study... colloidal fluid distribution in the porous structure after sorption of single/multiple droplets in powder beds. The spreading of the droplet on the surface...Feb-2015 Approved for Public Release; Distribution Unlimited Final Report: Computational Study of Colloidal Droplet Interactions with Three Dimensional

  15. Exotic crystal superstructures of colloidal crystals in confinement.

    PubMed

    Fontecha, Ana Barreira; Schöpe, Hans Joachim

    2008-06-01

    Colloidal model systems have been used for over three decades for investigating liquids, crystals, and glasses. Colloidal crystal superstructures have been observed in binary systems of repulsive spheres as well as oppositely charged sphere systems showing structures well known from atomic solids. In this work we study the structural transition of colloidal crystals under confinement. In addition to the known sequence of crystalline structures, crystal superstructures with dodecagonal and hexagonal symmetry are observed in one component systems. These structures have no atomic counterpart.

  16. Colloidal crystallization of colloidal silica grafted with iron(0) complex-tethered polymers in organic solvents

    NASA Astrophysics Data System (ADS)

    Yoshinaga, Kohji; Mouri, Emiko

    2007-09-01

    Incorporation of iron(0) complex into polymer-grafted silica and colloidal crystallization in organic solvent were studied. In this study, zero-valence iron complex, vinylferrocene (Vfc) and iron(0)tricarbonyl(4,4-dimethyl-1,-4-cyclohexadienyl) acrylate (Fe(0)Ac) or methacrylate (Fe(0)Me), were introduced into grafted polymer to prevent from increasing ionic strength in colloidal crystallization system. Poly(methyl methacrylate (MMA)-co-Vfc)-grafted silica never formed colloidal crystals in polar solvent, such as acetone or acetonitrile. However, increasing ferrocenyl group fraction in the polymer resulted in disturbing the crystallization. Poly(N-isopropylacrylamide (NIPAAm)-co-Vfc)-grafted silica, which was composed of mole fraction of Vfc, 1/3, afforded crystallization in ethanol over the particle fraction of 0.053. In the case of diene-Fe(0)(CO) 3/polymer-grafted silica, poly(MMA-co-Fe(0)Ac)-, poly(NIPAAm-co-Fe(0)Ac)- and poly(N.N-dimethylacrylamide (DMAAm)-co-Fe(0)Ac)-grafted silica gave colloidal crystallization in relatively low polar solvents, DMF, acetone, acetonirile and ethanol, critical volume fraction for which were in the range from 0.054 to 0.117. In the case of copolymer-grafted silica containing Fe(0)Me, poly(MMA-co-FeMe)-grafted silica crystallized in DMF, Interestingly, especially in cases of polymer-grafted silica containing Fe(0)Ac or Fe(0)Me composed of the highest mole fraction Fe(0)Me, 1/2, afforded crystallization in DMF. The iridescence color of the colloidal crystals was changed with the combination of grafted polymer and solvent. The characteristic coloration of the solution from reddish to greenish color is possibly due to absorption of blue light region by diene-Fe(0)(CO) 3 complex and Bragg deflection on colloidal crystals.

  17. Industrial Applications of LES in Mechanical Engineering

    DTIC Science & Technology

    2001-08-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP013624 TITLE: Industrial Applications of LES in Mechanical Engineering DISTRIBUTION...compilation report: ADP013620 thru ADP013707 UNCLASSIFIED INDUSTRIAL APPLICATIONS OF LES IN MECHANICAL ENGINEERING CHISACHI KATO Institute of Industrial...Science University of Tokyo, Tokyo, Japan MASAYUKI KAIHO, AKIRA MANABE Mechanical Engineering Research Laboratory Hitachi LTD., Ibaraki, Japan Abstract

  18. Sodium meta-autunite colloids: Synthesis, characterization,stability

    SciTech Connect

    zzuoping@lbl.gov

    2004-04-10

    Waste forms of U such as those in the United States Department of Energy's Hanford Site often contain high concentrations of Na and P. Low solubility sodium uranyl phosphates such as sodium meta-autunite have the potential to form mobile colloids that can facilitate transport of this radionuclide. In order to understand the geochemical behavior of uranyl phosphate colloids, we synthesized sodiummeta-autunite colloids, and characterized their morphology, chemical composition, structure, dehydration, and surface charge. The stability of these synthetic plate-shaped colloids was tested with respect to time and pH. The highest aggregation rate was observed at pH 3, and the rate decreases as pH increases, indicating that higher stability of colloid dispersion under neutral and alkaline pH conditions. The synthetic colloids are all negatively charged and no isoelectric points were found over a pH range of 3 to 9. The zeta-potentials of the colloids in the phosphate solution show a strong pH-dependence in the more acidic range over time, but are relatively constant in the neutral and alkaline pH range. The geochemical behavior of the synthetic colloids can be interpreted using DLVO theory. The results suggest that formation of mobile sodium meta-autunite colloids can enhance the transport of U in some contaminated sediments.

  19. Infrared colloidal lead chalcogenide nanocrystals: synthesis, properties, and photovoltaic applications.

    PubMed

    Fu, Huiying; Tsang, Sai-Wing

    2012-04-07

    Simple solution phase, catalyst-free synthetic approaches that offer monodispersed, well passivated, and non-aggregated colloidal semiconductor nanocrystals have presented many research opportunities not only for fundamental science but also for technological applications. The ability to tune the electrical and optical properties of semiconductor nanocrystals by manipulating the size and shape of the crystals during the colloidal synthesis provides potential benefits to a variety of applications including photovoltaic devices, light-emitting diodes, field effect transistors, biological imaging/labeling, and more. Recent advances in the synthesis and characterization of colloidal lead chalcogenide nanocrystals and the achievements in colloidal PbS or PbSe nanocrystals solar cells have demonstrated the promising application of infrared-emitting colloidal lead chalcogenide nanocrystals in photovoltaic devices. Here, we review recent progress in the synthesis and optical properties of colloidal lead chalcogenide nanocrystals. We focus in particular upon the size- and shape-controlled synthesis of PbS, PbSe, and PbTe nanocrystals by using different precursors and various stabilizing surfactants for the growth of the colloidal nanocrystals. We also summarize recent advancements in the field of colloidal nanocrystals solar cells based on colloidal PbS and PbSe nanocrystals.

  20. Tuning Colloid-Interface Interactions by Salt Partitioning

    NASA Astrophysics Data System (ADS)

    Everts, J. C.; Samin, S.; van Roij, R.

    2016-08-01

    We show that the interaction of an oil-dispersed colloidal particle with an oil-water interface is highly tunable from attractive to repulsive, either by varying the sign of the colloidal charge via charge regulation or by varying the difference in hydrophilicity between the dissolved cations and anions. In addition, we investigate the yet unexplored interplay between the self-regulated colloidal surface charge distribution with the planar double layer across the oil-water interface and the spherical one around the colloid. Our findings explain recent experiments and have direct relevance for tunable Pickering emulsions.

  1. Nonlinear Optical Properties of Colloids with Carbon Nanoparticles

    NASA Astrophysics Data System (ADS)

    Mayor, A. Yu.; Proschenko, D. Yu.; Golik, S. S.; Postnova, I. V.; Shchipunov, Yu. A.; Podlesnyh, A. A.

    Experimentally studied linear and nonlinear characteristics of colloid on the basis of a new class of carbon nanoparticles (CN) synthesized by hydrothermal synthesis. The spectral characteristics of supercontinuum of the colloids with CN in the range 420 - 700 nm were investigated. The effectiveness of excitation of one- and two-photon fluorescence colloids with UN was determined. The anomalous dependence of the nonlinear refractive index of the wavelength of the radiation was revealed. It was installed that the efficiency of spectral transformation of the supercontinuum process in the case of colloid with carbon nanoparticles is less in the anti-stokes region than in case with water.

  2. Zero-valent iron colloid emplacement in sand columns

    SciTech Connect

    Cantrell, K.J.; Kaplan, D.I.

    1997-05-01

    Application of chemically reactive barriers to mitigate contaminant migration is an active area of research and development. Studies were conducted to evaluate a novel approach of emplacing chemically reactive barriers composed of zero-valent iron (Fe{sup 0}) by injecting suspensions of colloidal-size Fe{sup 0} particles into porous media. The specific objective of this study was to evaluate the effect of influent colloid concentration, rate, and volume of colloidal suspensions on Fe{sup 0} colloid emplacement in sand columns. Relatively even distributions of Fe{sup 0} throughout a sand column were obtained at low influent colloid concentrations and high injection rates. As the concentration of influent suspensions was increased, a point was reached beyond which a significant increase in the filtration of Fe{sup 0} particles near the front of the column was observed. This point was also found to occur at lower influent colloid concentrations as the injection rate was decreased, i.e., there was an interactive effect of influent colloid concentration and injection rate on the extent of filtration that occurred near the front of the column. As the volume of the colloidal suspension injected into the column was increased, the distribution of Fe{sup 0} colloids within the column became increasingly even.

  3. Colloid mobilization by fluid displacement fronts in channels.

    PubMed

    Lazouskaya, Volha; Wang, Lian-Ping; Or, Dani; Wang, Gang; Caplan, Jeffrey L; Jin, Yan

    2013-09-15

    Understanding colloid mobilization during transient flow in soil is important for addressing colloid and contaminant transport issues. While theoretical descriptions of colloid detachment exist for saturated systems, corresponding mechanisms of colloid mobilization during drainage and imbibition have not been considered in detail. In this work, theoretical force and torque analyses were performed to examine the interactive effects of adhesion, drag, friction, and surface tension forces on colloid mobilization and to outline conditions corresponding to the mobilization mechanisms such as lifting, sliding, and rolling. Colloid and substrate contact angles were used as variables to determine theoretical criteria for colloid mobilization mechanisms during drainage and imbibition. Experimental mobilization of hydrophilic and hydrophobic microspheres with drainage and imbibition fronts was investigated in hydrophilic and hydrophobic channels using a confocal microscope. Colloid mobilization differed between drainage and imbibition due to different dynamic contact angles and interfacial geometries on the contact line. Experimental results did not fully follow the theoretical criteria in all cases, which was explained with additional factors not included in the theory such as presence of aggregates and trailing films. Theoretical force and torque analyses resulted in similar mobilization predictions and suggested that all mobilization mechanisms contributed to the observed colloid mobilization.

  4. Study of the stability coated and uncoated nanosilver colloid

    NASA Astrophysics Data System (ADS)

    Harsojo, Respitaningrum, Afrianto, Toto; Sosiati, Harini

    2013-09-01

    The stability of nanosilver colloids made using electrochemical process and chemical process were investigated. In the process using a DC generator cell, two silver electrodes under a DC voltage were used to generate the colloid. In the chemical process the colloid was made using the dilution of AgNO3 in deionized water with the addition of sodium citrate. To increase the stability to this colloid was added polyvinyl alcohol. The stability In those three colloids were investigated using UV-Vis spectrometer. The size of the nano Ag was measured using transmission electron microscope (TEM). The study reveals that within period of two weeks the trend toward a stable colloid is shown by colloid using DC generator. The addition of PVA may stabilize the unstable colloid made using the chemichal process and reduce the size particle to significantly smaller particle compared to the one made using DC generator cell. The condition of obtaining the stable nano colloid silver with smaller particle size was discussed.

  5. Colloid formation and laser-induced bleaching in fluorite

    SciTech Connect

    LeBret, Joel B.; Cramer, Loren P.; Norton, M. Grant; Dickinson, J. T.

    2004-11-08

    Colloid formation and subsequent laser-induced bleaching in fluorite has been studied by transmission electron microscopy and electron diffraction. At high incident electron-beam (e-beam) energies, Ca colloids with diameter {approx}10 nm form a simple cubic superlattice with lattice parameter a{approx}18 nm. The colloids themselves are topotactic with the fluorite matrix forming low-energy interfaces close to a {sigma}=21 special grain boundary in cubic materials. Laser irradiation using {lambda}=532 nm has been shown to effectively bleach the e-beam-irradiated samples returning the fluorite to its monocrystalline state. The bleached samples appear more resistant to further colloid formation.

  6. Statics and dynamics of colloidal particles on optical tray arrays

    SciTech Connect

    Reichardt, Charles; Reichhardt, Cynthia J

    2009-01-01

    We examine the statics and dynamics of charged colloids interacting with periodic optical trap arrays. In particular we study the regime where more than one colloid is confined in each trap, creating effective dimer, trimer, and higher order states called colloidal molecular crystals. The n-mer states have all effective orientational degree of freedom which can be controlled with an external driving field. In general, the external field causes a polarization effect where the orientation of the n-mers aligns with the external field, similar to liquid crystal systems. Additionally, under a rotating external drive the n-mers can rotate with the drive. In some cases a series of structural transitions in the colloidal crystal states occur in the rotating field due to a competition between the ordering of the colloidal molecular crystals and the polarization effect which orients the n-mers in the direction of the drive. We also show that for some parameters, the n-mers continuously rotate with the drive without witching, that depinning transitions can occur where the colloids jump from well to well, and that there are a number of distinct dynamical transitions between the phases. Finally, we illustrate colloidal orderings at fillings of more than four colloids per trap, indicating that it is possible to create higher order colloidal crystal cluster phases.

  7. Size and density of a /sup 242/Pu colloid

    SciTech Connect

    Rundberg, R.S.; Mitchell, A.J.; Torstenfelt, N.B.

    1987-01-01

    The size and density of a /sup 242/Pu colloid has been measured by autocorrelation photon spectrometry. The density of the colloid was determined by ultraspeed centrifugation. From the concentration profiles of /sup 242/Pu in the centrifuged test tubes, a standard sedimentation formula was used to calculate the density; the size of the colloid was known from the light scattering experiments. The determined density of the /sup 242/Pu colloid was unexpectedly low compared to the density of crystalline PuO/sub 2/. 5 refs., 1 tab.

  8. Anisotropic grid adaptation in LES

    NASA Astrophysics Data System (ADS)

    Toosi, Siavash; Larsson, Johan

    2016-11-01

    The modeling errors depend directly on the grid (or filter) spacing in turbulence-resolving simulations (LES, DNS, DES, etc), and are typically at least as significant as the numerical errors. This makes adaptive grid-refinement complicated, since it prevents the estimation of the local error sources through numerical analysis. The present work attempts to address this difficulty with a physics-based error-source indicator that accounts for the anisotropy in the smallest resolved scales, which can thus be used to drive an anisotropic grid-adaptation process. The proposed error indicator is assessed on a sequence of problems, including turbulent channel flow and flows in more complex geometries. The formulation is geometrically general and applicable to complex geometries.

  9. Fast microbial reduction of ferrihydrite colloids from a soil effluent

    NASA Astrophysics Data System (ADS)

    Fritzsche, Andreas; Bosch, Julian; Rennert, Thilo; Heister, Katja; Braunschweig, Juliane; Meckenstock, Rainer U.; Totsche, Kai U.

    2012-01-01

    Recent studies on the microbial reduction of synthetic iron oxide colloids showed their superior electron accepting property in comparison to bulk iron oxides. However, natural colloidal iron oxides differ in composition from their synthetic counterparts. Besides a potential effect of colloid size, microbial iron reduction may be accelerated by electron-shuttling dissolved organic matter (DOM) as well as slowed down by inhibitors such as arsenic. We examined the microbial reduction of OM- and arsenic-containing ferrihydrite colloids. Four effluent fractions were collected from a soil column experiment run under water-saturated conditions. Ferrihydrite colloids precipitated from the soil effluent and exhibited stable hydrodynamic diameters ranging from 281 (±146) nm in the effluent fraction that was collected first and 100 (±43) nm in a subsequently obtained effluent fraction. Aliquots of these oxic effluent fractions were added to anoxic low salt medium containing diluted suspensions of Geobacter sulfurreducens. Independent of the initial colloid size, the soil effluent ferrihydrite colloids were quickly and completely reduced. The rates of Fe2+ formation ranged between 1.9 and 3.3 fmol h-1 cell-1, and are in the range of or slightly exceeding previously reported rates of synthetic ferrihydrite colloids (1.3 fmol h-1 cell-1), but greatly exceeding previously known rates of macroaggregate-ferrihydrite reduction (0.07 fmol h-1 cell-1). The inhibition of microbial Fe(III) reduction by arsenic is unlikely or overridden by the concurrent enhancement induced by soil effluent DOM. These organic species may have increased the already high intrinsic reducibility of colloidal ferrihydrite owing to quinone-mediated electron shuttling. Additionally, OM, which is structurally associated with the soil effluent ferrihydrite colloids, may also contribute to the higher reactivity due to increasing solubility and specific surface area of ferrihydrite. In conclusion, ferrihydrite

  10. Physics of Colloids in Space (PCS): Microgravity Experiment Completed Operations on the International Space Station

    NASA Technical Reports Server (NTRS)

    Doherty, Michael P.; Sankaran, Subramanian

    2003-01-01

    Immediately after mixing, the two-phase-like colloid-polymer critical point sample begins to phase separate, or de-mix, into two phases-one that resembles a gas and one that resembles a liquid, except that the particles are colloids and not atoms. The colloid-poor black regions (colloidal gas) grow bigger, and the colloid-rich white regions (colloidal liquid) become whiter as the domains further coarsen. Finally, complete phase separation is achieved, that is, just one region of each colloid-rich (white) and colloid-poor (black) phase. This process was studied over four decades of length scale, from 1 micrometer to 1 centimeter.

  11. Regard sur les lazarets en terre canadienne

    PubMed Central

    Milot, Jean

    2008-01-01

    Puisant dans les nombreuses références qu’offrent les publications médicales canadiennes du milieu du XIXe siècle à nos jours, l’auteur fait découvrir l’existence de lazarets en terre canadienne, décrit l’impact de la maladie sur les conditions vie des lépreux qui y étaient confinés et en souligne les contrecoups tant sur le plan physique et psychologique que social. Il présente un bref aperçu de la maladie, ses symptômes, ses signes ainsi que ses complications oculaires et rappelle les premiers moyens thérapeutiques à base d’huile de chaulmoogra introduits dans la colonie de Tracadie vers 1901. Il illustre son propos en évoquant la vie dans les lazarets de l’île de Sheldrake (1844–1848) et de Tracadie (1848–1965) au Nouveau-Brunswick, puis dans ceux des îles D’Arcy (1891–1924) et de Bentinck (1924–1957) en Colombie-Britannique. PMID:19352451

  12. DNA hybridization and ligation for directed colloidal assembly

    NASA Astrophysics Data System (ADS)

    Shyr, Margaret

    Colloidal assembly using DNA hybridization has been pursued as a means assemble non-conventional ordered colloidal structures. However, to date it is undetermined whether DNA hybridization can be used to achieve non-FCC colloidal crystals. Using microcontact printing techniques, we have fabricated covalently bound single stranded DNA (ssDNA) two-dimensional arrays on glass surfaces, which were used to direct the assembly of complementary DNA functionalized polystyrene colloids. Two of the hallmarks of DNA hybridization, sequence specificity and thermal reversibility, were demonstrated. Due to the periodicity of these arrays, laser diffraction was used to directly monitor these structures during assembly. To demonstrate the versatility of the 2D colloidal array assembled via DNA hybridization, a catalytic DNA sequence or DNAzyme was incorporated into the colloidal array system. By tethering the enzymatic strand to the patterned glass surface and the substrate strand to polystyrene colloids, we showed that the DNAzyme could prevent the assembly of the arrays when the required Pb2+ cofactor was provided. Attempts to assemble the colloid arrays and disassemble via the Pb2+-DNAzyme induced cleavage were unsuccessful, likely due to the incomplete cleavage of the multitude of hybridized linkages between each colloid and the surface. Since DNA is not only capable of catalyzing reactions, but also capable of being reacted upon by a variety of biological enzymes, we examined the use of DNA ligase as a means to control the assembly of DNA-functionalized colloids. A three-sequence linker system was used for the hybridization mediated assembly of colloids: one sequence was tethered to the surface of the glass slide or colloids, one was tethered to another colloid surface, and the linker sequence hybridizes simultaneously to both tethered sequences. Once hybridized, the two tethered fragments can be ligated using DNA ligase, resulting in a continuous sequence tethered on one end

  13. Thermoelectricity and thermodiffusion in charged colloids.

    PubMed

    Huang, B T; Roger, M; Bonetti, M; Salez, T J; Wiertel-Gasquet, C; Dubois, E; Cabreira Gomes, R; Demouchy, G; Mériguet, G; Peyre, V; Kouyaté, M; Filomeno, C L; Depeyrot, J; Tourinho, F A; Perzynski, R; Nakamae, S

    2015-08-07

    The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K(-1). Such a property may be used to improve the thermoelectric coefficients in liquid thermocells.

  14. Trion decay in colloidal quantum dots.

    PubMed

    Jha, Praket P; Guyot-Sionnest, Philippe

    2009-04-28

    Using charged films of colloidal CdSe/CdS core/shell quantum dots of approximately 3.5 to 4.5 nm core diameters and 0.6 to 1.2 nm thick CdS shells, the radiative and nonradiative decay of the negatively charged exciton, the trion T-, are measured. The T- radiative rate is faster than the exciton by a factor of 2.2 +/- 0.4 and estimated at approximately 10 ns. The T- lifetime is approximately 0.7-1.5 ns for the samples measured and is longer than the biexciton lifetime by a factor or 7.5 +/- 1.7.

  15. Argyria associated with colloidal silver supplementation.

    PubMed

    McKenna, Jeffrey K; Hull, Christopher M; Zone, John J

    2003-07-01

    A 65-year-old male presented for skin examination and was incidentally noted to have discoloration of the fingernails. These findings were completely asymptomatic. The patient had been taking colloidal silver supplementation (Silverzone 140 ppm silver Gifts of Nature, St. George, UT, USA) for 2 years as therapy for diabetes. He first noticed the onset of nail discoloration 1 year ago. His past medical history included type II diabetes and hypertension. His current medications were metformin, glyburide, and benazepril. Physical examination revealed slate-gray discoloration involving the lunulae of the fingernails (Fig. 1). The skin, mucous membranes, and sclerae were unaffected.

  16. Duration test of an annular colloid thruster.

    NASA Technical Reports Server (NTRS)

    Perel, J.; Mahoney, J. F.; Daley, H. L.

    1972-01-01

    An annular colloid thruster was continuously operated for 1023 hours. Performance was stable with no sparking and negligible drain currents observed. An average thrust of 25.1 micropounds and an average specific impulse of 1160 seconds were obtained at an accelerating voltage of 15 k he thruster exhaust beam was continuously neutralized using electrons and electrostatic vectoring was demonstrated periodically. The only clear trend with time was an increase in specific impulse during the last third of the test period. From these results the thruster lifetime was estimated to be over an order of magnitude greater than the test duration.

  17. Colloidal polymeric nanoparticles and brain drug delivery.

    PubMed

    Khalil, Najeh Maissar; Mainardes, Rubiana Mara

    2009-07-01

    The blood brain barrier protects the brain from harmful substances in the blood stream and has stopped the development of many powerful and interesting drugs candidates for central nervous system due to the low poor distribution and by efflux mechanisms. Many different approaches have been developed in order to overcome this barrier and the drug gain access to the brain. The polymeric nanoparticles are efficient colloidal systems that have been investigated to the brain drug delivery. This review will focus on the current strategies for brain drug delivery emphasizing the properties and characteristics of polymeric nanoparticles for this purpose.

  18. Crystalline Colloidal Arrays in Polymer Matrices

    NASA Technical Reports Server (NTRS)

    Sunkara, Hari B.; Penn, B. G.; Frazier, D. O.; Ramachandran, N.

    1997-01-01

    Crystalline Colloidal Arrays (CCA, also known as colloidal crystals), composed of aqueous or nonaqueous dispersions of self-assembled nanosized polymer colloidal spheres, are emerging toward the development of advanced optical devices for technological applications. The spontaneous self assembly of polymer spheres in a dielectric medium results from the electrostatic repulsive interaction between particles of uniform size and charge distribution. In a way similar to atomic crystals that diffract X-rays, CCA dispersions in thin quartz cells selectively and efficiently Bragg diffract the incident visible light. The reason for this diffraction is because the lattice (body or face centered cubic) spacing is on the order of the wavelength of visible light. Unlike the atomic crystals that diffract a fixed wavelength, colloidal crystals in principle, depending on the particle size, particle number and charge density, can diffract W, Vis or IR light. Therefore, the CCA dispersions can be used as laser filters. Besides, the diffraction intensity depends on the refractive index mismatch between polymer spheres and dielectric medium; therefore, it is possible to modulate incident light intensities by manipulating the index of either the spheres or the medium. Our interest in CCA is in the fabrication of all-optical devices such as optical switches, limiters, and spatial light modulators for optical signal processing. The two major requirements from a materials standpoint are the incorporation of suitable nonlinear optical materials (NLO) into polymer spheres which will allow us to alter the refractive index of the spheres by intense laser radiation, and preparation of solid CCA filters which can resist laser damage. The fabrication of solid composite filters not only has the advantage that the films are easier to handle, but also the arrays in solid films are more robust than in liquid media. In this paper, we report the photopolymerization process used to trap CCA in polymer

  19. Colloid research for the Nevada Test Site

    SciTech Connect

    Bryant, E.A.

    1992-05-01

    Research is needed to understand the role of particulates in the migration of radionuclides away from the sites of nuclear tests at the Nevada Test Site. The process of testing itself may produce a reservoir of particles to serve as vectors for the transport of long-lived radionuclides in groundwater. Exploratory experiments indicate the presence of numerous particulates in the vicinity of the Cambric test but a much lower loading in a nearby well that has been pumped continuously for 15 years. Recent groundwater colloid research is briefly reviewed to identify sampling and characterization methods that may be applicable at the Nevada Test Site.

  20. Self-diffusiophoresis of chemically active colloids

    NASA Astrophysics Data System (ADS)

    Popescu, Mihail N.; Uspal, William E.; Dietrich, Siegfried

    2016-11-01

    Chemically active colloids locally change the chemical composition of their solvent via catalytic reactions which occur on parts of their surface. They achieve motility by converting the released chemical free energy into mechanical work through various mechanisms, such as phoresis. Here we discuss the theoretical aspects of self-diffusiophoresis, which - despite being one of the simplest motility mechanisms - captures many of the general features characterizing self-phoresis, such as self-generated and maintained hydrodynamic flows "driven" by surface activity induced inhomogeneities in solution. By studying simple examples, which provide physical insight, we highlight the complex phenomenology which can emerge from self-diffusiophoresis.

  1. Lateral optical binding between two colloidal particles

    PubMed Central

    Wei, Ming-Tzo; Ng, Jack; Chan, C. T.; Ou-Yang, H. Daniel

    2016-01-01

    An optical binding force between two nearby colloidal particles trapped by two coherent laser beams is measured by phase-sensitive detection. The binding force is long-range and spatially oscillatory. For identical linearly-polarized incident beams, the oscillation period is equal to the optical wavelength. For mutually perpendicular polarizations, a new force appears with half-wavelength periodicity, caused by double inter-particle scattering. This force is observable only with cross-polarized incident beams, for which the stronger single-scattering forces are forbidden by parity. PMID:27982052

  2. Numerical modeling of colloid facilitated virus transport in porus media

    NASA Astrophysics Data System (ADS)

    Katzourakis, Vasileios E.; Chrysikopoulos, Constantinos V.

    2013-04-01

    A conceptual mathematical model was developed to describethe simultaneous transport (cotransport) of viruses and colloids in three-dimensional, water saturated, homogeneous porous media with uniform flow. The model accounts for the migration of individual virus and colloid particles as well as viruses attached onto colloids. Viruses can be suspended in the aqueous phase, attached onto suspended colloids and the solid matrix, and attached onto colloids previously attached on the solid matrix. Colloids can be suspended in the aqueous phase or attached on the solid matrix. Viruses in all four phases (suspended in the aqueous phase, attached onto suspended colloid particles, attached onto the solid matrix, and attached onto colloids previously attached on the solid matrix) may undergo inactivation with different inactivation coefficients. The governing coupled partial differential equations were solved numerically by employing finite difference methods, which were implemented explicitly or implicitly so that both stability and accuracy factors were satisfied. Furthermore, available experimental data were used to test the newly developed cotransport model. The model was shown to simulate quite accurately the available experimental data.

  3. Collective behavior in out-of-equilibrium colloidal suspensions

    NASA Astrophysics Data System (ADS)

    Aranson, Igor S.

    2013-06-01

    Colloidal suspensions, heterogeneous fluids containing solid microscopic particles, play an important role in our everyday life, from food and pharmaceutical industries to medicine and nanotechnology. Colloidal suspensions can be divided in two major classes: equilibrium, and active, i.e. maintained out of thermodynamic equilibrium by external electric or magnetic fields, light, chemical reactions, or hydrodynamic shear flow. While the properties of equilibrium colloidal suspensions are fairly well understood, out-of-equilibrium colloids pose a formidable challenge and the research is in its early exploratory stage. The possibility of dynamic self-assembly, a natural tendency of simple building blocks to organize into complex functional architectures, is one of the most remarkable properties of out-of-equilibrium colloids. Examples range from tunable, self-healing colloidal crystals and membranes to self-assembled microswimmers and robots. In contrast to their equilibrium counterparts, out-of-equilibrium colloidal suspensions may exhibit novel material properties, e.g. reduced viscosity, enhanced self-diffusivity, etc. This work reviews recent developments in the field of self-assembly and collective behavior of out-of-equilibrium colloids, with the focus on the fundamental physical mechanisms.

  4. Feasibility of colloidal silver SERS for rapid bacterial screening

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Citrate-reduced silver colloids have been used extensively for surface-enhanced Raman scattering (SERS) study and are commonly characterized by UV-visible spectroscopy. In this work, relative standard deviation (RSD) of SERS spectra from silver colloidal suspensions and ratios of SERS peaks from sma...

  5. Fabrication and Characterization of Colloidal Crystal Thin Films

    ERIC Educational Resources Information Center

    Rodriguez, I.; Ramiro-Manzano, F.; Meseguer, F.; Bonet, E.

    2011-01-01

    We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained…

  6. Colloid adhesive parameters for chemical heterogeneous porous media

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A simple modeling approach was developed to calculate colloid adhesive parameters for chemically heterogeneous porous media. The area of the zone of electrostatic influence between a colloid and solid-water interface (Az) was discretized into a number of equally sized grid cells to capture chemical...

  7. Recent Results from the Physics of Colloids in Space

    NASA Technical Reports Server (NTRS)

    Weitz, David A.; Bailey, A.; Christianson, R.; Manley, S.; Prasad, V.; Segre, P.; Gasser, U.; Cipelletti, L.; Schoefield, A.; Pusey, P.

    2002-01-01

    The Physics of Colloids in Space is an experiment which flew in the ISS. Data on several different samples of colloidal particles were obtained. They provided unexpected information about the behavior of the samples in microgravity. The data are currently being analyzed. The most recent findings will be discussed in this talk.

  8. Physics of Colloids in Space: Flight Hardware Operations on ISS

    NASA Technical Reports Server (NTRS)

    Doherty, Michael P.; Bailey, Arthur E.; Jankovsky, Amy L.; Lorik, Tibor

    2002-01-01

    The Physics of Colloids in Space (PCS) experiment was launched on Space Shuttle STS-100 in April 2001 and integrated into EXpedite the PRocess of Experiments to Space Station Rack 2 on the International Space Station (ISS). This microgravity fluid physics investigation is being conducted in the ISS U.S. Lab 'Destiny' Module over a period of approximately thirteen months during the ISS assembly period from flight 6A through flight 9A. PCS is gathering data on the basic physical properties of simple colloidal suspensions by studying the structures that form. A colloid is a micron or submicron particle, be it solid, liquid, or gas. A colloidal suspension consists of these fine particles suspended in another medium. Common colloidal suspensions include paints, milk, salad dressings, cosmetics, and aerosols. Though these products are routinely produced and used, we still have much to learn about their behavior as well as the underlying properties of colloids in general. The long-term goal of the PCS investigation is to learn how to steer the growth of colloidal structures to create new materials. This experiment is the first part of a two-stage investigation conceived by Professor David Weitz of Harvard University (the Principal Investigator) along with Professor Peter Pusey of the University of Edinburgh (the Co-Investigator). This paper describes the flight hardware, experiment operations, and initial science findings of the first fluid physics payload to be conducted on ISS: The Physics of Colloids in Space.

  9. Avalanches, plasticity, and ordering in colloidal crystals under compression.

    PubMed

    McDermott, D; Reichhardt, C J Olson; Reichhardt, C

    2016-06-01

    Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compression, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or anisotropic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power-law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

  10. Composition and cycling of colloids in marine environments

    NASA Astrophysics Data System (ADS)

    Guo, Laodong; Santschi, Peter H.

    1997-02-01

    Colloidal (COM) or macromolecular organic matter makes up a significant portion of the bulk dissolved organic matter (DOM) pool in aquatic environments. Because of their high specific surface areas and complexation capacities, marine colloids are of great importance not only in the global carbon cycle but also in the biogeochemical cycling of many particle-reactive nuclides and trace elements in the ocean. However, the colloidal pool as a whole is still poorly understood and largely uncharacterized. Recently, cross-flow ultrafiltration and other separation techniques, which have been successfully used to isolate marine colloids, combined with a multitracer approach, have greatly advanced our understanding of the cycling of COM and its associated trace elements in marine environments. In this paper we focus on recent developments on isotopic and elemental composition of colloids which allow organic matter cycling in marine environments to be constrained. Major sections review sampling techniques for aquatic colloids, concentrations and distribution of COM, biochemical and elemental (organic and inorganic) characterization, and stable isotopic (13C and 15N) and radioisotopic (14C and 234Th) characterization of marine colloids. We discuss sources and turnover rates of organic matter in the ocean, importance of benthic boundary layer processes in the cycling of DOM, changes in the paradigms of marine organic matter cycling, and research needs for a better understanding of the biogeochemistry of marine colloids.

  11. Stable colloidal solutions of strontium hexaferrite hard magnetic nanoparticles.

    PubMed

    Trusov, Lev A; Vasiliev, Alexander V; Lukatskaya, Maria R; Zaytsev, Dmitry D; Jansen, Martin; Kazin, Pavel E

    2014-12-04

    Herein we demonstrate an approach to prepare a colloidal solution of strontium hexaferrite via a glass-ceramic route. The as obtained colloids are stable and resistive to aggregation or sedimentation. They reveal outstanding magnetic and magneto-optical properties because of their platelet-like anisotropic shape and high permanent magnetic moment.

  12. Predicting colloid transport through saturated porous media: A critical review

    NASA Astrophysics Data System (ADS)

    Molnar, Ian L.; Johnson, William P.; Gerhard, Jason I.; Willson, Clinton S.; O'Carroll, Denis M.

    2015-09-01

    Understanding and predicting colloid transport and retention in water-saturated porous media is important for the protection of human and ecological health. Early applications of colloid transport research before the 1990s included the removal of pathogens in granular drinking water filters. Since then, interest has expanded significantly to include such areas as source zone protection of drinking water systems and injection of nanometals for contaminated site remediation. This review summarizes predictive tools for colloid transport from the pore to field scales. First, we review experimental breakthrough and retention of colloids under favorable and unfavorable colloid/collector interactions (i.e., no significant and significant colloid-surface repulsion, respectively). Second, we review the continuum-scale modeling strategies used to describe observed transport behavior. Third, we review the following two components of colloid filtration theory: (i) mechanistic force/torque balance models of pore-scale colloid trajectories and (ii) approximating correlation equations used to predict colloid retention. The successes and limitations of these approaches for favorable conditions are summarized, as are recent developments to predict colloid retention under the unfavorable conditions particularly relevant to environmental applications. Fourth, we summarize the influences of physical and chemical heterogeneities on colloid transport and avenues for their prediction. Fifth, we review the upscaling of mechanistic model results to rate constants for use in continuum models of colloid behavior at the column and field scales. Overall, this paper clarifies the foundation for existing knowledge of colloid transport and retention, features recent advances in the field, critically assesses where existing approaches are successful and the limits of their application, and highlights outstanding challenges and future research opportunities. These challenges and opportunities

  13. Humic colloid-borne natural polyvalent metal ions: dissociation experiment.

    PubMed

    Geckeis, H; Rabung, Th; Ngo Manh, T; Kim, J I; Beck, H P

    2002-07-01

    The natural association nature of the humic colloid-borne trace elements is investigated. Rare earth elements (REE) Th and U are chosen as naturally occurring representatives and chemical homologues for actinides of different oxidation states present in nuclear waste. Tri- and tetravalent elements in two investigated Gorleben groundwaters (Gohy-532 and -2227) almost exclusively occur as humic or fulvic colloid-borne species. Their desorption behavior from colloids is examined in the unperturbed groundwater (pH approximately 8) under anaerobic conditions (Ar/1% CO2) by addition of a chelating cation exchanger resin. Particularly, the dissociation process of naturally occurring Eu(III) in the groundwater is compared with the Eu(III) desorption from its humate complex prepared with purified Aldrich humic acid in a buffered aqueous solution at pH approximately 8. The Eu(III) dissociation from the groundwater colloids is found to be considerably slower than found for the humate complex synthesized in the laboratory. This suggests that under natural aquatic conditions the Eu(III) binding in colloids is chemically different from the simple humate complexation as observed in the laboratory experiment. The colloid characterization bythe size exclusion chromatography (SEC) and the flow field-flow fractionation (FFFF) indicates that natural colloid-borne trace elements are found predominantly in colloids of larger size (>15 nm in size), while Eu(III) in its humate complex is found mainly in colloids of hydrodynamic diameters <5 nm. The slower desorption kinetics and the larger colloid size suggest that the polyvalent metal ion binding in natural humic colloids is associated to polynucleation with other co-present trace metal ions. Radiotracer experiments reveal that isotopic equilibria with the naturally colloid-borne trace elements are not attained within a period of more than 100 days, indicating irreversible binding of at least a part of colloid-borne polyvalent trace

  14. Colloid-facilitated radionuclide transport: a regulatory perspective

    NASA Astrophysics Data System (ADS)

    Dam, W. L.; Pickett, D. A.; Codell, R. B.; Nicholson, T. J.

    2001-12-01

    What hydrogeologic-geochemical-microbial conditions and processes affect migration of radionuclides sorbed onto microparticles or native colloid-sized radionuclide particles? The U.S. Nuclear Regulatory Commission (NRC) is responsible for protecting public health, safety, and the environment at numerous nuclear facilities including a potential high-level nuclear waste disposal site. To fulfill these obligations, NRC needs to understand the mechanisms controlling radionuclide release and transport and their importance to performance. The current focus of NRC staff reviews and technical interactions dealing with colloid-facilitated transport relates to the potential nuclear-waste repository at Yucca Mountain, Nevada. NRC staff performed bounding calculations to quantify radionuclide releases available for ground-water transport to potential receptors from a Yucca Mountain repository. Preliminary analyses suggest insignificant doses of plutonium and americium colloids could be derived from spent nuclear fuel. Using surface complexation models, NRC staff found that colloids can potentially lower actinide retardation factors by up to several orders of magnitude. Performance assessment calculations, in which colloidal transport of plutonium and americium was simulated by assuming no sorption or matrix diffusion, indicated no effect of colloids on human dose within the 10,000 year compliance period due largely to long waste-package lifetimes. NRC staff have identified information gaps and developed technical agreements with the U.S. Department of Energy (DOE) to ensure sufficient information will be presented in any potential future Yucca Mountain license application. DOE has agreed to identify which radionuclides could be transported via colloids, incorporate uncertainties in colloid formation, release and transport parameters, and conceptual models, and address the applicability of field data using synthetic microspheres as colloid analogs. NRC is currently

  15. Nonlinear machine learning and design of reconfigurable digital colloids.

    PubMed

    Long, Andrew W; Phillips, Carolyn L; Jankowksi, Eric; Ferguson, Andrew L

    2016-09-14

    Digital colloids, a cluster of freely rotating "halo" particles tethered to the surface of a central particle, were recently proposed as ultra-high density memory elements for information storage. Rational design of these digital colloids for memory storage applications requires a quantitative understanding of the thermodynamic and kinetic stability of the configurational states within which information is stored. We apply nonlinear machine learning to Brownian dynamics simulations of these digital colloids to extract the low-dimensional intrinsic manifold governing digital colloid morphology, thermodynamics, and kinetics. By modulating the relative size ratio between halo particles and central particles, we investigate the size-dependent configurational stability and transition kinetics for the 2-state tetrahedral (N = 4) and 30-state octahedral (N = 6) digital colloids. We demonstrate the use of this framework to guide the rational design of a memory storage element to hold a block of text that trades off the competing design criteria of memory addressability and volatility.

  16. Optical dispersive shock waves in defocusing colloidal media

    NASA Astrophysics Data System (ADS)

    An, X.; Marchant, T. R.; Smyth, N. F.

    2017-03-01

    The propagation of an optical dispersive shock wave, generated from a jump discontinuity in light intensity, in a defocusing colloidal medium is analysed. The equations governing nonlinear light propagation in a colloidal medium consist of a nonlinear Schrödinger equation for the beam and an algebraic equation for the medium response. In the limit of low light intensity, these equations reduce to a perturbed higher order nonlinear Schrödinger equation. Solutions for the leading and trailing edges of the colloidal dispersive shock wave are found using modulation theory. This is done for both the perturbed nonlinear Schrödinger equation and the full colloid equations for arbitrary light intensity. These results are compared with numerical solutions of the colloid equations.

  17. SUBSURFACE MOBILE PLUTONIUM SPECIATION: SAMPLING ARTIFACTS FOR GROUNDWATER COLLOIDS

    SciTech Connect

    Kaplan, D.; Buesseler, K.

    2010-06-29

    A recent review found several conflicting conclusions regarding colloid-facilitated transport of radionuclides in groundwater and noted that colloids can both facilitate and retard transport. Given these contrasting conclusions and the profound implications even trace concentrations of plutonium (Pu) have on the calculated risk posed to human health, it is important that the methodology used to sample groundwater colloids be free of artifacts. The objective of this study was: (1) to conduct a field study and measure Pu speciation, ({sup 239}Pu and {sup 240}Pu for reduced-Pu{sub aq}, oxidized-Pu{sub aq}, reduced-Pu{sub colloid}, and oxidized-Pu{sub colloid}), in a Savannah River Site (SRS) aquifer along a pH gradient in F-Area, (2) to determine the impact of pumping rate on Pu concentration, Pu speciation, and Pu isotopic ratios, (3) determine the impact of delayed sample processing (as opposed to processing directly from the well).

  18. Colloidal characterization of silicon nitride and silicon carbide

    NASA Technical Reports Server (NTRS)

    Feke, Donald L.

    1986-01-01

    The colloidal behavior of aqueous ceramic slips strongly affects the forming and sintering behavior and the ultimate mechanical strength of the final ceramic product. The colloidal behavior of these materials, which is dominated by electrical interactions between the particles, is complex due to the strong interaction of the solids with the processing fluids. A surface titration methodology, modified to account for this interaction, was developed and used to provide fundamental insights into the interfacial chemistry of these systems. Various powder pretreatment strategies were explored to differentiate between true surface chemistry and artifacts due to exposure history. The colloidal behavior of both silicon nitride and carbide is dominated by silanol groups on the powder surfaces. However, the colloid chemistry of silicon nitride is apparently influenced by an additional amine group. With the proper powder treatments, silicon nitride and carbide powder can be made to appear colloidally equivalent. The impact of these results on processing control will be discussed.

  19. Superlubric-pinned transition in sliding incommensurate colloidal monolayers

    NASA Astrophysics Data System (ADS)

    Mandelli, Davide; Vanossi, Andrea; Invernizzi, Michele; Paronuzzi, Stella; Manini, Nicola; Tosatti, Erio

    2015-10-01

    Two-dimensional (2D) crystalline colloidal monolayers sliding over a laser-induced optical lattice providing the periodic "corrugation" potential recently emerged as a new tool for the study of friction between ideal crystal surfaces. Here, we focus in particular on static friction, the minimal sliding force necessary to depin one lattice from the other. If the colloid and the optical lattices are mutually commensurate, the colloid sliding is always pinned by static friction; however, when they are incommensurate, the presence or absence of pinning can be expected to depend upon the system parameters, like in one-dimensional (1D) systems. If a 2D analogy to the mathematically established Aubry transition of one-dimensional systems were to hold, an increasing periodic corrugation strength U0 should turn an initially free-sliding, superlubric colloid into a pinned state, where the static friction force goes from zero to finite through a well-defined dynamical phase transition. We address this problem by the simulated sliding of a realistic model 2D colloidal lattice, confirming the existence of a clear and sharp superlubric-pinned transition for increasing corrugation strength. Unlike the 1D Aubry transition, which is continuous, the 2D transition exhibits a definite first-order character, with a jump of static friction. With no change of symmetry, the transition entails a structural character, with a sudden increase of the colloid-colloid interaction energy, accompanied by a compensating downward jump of the colloid-corrugation energy. The transition value for the corrugation amplitude U0 depends upon the misalignment angle θ between the optical and the colloidal lattices, superlubricity surviving until larger corrugations for angles away from the energetically favored orientation, which is itself generally slightly misaligned, as shown in recent work. The observability of the superlubric-pinned colloid transition is proposed and discussed.

  20. Colloidal motility and patterning by physical chemotaxis

    NASA Astrophysics Data System (ADS)

    Palacci, Jeremie; Abecassis, Benjamin; Cottin-Bizonne, Cecile; Ybert, Christophe; Bocquet, Lyderic

    2009-11-01

    We developped a microfluidic setup to show the motility of colloids or biomolecules under a controlled salt gradient thanks to the diffusiophoresis phenomenon [1,2]. We can therefore mimic chemotaxis on simple physical basis with thrilling analogies with the biological chemotaxis of E. Coli bacteria: salt dependance of the velocity [3] and log-sensing behavior [4]. In addition with a temporally tunable gradient we show we can generate an effective osmotic potential to trap colloids or DNA. These experimental observations are supported by numerical simulations and an asymptotic ratchet model. Finally, we use these traps to generate various patterns and because concentration gradients are ubiquitous in nature, we question for the role of such a mecanism in morphogenesis [5] or positioning perspectives in cells [6]. [4pt] [1] B. Abecassis, C. Cottin-Bizonne, C. Ybert, A. Ajdari, and L. Bocquet, Nat. Mat., 7(10):785--789, 2008. [2] Anderson, Ann. Rev. Fluid Mech, 21, 1989. [3] Y. L. Qi and J. Adler, PNAS, 86(21):8358--8362, 1989. [4] Y. V. Kalinin, L. L. Jiang, Y. H. Tu, and M. M. Wu, Biophys. J., 96(6):2439--2448, 2009. [4] J. B. Moseley, A. Mayeux, A. Paoletti, and P. Nurse, Nat., 459(7248):857--U8, 2009. [6] L. Wolpert, Dev., 107:3--12, 1989

  1. Sudden collapse of a colloidal gel.

    PubMed

    Bartlett, Paul; Teece, Lisa J; Faers, Malcolm A

    2012-02-01

    Metastable gels formed by weakly attractive colloidal particles display a distinctive two-stage time-dependent settling behavior under their own weight. Initially, a space-spanning network is formed that, for a characteristic time, which we define as the lag time τ(d), resists compaction. This solidlike behavior persists only for a limited time. Gels whose age t(w) is greater than τ(d) yield and suddenly collapse. We use a combination of confocal microscopy, rheology, and time-lapse video imaging to investigate both the process of sudden collapse and its microscopic origin in a refractive-index matched emulsion-polymer system. We show that the height h of the gel in the early stages of collapse is well described by the surprisingly simple expression, h(τ)=h(0)-Aτ(3/2), with h(0) the initial height and τ=t(w)-τ(d) the time counted from the instant where the gel first yields. We propose that this unexpected result arises because the colloidal network progressively builds up internal stress as a consequence of localized rearrangement events, which leads ultimately to collapse as thermal equilibrium is reestablished.

  2. Colloidal gelation with variable attraction energy.

    PubMed

    Zaccone, Alessio; Crassous, Jérôme J; Ballauff, Matthias

    2013-03-14

    We present an approximation scheme to the master kinetic equations for aggregation and gelation with thermal breakup in colloidal systems with variable attraction energy. With the cluster fractal dimension df as the only phenomenological parameter, rich physical behavior is predicted. The viscosity, the gelation time, and the cluster size are predicted in closed form analytically as a function of time, initial volume fraction, and attraction energy by combining the reversible clustering kinetics with an approximate hydrodynamic model. The fractal dimension df modulates the time evolution of cluster size, lag time and gelation time, and of the viscosity. The gelation transition is strongly nonequilibrium and time-dependent in the unstable region of the state diagram of colloids where the association rate is larger than the dissociation rate. Only upon approaching conditions where the initial association and the dissociation rates are comparable for all species (which is a condition for the detailed balance to be satisfied) aggregation can occur with df = 3. In this limit, homogeneous nucleation followed by Lifshitz-Slyozov coarsening is recovered. In this limited region of the state diagram the macroscopic gelation process is likely to be driven by large spontaneous fluctuations associated with spinodal decomposition.

  3. Flow of colloidal suspensions and gels

    NASA Astrophysics Data System (ADS)

    Zia, Roseanna

    Our recent studies of yield of colloidal gels under shear show that yield in such gels occurs in distinct stages. Under fixed stress, yield follows a finite delay period of slow solid-like creep. Post yield, the gel fluidizes and may undergo long-time viscous flow or, in some cases, may re-solidify. Under imposed strain rate, the transition from equilibrium to long-time flow is characterized by one or more stress overshoots, signifying a yield process here as well. These rheological changes are accompanied by evolution in morphology and dynamics of the gel network. Similar regimes have been observed in gels subjected to gravitational forcing; the gel initially supports its own weight, or perhaps undergoes slow, weak compaction. This may be followed by a sudden transition to rapid compaction or sedimentation. Various models have been put forth to explain these behaviors based on structural evolution, but this detail is difficult to observe in experiment. Here we examine the detailed microstructural evolution and rheology of reversible colloidal gels as they deform under gravity, identifying the critical buoyant force at which yield occurs, the role played by ongoing gel coarsening, and similarities and differences compared to yield under shear. We gratefully acknowledge the support of the NSF XSEDE Computational Resource, the NSF Early CAREER Program, and the Office of Naval Research Young Investigator Program.

  4. Localized Plastic Deformation in Colloidal Micropillars

    NASA Astrophysics Data System (ADS)

    Strickland, Daniel; Hor, Jyo Lyn; Ortiz, Carlos; Lee, Daeyeon; Gianola, Daniel

    When driven beyond yield, many amorphous solids exhibit concentrated regions of large plastic strain referred to as shear bands. Shear bands are the result of localized, cooperative rearrangements of particles known as shear transformations (STs). STs are dilatory: their operation results in an increase of free volume and local softening that leads to spatially concentrated plasticity. However, the evolution of STs into a macroscopic shear band remains poorly understood. To study the process, we perform compression experiments on amorphous colloidal micropillars. The micropillars, which are composed of fluorescent 3 μm PMMA particles, are made freestanding so that shear banding instabilities are not suppressed by confining boundaries. During compression, we observe strong localization of strain in a band of the pillar. As deformation proceeds, the sheared region continues to dilate until it reaches the colloidal glass transition, at which point dilation terminates. We quantify a length scale by measuring the extent of spatial correlations in strain. This length scale decreases gradually with increasing dilation and becomes static beyond the glass transition. Our results reinforce the idea of yield as a stress-induced glass transition in amorphous solids.

  5. Colloidal aggregation and dynamics in anisotropic fluids

    PubMed Central

    Mondiot, Frédéric; Botet, Robert; Snabre, Patrick; Mondain-Monval, Olivier; Loudet, Jean-Christophe

    2014-01-01

    We present experiments and numerical simulations to investigate the collective behavior of submicrometer-sized particles immersed in a nematic micellar solution. We use latex spheres with diameters ranging from 190 to 780 nm and study their aggregation properties due to the interplay of the various colloidal forces at work in the system. We found that the morphology of aggregates strongly depends on the particle size, with evidence for two distinct regimes: the biggest inclusions clump together within minutes into either compact clusters or V-like structures that are completely consistent with attractive elastic interactions. On the contrary, the smallest particles form chains elongated along the nematic axis, within comparable timescales. In this regime, Monte Carlo simulations, based on a modified diffusion-limited cluster aggregation model, strongly suggest that the anisotropic rotational Brownian motion of the clusters combined with short-range depletion interactions dominate the system coarsening; elastic interactions no longer prevail. The simulations reproduce the sharp transition between the two regimes on increasing the particle size. We provide reasonable estimates to interpret our data and propose a likely scenario for colloidal aggregation. These results emphasize the growing importance of the diffusion of species at suboptical-wavelength scales and raise a number of fundamental issues. PMID:24715727

  6. Colloidal drug delivery systems in vaccine delivery.

    PubMed

    Beg, Sarwar; Samad, Abdus; Nazish, Iram; Sultana, Ruksar; Rahman, Mahfoozur; Ahmad, Md Zaki; Akbar, Md

    2013-01-01

    Vaccines play a vital role in the field of community medicine to combat against several diseases of human existence. Vaccines primarily trigger the acquired immune system to develop long-lasting immunity against pathogens. Conventional approaches for vaccine delivery lacks potential to target a particular antigen to develop acquired immunity by specific antibodies. Recent advancements in vaccine delivery showed that inclusion of adjuvants in vaccine formulations or delivery of them in a carrier helps in achieving desired targeting ability, reducing the immunogenicity and significant augmentation in the immune response. Colloidal carriers (liposomes, niosomes, microspheres, proteosomes, virosomes and virus like particles (VLPs), antigen cochleates, dendrimers and carbon nanotubes) have been widely explored for vaccine delivery. Further, surface engineering of these carriers with ligands, functional moieties and monoclonal antibodies tend to enhance the immune recognition potential of vaccines by differentiation of antigen specific memory T-cells. The current review, therefore, provides an updated account on the recent advancements in various colloidal delivery systems in vaccine delivery, outlining the mechanism of immune response initiated by them along with potential applications and marketed instances in an explicit manner.

  7. The dielectric response of a colloidal spheroid.

    PubMed

    Chassagne, C; Bedeaux, D

    2008-10-01

    In this article, we present a theory for the dielectric behavior of a colloidal spheroid, based on an improved version of a previously published analytical theory [C. Chassagne, D. Bedeaux, G.J.M. Koper, Physica A 317 (2003) 321-344]. The theory gives the dipolar coefficient of a dielectric spheroid in an electrolyte solution subjected to an oscillating electric field. In the special case of the sphere, this theory is shown to agree rather satisfactorily with the numerical solutions obtained by a code based on DeLacey and White's [E.H.B. DeLacey, L.R. White, J. Chem. Soc. Faraday Trans. 2 77 (1981) 2007] for all zeta potentials, frequencies and kappa a1 where kappa is the inverse of the Debye length and a is the radius of the sphere. Using the form of the analytical solution for a sphere we were able to derive a formula for the dipolar coefficient of a spheroid for all zeta potentials, frequencies and kappa a1. The expression we find is simpler and has a more general validity than the analytical expression proposed by O'Brien and Ward [R.W. O'Brien, D.N. Ward, J. Colloid Interface Sci. 121 (1988) 402] which is valid for kappa a > 1 and zero frequency.

  8. Les Brulures Chimiques Par Le Laurier Rose

    PubMed Central

    Bakkali, H.; Ababou, M.; Nassim Sabah, T.; Moussaoui, A.; Ennouhi, A.; Fouadi, F.Z.; Siah, S.; Ihrai, H.

    2010-01-01

    Summary Le laurier rose ou Nerium oleander est un arbuste qui pousse naturellement dans les régions méditerranéennes. Au Maroc on le trouve dans les lieux humides. Il est réputé par ses risques de toxicité systémique en cas d'empoisonnement à cause de la présence de deux alcaloïdes, surtout l'oléandrine. La littérature illustre des cas d'utilisation locale des feuilles de cette plante contre la gale, les hémorroïdes et les furoncles. Nous rapportons deux cas de brûlures chimiques par le laurier rose de gravité différente. Cela doit aboutir à une information élargie de la population, ainsi qu'une réglementation stricte de sa commercialisation. PMID:21991211

  9. Large-scale assembly of colloidal particles

    NASA Astrophysics Data System (ADS)

    Yang, Hongta

    This study reports a simple, roll-to-roll compatible coating technology for producing three-dimensional highly ordered colloidal crystal-polymer composites, colloidal crystals, and macroporous polymer membranes. A vertically beveled doctor blade is utilized to shear align silica microsphere-monomer suspensions to form large-area composites in a single step. The polymer matrix and the silica microspheres can be selectively removed to create colloidal crystals and self-standing macroporous polymer membranes. The thickness of the shear-aligned crystal is correlated with the viscosity of the colloidal suspension and the coating speed, and the correlations can be qualitatively explained by adapting the mechanisms developed for conventional doctor blade coating. Five important research topics related to the application of large-scale three-dimensional highly ordered macroporous films by doctor blade coating are covered in this study. The first topic describes the invention in large area and low cost color reflective displays. This invention is inspired by the heat pipe technology. The self-standing macroporous polymer films exhibit brilliant colors which originate from the Bragg diffractive of visible light form the three-dimensional highly ordered air cavities. The colors can be easily changed by tuning the size of the air cavities to cover the whole visible spectrum. When the air cavities are filled with a solvent which has the same refractive index as that of the polymer, the macroporous polymer films become completely transparent due to the index matching. When the solvent trapped in the cavities is evaporated by in-situ heating, the sample color changes back to brilliant color. This process is highly reversible and reproducible for thousands of cycles. The second topic reports the achievement of rapid and reversible vapor detection by using 3-D macroporous photonic crystals. Capillary condensation of a condensable vapor in the interconnected macropores leads to the

  10. How colloid-colloid interactions and hydrodynamic effects influence the percolation threshold: A simulation study in alumina suspensions.

    PubMed

    Laganapan, Aleena Maria; Mouas, Mohamed; Videcoq, Arnaud; Cerbelaud, Manuella; Bienia, Marguerite; Bowen, Paul; Ferrando, Riccardo

    2015-11-15

    The percolation behavior of alumina suspensions is studied by computer simulations. The percolation threshold ϕc is calculated, determining the key factors that affect its magnitude: the strength of colloid-colloid attraction and the presence of hydrodynamic interactions (HIs). To isolate the effects of HIs, we compare the results of Brownian Dynamics, which do not include hydrodynamics, with those of Stochastic Rotation Dynamics-Molecular Dynamics, which include hydrodynamics. Our results show that ϕc decreases with the increase of the attraction between the colloids. The inclusion of HIs always leads to more elongated structures during the aggregation process, producing a sizable decrease of ϕc when the colloid-colloid attraction is not too strong. On the other hand, the effects of HIs on ϕc tend to become negligible with increasing attraction strength. Our ϕc values are in good agreement with those estimated by the yield stress model by Flatt and Bowen.

  11. LES versus DNS: A comparative study

    NASA Technical Reports Server (NTRS)

    Shtilman, L.; Chasnov, J. R.

    1992-01-01

    We have performed Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) of forced isotropic turbulence at moderate Reynolds numbers. The subgrid scale model used in the LES is based on an eddy viscosity which adjusts instantaneously the energy spectrum of the LES to that of the DNS. The statistics of the large scales of the DNS (filtered DNS field or fDNS) are compared to that of the LES. We present results for the transfer spectra, the skewness and flatness factors of the velocity components, the PDF's of the angle between the vorticity and the eigenvectors of the rate of strain, and that between the vorticity and the vorticity stretching tensor. The above LES statistics are found to be in good agreement with those measured in the fDNS field. We further observe that in all the numerical measurements, the trend was for the LES field to be more gaussian than the fDNS field. Future research on this point is planned.

  12. Les Elements Legers: Diffusion dans les Enveloppes Stellaires et Implications Cosmologiques

    NASA Astrophysics Data System (ADS)

    Richer, Jacques

    1992-01-01

    Les observations des abondances des elements legers (Z <= 5) sont utilisees pour estimer la quantitie de lithium qui a ete produite lors du Big -Bang, et obtenir simultanement des contraintes sur la nature des inhomogeneites qui ont pu exister durant la nucleosynthese primordiale. Nous utilisons un modele simple capable de simuler approximativement la diffusion et la retro-diffusion des neutrons a travers la matiere inhomogene durant les premieres minutes de l'expansion de l'Univers. Nous tenons compte de la difference possible entre l'abondance primordiale de Li et les abondances observees dans les plus vieilles etoiles. Cette difference (un facteur 2, environ) est estimee en construisant des modeles evolutifs d'etoiles peu massives de Population II, incluant la sedimentation gravitationnelle du lithium et de l'helium. Ces modeles montrent egalement que les ages des vieux amas stellaires sont grandement surestimes lorsqu'ils sont determines a partir de modeles stellaires n'incluant pas l'effet de la diffusion de He. Nous calculons ensuite comment evoluent les abondances de Li et Be dans des etoiles plus massives et plus jeunes, de la pre-sequence principale ou de la ZAMS, jusqu'a l'epuisement de leur hydrogene central. Les modeles incluent la sedimentation simultanee de l'helium a travers l'enveloppe. Une approche hierarchique (evolution du coeur--evolution de l'enveloppe --tri des elements traces) est utilisee pour simuler efficacement le grand nombre d'etoiles necessaire pour la construction d'isochrones. Une attention particuliere est portee aux consequences de la sedimentation de He sur l'etendue des zones convectives, et sur la diffusion de Li et Be. Les forces radiatives agissant sur ces deux elements sont calculees en detail a partir des donnees atomiques. Les etoiles simulees correspondent approximativement aux types spectraux A, F, et AmFm. Les abondances de Li et Be observees dans les etoiles jeunes de ces types sont comparees a nos predictions dans le

  13. Engineering colloidal assembly via biological adhesion

    NASA Astrophysics Data System (ADS)

    Hiddessen, Amy Lynn

    Due to highly specialized recognition properties, biological receptor-ligand interactions offer valuable tools for engineering the assembly of novel colloidal materials. A unique sub-class of these macromolecules, called selectins, was exploited to develop binary suspensions where particles are programmed to associate reversibly or irreversibly via specific biomolecular cross-linking. Flow cytometry and videomicroscopy were used to examine factors controlling suspension assembly and structure, including biomolecular affinity and density, and individual and total particle volume fractions. By functionalizing small (RA = 0.47 mum) and larger (RB = 2.75 mum) particles with high surface densities of complementary E-selectin/sialyl Lewis X (sLeX) carbohydrate chemistry, a series of structures, from colloidal micelles (large particle coated with smaller particles) and clusters, to rings and elongated chains, was synthesized by decreasing the number ratio, NA/NB, of small (A) to large (B) particles (2 ≤ NA/NB ≤ 200) at low total volume fraction (10-4 ≤ φT ≤ 10-3 ). Using significantly lower surface densities, the low affinity binding between E-selectin and sLeX was exploited to create particles that interact reversibly, and average particle interaction lifetimes were tuned from minutes down to single selectin-carbohydrate bond lifetimes (≈1 s) by reducing sLeX density, a significant step toward assembling ordered microstructures. Particle binding lifetimes were analyzed with a receptor-ligand binding model, yielding estimates for molecular parameters, including on rate, 10-2 s-1 < kon < 10-1 s-1, and unstressed off rate, 0.25 s-1 ≤ kor ≤ 1.0 s-1, that characterize the docking dynamics of particles. Finally, at significantly higher volume fraction (φ T ≥ 10-1) and low number ratio, the rheology of space-filling networks crosslinked by high affinity streptavidin-biotin chemistry was probed to acquire knowledge on bulk properties of biocolloidal suspensions

  14. Colloid Facilitated Transport of Plutonium in Fractured Volcanic Tuff

    NASA Astrophysics Data System (ADS)

    Kersting, A. B.; Zhao, P.; Walensky, J. R.; Roberts, S. K.; Johnson, M. R.; Zavarin, M.; Ramon, E. C.

    2004-12-01

    The transport of low-solubility radionuclides in a colloidal- or colloidal bound state is frequently suspected or observed. Groundwater contaminated with radionuclides associated with underground nuclear tests was collected from several different well locations at the Nevada Test Site (NTS). In each case, the low-levels of plutonium detected in the groundwater were overwhelmingly (>95percent) associated with the colloidal and not the dissolved fraction of the groundwater. The colloidal fractions consisted of secondary minerals such as clays and zeolites. To better understand the mechanisms controlling the potential colloidal transport of plutonium, colloid-facilitated fracture flow laboratory experiments are being conducted. Pseudocolloids consisting of Pu(IV) sorbed to clinoptilolite were combined with a radionuclide solution cocktail consisting of Np, U, Cs, Sr, Sm and 3H and Re (analog to Tc) tracers in NTS-type synthetic groundwater (4.5mM NaHCO3-). The cocktail was injected into a smooth fracture in a volcanic tuff rock core from the NTS and the effluent analyzed. Autoradiography and secondary ion mass spectrometry will be used to understand the mineral -colloid-radionuclide interactions in the fracture volcanic tuff.

  15. Experimental study of colloid filtration by compacted bentonite

    SciTech Connect

    Kurosawa, Susumu; Yui, Mikazu; Yoshikawa, Hideki

    1997-12-31

    In this study, the transport behavior of colloids through compacted bentonite and sand-bentonite mixtures was investigated. Colloidal gold was used to simulate mobile colloids because it was well characterized and its dispersivity was controlled. The bentonite used was a sodium bentonite. The sand-bentonite mixtures were prepared by mixing up to 50 wt.% silica sand with the bentonite. The bentonite and the sand-bentonite mixtures were compacted to dry densities of 1,000 and 1,800 kg/m{sup 3} and then saturated with distilled water. The sand-bentonite mixture was also saturated with synthetic sea-water. Column experiments were performed to investigate colloidal transport. Further, colloidal particles stabilities in high ionic strength water such as bentonite porewater or saline groundwater were interpreted based on the repulsion potential from the double layer force and the attraction potential from the van der Waals force. The results indicated that the colloidal particles were effectively filtered by both the compacted bentonite and the sand-bentonite mixtures. This study indicated that the effect of colloids on radionuclide transport in compacted bentonite is negligible for the safety assessment of high level radioactive waste (HLW) disposal.

  16. Batch leaching tests: Colloid release and PAH leachability

    SciTech Connect

    Bergendahl, J.

    2005-07-01

    The Toxicity Characteristic Leaching Procedure (TCLP) was developed by the U.S. Environmental Protection Agency to assess leaching potential of contaminants from waste, and to provide a test to classify, hazardous waste. It is a batch leaching test where a waste (such as contaminated soil) and an extraction fluid are agitated for a predetermined time. Since TCLP employs an aggressive mixing technique, it is possible that hydrophobic contaminant-laden colloidal fractions may appear as 'dissolved' constituents. In this study, TCLP was employed to determine the leachability of PAH contamination from a coal tar contaminated site. Generated colloids and the apparent aqueous concentrations of naphthalene and phenanthrene were measured at various mixing times in the extraction fluid. A mathematical model was developed that predicted the apparent aqueous contaminant concentration in the filtrate. This model accounted for the presence of colloids in the filtrate, and quantified contaminant desorption from colloids. The fraction of colloid-bound contaminant was predicted to be negligible for naphthalene. However, phenanthrene was predicted to have a significant fraction of the total contaminant in the colloidal phase, while naphthalene was primarily dissolved. The desorption model and PAH desorption data are presented here to determine the extent of colloid-facilitated desorption during leaching tests.

  17. Comparison of groundwater colloids in adjoining soils of Florida flatwoods

    SciTech Connect

    Tan, Z.X.; Harris, W.G.; Ma, L.Q.

    2000-02-01

    Colloids in soil water are a constituent of natural geochemical fluxes and have the potential to facilitate contaminant transport, but few data are available on their composition and concentration. This study addresses how the composition and concentration of groundwater solids relate to hydrological and soil morphological variables of the Florida flatwoods landscape. Groundwater from saturated soil horizons was sampled biweekly for 1 year along an Aquod/Udult boundary using piezometers designed specifically to minimize disturbance and to permit the valid assessment of suspended solids. Readily dispersible clay from core samples of soil horizons was collected and quantified. Groundwater and soil colloids were analyzed physically, chemically, and mineralogically. Aquod groundwater had consistently lower pH, higher electrical conductivity, and more total solids (TS) and organic carbon (OC) than did Udult groundwater. Significant decreases in both TS and OC concentrations in groundwater occurred with depth for both soils. In contrast, the mineralogy of groundwater colloids was insensitive to soil and horizon differences. Quartz dominated inorganic colloid fractions in groundwater samples from all horizons, even in argillic horizons where clay fractions contained little or no quartz. No statistical correlations were found between masses of groundwater colloids and soil water-dispersible clay. However, the proportion of organic carbon was higher in groundwater than in soil matrices. Results are consistent with carbon and colloidal quartz movement in shallow groundwater of the soil studied and document that natural colloid and solute fluxes can be highly soil specific.

  18. Colloid-borne forms of tetravalent actinides: a brief review.

    PubMed

    Zänker, Harald; Hennig, Christoph

    2014-02-01

    Tetravalent actinides, An(IV), are usually assumed to be little mobile in near-neutral environmental waters because of their low solubility. However, there are certain geochemical scenarios during which mobilization of An(IV) in a colloid-borne (waterborne) form cannot be ruled out. A compilation of colloid-borne forms of tetravalent actinides described so far for laboratory experiments together with several examples of An(IV) colloids observed in field experiments and real-world scenarios are given. They are intended to be a knowledge base and a tool for those who have to interpret actinide behavior under environmental conditions. Synthetic colloids containing structural An(IV) and synthetic colloids carrying adsorbed An(IV) are considered. Their behavior is compared with the behavior of An(IV) colloids observed after the intentional or unintentional release of actinides into the environment. A list of knowledge gaps as to the behavior of An(IV) colloids is provided and items which need further research are highlighted.

  19. Active colloids in the context of chemical kinetics

    NASA Astrophysics Data System (ADS)

    Oshanin, G.; Popescu, M. N.; Dietrich, S.

    2017-03-01

    We study a mesoscopic model of a chemically active colloidal particle which on certain parts of its surface promotes chemical reactions in the surrounding solution. For reasons of simplicity and conceptual clarity, we focus on the case in which only electrically neutral species are present in the solution and on chemical reactions which are described by first order kinetics. Within a self-consistent approach we explicitly determine the steady state product and reactant number density fields around the colloid as functionals of the interaction potentials of the various molecular species in solution with the colloid. By using a reciprocal theorem, this allows us to compute and to interpret—in a transparent way in terms of the classical Smoluchowski theory of chemical kinetics—the external force needed to keep such a catalytically active colloid at rest (stall force) or, equivalently, the corresponding velocity of the colloid if it is free to move. We use the particular case of triangular-well interaction potentials as a benchmark example for applying the general theoretical framework developed here. For this latter case, we derive explicit expressions for the dependences of the quantities of interest on the diffusion coefficients of the chemical species, the reaction rate constant, the coverage by catalyst, the size of the colloid, as well as on the parameters of the interaction potentials. These expressions provide a detailed picture of the phenomenology associated with catalytically-active colloids and self-diffusiophoresis.

  20. The Colloid Controversy: Are Colloids Bad and What Are the Options?

    PubMed

    Wong, Christine; Koenig, Amie

    2017-03-01

    Biologic and synthetic colloid solutions are frequently used to increase oncotic pressure and to treat shock. Research has shown that each product has both risks and benefits. Hydroxyethyl starches have gained a reputation for increasing risk of death, acute kidney injury, and coagulation abnormalities in people, but additional studies are needed to see whether these concerns hold true in veterinary patients. This article reviews the risks and benefits of currently available products.

  1. Surface adsorption of colloidal brushes at good solvents conditions.

    PubMed

    Striolo, Alberto

    2012-09-14

    Monte Carlo simulations are presented for a minimal model of one spherical colloidal particle as it interacts with one attractive flat substrate. The colloidal particle is decorated by either 6 or 14 grafted polymer chains. The chains are always rather short, with their radius of gyration, estimated at infinite dilution in good solvent conditions, never larger than the spherical colloid diameter. Although all simulations are conducted under "good-solvent" conditions for the grafted polymer chains, we find that small changes in the polymer segment-polymer segment energetic interaction parameter can lead to significantly different scenarios. When the Lennard-Jones attraction is weak, 0.12 k(B)T, increasing the polymer length decreases the likelihood of colloidal adsorption, as expected. On the contrary, when the attraction is 0.18 k(B)T, increasing the length of the grafted polymer chains promotes the adsorption of the colloidal brush onto the surface. When the Lennard-Jones energetic parameter that describes polymer segment-polymer segment interactions is 0.15 k(B)T, as the length of the grafted polymer chains increases the probability of colloidal adsorption decreases to a minimum, and then increases. The results, explained in terms of a competition between entropic (due to the reduction in degrees of freedom available to the grafted polymer chains upon colloidal brush adsorption) and enthalpic driving forces (due to favorable colloid-surface and polymer segment-surface interactions), could be useful for controlling the circulation lifetime of liposomes within the blood stream, and optimizing solar energy harvesting by depositing colloidal particles on solid surfaces.

  2. Colloids in sepsis: evenly distributed molecules surrounded by uneven questions.

    PubMed

    Zampieri, Fernando Godinho; Park, Marcelo; Azevedo, Luciano Cesar Pontes

    2013-05-01

    Colloids are frequently used for fluid expansion in the intensive care unit, although its use on several clinical scenarios remains unproven of any relevant clinical benefit. The purpose of this article was to carry out a narrative review regarding the safety and efficacy of colloids in patients with sepsis and septic shock, with emphasis on the most commonly used colloids, albumin and starches. Colloids are effective fluid expanders and are able to restore the hemodynamic profile with less total volume than crystalloids. These properties appear to be preserved even in patients with sepsis with increased capillary permeability. However, some colloids are associated with renal impairment and coagulation abnormalities. Starch use was associated with increased mortality in two large clinical trials. Also, starches probably have significant renal adverse effects and may be related to more need for renal replacement therapy in severe sepsis. Albumin is the only colloid that has been shown safe in patients with sepsis and that may be associated with improved outcomes on specific subpopulations. No trial so far found any robust clinical end point favoring colloid use in patients with sepsis. Because there is no proven benefit of the use of most colloids in patients with sepsis, its use should not be encouraged outside clinical trials. Albumin is the only colloid solution that has proven to be safe, and its use may be considered on hypoalbuminemic patients with sepsis. Nevertheless, there are no robust data to recommend routine albumin administration in sepsis. Starch use should be avoided in patients with sepsis because of the recent findings of a multicenter randomized study until further evidence is available.

  3. Study on Colloidal Model of Petroleum Residues through the Attraction Potential between Colloids

    PubMed Central

    Zhang, Long-li; Yang, Guo-hua; Yang, Chao-he; Que, Guo-he

    2016-01-01

    The samples of DaGang atmospheric residue (DG-AR), Middle East atmospheric residue (ME-AR), TaHe atmospheric residue (TH-AR), and their thermal reaction samples were chosen for study. All the samples were fractioned into six components separately, including saturates plus light aromatics, heavy aromatics, light resins, middle resins, heavy resins, and asphaltenes. The dielectric permittivity of the solutions of these components was measured, and the dielectric permittivity values of the components can be determined by extrapolation, which increased steadily from saturates plus light aromatics to asphaltenes. Moreover, the Hamaker constants of the components were calculated from their dielectric permittivity values. The Van der Waals attractive potential energy between colloids corresponding to various models could be calculated from the fractional composition and the Hamaker constants of every component. It was assumed that the cores of colloidal particles were formed by asphaltenes and heavy resins mainly; the other fractions acted as dispersion medium. For the three serials of thermal reaction samples, the Van der Waals attraction potential energy between colloids for this kind of model was calculated. For TH-AR thermal reaction samples, the Van der Waals attraction potential energy presented the maximum as thermal reaction is going on, which was near to the end of coke induction period. PMID:27274729

  4. Colloidal stability and chemical reactivity of complex colloids containing Fe³⁺.

    PubMed

    van Leeuwen, Y M; Velikov, K P; Kegel, W K

    2014-07-15

    The reactivity of iron contained within insoluble colloidal metal-pyrophosphate salts was determined and compared to the reactivity of a soluble iron salt (FeCl3). As a model system for the reactivity of iron in food products, the formation of an iron-polyphenol complex was followed with spectrophotometry. Three types of systems were prepared and their colloidal stability and reactivity studied: Fe(3+) pyrophosphate, protein-coated Fe(3+) pyrophosphate and mixed-metal pyrophosphates containing Fe(3+) and a second cation M. The additional cation used was either monovalent (sodium) or divalent (M(2+)). It was found that: (i) incorporating iron in a colloidal salt reduced its reactivity compared to free Fe(3+) ions; (ii) coating the particles with a layer of hydrophobic protein (zein) increased stability and further decreased the reactivity. Finally, the most surprising result was that (iii) a mixed system containing more Fe(3+) than M actually increased the reactivity of the contained iron, while the reverse, a system containing excess M, inhibited the reactivity completely.

  5. Self-replicating devices with dipolar colloids

    NASA Astrophysics Data System (ADS)

    Dempster, Joshua; Zhang, Rui; Olvera de La Cruz, Monica

    2014-03-01

    Ubiquitous in nature, self-replication on the nano-scale has been challenging to produce in the laboratory. Recent efforts with DNA tiles have shown great success in correctly replicating tile-sequence templates but require frequent manipulation by the experimenter. We propose a scheme for achieving self-replication with dipolar colloids. Dimers in these systems replicate exponentially over millisecond time scales with no intervention other than periodic energy pulses supplied by external fields. We develop a general formalism governing the rate of self-replication as a function of the interval between pulses. Results from kinetic Monte Carlo simulations show good agreement with the growth rates predicted by simple models of the replication process. We thank the Office of the Director of Defense Research and Engineering (DDR&E) and Air Force Office of Scientific Research (AFOSR) for their support under Award FA9550-10-1-0167.

  6. Self-assembly of colloidal rafts

    NASA Astrophysics Data System (ADS)

    Sharma, Prerna; Gibaud, Thoams; Ward, Andrew; Dogic, Zvonimir

    2013-03-01

    Interactions between nanometer-sized particles or molecules suspended in a bulk fluid are well understood. However, when such particles are embedded in a membrane, the inter-particle potential is significantly modified by membrane mediated forces and gives rise to novel phase behavior. Visualizing and manipulating such inclusions in a lipid bilayer is difficult due to the nanometer length scales involved. Here, we use a model system of micron sized colloidal membranes doped with molecules shorter or longer than that of the bulk. Surprisingly, the dopant molecules form self-limited finite size clusters. These clusters further self-organize into a wide variety of higher order structures such as hexagonal and square lattice arrays, lamellar patterns and saddle shaped surfaces. Understanding the phase behavior and measuring repulsive forces between such clusters may have implications for the similar mechanisms that operate in conventional lipid bilayers.

  7. Photoactivated colloidal dockers for cargo transportation.

    PubMed

    Palacci, Jérémie; Sacanna, Stefano; Vatchinsky, Adrian; Chaikin, Paul M; Pine, David J

    2013-10-30

    We introduce a self-propelled colloidal hematite docker that can be steered to a small particle cargo many times its size, dock, transport the cargo to a remote location, and then release it. The self-propulsion and docking are reversible and activated by visible light. The docker can be steered either by a weak uniform magnetic field or by nanoscale tracks in a textured substrate. The light-activated motion and docking originate from osmotic/phoretic particle transport in a concentration gradient of fuel, hydrogen peroxide, induced by the photocatalytic activity of the hematite. The docking mechanism is versatile and can be applied to various materials and shapes. The hematite dockers are simple single-component particles and are synthesized in bulk quantities. This system opens up new possibilities for designing complex micrometer-size factories as well as new biomimetic systems.

  8. Water evaporation in silica colloidal deposits.

    PubMed

    Peixinho, Jorge; Lefèvre, Grégory; Coudert, François-Xavier; Hurisse, Olivier

    2013-10-15

    The results of an experimental study on the evaporation and boiling of water confined in the pores of deposits made of mono-dispersed silica colloidal micro-spheres are reported. The deposits are studied using scanning electron microscopy, adsorption of nitrogen, and adsorption of water through attenuated total reflection-infrared spectroscopy. The evaporation is characterized using differential scanning calorimetry and thermal gravimetric analysis. Optical microscopy is used to observe the patterns on the deposits after evaporation. When heating at a constant rate and above boiling temperature, the release of water out of the deposits is a two step process. The first step is due to the evaporation and boiling of the surrounding and bulk water and the second is due to the desorption of water from the pores. Additional experiments on the evaporation of water from membranes having cylindrical pores and of heptane from silica deposits suggest that the second step is due to the morphology of the deposits.

  9. Emergent vortices in populations of colloidal rollers

    PubMed Central

    Bricard, Antoine; Caussin, Jean-Baptiste; Das, Debasish; Savoie, Charles; Chikkadi, Vijayakumar; Shitara, Kyohei; Chepizhko, Oleksandr; Peruani, Fernando; Saintillan, David; Bartolo, Denis

    2015-01-01

    Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking. Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex. Combining physical experiments and numerical simulations, we elucidate this collective behaviour. We demonstrate that the emergent-vortex structure lives on the verge of a phase separation, and single out the very constituents responsible for this state of polar active matter. Building on this observation, we establish a continuum theory and lay out a strong foundation for the description of vortical collective motion in a broad class of motile populations constrained by geometrical boundaries. PMID:26088835

  10. Colloidal microgels in drug delivery applications

    PubMed Central

    Vinogradov, Serguei V.

    2005-01-01

    Colloidal microgels have recently received attention as environmentally responsive systems and now are increasingly used in applications as carriers for therapeutic drugs and diagnostic agents. Synthetic microgels consist of a crosslinked polymer network that provides a depot for loaded drugs, protection against environmental hazards and template for post-synthetic modification or vectorization of the drug carriers. The aim of this manuscript is to review recent attempts to develop new microgel formulations for oral drug delivery, to design metal-containing microgels for diagnostic and therapeutic applications, and to advance approaches including the systemic administration of microgels. Novel nanogel drug delivery systems developed in the authors’ laboratory are discussed in details including aspects of their synthesis, vectorization and recent applications for encapsulation of low molecular weight drugs or formulation of biological macromolecules. The findings reviewed here are encouraging for further development of the nanogels as intelligent drug carriers with such features as targeted delivery and triggered drug release. PMID:17168773

  11. Active colloids that slosh through passive matrices

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Granick, Steve

    Studies of natural and artificial active matter have focused on systems with a large mismatch of the time and length scales for active and passive elements, but in a variety of non-equilibrium condensed matter systems, including numerous biological processes, actively driven elements have a crowded environment of surrounding passive ``solvent'' elements of comparable size. Here we study self-propelled colloidal particles in a passive matrix of comparable size. Particles with high activity take straight lines and sharp turns through the soft 2-D crystal matrix to ensure rapid healing of the crystal structure. Effective attraction between active particles arises when the concentration of active particles or the hardness of the matrix increases; active particles tend to segregate in the grain boundaries of the crystal matrix.

  12. Multimodal plasmonics in fused colloidal networks

    NASA Astrophysics Data System (ADS)

    Teulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L.; Li, Mei; Mann, Stephen; Dujardin, Erik

    2015-01-01

    Harnessing the optical properties of noble metals down to the nanometre scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of surface plasmon modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the surface plasmon modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy-loss spectroscopy with a nanometre-sized electron probe. We prepare the metallic bead strings by electron-beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low-energy surface plasmon modes that are capable of supporting long-range and spectrally tunable propagation in nanoscale waveguides.

  13. Magnetic Separation Dynamics of Colloidal Magnetic Nanoparticles

    SciTech Connect

    Kaur, M.; Huijin Zhang,; You Qiang,

    2013-01-01

    Surface functionalized magnetic nanoparticles (MNPs) are appealing candidates for analytical separation of heavy metal ions from waste water and separation of actinides from spent nuclear fuel. This work studies the separation dynamics and investigates the appropriate magnetic-field gradients. A dynamic study of colloidal MNPs was performed for steady-state flow. Measurements were conducted to record the separation time of particles as a function of magnetic field gradient. The drag and magnetic forces play a significant role on the separation time. A drop in saturation magnetization and variation of particle size occurs after surface functionalization of the MNPs; these are the primary factors that affect the separation time and velocity of the MNPs. The experimental results are correlated to a theoretical one-dimensional model.

  14. Concentration-dependent sedimentation of colloidal rods

    NASA Astrophysics Data System (ADS)

    Dogic, Z.; Philipse, A. P.; Fraden, S.; Dhont, J. K. G.

    2000-11-01

    In this paper we first develop an approximate theory for the leading order concentration dependence of the sedimentation coefficient for rodlike colloids/polymers/macromolecules. To first order in volume fraction φ of rods, the sedimentation coefficient is written as 1+αφ. For large aspect ratios L/D (L is the rod length, D its thickness) α is found to vary like ∝(L/D)2/ln(L/D). This theoretical prediction is compared to experimental results. Then, experiments on fd virus are described, both in the isotropic and nematic phase. First-order in concentration results for this very long and thin (semiflexible) rod are in agreement with the above-mentioned theoretical prediction. Sedimentation profiles for the nematic phase show two sedimentation fronts. This result indicates that the nematic phase becomes unstable with the respect to isotropic phase during sedimentation.

  15. Laser trapping of colloidal metal nanoparticles.

    PubMed

    Lehmuskero, Anni; Johansson, Peter; Rubinsztein-Dunlop, Halina; Tong, Lianming; Käll, Mikael

    2015-01-01

    Optical trapping using focused laser beams (laser tweezers) has been proven to be extremely useful for contactless manipulation of a variety of small objects, including biological cells, organelles within cells, and a wide range of other dielectric micro- and nano-objects. Colloidal metal nanoparticles have drawn increasing attention in the field of optical trapping because of their unique interactions with electromagnetic radiation, caused by surface plasmon resonance effects, enabling a large number of nano-optical applications of high current interest. Here we try to give a comprehensive overview of the field of laser trapping and manipulation of metal nanoparticles based on results reported in the recent literature. We also discuss and describe the fundamentals of optical forces in the context of plasmonic nanoparticles, including effects of polarization, optical angular momentum, and laser heating effects, as well as the various techniques that have been used to trap and manipulate metal nanoparticles. We conclude by suggesting possible directions for future research.

  16. Devitrification of colloidal glasses in real space.

    PubMed

    Simeonova, Nikoleta B; Dullens, Roel P A; Aarts, Dirk G A L; de Villeneuve, Volkert W A; Lekkerkerker, Henk N W; Kegel, Willem K

    2006-04-01

    Confocal scanning laser microscopy has been used to quantitatively analyze the structure and dynamics of concentrated suspensions of spherical colloids in which the magnitude of the short-range attractive potential is increased by adding nonadsorbing polymers. These systems undergo a reentrant glass transition upon increasing polymer concentration. We find that melting of the glass is accompanied by significant changes in the displacement distribution and its moments. However, no significant variations have been detected in the shapes of the displacement distributions. Moreover, structural correlation functions and the magnitude of local density fluctuations do not vary significantly between the glass states and the fluid. Considering our experimental setup, these observations imply that local density fluctuations cannot be larger than a few percent of the average density.

  17. Slow Electron Cooling in Colloidal Quantum Dots

    NASA Astrophysics Data System (ADS)

    Pandey, Anshu; Guyot-Sionnest, Philippe

    2008-11-01

    Hot electrons in semiconductors lose their energy very quickly (within picoseconds) to lattice vibrations. Slowing this energy loss could prove useful for more efficient photovoltaic or infrared devices. With their well-separated electronic states, quantum dots should display slow relaxation, but other mechanisms have made it difficult to observe. We report slow intraband relaxation (>1 nanosecond) in colloidal quantum dots. The small cadmium selenide (CdSe) dots, with an intraband energy separation of ~0.25 electron volts, are capped by an epitaxial zinc selenide (ZnSe) shell. The shell is terminated by a CdSe passivating layer to remove electron traps and is covered by ligands of low infrared absorbance (alkane thiols) at the intraband energy. We found that relaxation is markedly slowed with increasing ZnSe shell thickness.

  18. Brownian diffusion of a partially wetted colloid

    NASA Astrophysics Data System (ADS)

    Boniello, Giuseppe; Blanc, Christophe; Fedorenko, Denys; Medfai, Mayssa; Mbarek, Nadia Ben; in, Martin; Gross, Michel; Stocco, Antonio; Nobili, Maurizio

    2015-09-01

    The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than that observed in the more viscous fluid. Here, we show experimentally that a particle straddling an air/water interface feels a large viscous drag that is unexpectedly larger than that measured in the bulk. We suggest that such a result arises from thermally activated fluctuations of the interface at the solid/air/liquid triple line and their coupling to the particle drag through the fluctuation-dissipation theorem. Our findings should inform approaches for improved control of the kinetically driven assembly of anisotropic particles with a large triple-line-length/particle-size ratio, and help to understand the formation and structure of such arrested materials.

  19. Screening of charged spheroidal colloidal particles

    NASA Astrophysics Data System (ADS)

    Álvarez, Carlos; Téllez, Gabriel

    2010-10-01

    We study the effective screened electrostatic potential created by a spheroidal colloidal particle immersed in an electrolyte, within the mean field approximation, using Poisson-Boltzmann equation in its linear and nonlinear forms, and also beyond the mean field by means of Monte Carlo computer simulation. The anisotropic shape of the particle has a strong effect on the screened potential, even at large distances (compared to the Debye length) from it. To quantify this anisotropy effect, we focus our study on the dependence of the potential on the position of the observation point with respect with the orientation of the spheroidal particle. For several different boundary conditions (constant potential, or constant surface charge) we find that, at large distance, the potential is higher in the direction of the large axis of the spheroidal particle.

  20. Crystal nucleation of colloidal hard dumbbells.

    PubMed

    Ni, Ran; Dijkstra, Marjolein

    2011-01-21

    Using computer simulations, we investigate the homogeneous crystal nucleation in suspensions of colloidal hard dumbbells. The free energy barriers are determined by Monte Carlo simulations using the umbrella sampling technique. We calculate the nucleation rates for the plastic crystal and the aperiodic crystal phase using the kinetic prefactor as determined from event driven molecular dynamics simulations. We find good agreement with the nucleation rates determined from spontaneous nucleation events observed in event driven molecular dynamics simulations within error bars of one order of magnitude. We study the effect of aspect ratio of the dumbbells on the nucleation of plastic and aperiodic crystal phases, and we also determine the structure of the critical nuclei. Moreover, we find that the nucleation of the aligned close-packed crystal structure is strongly suppressed by a high free energy barrier at low supersaturations and slow dynamics at high supersaturations.

  1. Yielding and flow of colloidal glasses.

    PubMed

    Petekidis, Georgios; Vlassopoulos, Dimitris; Pusey, Peter N

    2003-01-01

    We investigate the yielding and flow of hard-sphere colloidal glasses by combining rheological measurements with the technique of light scattering echo. The polymethylmethacrylate particles used are sufficiently polydisperse that crystallization is suppressed. Creep and recovery measurements show that the glasses can tolerate surprisingly large strains, up to at least 15%, before yielding irreversibly. We attribute this behaviour to 'cage elasticity', the ability of a particle and its cage of neighbours to retain their identity under quite large distortion. Results from light scattering echo, which measures the extent of irreversible particle rearrangement under oscillatory shear, support the notion of cage elasticity. In the lower concentration glasses we find that particle trajectories are partly reversible under strains which significantly exceed the yield strain.

  2. Aqueous Black Colloids of Reticular Nanostructured Gold

    NASA Astrophysics Data System (ADS)

    Stanca, S. E.; Fritzsche, W.; Dellith, J.; Froehlich, F.; Undisz, A.; Deckert, V.; Krafft, C.; Popp, J.

    2015-01-01

    Since ancient times, noble gold has continuously contributed to several aspects of life from medicine to electronics. It perpetually reveals its new features. We report the finding of a unique form of gold, reticular nanostructured gold (RNG), as an aqueous black colloid, for which we present a one-step synthesis. The reticules consist of gold crystals that interconnect to form compact strands. RNG exhibits high conductivity and low reflection, and these features, coupled with the high specific surface area of the material, could prove valuable for applications in electronics and catalysis. Due to high absorption throughout the visible and infrared domain, RNG has the potential to be applied in the construction of sensitive solar cells or as a substrate for Raman spectroscopy.

  3. MOLECULAR DESIGN OF COLLOIDS IN SUPERCRITICAL FLUIDS

    SciTech Connect

    Keith P. Johnston

    2009-04-06

    The environmentally benign, non-toxic, non-flammable fluids water and carbon dioxide (CO2) are the two most abundant and inexpensive solvents on earth. Emulsions of these fluids are of interest in many industrial processes, as well as CO2 sequestration and enhanced oil recovery. Until recently, formation of these emulsions required stabilization with fluorinated surfactants, which are expensive and often not environmentally friendly. In this work we overcame this severe limitation by developing a fundamental understanding of the properties of surfactants the CO2-water interface and using this knowledge to design and characterize emulsions stabilized with either hydrocarbon-based surfactants or nanoparticle stabilizers. We also discovered a new concept of electrostatic stabilization for CO2-based emulsions and colloids. Finally, we were able to translate our earlier work on the synthesis of silicon and germanium nanocrystals and nanowires from high temperatures and pressures to lower temperatures and ambient pressure to make the chemistry much more accessible.

  4. Anomalous electrical conductivity of nanoscale colloidal suspensions.

    PubMed

    Chakraborty, Suman; Padhy, Sourav

    2008-10-28

    The electrical conductivity of colloidal suspensions containing nanoscale conducting particles is nontrivially related to the particle volume fraction and the electrical double layer thickness. Classical electrochemical models, however, tend to grossly overpredict the pertinent effective electrical conductivity values, as compared to those obtained under experimental conditions. We attempt to address this discrepancy by appealing to the complex interconnection between the aggregation kinetics of the nanoscale particles and the electrodynamics within the double layer. In particular, we model the consequent alterations in the effective electrophoretic mobility values of the suspension by addressing the fundamentals of agglomeration-deagglomeration mechanisms through the pertinent variations in the effective particulate dimensions, solid fractions, as well as the equivalent suspension viscosity. The consequent alterations in the electrical conductivity values provide a substantially improved prediction of the corresponding experimental findings and explain the apparent anomalous behavior predicted by the classical theoretical postulates.

  5. Multiple Exciton Generation in Colloidal Nanocrystals

    PubMed Central

    Smith, Charles; Binks, David

    2013-01-01

    In a conventional solar cell, the energy of an absorbed photon in excess of the band gap is rapidly lost as heat, and this is one of the main reasons that the theoretical efficiency is limited to ~33%. However, an alternative process, multiple exciton generation (MEG), can occur in colloidal quantum dots. Here, some or all of the excess energy is instead used to promote one or more additional electrons to the conduction band, potentially increasing the photocurrent of a solar cell and thereby its output efficiency. This review will describe the development of this field over the decade since the first experimental demonstration of multiple exciton generation, including the controversies over experimental artefacts, comparison with similar effects in bulk materials, and the underlying mechanisms. We will also describe the current state-of-the-art and outline promising directions for further development.

  6. Nanosecond colloidal quantum dot lasers for sensing.

    PubMed

    Guilhabert, B; Foucher, C; Haughey, A-M; Mutlugun, E; Gao, Y; Herrnsdorf, J; Sun, H D; Demir, H V; Dawson, M D; Laurand, N

    2014-03-24

    Low-threshold, gain switched colloidal quantum dot (CQD) distributed-feedback lasers operating in the nanosecond regime are reported and proposed for sensing applications for the first time to the authors' knowledge. The lasers are based on a mechanically-flexible polymeric, second order grating structure overcoated with a thin-film of CQD/PMMA composite. The threshold fluence of the resulting lasers is as low as 0.5 mJ/cm² for a 610 nm emission and the typical linewidth is below 0.3 nm. The emission wavelength of the lasers can be set at the design stage and laser operation between 605 nm and 616 nm, while using the exact same CQD gain material, is shown. In addition, the potential of such CQD lasers for refractive index sensing in solution is demonstrated by immersion in water.

  7. Multimodal Plasmonics in Fused Colloidal Networks

    PubMed Central

    Teulle, Alexandre; Bosman, Michel; Girard, Christian; Gurunatha, Kargal L.; Li, Mei; Mann, Stephen; Dujardin, Erik

    2014-01-01

    Harnessing the optical properties of noble metals down to the nanometer-scale is a key step towards fast and low-dissipative information processing. At the 10-nm length scale, metal crystallinity and patterning as well as probing of surface plasmon (SP) properties must be controlled with a challenging high level of precision. Here, we demonstrate that ultimate lateral confinement and delocalization of SP modes are simultaneously achieved in extended self-assembled networks comprising linear chains of partially fused gold nanoparticles. The spectral and spatial distributions of the SP modes associated with the colloidal superstructures are evidenced by performing monochromated electron energy loss spectroscopy with a nanometer-sized electron probe. We prepare the metallic bead strings by electron beam-induced interparticle fusion of nanoparticle networks. The fused superstructures retain the native morphology and crystallinity but develop very low energy SP modes that are capable of supporting long range and spectrally tunable propagation in nanoscale waveguides. PMID:25344783

  8. Electrostatic interaction between colloidal particles trapped at an electrolyte interface.

    PubMed

    Majee, Arghya; Bier, Markus; Dietrich, S

    2014-04-28

    The electrostatic interaction between colloidal particles trapped at the interface between two immiscible electrolyte solutions is studied in the limit of small inter-particle distances. Within an appropriate model analytic expressions for the electrostatic potential as well as for the surface and line interaction energies are obtained. They demonstrate that the widely used superposition approximation, which is commonly applied to large distances between the colloidal particles, fails qualitatively at small distances, and is quantitatively unreliable even at large distances. Our results contribute to an improved description of the interaction between colloidal particles trapped at fluid interfaces.

  9. [Effects of colloidal organic substrate on nitrification in biofilms].

    PubMed

    Li, Jiuyi; Luan, Zhaokun; Zhu, Baoxia; Chen, Futai; Jia, Zhiping

    2003-09-01

    The effects of colloidal and soluble organic substrates on nitrification in biofilms were investigated in biological aerated filters. The results showed that the hydrolysis process of colloidal organic matter took place rapidly, which could not be the limiting step of its oxidation in the biofilm. Some 70% organic matter oxidation was accomplished at the 40 cm at the bottom of the both filters, while the increase of organic matter in the influent resulted in the displacement of nitrification from the bottom to the upper part of filter bed. It was observed that the greater reduction on nitrification was caused by colloidal organic matter than by soluble organics at the same COD concentration.

  10. Ordering, dynamics and phase transitions in charged colloids

    NASA Astrophysics Data System (ADS)

    Tata, B. V. R.; Jena, Sidhartha S.

    2006-09-01

    Among the various soft matter systems, charge stabilized colloidal dispersions have gained recognition as tremendously useful model condensed matter systems because of their structural ordering and the rich phase behavior. This paper is a review of the work done in the last few years related to structural ordering and phase transitions brought about by parameters such as pressure, surface charge density and salt concentration. The dynamics in colloidal crystals and dense suspensions is influenced by hydrodynamic interactions arising due to the intervening viscous fluid. Lattice dynamics of colloidal crystals presents a nice testing ground for theories of hydrodynamic interaction. Apart from reviewing the measurements of phonon dispersion curves in thin colloidal crystals, we present here recent dynamic light scattering results on bulk colloidal crystals. The dynamics in colloidal liquids and colloidal glasses are also covered. Though colloidal liquids of low charge density particles freeze into a homogenous crystalline or a glassy state, they remain inhomogeneous when the charge density is beyond a critical value. Recently, this inhomogeneous state is confirmed to be a gas-solid coexistence. This observation of gas-solid coexistence in highly charged colloids along with the earlier observations of vapor-liquid condensation and a reentrant transition have created a debate on the existence of long-range attraction in the effective pair potential U(r) of like-charged colloidal particles. U(r) was measured directly using optical microscopy. However, the limitations in using the optical microscopy technique for determining U(r) in dilute suspensions are discussed. These limitations can be circumvented by employing confocal microscopy. We present our recent observation of stable bound pairs in very dilute and highly charged colloidal suspensions using confocal microscopy and the existence of an attractive minimum in the measured U(r) of like-charged particles. These

  11. Shape-induced frustration of hexagonal order in polyhedral colloids.

    PubMed

    Dullens, Roel P A; Mourad, Maurice C D; Aarts, Dirk G A L; Hoogenboom, Jacob P; Kegel, Willem K

    2006-01-20

    The effect of a nonspherical particle shape and shape polydispersity on the structure of densely packed hard colloidal particles was studied in real space by confocal microscopy. We show that the first layer at the wall of concentrated size-monodisperse but shape-polydisperse polyhedral colloids exhibits significant deviations from a hexagonal lattice. These deviations are identified as bond-orientational fluctuations which lead to percolating "mismatch lines." While the shape-induced geometrical frustration of the hexagonal symmetry suppresses translational order, bond-orientational order is clearly retained, indicating a hexaticlike structure of the polyhedral colloids.

  12. Photophysics and photochemistry of quantized ZnO colloids

    SciTech Connect

    Kamat, P.V.; Patrick, B.

    1992-08-06

    The photophysical and photochemical behavior of quantized ZnO colloids in ethanol has been investigated by time-resolved transient absorption and emission measurements. Trapping of electrons at the ZnO surface resulted in broad absorption in the red region. The green emission of ZnO colloids was readily quenched by hole scavengers such as SCN{sup -} and I{sup -}. The photoinduced charge transfer to these hole scavengers was studied by laser flash photolysis. The yield of oxidized product increased considerably when ZnO colloids were coupled with ZnSe. 36 refs., 11 figs., 1 tab.

  13. The Colloidal Stability of Magnetic Nanoparticles in Ionic Liquids

    DTIC Science & Technology

    2015-08-03

    Final 3. DATES COVERED (From - To) 14 May 2014 – 13 May 2015 4. TITLE AND SUBTITLE The Colloidal Stability of Magnetic Nanoparticles in...DATE 11 SEP 2015 2. REPORT TYPE Final 3. DATES COVERED 14-05-2014 to 13-05-2015 4. TITLE AND SUBTITLE The Colloidal Stability of Magnetic...Rev. 8-98) Prescribed by ANSI Std Z39-18 Final Report for AOARD Grant 144062 “The Colloidal Stability of Magnetic Nanoparticles in Ionic Liquids

  14. Self-assembly of colloidal pyramids in magnetic fields.

    PubMed

    Helseth, L E

    2005-08-02

    We study routes toward the construction of 2D colloidal pyramids. We find that magnetic beads may self-assemble into pyramids near a nonmagnetic 1D boundary as long as the number of beads in the pyramid does not exceed 10. We have also found that a strong magnetic field gradient could act as a boundary, thus assisting the self-assembly of magnetic colloids in water, and have observed the formation of stable microscopic pyramids within a certain magnetic field range. Our results indicate that colloidal pyramids can be formed in a number of ways by utilizing external fields.

  15. Binary Colloidal Alloy Test-5: Three-Dimensional Melt

    NASA Technical Reports Server (NTRS)

    Yodh, Arjun G.

    2008-01-01

    Binary Colloidal Alloy Test - 5: Three-Dimensional Melt (BCAT-5-3DMelt) photographs initially randomized colloidal samples in microgravity to determine their resulting structure over time. BCAT-5-3D-Melt will allow the scientists to capture the kinetics (evolution) of their samples, as well as the final equilibrium state of each sample. BCAT-5-3D-Melt will look at the mechanisms of melting using three-dimensional temperature sensitive colloidal crystals. Results will help scientists develop fundamental physics concepts previously shadowed by the effects of gravity.

  16. Liquid-vapor interfaces of patchy colloids

    NASA Astrophysics Data System (ADS)

    Oleksy, A.; Teixeira, P. I. C.

    2015-01-01

    We investigate the liquid-vapor interface of a model of patchy colloids. This model consists of hard spheres decorated with short-ranged attractive sites ("patches") of different types on their surfaces. We focus on a one-component fluid with two patches of type A and nine patches of type B (2 A 9 B colloids), which has been found to exhibit reentrant liquid-vapor coexistence curves and very low-density liquid phases. We have used the density-functional theory form of Wertheim's first-order perturbation theory of association, as implemented by Yu and Wu [J. Chem. Phys. 116, 7094 (2002), 10.1063/1.1463435], to calculate the surface tension, and the density and degree of association profiles, at the liquid-vapor interface of our model. In reentrant systems, where A B bonds dominate, an unusual thickening of the interface is observed at low temperatures. Furthermore, the surface tension versus temperature curve reaches a maximum, in agreement with Bernardino and Telo da Gama's mesoscopic Landau-Safran theory [Phys. Rev. Lett. 109, 116103 (2012), 10.1103/PhysRevLett.109.116103]. If B B attractions are also present, competition between A B and B B bonds gradually restores the monotonic temperature dependence of the surface tension. Lastly, the interface is "hairy," i.e., it contains a region where the average chain length is close to that in the bulk liquid, but where the density is that of the vapor. Sufficiently strong B B attractions remove these features, and the system reverts to the behavior seen in atomic fluids.

  17. The dynamical crossover in attractive colloidal systems

    SciTech Connect

    Mallamace, Francesco; Corsaro, Carmelo; Stanley, H. Eugene; Mallamace, Domenico; Chen, Sow-Hsin

    2013-12-07

    We study the dynamical arrest in an adhesive hard-sphere colloidal system. We examine a micellar suspension of the Pluronic-L64 surfactant in the temperature (T) and volume fraction (ϕ) phase diagram. According to mode-coupling theory (MCT), this system is characterized by a cusp-like singularity and two glassy phases: an attractive glass (AG) phase and a repulsive glass (RG) phase. The T − ϕ phase diagram of this system as confirmed by a previous series of scattering data also exhibits a Percolation Threshold (PT) line, a reentrant behavior (AG-liquid-RG), and a glass-to-glass transition. The AG phase can be generated out of the liquid phase by using T and ϕ as control parameters. We utilize viscosity and nuclear magnetic resonance (NMR) techniques. NMR data confirm all the characteristic properties of the colloidal system phase diagram and give evidence of the onset of a fractal-like percolating structure at a precise threshold. The MCT scaling laws used to study the shear viscosity as a function of ϕ and T show in both cases a fragile-to-strong liquid glass-forming dynamic crossover (FSC) located near the percolation threshold where the clustering process is fully developed. These results suggest a larger thermodynamic generality for this phenomenon, which is usually studied only as a function of the temperature. We also find that the critical values of the control parameters, coincident with the PT line, define the locus of the FSC. In the region between the FSC and the glass transition lines the system dynamics are dominated by clustering effects. We thus demonstrate that it is possible, using the conceptual framework provided by extended mode-coupling theory, to describe the way a system approaches dynamic arrest, taking into account both cage and hopping effects.

  18. Anomalous columnar order of charged colloidal platelets.

    PubMed

    Morales-Anda, L; Wensink, H H; Galindo, A; Gil-Villegas, A

    2012-01-21

    Monte Carlo computer simulations are carried out for a model system of like-charged colloidal platelets in the isothermal-isobaric ensemble (NpT). The aim is to elucidate the role of electrostatic interactions on the structure of synthetic clay systems at high particle densities. Short-range repulsions between particles are described by a suitable hard-core model representing a discotic particle. This potential is supplemented with an electrostatic potential based on a Yukawa model for the screened Coulombic potential between infinitely thin disklike macro-ions. The particle aspect-ratio and electrostatic parameters were chosen to mimic an aqueous dispersion of thin, like-charged, rigid colloidal platelets at finite salt concentration. An examination of the fluid phase diagram reveals a marked shift in the isotropic-nematic transition compared to the hard cut-sphere reference system. Several statistical functions, such as the pair correlation function for the center-of-mass coordinates and structure factor, are obtained to characterize the structural organization of the platelets phases. At low salinity and high osmotic pressure we observe anomalous hexagonal columnar structures characterized by interpenetrating columns with a typical intercolumnar distance corresponding to about half of that of a regular columnar phase. Increasing the ionic strength leads to the formation of glassy, disordered structures consisting of compact clusters of platelets stacked into finite-sized columns. These so-called "nematic columnar" structures have been recently observed in systems of charge-stabilized gibbsite platelets. Our findings are corroborated by an analysis of the static structure factor from a simple density functional theory.

  19. Observed Dependence of Colloid Detachment on the Concentration of Initially Attached Colloids and Collector Surface Heterogeneity in Porous Media.

    PubMed

    Li, Tiantian; Jin, Yan; Huang, Yuanfang; Li, Baoguo; Shen, Chongyang

    2017-03-07

    Sand column experiments were conducted to examine the effects of the concentration of attached colloids (CAC) on their subsequent detachment upon decreasing solution ionic strength (IS). Different pore volumes of latex microparticle suspensions were injected into the columns to allow different amounts of colloids to attach at ISs of 0.001, 0.01, and 0.2 M. Then, deionized water was introduced to release the attached colloids. Results show that the fraction of attachments that were reversible to reduction of IS (FRA) increased with increasing CAC at a given IS if the sand was extensively treated using acids to reduce surface charge heterogeneity. This indicates that colloids were preferentially immobilized in sites favoring irreversible attachment and then gradually occupied reversible sites. In contrast, the FRA decreased with increasing CAC at 0.001 M in sand without the acid treatment, illustrating the opposite attachment sequence. Scanning electron microscope examinations reveal that the concave regions favored irreversible colloid attachment. Reversible attachment is likely due to immobilization on flat surfaces with charge heterogeneities, retention in stagnation point regions via secondary minimum association, ripening in the acid-treated sand, and capture of colloids by protruding asperities with charge heterogeneity in the untreated sand. At ISs of 0.01 and 0.2 M, the FRA was essentially independent of CAC in the untreated sand because the colloids were randomly attached on the sand surfaces over time.

  20. Prise en charge de l’infection gonococcique chez les adultes et les jeunes

    PubMed Central

    Pogany, Lisa; Romanowski, Barbara; Robinson, Joan; Gale-Rowe, Margaret; Latham-Carmanico, Cathy; Weir, Christine; Wong, Tom

    2015-01-01

    Résumé Objectif Présenter des recommandations sur la prise en charge de l’infection gonococcique chez les adultes et les jeunes. Qualité des données Les recommandations thérapeutiques des lignes directrices canadiennes sur les infections transmissibles sexuellement reposent sur une recherche documentaire de même que sur des catégories de recommandations et des niveaux de qualité de données déterminés par au moins 2 évaluateurs. Les recommandations ont été revues par des pairs et sont en instance d’approbation par le groupe de travail d’experts. Message principal Les nouvelles recommandations portant sur la prise en charge de l’infection gonococcique chez les adultes et les jeunes préconisent les cultures à titre d’outil diagnostique lorsqu’elles sont pratiques, le traitement par antibiothérapie combinée (ceftriaxone associée à l’azithromycine) et le signalement sans délai de tous les cas dont le traitement a échoué aux autorités de santé publique. Conclusion Si elles sont suivies, ces nouvelles recommandations pourraient réduire l’échec thérapeutique, contribuer à une surveillance plus étroite des tendances à la résistance de Neisseria gonorrhoeae aux antibiotiques et contribuer à prévenir la transmission de gonorrhée résistante à plusieurs médicaments.

  1. Aborder les soins préventifs chez les aînés

    PubMed Central

    Tazkarji, Bachir; Lam, Robert; Lee, Shawn; Meiyappan, Soumia

    2016-01-01

    Résumé Objectif Guider les médecins de famille dans l’élaboration de plans de dépistage et de traitements préventifs à l’intention de leurs patients âgés. Sources de l’information Une recension a été effectuée dans la base de données MEDLINE pour trouver des lignes directrices canadiennes sur les soins de santé primaires et les personnes âgées; des lignes directrices, des méta-analyses, des guides de pratique clinique ou des révisions systématiques portant sur le dépistage de masse chez les 80 ans et plus et les aînés fragiles, se limitant à ceux publiés entre 2006 et juillet 2016; et des articles sur les services de santé préventifs à l’intention des aînés et présentant un intérêt pour la pratique familiale ou les médecins de famille, limités à ceux publiés en anglais entre 2012 et juillet 2016. Message principal L’estimation de l’espérance de vie n’est pas une science facile ou précise, mais la fragilité est un concept émergent susceptible d’être utile à cet égard. Le Groupe d’étude canadien sur les soins de santé préventifs propose des lignes directrices sur le dépistage du cancer, mais elles sont moins précises en ce qui concerne les patients de plus de 74 ans et il faut donc individualiser les plans de prise en charge. L’estimation des années de vie qui restent aide à orienter vos recommandations concernant les plans de dépistage et de traitements préventifs. Les risques augmentent souvent proportionnellement avec la fragilité et la comorbidité. D’autre part, les bienfaits diminuent souvent à mesure que l’espérance de vie raccourcit. Les plans de prise en charge préventive devraient tenir compte des points de vue du patient et être convenus d’un commun accord. Un moyen mnémonique pour se rappeler des principaux domaines de prévention en soins primaires – CCMF, abréviation pour cancer, cardiovasculaire, mauvais équilibre, chute et ostéoporose, fiche de vaccinations pr

  2. PCR detection of groundwater bacteria associated with colloidal transport

    SciTech Connect

    Cruz-Perez, P.; Stetzenbach, L.D.; Alvarez, A.J.

    1996-02-29

    Colloidal transport may increase the amount of contaminant material than that which could be transported by water flow alone. The role of colloids in groundwater contaminant transport is complicated and may involve many different processes, including sorption of elements onto colloidal particles, coagulation/dissolution, adsorption onto solid surfaces, filtration, and migration. Bacteria are known to concentrate minerals and influence the transport of compounds in aqueous environments and may also serve as organic colloids, thereby influencing subsurface transport of radionuclides and other contaminants. The initial phase of the project consisted of assembling a list of bacteria capable of sequestering or facilitating mineral transport. The development and optimization of the PCR amplification assay for the detection of the organisms of interest, and the examination of regional groundwaters for those organisms, are presented for subsequent research.

  3. Hydrogen emission under laser exposure of colloidal solutions of nanoparticles

    NASA Astrophysics Data System (ADS)

    Barmina, E. V.; Simakin, A. V.; Shafeev, G. A.

    2016-07-01

    We report the generation of molecular hydrogen from water by laser irradiation, without any electrodes and photocatalysts. A near infrared pulsed nanosecond laser is used for exposure of colloidal solution of Au nanoparticles suspended in water. Laser exposure of the colloidal solution results in formation of breakdown plasma in liquid and emission of H2. The rate of H2 emission depends critically on the energy of laser pulses. There is a certain threshold in laser fluence in liquid (around 50 J/cm2) below which plasma disappears and H2 emission stops. H2 emission from colloidal solution of Au nanoparticles in ethanol is higher than that from similar water colloid. It is found that formation of plasma and emission of H2 or D2 can be induced by laser exposure of pure liquids, either H2O or D2O, respectively. The results are interpreted as water molecules splitting by direct electron impact from breakdown plasma.

  4. Synthesis and characterization of colloidal fluorescent silver nanoclusters.

    PubMed

    Huang, Sherry; Pfeiffer, Christian; Hollmann, Jana; Friede, Sebastian; Chen, Justin Jin-Ching; Beyer, Andreas; Haas, Benedikt; Volz, Kerstin; Heimbrodt, Wolfram; Montenegro Martos, Jose Maria; Chang, Walter; Parak, Wolfgang J

    2012-06-19

    Ultrasmall water-soluble silver nanoclusters are synthesized, and their properties are investigated. The silver nanoclusters have high colloidal stability and show fluorescence in the red. This demonstrates that like gold nanoclusters also silver nanoclusters can be fluorescent.

  5. Charge-extraction strategies for colloidal quantum dot photovoltaics

    NASA Astrophysics Data System (ADS)

    Lan, Xinzheng; Masala, Silvia; Sargent, Edward H.

    2014-03-01

    The solar-power conversion efficiencies of colloidal quantum dot solar cells have advanced from sub-1% reported in 2005 to a record value of 8.5% in 2013. Much focus has deservedly been placed on densifying, passivating and crosslinking the colloidal quantum dot solid. Here we review progress in improving charge extraction, achieved by engineering the composition and structure of the electrode materials that contact the colloidal quantum dot film. New classes of structured electrodes have been developed and integrated to form bulk heterojunction devices that enhance photocharge extraction. Control over band offsets, doping and interfacial trap state densities have been essential for achieving improved electrical communication with colloidal quantum dot solids. Quantum junction devices that not only tune the optical absorption spectrum, but also provide inherently matched bands across the interface between p- and n-materials, have proven that charge separation can occur efficiently across an all-quantum-tuned rectifying junction.

  6. Collective behavior of chemotactic colloids: clusters, asters and oscillations

    NASA Astrophysics Data System (ADS)

    Saha, Suropriya; Golestanian, Ramin; Ramaswamy, Sriram

    2014-03-01

    Catalytic colloidal swimmers are a particularly promising example of systems that emulate properties of living matter, such as motility, gradient-sensing, signaling and replication. Here we present a comprehensive theoretical description of dynamics of an individual patterned catalytic colloid, leading controllably to chemotactic or anti-chemotactic behavior. We find that both the positional and the orientational degrees of freedom of the active colloids can exhibit condensation, signaling formation of clusters and asters. The kinetics of catalysis introduces a natural control parameter for the range of the interaction mediated by the diffusing chemical species. For various regimes in parameter space in the long-ranged limit our system displays precise analogs to gravitational collapse, plasma oscillations and electrostatic screening. We present prescriptions for how to tune the surface properties of the colloids during fabrication to achieve each type of behavior.

  7. Bulk synthesis of polymer-inorganic colloidal clusters.

    PubMed

    Perro, Adeline; Manoharan, Vinothan N

    2010-12-21

    We describe a procedure to synthesize colloidal clusters with polyhedral morphologies in high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. We show that the synthesis initially used for silica-polystyrene hybrid clusters can be generalized to create clusters from other inorganic and polymer particles. We also show that high yields of particular morphologies can be obtained by precise control of the inorganic seed particle size, a finding that can be explained using a hard-sphere packing model. These clusters can be further chemically modified for a variety of applications. Introducing a cross-linker leads to colloidal clusters that can be index matched in an appropriate solvent, allowing them to be used for particle tracking or optical studies of colloidal self-assembly. Also, depositing a thin silica layer on these colloids allows the surface properties to be controlled using silane chemistry.

  8. Universal Hydrodynamic Mechanisms for Crystallization in Active Colloidal Suspensions

    NASA Astrophysics Data System (ADS)

    Singh, Rajesh; Adhikari, R.

    2016-11-01

    The lack of detailed balance in active colloidal suspensions allows dissipation to determine stationary states. Here we show that slow viscous flow produced by polar or apolar active colloids near plane walls mediates attractive hydrodynamic forces that drive crystallization. Hydrodynamically mediated torques tend to destabilize the crystal but stability can be regained through critical amounts of bottom heaviness or chiral activity. Numerical simulations show that crystallization is not nucleational, as in equilibrium, but is preceded by a spinodal-like instability. Harmonic excitations of the active crystal relax diffusively but the normal modes are distinct from an equilibrium colloidal crystal. The hydrodynamic mechanisms presented here are universal and rationalize recent experiments on the crystallization of active colloids.

  9. Colloidal-crystal-assisted patterning of crystalline materials.

    PubMed

    Li, Cheng; Qi, Limin

    2010-04-06

    Colloidal crystals have shown great potential as versatile templates for the fabrication of patterned micro- and nanostructures with complex architectures and novel properties. The patterning of functional crystalline materials in two and three dimensions is essential to the realization of their applications in many technologically important fields. This article highlights some recent progress in the fabrication of 2D and 3D patterned crystalline materials with the assistance of colloidal crystals. By combining a bioinspired synthetic strategy based on a transient amorphous phase with a colloidal-crystal templating method, unique 3D ordered macroporous (3DOM) calcite single crystals can be created. Moreover, patterned arrays of regular ZnO nanopillars with controlled size, shape, and orientation can be fabricated via a facile wet chemical approach by using masks derived from monolayer colloidal crystals (MCC).

  10. Key role of hydrodynamic interactions in colloidal gelation.

    PubMed

    Furukawa, Akira; Tanaka, Hajime

    2010-06-18

    Colloidal gelation is caused by the formation of a percolated network of colloidal particles suspended in a liquid. Thus far the major transport process leading to gelation has been believed to be the brownian diffusion of particles. Contrary to this common belief, we reveal by numerical simulations that many-body hydrodynamic interactions between colloidal particles also play an essential role in gelation: They significantly promote gelation, or lower the colloid volume fraction threshold for percolation, as compared to their absence. We find that the incompressible nature of a liquid component and the resulting self-organization of hydrodynamic flow with a transverse (rotational) character are responsible for this enhancement of network-forming ability.

  11. Characterization of Gorleben groundwater colloids by atomic force microscopy.

    PubMed

    Plaschke, M; Römer, J; Kim, J I

    2002-11-01

    Groundwater colloids from the Gorleben site (Lower Saxony, Germany) are characterized in the presence of Eu(III) by tapping-mode atomic force microscopy (AFM) with phase contrast imaging. Using a liquid cell the method allows investigations of samples being in contact with aqueous solution. This ensures that complex structures are kept in their native hydrated state. Different types of colloids and aggregates are found by AFM, e.g., spherical particles, fibrous structures, and structures which appear to be hollow. A partial coating of the edges of clay particles with humic colloids can be assumed from phase contrast images. Therefore, aquatic colloids and their aggregates found in Gorleben groundwater can be characterized as a complex mixture of components, which may influence the migration of groundwater contaminants in different processes.

  12. Elasto-hydrodynamic network analysis of colloidal gels

    NASA Astrophysics Data System (ADS)

    Swan, James; Varga, Zsigmond

    Colloidal gels formed at low particle volume fractions result from a competition between two rate processes: aggregation of colloids and compaction of pre-gel aggregates. Recent work has shown that the former process is highly sensitive to the nature of the hydrodynamic interactions between suspended colloids. This same sensitivity to hydrodynamic flows within the gel leads to pronounced differences in the spectrum of relaxation times and response to deformation of the gel. This talk explores those differences and their consequences through computational simulations and the framework of elasto-hydrodynamic network analysis. We demonstrate a significant impact of hydrodynamic interactions between gelled colloids on macroscopic gel dynamics and rheology as well as the effect of hydrodynamic screening in gelled materials.

  13. Charge-Controlled Colloids on Liquid-Liquid Interfaces

    NASA Astrophysics Data System (ADS)

    Kunz, Daniel A.; Reck, Bernd; Manoharan, Vinothan N.

    2014-03-01

    The tendency of colloidal particles to stabilize interfaces has been exploited for many years to generate Pickering emulsions with a variety of industrial applications. However, the exact stabilization mechanism and its dependence on the surface properties of the colloidal particles are not yet fully understood. We provide new interfacial studies on the nonequilibrium dynamics of a colloidal system with tunable surface charge density. We push individual sub-micron colloidal particles towards an oil-water interface and track their motion in three-dimensions using holographic microscopy to examine the influence of zeta potential on the dynamics of the system. This project was funded by the BASF Advanced Research Initiative, BASF SE, Germany.

  14. Colloidal stability of iron oxide nanoparticles with multivalent polymer surfactants.

    PubMed

    Choi, Young-Wook; Lee, Hoik; Song, Youngjun; Sohn, Daewon

    2015-04-01

    This paper introduces a new approach for preparing magnetic colloidal suspensions with electrostatic repulsion between particles and polyelectrolyte surfactants. The surface charge of the iron oxide particles was positive in acidic aqueous conditions; however the surface charge of the colloid was negative in basic aqueous conditions due to the amphoteric property of Fe2O3. The long-term colloidal stability and particle distribution of the multivalent charged polymers, Poly(4-vinylbenzenesulfonate sodium salt) (PSS), Poly(acrylic acid) (PAA), and Poly(allylamine hydrochloride) (PAH) were compared with the monovalent surfactant sodium dodecyl sulfate (SDS). Both mono- and multivalent surfactant molecules showed good colloidal stability for extended periods of time. However, the particle distribution was dependent on the hydrophobicity of the surfactants' functional groups. Polyelectrolytes with a negatively charged functional group showed good long-term stability of particles and a narrow particle distribution regardless of the acid dissociation constant (pKa) of the polymer.

  15. Observation of a microcrystalline gel in colloids with competing interactions.

    PubMed

    Zhang, Tian Hui; Groenewold, Jan; Kegel, Willem K

    2009-12-14

    A stable short-range crystalline structure is observed in colloidal systems with competing short-range attractions and long-range repulsions. We term these structures "microcrystalline gels" as the microcrystals are embedded in a dense disordered network.

  16. 1. LOOKING EAST FROM 127125 JACKSON AVENUE (INDUSTRIAL COLLOIDS AND ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. LOOKING EAST FROM 127-125 JACKSON AVENUE (INDUSTRIAL COLLOIDS AND CHEMICALS, INC.) TO SULLIVAN'S SALOON (in background, with domed roof) - Jackson Avenue Warehouse District, 101-131 & 120-122 Jackson Avenue, Knoxville, Knox County, TN

  17. DEMONSTRATION BULLETIN: COLLOID POLISHING FILTER METHOD - FILTER FLOW TECHNOLOGY, INC.

    EPA Science Inventory

    The Filter Flow Technology, Inc. (FFT) Colloid Polishing Filter Method (CPFM) was tested as a transportable, trailer mounted, system that uses sorption and chemical complexing phenomena to remove heavy metals and nontritium radionuclides from water. Contaminated waters can be pro...

  18. 99M-Technetium labeled tin colloid radiopharmaceuticals

    DOEpatents

    Winchell, Harry S.; Barak, Morton; Van Fleet, III, Parmer

    1976-07-06

    An improved 99m-technetium labeled tin(II) colloid, size-stabilized for reticuloendothelial organ imaging without the use of macromolecular stabilizers and a packaged tin base reagent and an improved method for making it are disclosed.

  19. A Simple Experiment Illustrating the Structure of Association Colloids.

    ERIC Educational Resources Information Center

    Friberg, Stig. E.; Bendiksen, Beverly

    1979-01-01

    The experiment described is intended to illustrate the intermolecular phenomena involved in association colloids. These are normal and inverse micelles and lyotropic liquid crystals. Solubilization, microemulsion and emulsion are discussed. (Author/SA)

  20. Fundamental and applied aspects of luminescence of colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Razumov, V. F.

    2017-03-01

    The spectral luminescent characteristics of colloidal quantum dots as a new class of luminophores are discussed and state-of-the-art investigations, problems, and prospects for their applications are considered.

  1. Sonochromic effect in WO{sup 3} colloidal suspensions

    SciTech Connect

    Kamat, P.V.; Vinodgopal, K.

    1996-11-13

    In recent years there has been a burst of activities in investigating sonolytic reactions. The usefulness of this technique in synthesizing colloidal semiconductors and metals and dissolution of MnO{sup 2} colloids has also been demonstrated. We have now employed semiconductor colloids to investigate the radical reactions in sonolytic processes. In this study we present our preliminary results from the reaction of WO{sup 3} colloids with sonolytically generated H atoms. Sodium tungstate, oxalic acid, and Acid Orange 7 were obtained from Aldrich. Acid Orange 7 was purified by column chromatography. All other chemicals were analytical reagents of highest available purity. The analysis experiments were carried out with a 640 kHz sonolysis setup of Ultrasonic Energy Systems (Panama City, FL). 24 refs., 4 figs.

  2. Modified spin-coating technique to achieve directional colloidal crystallization.

    PubMed

    Bartlett, Andrew P; Pichumani, Moorthi; Giuliani, Maximiliano; González-Viñas, Wenceslao; Yethiraj, Anand

    2012-02-14

    Fabricating large single crystals with colloidal spheres as building blocks is challenging and of competitive interest. Spin-coating of colloids offers a robust technique, which is highly reproducible in obtaining colloidal crystals even at fast dynamical regimes; however, these crystals are intrinsically polycrystalline due to the axial symmetry of spin-coating. We report a new method that applies a nonuniform electric field during the spin-coating process. By arranging the field direction to be stationary in the rotating frame, we are able to break the axial symmetry and to orient the colloids along one predefined direction. By regulating the applied field strength, we demonstrate local control over the orientation of the crystallites, and thus, the orientation is determined by the applied field strength.

  3. Controlled assembly of jammed colloidal shells on fluid droplets.

    PubMed

    Subramaniam, Anand Bala; Abkarian, Manouk; Stone, Howard A

    2005-07-01

    Assembly of colloidal particles on fluid interfaces is a promising technique for synthesizing two-dimensional microcrystalline materials useful in fields as diverse as biomedicine, materials science, mineral flotation and food processing. Current approaches rely on bulk emulsification methods, require further chemical and thermal treatments, and are restrictive with respect to the materials used. The development of methods that exploit the great potential of interfacial assembly for producing tailored materials have been hampered by the lack of understanding of the assembly process. Here we report a microfluidic method that allows direct visualization and understanding of the dynamics of colloidal crystal growth on curved interfaces. The crystals are periodically ejected to form stable jammed shells, which we refer to as colloidal armour. We propose that the energetic barriers to interfacial crystal growth and organization can be overcome by targeted delivery of colloidal particles through hydrodynamic flows. Our method allows an unprecedented degree of control over armour composition, size and stability.

  4. Smoothed Profile Method to Simulate Colloidal Particles in Complex Fluids

    NASA Astrophysics Data System (ADS)

    Yamamoto, Ryoichi; Nakayama, Yasuya; Kim, Kang

    A new direct numerical simulation scheme, called "Smoothed Profile (SP) method," is presented. The SP method, as a direct numerical simulation of particulate flow, provides a way to couple continuum fluid dynamics with rigid-body dynamics through smoothed profile of colloidal particle. Our formulation includes extensions to colloids in multicomponent solvents such as charged colloids in electrolyte solutions. This method enables us to compute the time evolutions of colloidal particles, ions, and host fluids simultaneously by solving Newton, advection-diffusion, and Navier-Stokes equations so that the electro-hydrodynamic couplings can be fully taken into account. The electrophoretic mobilities of charged spherical particles are calculated in several situations. The comparisons with approximation theories show quantitative agreements for dilute dispersions without any empirical parameters.

  5. Colloid Formation by Drugs in Simulated Intestinal Fluid

    PubMed Central

    2010-01-01

    Many organic molecules form colloidal aggregates in aqueous solution at micromolar concentrations. These aggregates promiscuously inhibit soluble proteins and are a major source of false positives in high-throughput screening. Several drugs also form colloidal aggregates, and there has been speculation that this may affect the absorption and distribution of at least one drug in vivo. Here we investigate the ability of drugs to form aggregates in simulated intestinal fluid. Thirty-three Biopharmaceutics Classification System (BCS) class II and class IV drugs, spanning multiple pharmacological activities, were tested for promiscuous aggregation in biochemical buffers. The 22 that behaved as aggregators were then tested for colloid formation in simulated intestinal fluid, a buffer mimicking conditions in the small intestine. Six formed colloids at concentrations equal to or lower than the concentrations reached in the gut, suggesting that aggregation may have an effect on the absorption and distribution of these drugs, and potentially others, in vivo. PMID:20426472

  6. Linking Colloid Deposit Morphology and Clogging in Porous Media

    NASA Astrophysics Data System (ADS)

    Roth, E. J.; Mont-eton, M. E.; Mays, D. C.

    2012-12-01

    Innovations in the field of groundwater remediation have been hampered by delivery limitations in the porous media. For example, colloid deposits (comprising clays or silts) can cause a detrimental reduction in permeability, or clogging, which is problematic for groundwater remediation as well as granular media filtration and aquifer storage and recovery. During remediation, clogging creates preferential pathways in the media, leading to localized rather than spatially extensive contaminant treatment. Consequentially, remediation efforts become more expensive, less effective, and take a very long time. This presentation describes ongoing research investigating the link between colloid deposit morphology and clogging in porous media. As described by Darcy's Law, the velocity of fluid flow through porous media is proportional to permeability, which depends, in part, on porosity. However, changes in permeability are not in accord with changes in porosity as predicted by the Kozeny-Carman equation. It is hypothesized that unmeasured aspects of colloid deposit morphology could be the cause of this anomaly. Colloidal phenomena have important and dynamic effects on the permeability of natural porous media, and several lines of evidence suggest a correlation between clogging in porous media and the fractal dimension of colloid deposits. Here, a custom-built static light scattering apparatus is used to measure the fractal dimension of colloid deposits in refractive index matched porous media within a flow column. The media in our flow column is Nafion, which becomes essentially invisible when saturated by a solution of isopropanol and water. Polystyrene microspheres are then added to the influent through the column as a surrogate for natural colloids. Light from a laser is passed through the column, scattering from the deposited colloids, but not from the index matched Nafion. The resulting intensity of scattered light is measured as a function of scattering angle, and then

  7. {Quantification of Colloidal Blocking by Humic Acids in Porous Media

    NASA Astrophysics Data System (ADS)

    Yang, X.; Flynn, R.; von der Kammer, F.; Hofmann, T.

    2009-04-01

    Humic acids (humics), resulting from the partial decomposition of organic matter, occur widely in nature and form a major constituent of environmental natural organic matter (NOM). Although their ability to promote the dissolution of many substances has been widely recognized, quantification of the influence of humics on the fate and transport of particulate matter has proven less conclusive. One dimensional dynamic column tests involving the injection of suspensions of fluorescence stained 200nm latex microspheres (microspheres) and Suwannee River Humic Acid (SRHA) through columns filled with partly iron-coated quartz sand permitted the influence of humics on colloid deposition in water saturated porous media under controlled conditions to be studied. Tests consisted of two series of experiments. The first involved the injection of an initial pulse of 13 pore volumes (PV) of 10.4ppm microspheres that resulted in a gradual rise in the colloid's concentration in the column effluent to 8.4% of that injected. Injection of further two identical pulses of 13 PV of colloid, separated by pulses of about 10 PV of colloid-free flushing water resulted in a sustained rise in effluent concentration in the breakthrough of successive pulses. Colloid response, modeled using a random sequential adsorption (RSA) model, suggested that the system required the deposition 1.35x1010 colloids on the sand surface for each 1% rise in relative concentration observed in column effluent. The second series of experiments involved the injection of an initial pulse of 13 pore volumes of colloid suspension followed by the injection of four pore volumes of 5 mg/l SRHA. A mass balance of column effluent suggested that the column retained 98.8% of SRHA injected. Subsequent injection of a second pulse of 13 PV of microspheres saw colloidal concentration breakthrough in column effluent jump to 16% after which it continued to rise at a rate comparable to that in SRHA-free experiments. RSA modeling of

  8. Generation of colloidal granules and capsules from double emulsion drops

    NASA Astrophysics Data System (ADS)

    Hess, Kathryn S.

    Assemblies of colloidal particles are extensively used in ceramic processing, pharmaceuticals, inks and coatings. In this project, the aim was to develop a new technique to fabricate monodispersed colloidal assemblies. The use of microfluidic devices and emulsion processing allows for the fabrication of complex materials that can be used in a variety of applications. A microfluidic device is used to create monodispersed water/oil/water (w/o/w) double emulsions with interior droplets of colloidal silica suspension ranging in size from tens to hundreds of microns. By tailoring the osmotic pressure using glycerol as a solute in the continuous and inner phases of the emulsion, we can control the final volume size of the monodispersed silica colloidal crystals that form in the inner droplets of the double emulsion. Modifying the ionic strength in the colloidal dispersion can be used to affect the particle-particle interactions and crystal formation of the final colloidal particle. This w/o/w technique has been used with other systems of metal oxide colloids and cellulose nanocrystals. Encapsulation of the colloidal suspension in a polymer shell for the generation of ceramic-polymer core-shell particles has also been developed. These core-shell particles have spawned new research in the field of locally resonant acoustic metamaterials. Systems and chemistries for creating cellulose hydrogels within the double emulsions have also been researched. Water in oil single emulsions and double emulsions have been used to create cellulose hydrogel spheres in the sub-100 micron diameter range. Oil/water/oil double emulsions allow us to create stable cellulose capsules. The addition of a second hydrogel polymer, such as acrylate or alginate, further strengthens the cellulose gel network and can also be processed into capsules and particles using the microfluidic device. This work could have promising applications in acoustic metamaterials, personal care products, pharmaceuticals

  9. Synthesis of colloidal solutions with silicon nanocrystals from porous silicon

    PubMed Central

    2014-01-01

    In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm-2, 1 A cm-2, and 1.2 A cm-2. Thus obtained, PSi was mechanically pulverized in a mortar agate; then, the PSi powders were poured into different solutions to get the final Si-ncs colloidal solutions. The different optical, morphological, and structural characteristics of the colloidal solutions with Si-ncs were measured and studied. These Si-ncs colloidal solutions, measured by photoluminescence (PL), revealed efficient blue-green or violet emission intensities. The results of X-ray diffraction (XRD) indicate that the colloidal solutions are mainly composed of silicon nanocrystallites. The result of UV–vis transmittance indicates that the optical bandgap energies of the colloidal solutions varied from 2.3 to 3.5 eV for colloids prepared in methanol, ethanol, and acetone. The transmission electron microscopy (TEM) images showed the size of the nanocrystals in the colloidal solutions. Fourier transform infrared spectroscopy (FTIR) spectra showed different types of chemical bonds such as Si-O-Si, Si-CH2, and SiH x , as well as some kind of defects. PACS 61.46Df.-a; 61.43.Gt; 61.05.cp; 78.55.-m; 81.15.Gh PMID:25324709

  10. SANS (small-angle neutron scattering) from polymers and colloids

    SciTech Connect

    Hayter, J.B.

    1987-01-01

    Small-angle neutron scattering (SANS) has been remarkably successful in providing detailed quantitative structural information on complex everyday materials, such as polymers and colloids, which are often of considerable industrial as well as academic interest. This paper reviews some recent SANS experiments on polymers and colloids, including ferrofluids, and discusses the use of these apparently complex systems as general physical models of the liquid or solid state.

  11. Fourier-transform light scattering of individual colloidal clusters.

    PubMed

    Yu, HyeonSeung; Park, HyunJoo; Kim, Youngchan; Kim, Mahn Won; Park, YongKeun

    2012-07-01

    We present measurements of the scalar-field light scattering of individual dimer, trimer, and tetrahedron shapes among colloidal clusters. By measuring the electric field with quantitative phase imaging at the sample plane and then numerically propagating to the far-field scattering plane, the two-dimensional light-scattering patterns from individual colloidal clusters are effectively and precisely retrieved. The measured scattering patterns are consistent with simulated patterns calculated from the generalized multiparticle Mie solution.

  12. Orientational structure of dipolar hard-spherical colloids.

    PubMed

    Alarcón-Waess, O; Diaz-Herrera, E; Gil-Villegas, A

    2002-03-01

    We have studied the orientational structure of a dipolar hard-spherical colloid on a homogeneous isotropic phase. The results are expressed as a function of the dipolar strength mu and volume fraction phi of dipolar colloids, and the refractive index of the scattering medium, n(s). The study is based on the self-correlation of the orientation density of the dipolar colloids, which is the static orientational structure factor [F(q)], where q is the wave vector. The importance of this quantity is that for very low phi values, it can be probed in a depolarized light scattering experiment. We have found that the structure of the suspension is better observed for high n(s). F(q) presents a different behavior for dilute and dense concentrations, it is also observed that the position of its minimum depends on phi. The response of a dipolar colloid due to its collective orientational behavior is also studied, using as an "ordering parameter" the static orientational structure factor at q=0[F(q=0)]. The study is performed for isochores as a function of mu. We have divided the analysis into five regimes, from very low to very high phi; values, i.e., phi=0.005 24, 0.1, 0.2, 0.35, and 0.45. Our analysis suggests that the dipolar colloid evolves to an orientationally ordered phase when the dipolar strength is increased, for all concentrations except for the lowest value case, phi=0.005 24. When phi=0.1 the dipolar colloid reaches the transition suddenly, whereas for the very low regime, the slope of F(q=0) first increases as if the dipolar colloid would evolve to an orientationally ordered phase; but near the transition the slope is inverted, resulting in a no global orientational order. Thus, our results suggest that in the very low regime a dipolar colloid may have a reentrant transition.

  13. Porous Emitter Colloid Thruster Performance Characterization Using Optical Techniques

    DTIC Science & Technology

    2013-03-01

    Pressure change Pa dP Internal droplet pressure Pa inP Input power W jetP Jet power W tP Tank pressure Pa P Atmospheric pressure Pa Q...KJLC 979 pressure transducer used on bell vacuum chamber. ........................ 45 Figure 10. Zeiss Discovery V12 light microscope used to...systems. First, hazardous chemicals and high pressure vessels are avoided with the colloid thruster. Second, the colloid thruster has the ability

  14. Binary Colloidal Alloy Test-3 and 4: Critical Point

    NASA Technical Reports Server (NTRS)

    Weitz, David A.; Lu, Peter J.

    2007-01-01

    Binary Colloidal Alloy Test - 3 and 4: Critical Point (BCAT-3-4-CP) will determine phase separation rates and add needed points to the phase diagram of a model critical fluid system. Crewmembers photograph samples of polymer and colloidal particles (tiny nanoscale spheres suspended in liquid) that model liquid/gas phase changes. Results will help scientists develop fundamental physics concepts previously cloaked by the effects of gravity.

  15. Causes and implications of colloid and microorganism retention hysteresis.

    PubMed

    Bradford, Scott A; Kim, Hyunjung

    2012-09-01

    Experiments were designed to better understand the causes and implications of colloid and microorganism retention hysteresis with transients in solution ionic strength (IS). Saturated packed column experiments were conducted using two sizes of carboxyl modified latex (CML) microspheres (0.1 and 1.1 μm) and microorganisms (coliphage φX174 and E. coli D21g) under various transient solution chemistry conditions, and 360 μm Ottawa sand that was subject to different levels of cleaning, namely, a salt cleaning procedure that removed clay particles, and a salt+acid cleaning procedure that removed clay and reduced microscopic heterogeneities due to metal oxides and surface roughness. Comparison of results from the salt and salt+acid treated sand indicated that microscopic heterogeneity was a major contributor to colloid retention hysteresis. The influence of this heterogeneity increased with IS and decreasing colloid/microbe size on salt treated sand. These trends were not consistent with calculated mean interaction energies (the secondary minima), but could be explained by the size of the electrostatic zone of influence (ZOI) near microscopic heterogeneities. In particular, the depth of local minima in the interaction energy has been predicted to increase with a decrease in the ZOI when the colloid size and/or the Debye length decreased (IS increased). The adhesive interaction was therefore largely irreversible for smaller sized 0.1 μm CML colloids, whereas it was reversible for larger 1.1 μm CML colloids. Similarly, the larger E. coli D21g exhibited greater reversibility in retention than φX174. However, direct comparison of CML colloids and microbes was not possible due to differences in size, shape, and surface properties. Retention and release behavior of CML colloids on salt+acid treated sand was much more consistent with mean interaction energies due to reduction in microscopic heterogeneities.

  16. Causes and implications of colloid and microorganism retention hysteresis

    NASA Astrophysics Data System (ADS)

    Bradford, Scott A.; Kim, Hyunjung

    2012-09-01

    Experiments were designed to better understand the causes and implications of colloid and microorganism retention hysteresis with transients in solution ionic strength (IS). Saturated packed column experiments were conducted using two sizes of carboxyl modified latex (CML) microspheres (0.1 and 1.1 μm) and microorganisms (coliphage φX174 and E. coli D21g) under various transient solution chemistry conditions, and 360 μm Ottawa sand that was subject to different levels of cleaning, namely, a salt cleaning procedure that removed clay particles, and a salt + acid cleaning procedure that removed clay and reduced microscopic heterogeneities due to metal oxides and surface roughness. Comparison of results from the salt and salt + acid treated sand indicated that microscopic heterogeneity was a major contributor to colloid retention hysteresis. The influence of this heterogeneity increased with IS and decreasing colloid/microbe size on salt treated sand. These trends were not consistent with calculated mean interaction energies (the secondary minima), but could be explained by the size of the electrostatic zone of influence (ZOI) near microscopic heterogeneities. In particular, the depth of local minima in the interaction energy has been predicted to increase with a decrease in the ZOI when the colloid size and/or the Debye length decreased (IS increased). The adhesive interaction was therefore largely irreversible for smaller sized 0.1 μm CML colloids, whereas it was reversible for larger 1.1 μm CML colloids. Similarly, the larger E. coli D21g exhibited greater reversibility in retention than φX174. However, direct comparison of CML colloids and microbes was not possible due to differences in size, shape, and surface properties. Retention and release behavior of CML colloids on salt + acid treated sand was much more consistent with mean interaction energies due to reduction in microscopic heterogeneities.

  17. Melting line of charged colloids from primitive model simulations.

    PubMed

    Hynninen, Antti-Pekka; Dijkstra, Marjolein

    2005-12-22

    We develop an efficient simulation method to study suspensions of charged spherical colloids using the primitive model. In this model, the colloids and the co- and counterions are represented by charged hard spheres, whereas the solvent is treated as a dielectric continuum. In order to speed up the simulations, we restrict the positions of the particles to a cubic lattice, which allows precalculation of the Coulombic interactions at the beginning of the simulation. Moreover, we use multiparticle cluster moves that make the Monte Carlo sampling more efficient. The simulations are performed in the semigrand canonical ensemble, where the chemical potential of the salt is fixed. Employing our method, we study a system consisting of colloids carrying a charge of 80 elementary charges and monovalent co- and counterions. At the colloid densities of our interest, we show that lattice effects are negligible for sufficiently fine lattices. We determine the fluid-solid melting line in a packing fraction eta-inverse screening length kappa plane and compare it with the melting line of charged colloids predicted by the Yukawa potential of the Derjaguin-Landau-Verwey-Overbeek theory. We find qualitative agreement with the Yukawa results, and we do not find any effects of many-body interactions. We discuss the difficulties involved in the mapping between the primitive model and the Yukawa model at high colloid packing fractions (eta>0.2).

  18. Non-equilibrium phenomena in disordered colloidal solids

    NASA Astrophysics Data System (ADS)

    Yunker, Peter

    Colloidal particles are a convenient tool for studying a variety of non-equilibrium phenomena. I will discuss experiments that investigate the aging and non-equilibrium growth of disordered solids. In the first set of experiments, colloidal glasses are rapidly formed to study aging in jammed packings. A colloidal fluid, composed of micron-sized temperature-sensitive pNIPAM particles, is rapidly quenched into a colloidal glass. After the glass is formed, collective rearrangements occur as the glass ages. Particles that undergo irreversible rearrangements, which break nearest-neighbor pairings and allow the glass to relax, are identified. These irreversible rearrangements are accompanied by large clusters of fast moving particles; the number of particles involved in these clusters increases as the glass ages, leading to the slowing of dynamics that is characteristic of aging. In the second set of experiments, we study the role particle shape, and thus, interparticle interaction, plays in the formation of disordered solids with different structural and mechanical properties. Aqueous suspensions of colloidal particles with different shapes evaporate on glass slides. Convective flows during evaporation carry particles from drop center to drop edge, where they accumulate. The resulting particle deposits grow heterogeneously from the edge on the air-water interface. Three distinct growth processes were discovered in the evaporating colloidal suspensions by tuning particle shape-dependent capillary interactions and thus varying the microscopic rules of deposition. Mechanical testing of these particulate deposits reveals that the deposit bending rigidity increases as particles become more anisotropic in shape.

  19. Temperature dependence of the colloidal agglomeration inhibition: computer simulation study.

    PubMed

    Barcenas, Mariana; Douda, Janna; Duda, Yurko

    2007-09-21

    There exist experimental evidences that the structure and extension of colloidal aggregates in suspensions change dramatically with temperature. This results in an associated change in the suspension rheology. Experimental studies of the inhibitor applications to control the particle clustering have revealed some unexpected tendencies. Namely, the heating of colloidal suspensions has provoked either extension or reduction of the colloidal aggregates. To elucidate the origin of this behavior, we investigate the influence of temperature on the stabilizing effect of the inhibitor, applying an associative two-component fluid model. Our results of the canonical Monte Carlo simulations indicate that the anomalous effect of the temperature may not be necessarily explained by the temperature dependent changes in the inhibitor tail conformation, as has been suggested recently by Won et al. [Langmuir 21, 924 (2005)]. We show that the competition between colloid-colloid and colloid-inhibitor associations, which, in turn, depends on the temperature and the relative concentrations, may be one of the main reasons for the unexpected temperature dependence of inhibitor efficacy.

  20. Interaction of latex colloids with mineral surfaces and Grimsel granodiorite.

    PubMed

    Filby, A; Plaschke, M; Geckeis, H; Fanghänel, Th

    2008-12-12

    Bentonite clay is considered as possible backfill material for nuclear waste repositories in crystalline rock. The same material may also be a source of clay colloids, which may act as carriers for actinide ions possibly released from the repository. Depending on the geochemical parameters, these colloids may be retained by interaction with mineral surfaces of the host rock. In the present study interaction of carboxylated fluorescent latex colloids, used as a model for bentonite colloids, with natural Grimsel granodiorite and some of its component minerals is studied by fluorescence microscopy and SEM/EDX. The experiments are carried out by varying the pH from 2-10. Strong adsorption is observed at pH values close to or below the points of zero charge (pHpzc) of the mineral surfaces. The influence of Eu(III), used as a chemical homologue for trivalent actinide ions, on colloid adsorption is investigated. Depending on mineral phase and pH, a significant increase of colloid adsorption is observed in the presence of Eu(III).

  1. Sedimentation of Colloidal Particles through a Polymer Solution

    NASA Astrophysics Data System (ADS)

    Tong, Penger; Ye, Xi; Ackerson, Bruce J.

    1997-03-01

    We report recent sedimentation measurements of colloidal particles through a polymer solution. The colloidal particles used were sterically stabilized CaCO3 suspended in decane and the polymer was hydrogenated polyisoprene. Our previous light and neutron scattering measurements have shown that the polymer chains do not adsorb onto the colloidal surfaces. Using a commercial ultracentrifuge, we measured the sedimentation rate of the colloidal particles, from which the microscopic viscosity experienced by the particles was obtained at different polymer concentration C_p. The experiment reveals that at low colloid concentration φ_c, the particles feel the single-chain viscosity when their size Rh is smaller than the correlation length ξ of the polymer solution. The particles experience the macroscopic viscosity of the polymer solution when Rh >> ξ. The transition for the particles to feel the macroscopic viscosity is well described by a switch function f_c(C_p)=exp[-(C_0/C_p)^α], which can be written as a function of R_h/ξ. It is found that f_c(C_p) is independent of the polymer molecular weight. As φc increases, the colloidal particles feel more and more depletion attraction and their settling velocity increases with increasing C_p.

  2. Surface forces of colloidal particles from micrometer to nanometer

    NASA Astrophysics Data System (ADS)

    Cho, Jeong-Min

    2003-10-01

    Surface forces of colloidal particles play critical roles in the macroscopic behavior of particulate systems such as dispersion and coagulation, adhesion and coating, and the rheological behavior of ceramic slurries. As particle size is decreased from micrometer to nanometer range, surface forces are increasingly important. Polyelectrolytes are the chemical additives commonly used to efficiently control the stabilization of the colloidal system. Their conformations on the solid surfaces as well as the interactions between the adsorbed polyelectrolytes are important issues in colloidal processing. Most experimental and theoretical approaches to the surface forces are based on particle sizes in the micrometer range. However, nanoparticles at close proximity or high solids loading are expected to show different behavior than what can be estimated from conventional theories such as continuum or mean field theories. My study examined the effect of pH, ionic strength, and molecular weight of the polyelectrolytes on the surface forces of colloidal particles by the interplay with the adsorption, turbidity, and direct surface force measurement in terms of the conformation on the solid surfaces. The colloid probe technique based on atomic force microscopy (AFM) is well established for micron size particles; and could be extended for nanosize particles by using carbon nanotubes as proximal probes. Nanotubes with their high aspect ratio avoid the contribution from cone shapes that happens with AFM tips. The difference in particle size significantly influences surface forces for sterically dispersed colloidal systems.

  3. Interaction of latex colloids with mineral surfaces and Grimsel granodiorite

    NASA Astrophysics Data System (ADS)

    Filby, A.; Plaschke, M.; Geckeis, H.; Fanghänel, Th.

    2008-12-01

    Bentonite clay is considered as possible backfill material for nuclear waste repositories in crystalline rock. The same material may also be a source of clay colloids, which may act as carriers for actinide ions possibly released from the repository. Depending on the geochemical parameters, these colloids may be retained by interaction with mineral surfaces of the host rock. In the present study interaction of carboxylated fluorescent latex colloids, used as a model for bentonite colloids, with natural Grimsel granodiorite and some of its component minerals is studied by fluorescence microscopy and SEM/EDX. The experiments are carried out by varying the pH from 2-10. Strong adsorption is observed at pH values close to or below the points of zero charge (pH pzc) of the mineral surfaces. The influence of Eu(III), used as a chemical homologue for trivalent actinide ions, on colloid adsorption is investigated. Depending on mineral phase and pH, a significant increase of colloid adsorption is observed in the presence of Eu(III).

  4. Assembly of colloidal strings in a simple fluid flow

    NASA Astrophysics Data System (ADS)

    Abe, Yu; Francis, Lorraine; Cheng, Xiang

    Colloidal particles self-assemble into ordered structures ranging from face- and body-centered cubic crystals to binary ionic crystals and to kagome lattices. Such diverse micron-scale structures are of practical importance for creating photonic materials and also of fundamental interest for probing equilibrium and non-equilibrium statistical mechanics. As a particularly interesting example, 1D colloidal strings provide a unique system for investigating non-equilibrium dynamics of crystal lattices. Here, we report a simple experimental method for constructing 1D colloidal crystals, where colloidal particles self-assemble into flow-aligned string structures near solid boundary under unidirectional flows. Using fast confocal microscopy, we explore the degree of particle alignment as functions of flow rate, particle concentrations, wetting properties of solid boundary and ionic strength of solvent. Through our systematic experiments, we show that these colloidal strings arise from hydrodynamic coupling, facilitated by electrostatic attractions between particles and the boundary. Compared with previous methods, our work provides a much simpler experimental procedure for assembling a large number of colloidal strings.

  5. Physics of Colloids in Space-2 (PCS-2)

    NASA Technical Reports Server (NTRS)

    Sankaran, Subramanian; Gasser, Urs; Manley, Suliana; Valentine, Megan; Prasad, Vikram; Rudhardt, Daniel; Bailey, Arthur; Dinsmore, Anthony; Segre, Phil; Doherty, Michael P.

    2001-01-01

    The Physics of Colloids-2 (PCS-2) experiment is aimed at investigating the basic physical properties of several types of colloidal suspensions. The three broad classes of colloidal systems of interest are binary colloids, colloid-polymer mixtures, and fractal gels. The objective is to understand their phase behavior as well as the kinetics of the phase transitions in the absence of gravity. The nucleation, growth, and morphology characteristics of the crystals and gels that form would be studied using confocal microscopy. These will be observed directly with excellent time resolution, and therefore extensive information about the different phases and their growth mechanisms will be gained. With the laser tweezers, it will be possible to measure the strength of these structures and to modify them in a controlled way, and the spectrophotometer will provide the possibility to probe their optical properties. We believe that this experiment will provide the basis for future 'colloid engineering' in which complicated structures with novel properties (e.g., photonic crystals) will be grown by controlled self-assembly.

  6. Microwave-accelerated ultrafast nanoparticle aggregation assays using gold colloids.

    PubMed

    Aslan, Kadir; Geddes, Chris D

    2007-03-01

    In this paper, the proof of principle of microwave-accelerated aggregation assay technology, which shortens the solution-based aggregation assays' run time to seconds (>100-fold increase in kinetics) with microwave heating, was demonstrated using a model aggregation assay based on the well-known interactions of biotin and avidin. Biotinylated gold colloids were aggregated in solution with the addition of streptavidin, which takes 20 min at room temperature to reach >90% completion and only 10 s with microwave heating. The initial velocity (after 1-s microwave heating) of the biotinylated gold colloids reaches up to 10.5 m/s, which gives rise to greater sampling of the total volume but not a large increase in bulk temperature. The room-temperature, steady-state velocity of the colloids was <0.5 microm/s. In control experiments, where streptavidin preincubated with d-biotin in solution is added to biotinylated gold colloids and microwave heated, gold colloids did not aggregate, demonstrating that nonspecific interactions between biotinylated gold colloids and streptavidin were negligible.

  7. Solidification of a Charged Colloidal Dispersion Investigated Using Microfluidic Pervaporation.

    PubMed

    Ziane, Nadia; Salmon, Jean-Baptiste

    2015-07-28

    We investigate the dynamics of solidification of a charged colloidal dispersion using an original microfluidic technique referred to as micropervaporation. This technique exploits pervaporation within a microfluidic channel to extract the solvent of a dilute colloidal dispersion. Pervaporation concentrates the colloids in a controlled way up to the tip of the channel until a wet solid made of closely packed colloids grows and invades the microfluidic channel. For the charged dispersion under study, we however evidence a liquid to solid transition (LST) preceding the formation of the solid, owing to the presence of long-range electrostatic interactions. This LST is associated with the nucleation and growth of domains confined in the channel. These domains are then compacted anisotropically up to forming a wet solid of closely packed colloids. This solid then invades the whole channel as in directional drying with a growth rate which depends on the microfluidic geometry. In the final steps of the solidification, we observed the occurrence of cracks and shear bands, the delamination of the wet solid from the channel walls, and its invasion by a receding air front. Interestingly, this air front follows specific patterns within the solid which reveal different microscopic colloidal organizations.

  8. Self-assembly of active colloidal molecules with dynamic function

    NASA Astrophysics Data System (ADS)

    Soto, Rodrigo; Golestanian, Ramin

    Catalytically active colloids maintain non-equilibrium conditions in which they produce and deplete chemicals at their surface. While individual colloids that are symmetrically coated do not exhibit dynamical activity, the concentration fields resulting from their chemical activity decay as 1/r and produce gradients that attract or repel other colloids depending on their surface chemistry and ambient variables. This results in a non-equilibrium analogue of ionic systems, but with the remarkable novel feature of action-reaction symmetry breaking. In dilute conditions these active colloids join up to form molecules via generalized ionic bonds. Colloids are found to join up to form self-assembled molecules that could be inert or have spontaneous activity in the form of net translational velocity and spin depending on their symmetry properties and their constituents. As the interactions do not satisfy detailed-balance, it is possible to achieve structures with time dependent functionality. We study a molecule that adopts spontaneous oscillations and another that exhibits a run-and-tumble dynamics similar to bacteria. Our study shows that catalytically active colloids could be used for designing self-assembled structures that posses dynamical functionalities.

  9. Luminescent Colloidal Semiconductor Nanocrystals Containing Copper: Synthesis, Photophysics, and Applications.

    PubMed

    Knowles, Kathryn E; Hartstein, Kimberly H; Kilburn, Troy B; Marchioro, Arianna; Nelson, Heidi D; Whitham, Patrick J; Gamelin, Daniel R

    2016-09-28

    Copper-doped semiconductors are classic phosphor materials that have been used in a variety of applications for many decades. Colloidal copper-doped semiconductor nanocrystals have recently attracted a great deal of interest because they combine the solution processability and spectral tunability of colloidal nanocrystals with the unique photoluminescence properties of copper-doped semiconductor phosphors. Although ternary and quaternary semiconductors containing copper, such as CuInS2 and Cu2ZnSnS4, have been studied primarily in the context of their photovoltaic applications, when synthesized as colloidal nanocrystals, these materials have photoluminescence properties that are remarkably similar to those of copper-doped semiconductor nanocrystals. This review focuses on the luminescent properties of colloidal copper-doped, copper-based, and related copper-containing semiconductor nanocrystals. Fundamental investigations into the luminescence of copper-containing colloidal nanocrystals are reviewed in the context of the well-established luminescence mechanisms of bulk copper-doped semiconductors and copper(I) molecular coordination complexes. The use of colloidal copper-containing nanocrystals in applications that take advantage of their luminescent properties, such as bioimaging, solid-state lighting, and luminescent solar concentrators, is also discussed.

  10. Les modèles de calcul de dose en radiothérapie clinique

    NASA Astrophysics Data System (ADS)

    Rosenwald, J. C.

    1998-04-01

    In radiation therapy, it is important to know precisely the dose distribution in the target volume and in the critical organs. To be clinically applicable, the dose calculation models must account for the actual characteristics of the beams and for the tissue densities. An accuracy of 2% in low dose gradient regions and 2mm in high dose gradient is expected, while keeping the computation time consistent with an interactive approach. We describe and discuss briefly the dose calculation models currently used. En radiothérapie, il est indispensable d'avoir une connaissance précise de la dose délivrée dans le volume cible et dans les organes critiques avoisinants. Pour être utilisables cliniquement, les modèles de calcul doivent tenir compte des caractéristiques exactes des faisceaux utilisés et des densités des tissus. Une précision de l'ordre de 2% dans les régions à faible gradient de dose, et de 2mm dans les régions à fort gradient est nécessaire tout en conservant un temps de calcul compatible avec une approche interactive. Les modèles de calcul utilisés sont ici succintement décrits et commentés.

  11. Merging RANS & LES approaches in submesoscale modeling

    NASA Astrophysics Data System (ADS)

    Fock, B. H.; Schluenzen, K. H.

    2010-09-01

    Merging LES and RANS simulation is important for extending the application range of mesoscale models to the sub-mesoscale. Hence many traditional mesoscale modeling groups are currently working on adding LES capabilities to their models. To investigate the differences, which occur by switching from RANS to LES approaches, simulations with the METRAS and METRAS-LES (Fock, 2007) are presented. These differences are investigated in terms of effects caused by the choice of the computational grid and the sub-grid scale closures. Simulations of convective boundary layers on two different grids are compared to investigate the influence of vertical grid spacing and extension. One simulation is carried out on a high-resolution vertical homogeneous grid and the other with a vertical stretched grid, which has coarser resolution in higher altitudes. The stretched grid is vertical defined, as it would be done in the standard setup for the mesoscale model. Hence, this investigation shows to what amount the eddy resolving capabilities of a LES model is effected by the transition of the grid to a grid, which is vertically the same as typically used in mesoscale modeling. The differences, which occur by using different approaches for subgrid scale turbulence, are quantified and compared with the effects caused by the computational grid. Additional some details of the used LES SGS closure (Deardorff, 1980) are investigated. These details deal on evaluating the importance of the reduced characteristic filter length scale for stable stratification. But the main focus is on comparing RANS and LES and discussion of combination in a mixed turbulence scheme, which applies a the LES closure in the atmospheric boundary layer and a RANS based turbulence model in the stable atmosphere above. References: Deardorff J. W. (1980): Stratocumulus-capped mixed layers derived from a three-dimensional model. Boundary-Layer Meteorology. 18. (4). 495-527. DOI:10.1007/BF00119502 Fock B. H. (2007): METRAS

  12. Interfacial & colloidal aspects of lipid digestion.

    PubMed

    Wilde, P J; Chu, B S

    2011-06-09

    Amongst the main issues challenging the food manufacturing sector, health and nutrition are becoming increasingly important. Global concerns such as obesity, the ageing population and food security will have to be addressed. Food security is not just about assuring food supply, but is also about optimising nutritional delivery from the food that is available [1]. Therefore one challenge is to optimise the health benefits from the lipids and lipid soluble nutrients. Colloid scientists have an affinity for lipids because they are water insoluble, however this presents a challenge to the digestive system, which has to convert them to structures that are less insoluble so they are available for uptake. Despite this, the human digestive system is remarkably effective at digesting and absorbing most lipids. This is primarily driven through maximising energy intake, as lipids possess the highest calorific value, which was a survival trait to survive times of famine, but is now an underlying cause of obesity in developed countries with high food availability. The critical region here is the lipid-water interface, where the key reactions take place to solubilise lipids and lipid soluble nutrients. Digestive lipases have to adsorb to the oil water interface in order to hydrolyse triacylglycerols into fatty acids and mono glycerides, which accumulate at the interface [2], and inhibit lipase activity. Pancreatic lipase, which is responsible for the majority of lipid hydrolysis, also requires the action of bile salts and colipase to function effectively. Bile salts both aid the adsorption of co-lipase and lipase, and help solubilise the lipolysis products which have accumulated at the interface, into mixed micelles composing bile salts and a range of other lipids, to facilitate transport to the gut mucosal surface prior to uptake and absorption. The process can be affected by the lipid type, as shorter chain, fatty acids are more easily absorbed, whereas the uptake of longer

  13. Chancellor Water Colloids: Characterization and Radionuclide Associated Transport

    SciTech Connect

    Reimus, Paul William; Boukhalfa, Hakim

    2014-09-26

    Column transport experiments were conducted in which water from the Chancellor nuclear test cavity was transported through crushed volcanic tuff from Pahute Mesa. In one experiment, the cavity water was spiked with solute 137Cs, and in another it was spiked with 239/240Pu(IV) nanocolloids. A third column experiment was conducted with no radionuclide spike at all, although the 137Cs concentrations in the water were still high enough to quantify in the column effluent. The radionuclides strongly partitioned to natural colloids present in the water, which were characterized for size distribution, mass concentration, zeta potential/surface charge, critical coagulation concentration, and qualitative mineralogy. In the spiked water experiments, the unanalyzed portion of the high-concentration column effluent samples were combined and re-injected into the respective columns as a second pulse. This procedure was repeated again for a third injection. Measurable filtration of the colloids was observed after each initial injection of the Chancellor water into the columns, but the subsequent injections (spiked water experiments only) exhibited no apparent filtration, suggesting that the colloids that remained mobile after relatively short transport distances were more resistant to filtration than the initial population of colloids. It was also observed that while significant desorption of 137Cs from the colloids occurred after the first injection in both the spiked and unspiked waters, subsequent injections of the spiked water exhibited much less 137Cs desorption (much greater 137Cs colloid-associated transport). This result suggests that the 137Cs that remained associated with colloids during the first injection represented a fraction that was more strongly adsorbed to the mobile colloids than the initial 137Cs associated with the colloids. A greater amount of the 239/240

  14. Cross Interaction Drives Stratification in Drying Film of Binary Colloidal Mixtures

    NASA Astrophysics Data System (ADS)

    Zhou, Jiajia; Jiang, Ying; Doi, Masao

    2017-03-01

    When a liquid film of a colloidal solution consisting of particles of different sizes is dried on a substrate, the colloids often stratify, where smaller colloids are laid upon larger colloids. This phenomenon is counterintuitive because larger colloids which have a smaller diffusion constant, are expected to remain near the surface during the drying process, leaving a layer of larger colloids on top of smaller colloids. Here we show that the phenomenon is caused by the interaction between the colloids, and can be explained by a diffusion model accounting for the interaction between the colloids. By studying the evolution equations both numerically and analytically, we derive the condition at which the stratified structures are obtained.

  15. Analysis report for WIPP colloid model constraints and performance assessment parameters

    SciTech Connect

    Mariner, Paul E.; Sassani, David Carl

    2014-03-01

    An analysis of the Waste Isolation Pilot Plant (WIPP) colloid model constraints and parameter values was performed. The focus of this work was primarily on intrinsic colloids, mineral fragment colloids, and humic substance colloids, with a lesser focus on microbial colloids. Comments by the US Environmental Protection Agency (EPA) concerning intrinsic Th(IV) colloids and Mg-Cl-OH mineral fragment colloids were addressed in detail, assumptions and data used to constrain colloid model calculations were evaluated, and inconsistencies between data and model parameter values were identified. This work resulted in a list of specific conclusions regarding model integrity, model conservatism, and opportunities for improvement related to each of the four colloid types included in the WIPP performance assessment.

  16. [Characteristics of DNA adsorption and desorption in variable and constant charge soil colloids].

    PubMed

    Wang, Dai-Zhang; Wang, Shen-Yang; Jiang, Xin; Heng, Li-Sha; Tan, Jin-Fang; Liu, Shi-Liang; Cao, Yong-Xian

    2009-09-15

    The characteristics of adsorption and desorption of DNA by Red soil colloid, Latosol colloid, Chao colloid and Cinnamon colloid at different pH values were studied using a batch method. It showed that there was an increase of solution pH after adsorption of DNA by the four soil colloids in both NaCl and KCl electrolyte systems. The increasing ranges of pH values were in order of Red soil colloid > Latosol colloid > Chao colloid > Cinnamon colloid, and NaCl electrolyte system > KCl electrolyte system. The amounts of DNA adsorption on soil colloids decreased with the increase of pH value. The maximum amounts of DNA adsorption in different colloids were about 13.1-14.8 microg x mg(-1) when pH values were 2-4. The decreasing ranges of the amounts of DNA adsorption were about 5.5 microg x mg(-1) in NaCl electrolyte system and 2.1 Mg x mg(-1) in KCl electrolyte system in Red soil colloid and Latosol colloid after the rising of equilibrium solution pH from 4.2 to 8.6, whereas the remarked decreasing ranges of the adsorption amounts of DNA were about 8.3-12.2 microg x mg(-1) on Chao colloid and Cinnamon colloid in two electrolyte systems. The decreasing ranges of DNA adsorption were in order of the constant charge (Chao soil and Cinnamon) colloids > the variable charge (Red soil and Latosol) colloids. The differences of desorption on the variable and the constant charge colloids are very significant while the DNA adsorbed was desorbed with NaOAc solution and NaH2 PO4 solution. The desorption percent desorption of DNA as NaH2PO4 desorbent was 23.5%-40.2% larger on the variable charge colloids than 8.8%-21.6% on the constant charge of colloids at the three different solution pH values of 3, 5 and 7, while that as NaOAc desorbent was 72.3%-85.9% larger on the constant charge colloids than 10%-24.5% on the variable charge colloids. These results implied that the ligand exchange played a more important role in DNA adsorption on the variable charge colloids, and electrostatic

  17. Colloid-Mediated Transport of Pharmaceutical and Personal Care Products through Porous Media

    PubMed Central

    Xing, Yingna; Chen, Xijuan; Chen, Xin; Zhuang, Jie

    2016-01-01

    Pharmaceutical and personal care products (PPCPs) enter soils through reclaimed water irrigation and biosolid land applications. Colloids, such as clays, that are present in soil may interact with PPCPs and thus affect their fate and transport in the subsurface environment. This study addresses the influence of soil colloids on the sorption and transport behaviors of PPCPs through laboratory column experiments. Results show that the affinities of PPCPs for colloids vary with their molecular chemistry and solution ionic strength. The presence of colloids promotes the breakthrough of ciprofloxacin (over 90% sorbed on colloids) from ~4% to 30–40%, and the colloid-facilitated effect was larger at lower ionic strength (e.g., 2 mM). In comparison, the net effect of colloids on the transport of tetracycline (~50% sorbed on colloids) could be facilitation or inhibition, depending on solution chemistry. This dual effect of colloids is primarily due to the opposite response of migration of dissolved and colloid-bound tetracycline to the change in solution ionic strength. Colloids could also facilitate the transport of ibuprofen (~10% sorbed on colloids) by ~50% due likely to exclusion of dispersion pathways by colloid straining. This study suggests that colloids are significant carriers or transport promoters of some PPCPs in the subsurface environment and could affect their off-site environmental risks. PMID:27734948

  18. Colloid-Mediated Transport of Pharmaceutical and Personal Care Products through Porous Media

    NASA Astrophysics Data System (ADS)

    Xing, Yingna; Chen, Xijuan; Chen, Xin; Zhuang, Jie

    2016-10-01

    Pharmaceutical and personal care products (PPCPs) enter soils through reclaimed water irrigation and biosolid land applications. Colloids, such as clays, that are present in soil may interact with PPCPs and thus affect their fate and transport in the subsurface environment. This study addresses the influence of soil colloids on the sorption and transport behaviors of PPCPs through laboratory column experiments. Results show that the affinities of PPCPs for colloids vary with their molecular chemistry and solution ionic strength. The presence of colloids promotes the breakthrough of ciprofloxacin (over 90% sorbed on colloids) from ~4% to 30–40%, and the colloid-facilitated effect was larger at lower ionic strength (e.g., 2 mM). In comparison, the net effect of colloids on the transport of tetracycline (~50% sorbed on colloids) could be facilitation or inhibition, depending on solution chemistry. This dual effect of colloids is primarily due to the opposite response of migration of dissolved and colloid-bound tetracycline to the change in solution ionic strength. Colloids could also facilitate the transport of ibuprofen (~10% sorbed on colloids) by ~50% due likely to exclusion of dispersion pathways by colloid straining. This study suggests that colloids are significant carriers or transport promoters of some PPCPs in the subsurface environment and could affect their off-site environmental risks.

  19. Colloid-Mediated Transport of Pharmaceutical and Personal Care Products through Porous Media.

    PubMed

    Xing, Yingna; Chen, Xijuan; Chen, Xin; Zhuang, Jie

    2016-10-13

    Pharmaceutical and personal care products (PPCPs) enter soils through reclaimed water irrigation and biosolid land applications. Colloids, such as clays, that are present in soil may interact with PPCPs and thus affect their fate and transport in the subsurface environment. This study addresses the influence of soil colloids on the sorption and transport behaviors of PPCPs through laboratory column experiments. Results show that the affinities of PPCPs for colloids vary with their molecular chemistry and solution ionic strength. The presence of colloids promotes the breakthrough of ciprofloxacin (over 90% sorbed on colloids) from ~4% to 30-40%, and the colloid-facilitated effect was larger at lower ionic strength (e.g., 2 mM). In comparison, the net effect of colloids on the transport of tetracycline (~50% sorbed on colloids) could be facilitation or inhibition, depending on solution chemistry. This dual effect of colloids is primarily due to the opposite response of migration of dissolved and colloid-bound tetracycline to the change in solution ionic strength. Colloids could also facilitate the transport of ibuprofen (~10% sorbed on colloids) by ~50% due likely to exclusion of dispersion pathways by colloid straining. This study suggests that colloids are significant carriers or transport promoters of some PPCPs in the subsurface environment and could affect their off-site environmental risks.

  20. Transport of barrel and spherical shaped colloids in unsaturated porous media.

    PubMed

    Knappenberger, Thorsten; Aramrak, Surachet; Flury, Markus

    2015-09-01

    Model colloids are usually spherical, but natural colloids have irregular geometries. Transport experiments of spherical colloids may not reflect the transport characteristics of natural colloids in porous media. We investigated saturated and unsaturated transport of colloids with spherical and angular shapes under steady-state, flow conditions. A pulse of negatively-charged colloids was introduced into a silica sand column at three different effective water saturations (Se = 0.31, 0.45, and 1.0). Colloids were introduced under high ionic strength of [106]mM to cause attachment to the secondary energy minimum and later released by changing the pore water to low ionic strength. After the experiment, sand was sampled from different depths (0, -4, and -11 cm) for scanning electron microscopy (SEM) analysis and colloid extraction. Water saturation affected colloid transport with more retention under low than under high saturation. Colloids were retained and released from a secondary energy minimum with more angular-shaped colloids being retained and released. Colloids extracted from the sand revealed highest colloid deposition in the top layer and decreasing deposition with depth. Pore straining and grain-grain wedging dominated colloid retention.

  1. Transport of barrel and spherical shaped colloids in unsaturated porous media

    NASA Astrophysics Data System (ADS)

    Knappenberger, Thorsten; Aramrak, Surachet; Flury, Markus

    2015-09-01

    Model colloids are usually spherical, but natural colloids have irregular geometries. Transport experiments of spherical colloids may not reflect the transport characteristics of natural colloids in porous media. We investigated saturated and unsaturated transport of colloids with spherical and angular shapes under steady-state, flow conditions. A pulse of negatively-charged colloids was introduced into a silica sand column at three different effective water saturations (Se = 0.31, 0.45, and 1.0). Colloids were introduced under high ionic strength of [106]mM to cause attachment to the secondary energy minimum and later released by changing the pore water to low ionic strength. After the experiment, sand was sampled from different depths (0, -4, and -11 cm) for scanning electron microscopy (SEM) analysis and colloid extraction. Water saturation affected colloid transport with more retention under low than under high saturation. Colloids were retained and released from a secondary energy minimum with more angular-shaped colloids being retained and released. Colloids extracted from the sand revealed highest colloid deposition in the top layer and decreasing deposition with depth. Pore straining and grain-grain wedging dominated colloid retention.

  2. Chemical colloids versus biological colloids: a comparative study for the elucidation of the mechanism of protein fiber formation

    NASA Technical Reports Server (NTRS)

    Xu, Shaohua; Wu, David; Arnsdorf, Morton; Johnson, Robert; Getz, Godfrey S.; Cabana, Veneracion G.

    2005-01-01

    Fiber formation from murine serum amyloid A1 (SAA) was compared to the linear aggregation and fiber formation of colloidal gold particles. Here we report the similarities of these processes. Upon incubation with acetic acid, SAA misfolds and adopts a new conformation, which we termed saa. saa apparently is less soluble than SAA in aqueous solution; it aggregates and forms nucleation units and then fibers. The fibers appear as a string of the nucleation units. Additionally, an external electric field promotes saa fiber formation. These properties of saa are reminiscent of colloidal gold formation from gold ions and one-dimensional aggregation of the gold colloids. Colloidal gold particles were also found to be capable of aggregating one-dimensionally under an electric field or in the presence of polylysine. These gold fibers resembled in structure that of saa fibers. In summary, protein aggregation and formation of fibers appear to follow the generalized principles derived in colloidal science for the aggregation of atoms and molecules, including polymers such as polypeptides. The analysis of colloidal gold formation and of one-dimensional aggregation provides a simple model system for the elucidation of some aspects of protein fiber formation.

  3. Colloidal Material Box: In-situ Observations of Colloidal Self-Assembly and Liquid Crystal Phase Transitions in Microgravity

    NASA Astrophysics Data System (ADS)

    Li, WeiBin; Lan, Ding; Sun, ZhiBin; Geng, BaoMing; Wang, XiaoQing; Tian, WeiQian; Zhai, GuangJie; Wang, YuRen

    2016-05-01

    To study the self-assembly behavior of colloidal spheres in the solid/liquid interface and elucidate the mechanism of liquid crystal phase transition under microgravity, a Colloidal Material Box (CMB) was designed which consists of three modules: (i) colloidal evaporation experimental module, made up of a sample management unit, an injection management unit and an optical observation unit; (ii) liquid crystal phase transition experimental module, including a sample management unit and an optical observation unit; (iii) electronic control module. The following two experimental plans will be performed inside the CMB aboard the SJ-10 satellite in space. (i) Self-assembly of colloidal spheres (with and without Au shell) induced by droplet evaporation, allowing observation of the dynamic process of the colloidal spheres within the droplet and the change of the droplet outer profile during evaporation; (ii) Phase behavior of Mg2Al LDHs suspensions in microgravity. The experimental results will be the first experimental observations of depositing ordered colloidal crystals and their self-assembly behavior under microgravity, and will illustrate the influence of gravity on liquid crystal phase transition.

  4. 3-D Distribution of Retained Colloids in Unsaturated Porous Media

    NASA Astrophysics Data System (ADS)

    Morales, V. L.; Perez-Reche, F. J.; Holzner, M.; Kinzelbach, W. K.; Otten, W.

    2013-12-01

    It is well accepted that colloid transport processes in porous media differ substantially between water saturated and unsaturated conditions. Differences are frequently ascribed to colloid immobilization by association with interfaces with the gas, as well as to restrictions of the liquid medium through which colloids are transported. Such factors depend on interfacial conditions provided by the water saturation of the porous medium. Yet, the current understanding of the importance of colloid retention at gas interfaces is based on observations of single pores or two-dimensional pore network representations, leaving open the question of their statistical significance when all pores in the medium are considered. In order to address this question, column experiments were performed using a model porous medium of glass beads through which colloidal silver particles were transported for conditions of varying water content. X-ray microtomography was subsequently employed as a non-destructive imaging technique to obtain pore-scale information of the entire column regarding: i) the presence and distribution of the four main locations where colloids can become retained (interfaces with the liquid-solid, gas-liquid and gas-solid, and the bulk liquid), ii) deposition profiles of colloids along the column classified by the available retention location, iii) morphological characteristics of the deposited colloidal aggregates, and iv) channel widths of 3-dimensional pore-water network representations. The results presented provide, for the first time, a direct statistical evaluation on the significance of colloid retention by attachment to the liquid-solid, gas-liquid, gas-solid interfaces, and by straining in the bulk liquid. Additionally, an effective-pore structure characteristic is proposed to improve predictions of mass removal by straining under various water saturations. A) Unsaturated conditions. B) Saturated conditions. Left: Tomograph slice illustrating with false

  5. Fractures as Carriers for Colloid and Nano-Particles

    NASA Astrophysics Data System (ADS)

    Weisbrod, N.; Cohen, M.; Tang, X.; Zvikelsky, O.; Meron, H.

    2013-12-01

    One of the major questions in studies in which transport of colloids and nano particles (NPs) is being explored is whether or not they will be mobile on large scales and in large conduits such as fractures and cracks. While many studies explore the migration on a small scale and mostly in ideal porous media, less is known about this topic on larger scales and in fractured rocks or cracked soils. Fractures are likely to be favorable carriers for colloids and NPs due to their large aperture, enabling relatively high flow velocity and smaller tortuosity of the flow path. Transport of various colloids including microspheres, clay particles and viruses, as well as colloid-facilitated transport of lead and cesium was explored in a naturally discrete fractured chalk cores. Preliminary work exploring the transport of NZVIs and TiO2 NPs is being carried out through these cores as well. Our results indicate very high recovery of large microspheres (0.2 and 1 micron) and lower recovery of the small spheres (0.02 micron). It was observed that clay particles, with similar surface properties and sizes to that of the microspheres, show significantly lower recoveries (50 vs over 90%), probably due to the high density of clay particles in respect to the microspheres (2.65 vs. 1.05 g/cm3). High recovery of bacteriophages was also observed, but they exhibit some differences in respect to microspheres with similar properties. In all cases, including the 0.02 micron colloids exhibiting lower recovery rates, arrival times were earlier than that of the bromide that was used as a reference. It was found that colloid-facilitated transport played a major role in the migration of lead and cesium through the fracture. In practice, lead was found to be mobile only in a colloidal form. The on-going work on NP transport through fractures is still in a preliminary phase. Nevertheless, TiO2 recovery was found to be very low. In conclusion, it was observed that in many cases fractures are favorable

  6. Colloidal polycrystalline monolayers under oscillatory shear

    NASA Astrophysics Data System (ADS)

    Buttinoni, Ivo; Steinacher, Mathias; Spanke, Hendrik Th.; Pokki, Juho; Bahmann, Severin; Nelson, Bradley; Foffi, Giuseppe; Isa, Lucio

    2017-01-01

    In this paper we probe the structural response to oscillatory shear deformations of polycrystalline monolayers of soft repulsive colloids with varying area fraction over a broad range of frequencies and amplitudes. The particles are confined at a fluid interface, sheared using a magnetic microdisk, and imaged through optical microscopy. The structural and mechanical response of soft materials is highly dependent on their microstructure. If crystals are well understood and deform through the creation and mobilization of specific defects, the situation is much more complex for disordered jammed materials, where identifying structural motifs defining plastically rearranging regions remains an elusive task. Our materials fall between these two classes and allow the identification of clear pathways for structural evolution. In particular, we demonstrate that large enough strains are able to fluidize the system, identifying critical strains that fulfill a local Lindemann criterion. Conversely, smaller strains lead to localized and erratic irreversible particle rearrangements due to the motion of structural defects. In this regime, oscillatory shear promotes defect annealing and leads to the growth of large crystalline domains. Numerical simulations help identify the population of rearranging particles with those exhibiting the largest deviatoric stresses and indicate that structural evolution proceeds towards the minimization of the stress stored in the system. The particles showing high deviatoric stresses are localized around grain boundaries and defects, providing a simple criterion to spot regions likely to rearrange plastically under oscillatory shear.

  7. Colloidal quantum dot materials for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Arinze, Ebuka S.; Nyirjesy, Gabrielle; Cheng, Yan; Palmquist, Nathan; Thon, Susanna M.

    2015-09-01

    Colloidal quantum dots (CQDs) are an attractive material for optoelectronic applications because they combine flexible, low-cost solution-phase synthesis and processing with the potential for novel functionality arising from their nanostructure. Specifically, the bandgap of films composed of arrays of CQDs can be tuned via the quantum confinement effect for tailored spectral utilization. PbS-based CQDs can be tuned throughout the near and mid-infrared wavelengths and are a promising materials system for photovoltaic devices that harvest non-visible solar radiation. The performance of CQD solar cells is currently limited by an absorption-extraction compromise, whereby photon absorption lengths in the near infrared spectral regime exceed minority carrier diffusion lengths in the bulk films. Several light trapping strategies for overcoming this compromise and increasing the efficiency of infrared energy harvesting will be reviewed. A thin-film interference technique for creating multi-colored and transparent solar cells will be presented, and a discussion of designing plasmonic nanomaterials based on earth-abundant materials for integration into CQD solar cells is developed. The results indicate that it should be possible to achieve high absorption and color-tunability in a scalable nanomaterials system.

  8. Ultrathin Colloidal Cesium Lead Halide Perovskite Nanowires.

    PubMed

    Zhang, Dandan; Yu, Yi; Bekenstein, Yehonadav; Wong, Andrew B; Alivisatos, A Paul; Yang, Peidong

    2016-10-12

    Highly uniform single crystal ultrathin CsPbBr3 nanowires (NWs) with diameter of 2.2 ± 0.2 nm and length up to several microns were successfully synthesized and purified using a catalyst-free colloidal synthesis method followed by a stepwise purification strategy. The NWs have bright photoluminescence (PL) with a photoluminescence quantum yield (PLQY) of about 30% after surface treatment. Large blue-shifted UV-vis absorption and PL spectra have been observed due to strong two-dimensional quantum confinement effects. A small angle X-ray scattering (SAXS) pattern shows the periodic packing of the ultrathin NWs along the radial direction, demonstrates the narrow radial distribution of the wires, and emphasizes the deep intercalation of the surfactants. Despite the extreme aspect ratios of the ultrathin NWs, their composition and the resulting optical properties can be readily tuned by an anion-exchange reaction with good morphology preservation. These bright ultrathin NWs may be used as a model system to study strong quantum confinement effects in a one-dimensional halide perovskite system.

  9. Maximizing exosome colloidal stability following electroporation.

    PubMed

    Hood, Joshua L; Scott, Michael J; Wickline, Samuel A

    2014-03-01

    Development of exosome-based semisynthetic nanovesicles for diagnostic and therapeutic purposes requires novel approaches to load exosomes with cargo. Electroporation has previously been used to load exosomes with RNA. However, investigations into exosome colloidal stability following electroporation have not been considered. Herein, we report the development of a unique trehalose pulse media (TPM) that minimizes exosome aggregation following electroporation. Dynamic light scattering (DLS) and RNA absorbance were employed to determine the extent of exosome aggregation and electroextraction post electroporation in TPM compared to common PBS pulse media or sucrose pulse media (SPM). Use of TPM to disaggregate melanoma exosomes post electroporation was dependent on both exosome concentration and electric field strength. TPM maximized exosome dispersal post electroporation for both homogenous B16 melanoma and heterogeneous human serum-derived populations of exosomes. Moreover, TPM enabled heavy cargo loading of melanoma exosomes with 5nm superparamagnetic iron oxide nanoparticles (SPION5) while maintaining original exosome size and minimizing exosome aggregation as evidenced by transmission electron microscopy. Loading exosomes with SPION5 increased exosome density on sucrose gradients. This provides a simple, label-free means of enriching exogenously modified exosomes and introduces the potential for MRI-driven theranostic exosome investigations in vivo.

  10. Freezing of charged colloids in slit pores.

    PubMed

    Grandner, Stefan; Klapp, Sabine H L

    2008-12-28

    Using Monte Carlo simulations in the grand canonical and isobaric ensembles we investigate freezing phenomena in a charged colloidal suspension confined to narrow slit pores. Our model involves only the macroions which interact via a Derjaguin-Landau-Verwey-Overbeek (DLVO) potential supplemented by a soft-sphere potential. We focus on DLVO parameters typical for moderately charged silica particles (with charges Z approximately 35) in solvents of low ionic strengths. The corresponding DLVO interactions are too weak to drive a (bulk) freezing transition. Nevertheless, for sufficiently small surface separations L(z) the confined systems display not only layering but also significant in-plane crystalline order at chemical potentials where the bulk system is a globally stable fluid (capillary freezing). At confinement conditions related to two-layer systems the observed in-plane structures are consistent with those detected in ground state calculations for perfect Yukawa bilayers [R. Messina and H. Lowen, Phys. Rev. Lett. 91, 146101 (2003)]. Here we additionally observe (at fixed L(z)) a compression-induced first-order phase transition from a two-layer to a three-layer system with different in-plane structure, in agreement with previous findings for pure hard spheres.

  11. Advancing colloidal quantum dot photovoltaic technology

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Arinze, Ebuka S.; Palmquist, Nathan; Thon, Susanna M.

    2016-06-01

    Colloidal quantum dots (CQDs) are attractive materials for solar cells due to their low cost, ease of fabrication and spectral tunability. Progress in CQD photovoltaic technology over the past decade has resulted in power conversion efficiencies approaching 10%. In this review, we give an overview of this progress, and discuss limiting mechanisms and paths for future improvement in CQD solar cell technology.We briefly summarize nanoparticle synthesis and film processing methods and evaluate the optoelectronic properties of CQD films, including the crucial role that surface ligands play in materials performance. We give an overview of device architecture engineering in CQD solar cells. The compromise between carrier extraction and photon absorption in CQD photovoltaics is analyzed along with different strategies for overcoming this trade-off. We then focus on recent advances in absorption enhancement through innovative device design and the use of nanophotonics. Several light-trapping schemes, which have resulted in large increases in cell photocurrent, are described in detail. In particular, integrating plasmonic elements into CQD devices has emerged as a promising approach to enhance photon absorption through both near-field coupling and far-field scattering effects. We also discuss strategies for overcoming the single junction efficiency limits in CQD solar cells, including tandem architectures, multiple exciton generation and hybrid materials schemes. Finally, we offer a perspective on future directions for the field and the most promising paths for achieving higher device efficiencies.

  12. Particle cage dynamics in flowing colloidal dispersions

    NASA Astrophysics Data System (ADS)

    Marenne, Stephanie; Morris, Jeffrey F.

    2016-11-01

    The idea of the particle in a suspension at rest being trapped in a cage formed by its neighbors, widely used to understand glassy suspensions, has been applied to freely flowing suspensions. Stokesian Dynamics, a discrete particle simulation, is used to simulate the flow of monodisperse colloidal hard sphere suspensions. The cage analogy is useful to study the nonlinear stress in the material during start-up of shear flow, where the neighbor cage deforms and breaks, and during oscillatory shear flow where, depending on the amplitude of oscillation, the particle is trapped inside the cage or escapes during the oscillation cycle. A precise statistical definition of the cage in terms of the nearest neighbor ring in the pair distribution function is developed. We examine the dependence of the cage dynamics on the volume fraction of particles and the Peclet number Pe , the ratio between shear and Brownian forces. Under flow, the cage is found to break at quite definite positions, and the structural distortion is found to be clearly related to the shear and normal stress response. The shear strain needed to break the neighbor cage depends on Pe as Brownian motion enhances the total deformation. A simple model captures the strain at the stress overshoot for start-up of steady shear.

  13. Colloidal sorting in dynamic optical lattices

    NASA Astrophysics Data System (ADS)

    Smith, Ryan L.; Spalding, G. C.; Dholakia, K.; MacDonald, M. P.

    2007-08-01

    Passive microfluidic sorting techniques based upon the interaction of particles with an optically defined potential energy landscape have possible advantages over active sorting techniques such as microfluorescence activated cell sorting (FACS), including ease of integration into lab-on-a-chip systems, reconfigurability, and scalability. Rather than analysing and deflecting a single-file stream of particles one by one, a passive approach intrinsically aimed at parallel processing may, ultimately, offer greater potential for high throughput. However attempts to sort many particles simultaneously in high density suspensions are inevitably limited by particle particle interactions, which lead to a reduction in the efficiency of the sorting. In this paper we describe two different approaches aimed at reducing colloidal traffic flow problems. We find that continuous translation of the sorting lattice helps to reduce nearest neighbour particle spacing, providing promise for efficiency improvements in future high throughput applications, and that a flashing lattice yields a reduction in unwanted pile-up and spillover effects which otherwise limit the efficiency of sorting.

  14. The nature of the colloidal 'glass' transition.

    PubMed

    Dawson, Kenneth A; Lawlor, A; DeGregorio, Paolo; McCullagh, Gavin D; Zaccarelli, Emanuela; Foffi, Giuseppe; Tartaglia, Piero

    2003-01-01

    The dynamically arrested state of matter is discussed in the context of athermal systems, such as the hard sphere colloidal arrest. We believe that the singular dynamical behaviour near arrest expressed, for example, in how the diffusion constant vanishes may be 'universal', in a sense to be discussed in the paper. Based on this we argue the merits of studying the problem with simple lattice models. This, by analogy with the the critical point of the Ising model, should lead us to clarify the questions, and begin the program of establishing the degree of universality to be expected. We deal only with 'ideal' athermal dynamical arrest transitions, such as those found for hard sphere systems. However, it is argued that dynamically available volume (DAV) is the relevant order parameter of the transition, and that universal mechanisms may be well expressed in terms of DAV. For simple lattice models we give examples of simple laws that emerge near the dynamical arrest, emphasising the idea of a near-ideal gas of 'holes', interacting to give the power law diffusion constant scaling near the arrest. We also seek to open the discussion of the possibility of an underlying weak coupling theory of the dynamical arrest transition, based on DAV.

  15. Multiple exciton generation in colloidal silicon nanocrystals.

    PubMed

    Beard, Matthew C; Knutsen, Kelly P; Yu, Pingrong; Luther, Joseph M; Song, Qing; Metzger, Wyatt K; Ellingson, Randy J; Nozik, Arthur J

    2007-08-01

    Multiple exciton generation (MEG) is a process whereby multiple electron-hole pairs, or excitons, are produced upon absorption of a single photon in semiconductor nanocrystals (NCs) and represents a promising route to increased solar conversion efficiencies in single-junction photovoltaic cells. We report for the first time MEG yields in colloidal Si NCs using ultrafast transient absorption spectroscopy. We find the threshold photon energy for MEG in 9.5 nm diameter Si NCs (effective band gap identical with Eg = 1.20 eV) to be 2.4 +/- 0.1Eg and find an exciton-production quantum yield of 2.6 +/- 0.2 excitons per absorbed photon at 3.4Eg. While MEG has been previously reported in direct-gap semiconductor NCs of PbSe, PbS, PbTe, CdSe, and InAs, this represents the first report of MEG within indirect-gap semiconductor NCs. Furthermore, MEG is found in relatively large Si NCs (diameter equal to about twice the Bohr radius) such that the confinement energy is not large enough to produce a large blue-shift of the band gap (only 80 meV), but the Coulomb interaction is sufficiently enhanced to produce efficient MEG. Our findings are of particular importance because Si dominates the photovoltaic solar cell industry, presents no problems regarding abundance and accessibility within the Earth's crust, and poses no significant environmental problems regarding toxicity.

  16. Maximizing Exosome Colloidal Stability Following Electroporation

    PubMed Central

    Hood, Joshua L.; Scott, Michael J.; Wickline, Samuel A.

    2014-01-01

    Development of exosome based semi-synthetic nanovesicles for diagnostic and therapeutic purposes requires novel approaches to load exosomes with cargo. Electroporation has previously been used to load exosomes with RNA. However, investigations into exosome colloidal stability following electroporation have not been considered. Herein, we report the development of a unique trehalose pulse media (TPM) that minimizes exosome aggregation following electroporation. Dynamic light scattering (DLS) and RNA absorbance were employed to determine the extent of exosome aggregation and electroextraction post electroporation in TPM compared to common PBS pulse media or sucrose pulse media (SPM). Use of TPM to disaggregate melanoma exosomes post electroporation was dependent on both exosome concentration and electric field strength. TPM maximized exosome dispersal post electroporation for both homogenous B16 melanoma and heterogeneous human serum derived populations of exosomes. Moreover, TPM enabled heavy cargo loading of melanoma exosomes with 5 nm superparamagnetic iron oxide nanoparticles (SPION5) while maintaining original exosome size and minimizing exosome aggregation as evidenced by transmission electron microscopy. Loading exosomes with SPION5 increased exosome density on sucrose gradients. This provides a simple, label free means to enrich exogenously modified exosomes and introduces the potential for MRI driven theranostic exosome investigations in vivo. PMID:24333249

  17. Crystalloids and colloids in critical patient resuscitation.

    PubMed

    Garnacho-Montero, J; Fernández-Mondéjar, E; Ferrer-Roca, R; Herrera-Gutiérrez, M E; Lorente, J A; Ruiz-Santana, S; Artigas, A

    2015-01-01

    Fluid resuscitation is essential for the survival of critically ill patients in shock, regardless of the origin of shock. A number of crystalloids and colloids (synthetic and natural) are currently available, and there is strong controversy regarding which type of fluid should be administered and the potential adverse effects associated with the use of these products, especially the development of renal failure requiring renal replacement therapy. Recently, several clinical trials and metaanalyses have suggested the use of hydroxyethyl starch (130/0.4) to be associated with an increased risk of death and kidney failure, and data have been obtained showing clinical benefit with the use of crystalloids that contain a lesser concentration of sodium and chlorine than normal saline. This new information has increased uncertainty among clinicians regarding which type of fluid should be used. We therefore have conducted a review of the literature with a view to developing practical recommendations on the use of fluids in the resuscitation phase in critically ill adults.

  18. Colloidal quantum dot light-emitting devices.

    PubMed

    Wood, Vanessa; Bulović, Vladimir

    2010-01-01

    Colloidal quantum dot light-emitting devices (QD-LEDs) have generated considerable interest for applications such as thin film displays with improved color saturation and white lighting with a high color rendering index (CRI). We review the key advantages of using quantum dots (QDs) in display and lighting applications, including their color purity, solution processability, and stability. After highlighting the main developments in QD-LED technology in the past 15 years, we describe the three mechanisms for exciting QDs - optical excitation, Förster energy transfer, and direct charge injection - that have been leveraged to create QD-LEDs. We outline the challenges facing QD-LED development, such as QD charging and QD luminescence quenching in QD thin films. We describe how optical downconversion schemes have enabled researchers to overcome these challenges and develop commercial lighting products that incorporate QDs to achieve desirable color temperature and a high CRI while maintaining efficiencies comparable to inorganic white LEDs (>65 lumens per Watt). We conclude by discussing some current directions in QD research that focus on achieving higher efficiency and air-stable QD-LEDs using electrical excitation of the luminescent QDs.

  19. Nonvolatile optically-erased colloidal memristors

    NASA Astrophysics Data System (ADS)

    Huebner, Christopher F.; Tsyalkovsky, Volodymyr; Bandera, Yuriy; Burdette, Mary K.; Shetzline, Jamie A.; Tonkin, Charles; Creager, Stephen E.; Foulger, Stephen H.

    2015-01-01

    A nonconjugated methacrylate terpolymer containing carbazole moieties (electron donors), 1,3,4-oxadiazole moieties (electron acceptors), and Coumarin-6 in the pendant groups was synthesized via free radical copolymerization of methacrylate monomers containing the respective functional groups. The terpolymer was formed into 57 nm particles through a mini-emulsion route. For a thin 100 nm film of the fused particles sandwiched between an indium-tin oxide (ITO) electrode and an Al electrode, the structure behaved as a nonvolatile flash (rewritable) memory with accessible electronic states that could be written, read, and optically erased. The device exhibited a turn-on voltage of ca. -4.5 VDC and a 106 current ratio. A device in the ON high conductance state could be reverted to the OFF state with a short exposure to a 360 nm light source. The development of semiconducting colloidal inks that can be converted into electroactive devices through a continuous processing method is a critical step in the widespread adoption of these 2D manufacturing technologies for printed electronics.

  20. Core/shell colloidal semiconductor nanoplatelets.

    PubMed

    Mahler, Benoit; Nadal, Brice; Bouet, Cecile; Patriarche, Gilles; Dubertret, Benoit

    2012-11-14

    We have recently synthesized atomically flat semiconductor colloidal nanoplatelets with quasi 2D geometry. Here, we show that core/shell nanoplatelets can be obtained with a 2D geometry that is conserved. The epitaxial growth of the shell semiconductor is performed at room temperature. We report the detailed synthesis of CdSe/CdS and CdSe/CdZnS structures with different shell thicknesses. The shell growth is characterized both spectroscopically and structurally. In particular, the core/shell structure appears very clearly on high-resolution, high-angle annular dark-field transmission electron microscope images, thanks to the difference of atomic density between the core and the shell. When the nanoplatelets stand on their edge, we can precisely count the number of atomic planes forming the core and the shell. This provides a direct measurement, with atomic precision, of the core nanoplatelets thickness. The constraints exerted by the shell growth on the core is analyzed using global phase analysis. The core/shell nanoplatelets we obtained have narrow emission spectra with full-width at half-maximum close to 20 nm, and quantum yield that can reach 60%.

  1. Dynamics of hard sphere colloidal dispersions

    NASA Technical Reports Server (NTRS)

    Zhu, J. X.; Chaikin, Paul M.; Phan, S.-E.; Russel, W. B.

    1994-01-01

    Our objective is to perform on homogeneous, fully equilibrated dispersions the full set of experiments characterizing the transition from fluid to solid and the properties of the crystalline and glassy solid. These include measurements quantifying the nucleation and growth of crystallites, the structure of the initial fluid and the fully crystalline solid, and Brownian motion of particles within the crystal, and the elasticity of the crystal and the glass. Experiments are being built and tested for ideal microgravity environment. Here we describe the ground based effort, which exploits a fluidized bed to create a homogeneous, steady dispersion for the studies. The differences between the microgravity environment and the fluidized bed is gauged by the Peclet number Pe, which measures the rate of convection/sedimentation relative to Brownian motion. We have designed our experiment to accomplish three types of measurements on hard sphere suspensions in a fluidized bed: the static scattering intensity as a function of angle to determine the structure factor, the temporal autocorrelation function at all scattering angles to probe the dynamics, and the amplitude of the response to an oscillatory forcing to deduce the low frequency viscoelasticity. Thus the scattering instrument and the colloidal dispersion were chosen such as that the important features of each physical property lie within the detectable range for each measurement.

  2. Kibble–Zurek mechanism in colloidal monolayers

    PubMed Central

    Deutschländer, Sven; Dillmann, Patrick; Maret, Georg; Keim, Peter

    2015-01-01

    The Kibble–Zurek mechanism describes the evolution of topological defect structures like domain walls, strings, and monopoles when a system is driven through a second-order phase transition. The model is used on very different scales like the Higgs field in the early universe or quantum fluids in condensed matter systems. A defect structure naturally arises during cooling if separated regions are too far apart to communicate (e.g., about their orientation or phase) due to finite signal velocity. This lack of causality results in separated domains with different (degenerated) locally broken symmetry. Within this picture, we investigate the nonequilibrium dynamics in a condensed matter analog, a 2D ensemble of colloidal particles. In equilibrium, it obeys the so-called Kosterlitz–Thouless–Halperin–Nelson–Young (KTHNY) melting scenario with continuous (second order-like) phase transitions. The ensemble is exposed to a set of finite cooling rates covering roughly three orders of magnitude. Along this process, we analyze the defect and domain structure quantitatively via video microscopy and determine the scaling of the corresponding length scales as a function of the cooling rate. We indeed observe the scaling predicted by the Kibble–Zurek mechanism for the KTHNY universality class. PMID:25902492

  3. Flow dichroism in critical colloidal fluids

    SciTech Connect

    Lenstra, T. A. J.; Dhont, J. K. G.

    2001-06-01

    Due to long-range correlations and slow dynamics of concentration fluctuations in the vicinity of the gas-liquid critical point, shear flow is very effective in distorting the microstructure of near-critical fluids. The anisotropic nature of the shear-field renders the microstructure highly anisotropic, leading to dichroism. Experiments on the dichroic behavior can thus be used to test theoretical predictions on microstructural order under shear flow conditions. We performed both static and dynamic dichroism and turbidity measurements on a colloid-polymer mixture, existing of silica spheres (radius 51 nm) and polydimethylsiloxane polymer (molar weight 204 kg/mol). Sufficiently far away from the critical point, in the mean-field region, the experimental data are in good agreement with theory. Very close to the critical point, beyond mean field, for which no theory exists yet, an unexpected decrease of dichroism on approach of the critical point is observed. Moreover, we do not observe critical slowing down of shear-induced dichroism, right up to the critical point, in contrast to the turbidity.

  4. Particle and substrate charge effects on colloidal self-assembly in a sessile drop.

    PubMed

    Yan, Qingfeng; Gao, Li; Sharma, Vyom; Chiang, Yet-Ming; Wong, C C

    2008-10-21

    By direct video monitoring of dynamic colloidal self-assembly during solvent evaporation in a sessile drop, we investigated the effect of surface charge on the ordering of colloidal spheres. The in situ observations revealed that the interaction between charged colloidal spheres and substrates affects the mobility of colloidal spheres during convective self-assembly, playing an important role in the colloidal crystal growth process. Both ordered and disordered growth was observed depending on different chemical conditions mediated by surface charge and surfactant additions to the sessile drop system. These different self-assembly behaviors were explained by the Coulombic and hydrophobic interactions between surface-charged colloidal spheres and substrates.

  5. Diffusion of colloidal fluids in random porous media.

    PubMed

    Chávez-Rojo, M A; Juárez-Maldonado, R; Medina-Noyola, M

    2008-04-01

    The diffusive relaxation of a colloidal fluid adsorbed in a porous medium depends on many factors, including the concentration and composition of the adsorbed colloidal fluid, the average structure of the porous matrix, and the nature of the colloid-colloid and colloid-substrate interactions. A simple manner to describe these effects is to model the porous medium as a set of spherical particles fixed in space at random positions with prescribed statistical structural properties. Within this model one may describe the relaxation of concentration fluctuations of the adsorbed fluid by simply setting to zero the short-time mobility of one species (the porous matrix) in a theory of the dynamics of equilibrium colloidal mixtures, or by extending such dynamic theory to explicitly consider the porous matrix as a random external field, as recently done in the framework of mode coupling theory [V. Krakoviack, Phys. Rev. Lett. 94, 065703 (2005)]. Here we consider the first approach and employ the self-consistent generalized Langevin equation (SCGLE) theory of the dynamics of equilibrium colloidal mixtures, to describe the dynamics of the mobile component. We focus on the short- and intermediate-time regimes, which we compare with Brownian dynamics simulations involving a binary mixture with screened Coulomb interactions for two models of the average static structure of the matrix: a porous matrix constructed by quenching configurations of an equilibrium mixture in which both species were first equilibrated together, and a preexisting matrix with prescribed average structure, in which we later add the mobile species. We conclude that in both cases, if the correct static structure factors are provided as input, the SCGLE theory correctly predicts the main features of the dynamics of the permeating fluid.

  6. Towards high resolution ^1H NMR spectra of tannin colloidal aggregates

    NASA Astrophysics Data System (ADS)

    Mirabel, M.; Glories, Y.; Pianet, I.; Dufourc, E. J.

    1999-10-01

    The time dependent colloidal formation of tannins in hydro-alcoholic medium has been studied by 1H-NMR. Line broadening observed with time can be cancelled by making use of magic angle sample spinning (MASS) thus yielding sharp lines that allow structural studies. We used as an example catechin, a constitutive monomer of Bordeaux young red wine tannins. Chemical shift variations of polyphenol protons allow monitoring the time course of aggregation. La formation de tanins colloïdaux au cours du temps, en milieu hydroalcoolique, a été suivie par RMN-^1H. Un élargissement marqué des résonances est observé et peut être supprimé par la rotation de l'échantillon à l'angle magique ce qui ouvre tout un champ d'études structurales sur ces composés colloïdaux. L'exemple proposé est celui de la catéchine, monomère constitutif de tannins présents en grande quantité dans les vins rouges jeunes de Bordeaux. Des variations du déplacement chimique de certains protons polyphénoliques permettent de suivre l'évolution temporelle de l'agrégation.

  7. Size-dependent Turbidimatric Quantification of Mobile Colloids in Field Samples

    NASA Astrophysics Data System (ADS)

    Yan, J.; Meng, X.; Jin, Y.

    2015-12-01

    Natural colloids, often defined as entities with sizes < 1.0 μm, have attracted much research attention because of their ability to facilitate the transport of contaminants in the subsurface environment. However, due to their small size and generally low concentrations in field samples, quantification of mobile colloids, especially the smaller fractions (< 0.45 µm), which are operationally defined as dissolved, is largely impeded and hence the natural colloidal pool is greatly overlooked and underestimated. The main objectives of this study are to: (1) develop an experimentally and economically efficient methodology to quantify natural colloids in different size fractions (0.1-0.45 and 0.45-1 µm); (2) quantify mobile colloids including small colloids, < 0.45 µm particularly, in different natural aquatic samples. We measured and generated correlations between mass concentration and turbidity of colloid suspensions, made by extracting and fractionating water dispersible colloids in 37 soils from different areas in the U.S. and Denmark, for colloid size fractions 0.1-0.45 and 0.45-1 µm. Results show that the correlation between turbidity and colloid mass concentration is largely affected by colloid size and iron content, indicating the need to generate different correlations for colloids with constrained size range and iron content. This method enabled quick quantification of colloid concentrations in a large number of field samples collected from freshwater, wetland and estuaries in different size fractions. As a general trend, we observed high concentrations of colloids in the < 0.45 µm fraction, which constitutes a significant percentage of the total mobile colloidal pool (< 1 µm). This observation suggests that the operationally defined cut-off size for "dissolved" phase can greatly underestimate colloid concentration therefore the role that colloids play in the transport of associated contaminants or other elements.

  8. Detachment of colloids from a solid surface by a moving air-water interface.

    PubMed

    Sharma, Prabhakar; Flury, Markus; Zhou, Jun

    2008-10-01

    Colloid attachment to liquid-gas interfaces is an important process used in industrial applications to separate suspended colloids from the fluid phase. Moving gas bubbles can also be used to remove colloidal dust from surfaces. Similarly, moving liquid-gas interfaces lead to colloid mobilization in the natural subsurface environment, such as in soils and sediments. The objective of this study was to quantify the effect of moving air-water interfaces on the detachment of colloids deposited on an air-dried glass surface, as a function of colloidal properties and interface velocity. We selected four types of polystyrene colloids (positive and negative surface charge, hydrophilic and hydrophobic). The colloids were deposited on clean microscope glass slides using a flow-through deposition chamber. Air-water interfaces were passed over the colloid-deposited glass slides, and we varied the number of passages and the interface velocity. The amounts of colloids deposited on the glass slides were visualized using confocal laser scanning microscopy and quantified by image analysis. Our results showed that colloids attached under unfavorable conditions were removed in significantly greater amounts than those attached under favorable conditions. Hydrophobic colloids were detached more than hydrophilic colloids. The effect of the air-water interface on colloid removal was most pronounced for the first two passages of the air-water interface. Subsequent passages of air-water interfaces over the colloid-deposited glass slides did not cause significant additional colloid removal. Increasing interface velocity led to decreased colloid removal. The force balances, calculated from theory, supported the experimental findings, and highlight the dominance of detachment forces (surface tension forces) over the attachment forces (DLVO forces).

  9. Does water content or flow rate control colloid transport in unsaturated porous media?

    PubMed

    Knappenberger, Thorsten; Flury, Markus; Mattson, Earl D; Harsh, James B

    2014-04-01

    Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations Se ranging from 0.1 to 1.0, with Se = (θ - θr)/(θs - θr)) and flow rates (pore water velocities v of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (Se < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transport in unsaturated porous media and highlight the dominant role of water content.

  10. Does Water Content or Flow Rate Control Colloid Transport in Unsaturated Porous Media?

    SciTech Connect

    Thorsten Knappenberger; Markus Flury; Earl D. Mattson; James B. Harsh

    2014-03-01

    Mobile colloids can play an important role in contaminant transport in soils: many contaminants exist in colloidal form, and colloids can facilitate transport of otherwise immobile contaminants. In unsaturated soils, colloid transport is, among other factors, affected by water content and flow rate. Our objective was to determine whether water content or flow rate is more important for colloid transport. We passed negatively charged polystyrene colloids (220 nm diameter) through unsaturated sand-filled columns under steady-state flow at different water contents (effective water saturations Se ranging from 0.1 to 1.0, with Se = (? – ?r)/(?s – ?r)) and flow rates (pore water velocities v of 5 and 10 cm/min). Water content was the dominant factor in our experiments. Colloid transport decreased with decreasing water content, and below a critical water content (Se < 0.1), colloid transport was inhibited, and colloids were strained in water films. Pendular ring and water film thickness calculations indicated that colloids can move only when pendular rings are interconnected. The flow rate affected retention of colloids in the secondary energy minimum, with less colloids being trapped when the flow rate increased. These results confirm the importance of both water content and flow rate for colloid transport in unsaturated porous media and highlight the dominant role of water content.

  11. Colloid facilitated transport of lanthanides through discrete fractures in chalk

    NASA Astrophysics Data System (ADS)

    Tran, Emily; Klein Ben-David, Ofra; Teutsch, Nadya; Weisbrod, Noam

    2015-04-01

    Geological disposal of high-level radioactive waste is the internationally agreed-upon, long term solution for the disposal of long lived radionuclides and spent fuel. Eventually, corrosion of the waste canisters may lead to leakage of their hazardous contents, and the radionuclides can ultimately make their way into groundwater and pose a threat to the biosphere. Engineered bentonite barriers placed around nuclear waste repositories are generally considered sufficient to impede the transport of radionuclides from their storage location to the groundwater. However, colloidal-sized mobile bentonite particles eroding from these barriers have come under investigation as a potential transport vector for radionuclides sorbed to them. In addition, the presence of organic matter in groundwater has been shown to additionally facilitate the uptake of radionuclides by the clay colloids. This study aims to evaluate the transport behaviors of radionuclides in colloid-facilitated transport through a fractured chalk matrix and under geochemical conditions representative of the Negev desert, Israel. Lanthanides are considered an acceptable substitute to actinides for research on radionuclide transportation due to their similar chemical behavior. In this study, the migration of Ce both with and without colloidal particles was explored and compared to the migration of a conservative tracer (bromide). Tracer solutions containing known concentrations of Ce, bentonite colloids, humic acid and bromide were prepared in a matrix solution containing salt concentrations representative of that of the average rain water found in the Negev. These solutions were then injected into a flow system constructed around a naturally fractured chalk core. Samples were analyzed for Ce and Br using ICP-MS, and colloid concentrations were determined using spectrophotographic analysis. Breakthrough curves comparing the rates of transportation of each tracer were obtained, allowing for comparison of

  12. Comparison of Transport of Carboxylate-Modified Latex Microspheres and Silica Colloids in Fractured and Porous Media: The Case for Microspheres as Conservative Colloid Tracers

    NASA Astrophysics Data System (ADS)

    Anghel, I.; Haga, M. J.; Reimus, P. W.

    2001-12-01

    Carboxylate-modified latex (CML) polystyrene microspheres have frequently been used as colloid tracers in laboratory and field tracer experiments because of the ability to discriminate them from natural colloids and to achieve very low detection limits by tagging them with fluorescent dyes. However, the use of CML microspheres as surrogates for inorganic colloids to obtain estimates of colloid transport parameters for use in predictive models is sometimes called into question because there are many differences in the physical and chemical characteristics of the two types of colloids. We conducted several transport experiments in both fractured and porous media to compare the transport behavior of CML microspheres and silica colloids. Silica colloids were used to represent inorganic colloids because previous experiments had established that they transported through fractures with less attenuation than montmorillonite colloids. We conducted fracture experiments at varying flow rates and in both vertical and horizontal fracture orientations. We found that the microspheres always had either the same attenuation or less attenuation than the silica colloids, with the greatest difference occurring at low flow rates and in the horizontal fracture orientation. The greater silica attenuation in the horizontal orientation was largely due to gravitational settling, which did not noticeably affect the CML microspheres, despite their greater size compared to the silica (330 vs. 100 nm), because of the near-neutral buoyancy of the polystyrene latex (density = 1.06 g/ml). The smaller silica colloids also presumably had more collisions with fracture walls in either orientation because of their larger diffusivity compared to the CML microspheres. This greater number of collisions apparently resulted in greater attenuation, even in the vertical orientation. The results of the porous media experiments were generally consistent with the fracture experiment results. Our preliminary

  13. COLLOID-FACILITATED TRANSPORT OF RADIONUCLIDES THROUGH THE VADOSE ZONE

    SciTech Connect

    Flury, Markus

    2003-09-14

    Contaminants have leaked into the vadose zone at the USDOE Hanford reservation. It is important to understand the fate and transport of these contaminants to design remediation strategies and long-term waste management plans at the Hanford reservation. Colloids may play an important role in fate and transport of strongly sorbing contaminants, such as Cs or Pu. This project seeks to improve the basic understanding of colloid and colloid-facilitated transport of contaminants in the vadose zone. The specific objectives addressed are: (1) Determine the structure, composition, and surface charge characteristics of colloidal particles formed under conditions similar to those occurring during leakage of waste typical of Hanford tank supernatants into soils and sediments surrounding the tanks. (2) Characterize the mutual interactions between colloids, contaminant, and soil matrix in batch experiments under various ionic strength and pH conditions. We will investigate the nature of the solid-liquid interactions and the kinetics of the reactions. (3) Evaluate mobility of colloids through soil under different degrees of water saturation and solution chemistry (ionic strength and pH). (4) Determine the potential of colloids to act as carriers to transport the contaminant through the vadose zone and verify the results through comparison with field samples collected under leaking tanks. (5) Improve conceptual characterization of colloid-contaminant-soil interactions and colloid-facilitated transport for implementation into reactive chemical transport models. This project was in part supported by an NSF-IGERT grant to Washington State University. The IGERT grant provided funding for graduate student research and education, and two graduate students were involved in the EMSP project. The IGERT program also supported undergraduate internships. The project is part of a larger EMSP program to study fate and transport of contaminants under leaking Hanford waste tanks. The project has

  14. Coffee-rings and glasses: Colloids out of equilibrium

    NASA Astrophysics Data System (ADS)

    Yunker, Peter Joseph

    This thesis describes experiments that utilize colloids to explore nonequilibrium phenomena. Specifically, the deposition of particles during evaporation and the glass transition are explored. In the first set of experiments, we found that particle shape has a profound effect on particle deposition. We evaporated drops of colloidal suspensions containing micron-sized particles that range in shape from isotropic spheres to very anisotropic ellipsoids. For sessile drops, i.e., drops sitting on a solid surface, spheres are deposited in a ring-like stain, while ellipsoids are deposited uniformly. We also confined drops between glass plates and allowed them to evaporate. During evaporation, colloidal particles coat the air-water interface, forming colloidal monolayer membranes (CMMs). As particle anisotropy increases, CMM bending rigidity was found to increase. This increase in bending rigidity provides a new mechanism that produces a uniform deposition of ellipsoids and a heterogeneous deposition of spheres. In the second set of experiments, we employed colloidal suspensions to investigate the character of glassy materials. "Anisotropic glasses'' were investigated with ellipsoidal particles confined to two-dimensional chambers at high packing fractions; this system enabled the study of the effects of particle shape on the vibrational properties of colloidal glasses. Low frequency modes in glasses composed of slightly anisotropic particles are found to have predominantly rotational character. Conversely, low frequency modes in glasses of highly anisotropic particles exhibit a mix of rotational and translational character. Aging effects in glasses were explored using suspensions of temperature-sensitive microgel spheres. We devised a method to rapidly quench from liquid to glass states, and then observed the resultant colloidal glasses as they aged. Particle rearrangements in glasses occur collectively, i.e., many particles move in a correlated manner. During aging, we

  15. Colloid and Colloid-Facilitated Contaminant Transport Experiments and Models to Support Assessments of Radionuclide Migration at Yucca Mountain and the Nevada Test Site

    SciTech Connect

    P. Reimus

    2004-06-01

    In recent years, numerous laboratory and field experiments have been conducted to assess and parameterize colloid and colloid-facilitated radionuclide transport for the Yucca Mountain Project and the Nevada Test Site (NTS) Environmental Restoration Project. Radionuclide contamination of ground water currently exists within or near underground nuclear test cavities at the NTS, and the proposed Yucca Mountain high-level nuclear waste repository represents a potential future source of radionuclide contamination of ground water at the NTS. Furthermore, recent field observations have indicated that small amounts of Plutonium, which normally adsorbs very strongly to mineral surfaces in aquifers, can transport quite rapidly and over significant distances in ground water when associated with inorganic colloids (Kersting et al., 1999). Groundwater samples from all over the Nevada Test Site have been analyzed for colloid concentrations and size distributions, and it is clear that there are significant mass loadings of colloids in the ground water at some locations. These colloids represent mobile surface area for potentially transporting strongly-adsorbed radionuclides. Field transport experiments have involved the use of fluorescent-dyed carboxylate-modified latex (CML) microspheres in the 250- to 650-nm diameter size range as surrogates for natural colloids in forced-gradient tracer tests. These experiments have indicated that effective colloid filtration coefficients appear to decrease as time and length scales increase. They suggest that a small fraction of colloids may be able to transport significant distances in groundwater systems. Laboratory experiments have been conducted to determine radionuclide sorption and desorption parameters onto inorganic colloids present in the groundwater systems and also to determine transport parameters for inorganic colloids in both fractured and porous media present at the Nevada Test Site. More recent laboratory experiments have

  16. Effects of Nanoscale Surface Roughness on Colloid Detachment

    NASA Astrophysics Data System (ADS)

    Rasmuson, J. A.; Johnson, W. P.

    2015-12-01

    Recent advances in colloid transport science have demonstrated the importance of surface roughness on colloid attachment; however, few studies have investigated the influence of nano-scale roughness on colloid detachment. This study explores the effects of flow perturbations on a variety of mineral surfaces, as well as NaOH treated (i.e. rough, Figure 1a) and untreated (i.e. smooth, Figure 1b) surfaces for colloids of various sizes attached in an impinging jet system under flowing and stagnant conditions. These experiments showed minimal detachment from the roughened surfaces (treated glass) and significant detachment from the smooth surfaces (untreated glass and mica). A correlation between residence time and attachment irreversibility was also revealed, indicating that the particles that spent the longest time attached to the surface developed the strongest adhesion. The representative surface-heterogeneity model developed by Pazmino et al. (2014) was used to conduct detachment simulations under similar geochemical and flow conditions. While simulated results show qualitative agreement with experimental results, they tend to over-predict detachment, highlighting differences among simulated versus real surfaces, which may be related to surface roughness. These results suggest that more sophisticated models that incorporate surface roughness and time-based adhesion are needed to accurately predict colloid detachment in environmental systems.

  17. Evaporation induced ordering in polymer-colloid suspensions

    NASA Astrophysics Data System (ADS)

    Senses, Erkan; Black, Matthew; Cunningham, Thomas; Akcora, Pinar

    2013-03-01

    When evaporated from aqueous solutions, colloidal particles tend to deposit non-uniformly on hydrophilic substrates due to capillary flow from the center of droplet to the pinned contact line. The so called ``coffee-ring'' deposition has been extensively studied in polymer solutions and colloidal suspensions; however, the behavior of the mixtures of polymer-colloid suspensions under evaporation remains unexplored. The competition between the homogenous fluid phase and the depletion induced phase separation offers rich phase behavior to these three component systems over a wide range of size ratios and concentrations. In this work, we present the formation of long-range, ordered colloid-rich and polymer-rich phases with a well-defined periodicity from homogenous mixture of colloids and polymer via solvent evaporation. The kinetics of the phase separation, studied by video microscopy and Fourier transform analysis of the images obtained at different times, suggests that the early growth of the phases can be quantitatively described by spinodal decomposition kinetics. The effect of particle and polymer concentrations, polymer and particle size ratios, interparticle bridging and substrate on microscopic phase separation will be discussed.

  18. Nonequilibrium Equation of State in Suspensions of Active Colloids

    NASA Astrophysics Data System (ADS)

    Ginot, Félix; Theurkauff, Isaac; Levis, Demian; Ybert, Christophe; Bocquet, Lydéric; Berthier, Ludovic; Cottin-Bizonne, Cécile

    2015-01-01

    Active colloids constitute a novel class of materials composed of colloidal-scale particles locally converting chemical energy into motility, mimicking micro-organisms. Evolving far from equilibrium, these systems display structural organizations and dynamical properties distinct from thermalized colloidal assemblies. Harvesting the potential of this new class of systems requires the development of a conceptual framework to describe these intrinsically nonequilibrium systems. We use sedimentation experiments to probe the nonequilibrium equation of state of a bidimensional assembly of active Janus microspheres and conduct computer simulations of a model of self-propelled hard disks. Self-propulsion profoundly affects the equation of state, but these changes can be rationalized using equilibrium concepts. We show that active colloids behave, in the dilute limit, as an ideal gas with an activity-dependent effective temperature. At finite density, increasing the activity is similar to increasing adhesion between equilibrium particles. We quantify this effective adhesion and obtain a unique scaling law relating activity and effective adhesion in both experiments and simulations. Our results provide a new and efficient way to understand the emergence of novel phases of matter in active colloidal suspensions.

  19. Organized thiol functional groups in mesoporous core shell colloids

    SciTech Connect

    Marchena, Martin H.; Granada, Mara; Bordoni, Andrea V.; Joselevich, Maria; Troiani, Horacio; Williams, Federico J.; Wolosiuk, Alejandro

    2012-03-15

    The co-condensation in situ of tetraethoxysilane (TEOS) and mercaptopropyltrimethoxysilane (MPTMS) using cetyltrimethylammonium bromide (CTAB) as a template results in the synthesis of multilayered mesoporous structured SiO{sub 2} colloids with 'onion-like' chemical environments. Thiol groups were anchored to an inner selected SiO{sub 2} porous layer in a bilayered core shell particle producing different chemical regions inside the colloidal layered structure. X-Ray Photoelectron Spectroscopy (XPS) shows a preferential anchoring of the -SH groups in the double layer shell system, while porosimetry and simple chemical modifications confirm that pores are accessible. We can envision the synthesis of interesting colloidal objects with defined chemical environments with highly controlled properties. - Graphical abstract: Mesoporous core shell SiO{sub 2} colloids with organized thiol groups. Highlights: Black-Right-Pointing-Pointer Double shell mesoporous silica colloids templated with CTAB. Black-Right-Pointing-Pointer Sequential deposition of mesoporous SiO{sub 2} layers with different chemistries. Black-Right-Pointing-Pointer XPS shows the selective functionalization of mesoporous layers with thiol groups.

  20. Treatment of malignant pericardial effusion with 32P-colloid

    PubMed Central

    Dempke, W; Firusian, N

    1999-01-01

    Malignant pericardial effusion is usually treated only when signs of cardiac tamponade develop. Several methods of treatment have been reported with an overall response rate of approximately 75%. Since our initial study using intrapericardial 32P-colloid instillation as a treatment modality for pericardial effusion demonstrated a significant higher response rate, this study was conducted to further evaluate the efficacy of intrapericardial 32P-colloid in terms of response rates and duration of remissions. Intrapericardial instillation of 185–370 MBq (5–10 mCi) 32P-colloid in 36 patients with malignant pericardial effusion resulted in a complete remission rate of 94.5% (34 patients) whereas two patients did not respond to treatment due to a foudroyant formation of pericardial fluid. The median duration time was 8 months. No side-effects were observed. These results suggest that intrapericardial instillation of 32P-colloid is a simple, reliable and safe treatment strategy for patients with malignant pericardial effusions. Therefore, since further evidence is provided that 32P-colloid is significantly more effective than external radiation or non-radioactive sclerosing agents, this treatment modality should be considered for the management of malignant pericardial effusion. © 1999 Cancer Research Campaign PMID:10471044