Showing papers in "Current Opinion in Colloid and Interface Science in 1997"
TL;DR: In this article, experimental studies of wetting phenomena have helped to bridge the gap between the progress made in theory and simulation over the past decade, and the experimental evidence or verification of the theoretical predictions.
Abstract: Recent advancements in experimental studies of wetting phenomena have helped to bridge the gap between the progress made in theory and simulation over the past decade, and the experimental evidence or verification of the theoretical predictions. These developments include new measurements of the equilibrium thickness of precursor wetting films on solid and liquid substrates and at the liquid/gas interface, experimental studies of critical adsorption, as well as measurements of the dynamics of wetting and spreading and the nucleation of wetting layers in simple and complex systems. There have also been some recent results on dewetting of solid substrates by liquid films.
1,061 citations
TL;DR: Water soluble polymers with pendant hydrophobic substituents associate in water to form extended structures as mentioned in this paper, which have important applications in technologies ranging from paints and paper coatings (as rheology modifiers) to DNA sequencing (where the network structure serves as a sieving medium).
Abstract: Water soluble polymers with pendant hydrophobic substituents associate in water to form extended structures. Solutions of the polymers have important applications in technologies ranging from paints and paper coatings (as rheology modifiers) to DNA sequencing (where the network structure serves as a sieving medium). Recent experiments are beginning to reveal the nature of the structures formed and their response to shear. Many facets of the behavior of these polymers are under active investigation.
437 citations
TL;DR: The network structure and the thermodynamic nature of the components of these networks play a key role in their diffusional behavior, molecular mesh size changes (especially in environmentally responsive hydrogels), and the associated molecular stability of the incorporated bioactive agents.
Abstract: Recent developments include the use of water-swollen, crosslinked biomedical polymers as carriers for the delivery of drugs, peptides and proteins, as targeting agents for site-specific delivery, or as components for preparation of protein or enzyme conjugates. The network structure and the thermodynamic nature of the components of these networks play a key role in their diffusional behavior, molecular mesh size changes (especially in environmentally responsive hydrogels), and the associated molecular stability of the incorporated bioactive agents.
406 citations
TL;DR: In this article, the copolymer micellization in water as affected by cosolutes, and on the time-dependency of surface activity have also been reported, as well as the structural characterization of the morphologies using primarily small angle scattering techniques.
Abstract: Block copolymers consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) can self-assemble in water and water/oil mixtures (where water is a selective solvent for PEO and oil a selective solvent for PPO) to form thermodynamically stable spherical micelles as well as an array of lyotropic liquid crystalline mesophases of varying morphology. Significant advances have been made over the past year on the identification of different morphologies, the delineation of the composition-temperature ranges where they occur, and the structural characterization of the morphologies using primarily small angle scattering techniques. Important new findings on the copolymer micellization in water as affected by cosolutes, and on the time-dependency of the surface activity have also been reported.
372 citations
TL;DR: The diffusing-wave spectroscopy (DWS) has become a particularly important quantitative tool in colloid physics because of its applicability to systems containing very high concentrations of scatterers, and its extreme sensitivity to small motions as mentioned in this paper.
Abstract: Since its invention about a decade ago, dynamic multiple light scattering has found many applications in various areas of soft condensed matter science. It has become a particularly important quantitative tool in colloid physics because of its applicability to systems containing very high concentrations of scatterers, and its extreme sensitivity to small motions. Recent advances of this technique, currently called diffusing-wave spectroscopy because of the diffusive transport of the light waves, include remote optical measurements of frequency-dependent viscoelasticity, studies of the microscopic dynamical processes in flowing sand and aging foam, a theoretical description of dynamic scattering from orientational fluctuations in liquid crystals and imaging of dynamic heterogeneities buried inside a turbid background medium.
318 citations
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TL;DR: A detailed study of the mechanism of film formation from aqueous dispersions of latex particles and the evolution of the mechanical properties of these films can be found in this article, which is important for the design of high performance coatings that are friendly to the environment.
Abstract: Modern microscopy and spectroscopic techniques have made possible deep insights into the process of film formation from aqueous dispersions of latex particles and the evolution of the mechanical properties of these films. This knowledge is important for the design of high performance coatings that are friendly to the environment. Although all aspects of the mechanism of film formation have received active attention over the past several years, some of the most important recent advances have occurred in three areas. First, there have been detailed studies of the drying process, from which we have a deeper understanding of the ways in which water evaporates from a wet latex dispersion. Second, further information is available about the compaction process, leading to the formation of a void free film. Finally, there have been several new studies of the polymer diffusion process, particularly in films formed from structured latex.
248 citations
TL;DR: The use of optical tweezers has been widely used in colloidal and interface science, from measurement of thermal-scale forces to manipulation of membrane structures as mentioned in this paper, and the development of novel optical tweezer techniques promises to extend this facility to the broadest class of soft condensed matter systems.
Abstract: The controlled manipulation of matter using radiation pressure, otherwise known as optical trapping, has emerged as a powerful experimental tool in the physical sciences. One particular trapping technique is known colloquially as the ‘optical tweezer’. Even though the theory of optical tweezer operation is still evolving, its use has provided exciting new insights into fundamental processes in colloid and interface science. From measurement of thermal-scale forces in colloidal suspensions to manipulation of membrane structures, optical tweezers provide pin-point access to the mesoscopic world. The development of novel optical tweezer techniques promises to extend this facility to the broadest class of soft condensed matter systems.
206 citations
TL;DR: In the past few years there have been dozens of reports of atomic-scale molecular dynamics simulations of lipid membranes as mentioned in this paper, and it is now generally accepted that there are advantages to doing membrane simulations at constant pressure, but there is also a debate on whether the external pressure should be isotropic or tension should be applied in the plane of the bilayer.
Abstract: In the past few years there have been dozens of reports of atomic-scale molecular dynamics simulations of lipid membranes Regarding recent methodological developments, it is now generally accepted that there are advantages to doing membrane simulations at constant pressure, but there is also a debate on whether the external pressure should be isotropic or whether tension should be applied in the plane of the bilayer Also, it has become clear that serious artifacts can be introduced into computer simulations if all electrostatic interactions are not taken into account Simulations can now faithfully reproduce many known aspects of the structures of gel and liquid crystal phase bilayers, and simulators have begun to include cholesterol and proteins in membrane simulations There is some disagreement between simulations on the details of the bilayer/water interface, and there has not been enough effort to analyze the dynamics afforded by simulations
198 citations
TL;DR: Hydrophobic interaction and hydrophilic repulsion occur in aqueous media and are caused by Lewis acid-base interactions of molecules, membranes or vesicles, with and among the surrounding water molecules.
Abstract: Hydrophobic interaction and hydrophilic repulsion occur in aqueous media and are caused by Lewis acid-base interactions of molecules, membranes or vesicles, with and among the surrounding water molecules. Recent scientific literature has been concerned with hydrophobicity/hydrophilicity of amino acids and proteins; protein adsorption and desorption (including influence of the secondary configuration of proteins, kinetics of protein adsorption and desorption, desorption and attenuation of adsorption of proteins, role of hydrophobic sites of proteins); hydrophilic repulsion and stabilization; aqueous partitioning (including coacervation and complex-coacervation); and phospholipids, membranes and vesicles (including inclusion of peptides into phospholipid layers, inclusion of polyethylene oxide into phospholipid layers, dissociation and lysis of phospholipid bilayers, removal of sterols from phospholipid monolayers, influence of plurivalent cations on charged and neutral phospholipid layers).
160 citations
TL;DR: The 3D self-assembled monolayer (3D-SAM) as mentioned in this paper can be studied by powerful techniques unavailable to conventional 2D -SAMs, such as differential scanning calorimetry, NMR spectroscopy, and transmission infrared spectroglobalization.
Abstract: The fusion of disparate areas of study can produce results that give insight both into the original topics and into new subjects. Such has been the case for the areas of colloids and self-assembled monolayers (SAMs). For example, an alkanethiolate monolayer bound to the surface of a gold colloid prevents aggregation of the metal particles, stabilizes them to harsh reaction conditions, and enhances their solubility in many organic solvents. The monolayer on the colloid (referred to as a 3D-SAM) can be studied by powerful techniques unavailable to conventional 2D-SAMs, including differential scanning calorimetry, NMR spectroscopy, and transmission infrared spectroscopy. Finally, other areas, such as the behavior of nanoelectrodes, the production of improved substrates for surface-enhanced Raman spectroscopy, and the advent of scanning tunneling microscopy (STM) measurements on the electronic properties of single clusters and molecules, have directly benefited from the interaction of colloids and SAMs.
125 citations
TL;DR: The authors proposed a pseudophase approach to accelerate or catalyze thermal reactions, but they also inhibit reactions and current pseudophases treat both phenomena and apply it to more complex mixtures and novel applications.
Abstract: Aggregates of amphiphiles often accelerate or ‘catalyze’ thermal reactions, but they also inhibit reactions and current pseudophase models treat both phenomena. Recent advances refine current models, offer new ones, treat solute and ion binding with more sophistication, enhance reactivity and selectivity with special catalysts, and apply the pseuodophase approach to more complex mixtures and novel applications.
TL;DR: A wide variety of morphologies exhibited by linear block copolymers made from two chemically distinct monomers has been extensively studied over many years and is now fairly well understood.
Abstract: Block copolymers have been the focus of intense scientific and commercial development because of their ability to organize into precise structures on the scale of ten to one hundred nanometers The wide variety of morphologies exhibited by linear block copolymers made from two chemically distinct monomers has been extensively studied over many years and is now fairly well understood Three extensions of these studies have uncovered new classes of structures and new relations between copolymer composition and morphology These include block copolymers with a nonlinear chain architecture, linear terpolymers with three chemically different blocks, and mixtures of linear diblocks with molecular weight or compositional differences These results have greatly expanded the range of domain sizes and types of morphology that can be found in block copolymer materials
TL;DR: The block copolymer micelles provide a means for controlled mineralization of inorganic particles having diameters between 1 and 20 nm and self-assembly of the macromolecules allows the defined arrangement of nanoparticles on substrates in thin films or in bulk samples and provides a concept to manipulate and transport particles that are much smaller than the wavelength of visible light as mentioned in this paper.
Abstract: Block copolymer micelles provide a means for controlled mineralization of inorganic particles having diameters between 1 and 20 nm. Besides the control over the particle growth, self-assembly of the macromolecules allows the defined arrangement of nanoparticles on substrates in thin films or in bulk samples and provides a concept to manipulate and transport particles that are much smaller than the wavelength of visible light. It has been demonstrated how thin polymer films can be prepared with monodisperse noble metal particles, that is, gold, silver, palladium and so on, or small semiconductor crystallites, for example, CdS and PbS. Other advances include the first successful attempt to control the formation of superlattices and the orientation and modification of the crystallites, aswell as their particle size and the topological arrangement.
TL;DR: The total internal reflection microscopy (TIRM) has proven to be a powerful tool for studying the interactions between a single, colloidal particle and a planar surface as discussed by the authors.
Abstract: Since its introduction in 1987, the optical technique of total internal reflection microscopy (TIRM) has evolved into a powerful tool for studying the interactions between a single, colloidal particle and a planar surface. In addition to being a highly sensitive method for quantifying the potential energy profile between a particle and plate (sensitivity of order 0.1 kT), the technique has also proven capable of measuring the hindered diffusion coefficient and mobility of a particle when the particle-plate gap width is much less than the particle radius. One of the most useful improvements in TIRM has been the incorporation of optical radiation pressure, which allows micromanipulating a single particle in three spatial dimensions. A similar method, termed evanescent wave light scattering (EWS), offers the possibility of measuring colloidal interactions using nanometer-sized particles.
TL;DR: In this article, the gradual association of surfactant aggregation in nonaqueous polar solvents (mainly formamide, ethylene glycol or glycerol) has been investigated.
Abstract: The research on surfactant aggregation in nonaqueous polar solvents (mainly formamide, ethylene glycol or glycerol) has, during the past year, been focused on elucidating further details of the interactions in previously investigated model systems. Some progress has been made in modelling the gradual association often found in these systems.
TL;DR: Water-soluble lipolytic enzymes act mainly at the water/lipid interface where their catalytic reactions are coupled with various interfacial phenomena such as penetration and activation of the enzyme, as well as desorption of the soluble products, solubilization in the presence of acceptors or molecular reorganization of the insoluble reaction products, inhibition, and so on as discussed by the authors.
Abstract: Water-soluble lipolytic enzymes act mainly at the water/lipid interface where their catalytic reactions are coupled with various interfacial phenomena such as penetration and activation of the enzyme, as well as desorption of the soluble products, solubilization in the presence of acceptors or molecular reorganization of the insoluble reaction products, inhibition, and so on. Various models have been proposed to analyze the kinetic data.
TL;DR: In this paper, it was shown that at sufficiently strong interparticle interaction, colloidal particles may form ordered crystalline arrays much in analogy to atomic systems, and well characterized model colloidal suspensions have therefore become valuable model systems for the study of the kinetics of crystal nucleation, growth and ripening.
Abstract: At sufficiently strong interparticle interaction, colloidal particles may form ordered crystalline arrays much in analogy to atomic systems. Well characterized model colloidal suspensions have therefore become valuable model systems for the study of the kinetics of crystal nucleation, growth and ripening. Significant progress has been made in this area throughout the past few years. Precise control of interaction parameters and new instrumental developments have allowed for quantitative determination of nucleation rate densities and growth velocities in monodisperse ‘hard’ and ‘soft sphere’ systems. Results confirm classical theories of nucleation and growth adapted to colloidal systems. The current emphasis of research is on modifications to the ideal scenario leading to a deeper qualitative understanding of underlying microscopic mechanisms.
TL;DR: Dendrimers are a class of polymers possessing hyperbranched structures as discussed by the authors, which makes them ideal building blocks for supramolecular chemistry, and they have a globular structure combined with a high number of end-groups and open cavities within.
Abstract: Dendrimers are a novel class of polymers possessing hyperbranched structures. A globular structure combined with a high number of end-groups and open cavities within makes these molecules ideal building blocks for supramolecular chemistry.
TL;DR: Advances in techniques that can pattern and control the topography of surfaces can create tailored substrates for attached cell culture and also surfaces to which proteins can be covalently or reversibly immobilized.
Abstract: Self-assembled monolayers of alkanethiolates on gold and of supported lipids are structurally well defined surfaces that have been important in understanding the relationships between the structure of a material and the interaction of proteins with the material. The synthetic flexibility available with these model surfaces makes it possible to design surfaces that resist the adsorption of protein, and also surfaces to which proteins can be covalently or reversibly immobilized. The past several years have seen advances in techniques that can pattern and control the topography of surfaces, these methods can create tailored substrates for attached cell culture.
TL;DR: The past year has seen a good deal of consolidation of knowledge concerning adsorption of proteins by a variety of existing techniques, and the start of the application of some newer methods to the study of adsorbed proteins as mentioned in this paper.
Abstract: The past year has seen a good deal of consolidation of knowledge concerning adsorption of proteins by a variety of existing techniques, and the start of the application of some newer methods to the study of adsorbed proteins. Direct, rather than inferential, studies of emulsion droplets remain, however, difficult to do.
TL;DR: In this paper, a consistent phenomenological description of the effects of undulations is given, but conclusive experimental evidence for or against the predicted effects remains elusive in all but the lamellar phase.
Abstract: Conformational entropy of the interfaces in microemulsions and surfactant solutions has been predicted, under some circumstances, to have significant effect upon their thermodynamic behavior. Continuum theories have led to a consistent phenomenological description of the effects of undulations, but conclusive experimental evidence for or against the predicted effects remains elusive in all but the lamellar phase. Work on the bicontinuous phases has led to an increasing focus on the role of topology and Gaussian rigidity, and on the role of anharmonic (in curvature) contributions to the bending energy.
TL;DR: In this article, the composition of the surfactant films separating micro-water and oil domains in bicontinuous type microemulsions has been determined on the basis of mass balance analysis and the geometry of three-phase tie triangles.
Abstract: Research effort in past years has focused on the development of microemulsions with specific properties, namely, high solubilizing power and temperature insensitivity. Phase behavior studies have provided the foundations for this development. On the basis of mass balance analysis and the geometry of three-phase tie triangles, the composition of the surfactant films separating micro-water and oil domains in bicontinuous type microemulsions has been determined. This information allows a better comparison of the solubilizing power of surfactants. In addition, decisive progress has been made in the development of surfactant systems for the preparation of biocompatible microemulsions.
TL;DR: Significant progress has been made in the understanding of various aspects of the processes of sedimentation and filtration of (mixtures of) colloidal spheres, such as hydrodynamic friction and the equation of state over a wide range of particle densities, the strongly hindered settling for charged spheres with long-range repulsions, and spontaneous layer formation as discussed by the authors.
Abstract: Significant progress has been made in the understanding of various aspects of the processes of sedimentation and filtration of (mixtures of) colloidal spheres. These aspects include the hydrodynamic friction and the equation of state over a wide range of particle densities, the strongly hindered settling for charged spheres with long-range repulsions, and spontaneous layer formation. For nonspherical colloids, many issues, such as the sedimentation dynamics of interacting rods or platelets, are still unresolved.
TL;DR: In this paper, simulations of end-grafted polymers show that whereas some of the individual polymer chains stretch in the direction of flow, the height of the grafted layer is only weakly dependent on the shear rate.
Abstract: Surface-polymer interactions are important in many technological applications, such as colloidal stabilization and adherence. During the past few years, considerable progress has been made in understanding these interactions and the forces between polymer-bearing surfaces. Under steady-state shear flow, simulations of end-grafted polymers show that whereas some of the individual polymer chains stretch in the direction of flow, the height of the grafted layer is only weakly dependent on the shear rate. When two surfaces bearing end-grafted chains are brought into contact, the normal force is observed in simulation to increase rapidly whereas the shear force is much smaller leading to a very small effective coefficient of friction. This behavior is in agreement with experiment.
TL;DR: NMR relaxation studies have been applied, and continue to be applied, to isotropic surfactant systems -were now also increasingly applied to anisotropic liquid crystalline systems.
Abstract: NMR continues to be of importance in experimental studies of surfactant systems. NMR-based diffusion studies play a central role as a routine tool in the investigation of the solution structure of microemulsions and related systems. Recently, we have also seen that the scope of the method has widened, as it is now being applied to liquid crystals, vesicles and emulsions, as well as to the question of the rheological properties of surfactant solutions. NMR relaxation studies—which over the years have been applied, and continue to be applied, to isotropic surfactant systems -are now also increasingly applied to anisotropic liquid crystalline systems. Finally, during the past couple of years, we have seen the first applications of modern multi-dimensional NMR techniques to surfactant systems.
TL;DR: In this paper, the formation of mixed micelles is described by the pseudophase separation approximation and modifications of the regular solution theory, although the size and composition distributions of mixed mouselles have also been modeled in the context of broader thermodynamic descriptions.
Abstract: Thermodynamic theories of surfactant self-assembly in aqueous solution describe the formation and unique characteristics of aggregates such as micelles and vesicles by considering both intra- and inter-aggregate interactions. Recent developments for single surfactant systems include new descriptions of micelle formation and growth, as well as detailed modeling of micellar size polydispersity and intermicellar interactions. In mixed surfactant systems, the formation of mixed micelles continues to be described by the pseudophase separation approximation and modifications of the regular solution theory, although the size and composition distributions of mixed micelles have also been modeled in the context of broader thermodynamic descriptions. Recent thermodynamic theories have also aimed at a more accurate description of the spontaneous formation and stabilization of mixed surfactant vesicles.
TL;DR: In this article, the authors used microscopic measurements to investigate adhesion hysteresis and the effects of hydrogen bonding and acid base interactions on this process using self-assembled monolayers.
Abstract: Recent advances in the study of friction and adhesion using self-assembled monolayers (SAMs) include the use of microscopic measurements to investigate adhesion hysteresis and the effects of hydrogen bonding and acid-base interactions on this process. Also, recent molecular dynamics simulations have enabled several important observations to be made concerning friction between surfaces and the role that surface molecules play in systems.
TL;DR: In this paper, a linear solvation free energy relationship has been developed for micelle-water partition coefficients, and the factors that influence the solubilization of proteins into and their release from reverse micelles in nonpolar solvents have been investigated.
Abstract: Solubilization of organic molecules in aqueous surfactant solutions has been actively investigated. Correlations for micelle-water partition coefficients have been developed using linear solvation free energy relationships. The solubilization of vesicles by surfactants and the accompanying structural transitions have been explored. The solubilization behavior of aggregates adsorbed on solid surfaces has been compared to that of micelles in solution. The factors that influence the solubilization of proteins into and their release from reverse micelles in nonpolar solvents have been investigated. The solubilization of hydrophobic molecules has been shown to induce shape transitions in block copolymer aggregates. The solubilization of metal salts by micelles has been made possible via novel lipophilic/metalophilic block copolymers.
TL;DR: In this paper, the use of confocal microscopy for examining colloids in their natural state has been discussed, including phase continuity in polymer blends, and a few examples with emulsions and gels.
Abstract: Confocal microscopy is one of the most useful morphological methods for examining specimens in their natural state. Its application to the study of colloids has been relatively limited in scope. The published work spans silica and polymer microsphere packing, phase continuity in polymer blends, and a few examples with emulsions and gels.
TL;DR: The structure and permeability of lipid bilayers have been probed by molecular dynamics (MD), the phase diagrams of idealized surfactants in water and oil have been computed, the effect of shear on the orientation of lamellar block copolymers has been simulated, and progress has been made toward the modeling of protein folding as discussed by the authors.
Abstract: Through the development of numerical methods that target time scales of interest, in the past year the structure and permeability of lipid bilayers have been probed by molecular dynamics (MD), the phase diagrams of idealized surfactants in water and oil have been computed, the effect of shear on the orientation of lamellar block copolymers has been simulated, and progress has been made toward the modeling of protein folding.