Latex particles colloidal behavior

Taniguchi T, Duracher D, Delair T, Elaissari A, Pichot C (2003) Adsorption/desorption behavior and covalent grafting of an antibody onto cationic amino-functionalized poly(styrene-/V-isopropyl aery I am i de) core-shell latex particles. Colloids Surf B Biointerfaces 29 53-65... 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

The object of this study was to clarify some aspects of the mechanism of shear-induced flocculation in colloidal dispersions. Vinyl chloride homopolymer and copolymer latices were prepared by emulsion polymerization using sodium dodecyl sulphate as emulsifier. Agglomeration behavior in these latices was studied by measuring the mechanical stability using a high speed stirring test. The latex particle size was measured by an analytical centrifuge. Molecular areas of emulsifier in the saturated adsorption layer at the surface of homopolymer and copolymer latex particles were estimated from adsorption titration data. 

Poly(methylmethacrylate), PMMA, latex particles have also served as a model colloidal system for many years (mainly as hard spheres with hydroxy stearic acid (HSA) chains being the grafting choice [91,113,114]). Tunability was achieved by varying the core size and the size of the corona chains. The comparison between chemically grafted (stable) and end-adsorbed temperature-sensitive chains (usually surfactants) has shown that the adsorbed chain particles exhibit similar rheological behavior with chemically grafted particles [115]. 

In order to control protein adsorption, to enhance it in some cases and prevent it in others, it is necessary to understand the various stages involved in the process. The interaction of protein molecules with polystyrene (PS) latex particles having a well-defined surface has proved to be a very useful model system with which to study the interfacial behavior of proteins. Other colloidal systems, including silica and metal particles, have also been used in these investigations, and although this review concentrates mainly on interactions between proteins and latex particles, other systems are also mentioned where appropriate. Before looking at the interactions of proteins with PS latex particles in detail, it is worthwhile to take a brief overview of the two major components in the system. 

The basic parameter determining the behavior of an emulsion polymer latex is the population density of latex particles. If the number of particles is controlled, then control of other colloidal features of the system can be realized. 

Latex particles can be used for micromanipulation by taking into account that some of their colloidal properties (particle size and dielectric behavior) can be affected for instance imder the action of a laser beam or an electric field. 

Syntheses of different types of latex particles by emulsion polymerization that differ in particle size, polymer hydrophificity, and surface coverage with functional groups were presented by Paulke et al. [51 ]. The particles were equipped with intensive fluorescence. Concentrated particle suspensions were injected into the brain tissue of mice and the effect of two kinds of beads is shown in brain sections. The same research group [52] presented a very different work on electrophoretic three-dimensional (3D)-mobility profiles of latex particles with different surface groups. In particular, hydroxyl functions were studied in different surroundings. The latexes gave model colloids with different electrophoretic behavior in comparison with classical anionic monodisperse PS latex particles. 

Surface charge on functionalized latex particles having carboxyl groups and additionally ioniz-able groups were used [53] to study the behavior of uniformly charged and zwitterionic colloids in electrolytes of different ionic strength. 

Addition of different kinds of charged polymers (polyelectrolytes) offers one effective way to control the stability of a colloidal solution. When charged polymers adsorb on neutral colloids, the colloids repel each other for electrostatic reasons. This behavior is called electrostatic stabilization and is responsible for the long shelf-life of certain latex paints. Polymers can also stabilize a dispersion for steric reasons when they are grafted or adsorbed to the particles. If two polymer covered particles approach it will lead to a restriction on the configurational freedom for the polymers giving rise to a repulsive force. 

Steric hyperlayer-FFF is well established as a fast separation technique for mi-cron-sized particles, although the hydrodynamic lift forces are not yet well understood. This is worse for the steric elution of non-spherical particles. Despite over thirty years of application of FFF techniques, only very little has been reported about the fractionation of non-spherical particles by any FFF mode. The few available studies so far reported are the investigation of coal particles [423,424], inorganic colloids [462], metal particles [69] and doublets of polystyrene beads, rod-shaped glass fibers, compressed latex discs and quartz particles with complex shape [427]. In the latter paper, systematic studies of particle shape on the retention behavior of non-spherical particles are reported with the result that the qualitative major retention behavior of spheres and other shapes is equal (e.g. response to increase in the field strength, etc.). However, the quantitative differences in the retention behavior were found to depend on numerous factors in a complex way so that no quantitative relation between the hydrodynamic radius and the retention ratio could be established. 

In addition to giving information about the shape and internal structure of colloidal aggregates, SANS studies can also be used profitably to determine the thickness and conformation of polymer layers adsorbed onto the surface of colloidal particles such as latex nanoparticles, and in some special cases, the surface of emulsion droplets. ° In such studies, the particles on which the polymer is adsorbed must generally be very accurately contrast matched to the solvent so as to allow information to be obtained only about the adsorbed layer. SANS studies have also been recently used in combination with differential scanning calorimetry and visual inspection of the solutions, to draw up a (simplified) partial phase diagram of the aggregation behavior of a polymeric surfactant in water.t ... 

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