Polystyrene-silica latex system

Figure 10. Electron micrograph of composite silica-polystyrene latex system,SPL(-), prepared by using bare silica particles as the seed.

Figure 12. Gel permeation chromatogram of latex polymer separated from composite silica-polystyrene latex system, SPL(HPC).

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. 

Charged colloids in solution are ubiquitous in a wide variety of biological and technical systems. Some examples are proteins made by amino acids, micelles formed by charged surfactants or charged block copolymers, microemulsions formed by water, oil, and charged surfactants, silica particles made by silica oxide, and polystyrene based latex particles. In these systems, the physicochemical properties are to a large degree determined by electrostatic forces. Despite extensive studies of these forces for the last 50 years, the electrostatic interactions in such systems remain a central problem in colloidal science [1,2]. 

Figure 6.2. (a). Colloidal silica network on the surface of spores from Isoetes pantii (quill wort). Scale = 20 pm. (b). Polystyrene networks and foams produced as a biproduct of colloidal latex formation. Both types of colloidal system are typical of the diversity of patterns that can be derived from the interactions of minute particles. Scale (in (a)) = 50pm. 

There continues to be extensive interest in latexes and micellar systems. The structure of acrylic latex particles has been investigated by non-radiative energy transfer by labelling the co-monomers with fluorescent acceptor-donor systems. Phase separations could also be measured in this way. Excimer fluorescence has been used to measure the critical micelle temperature in diblock copolymers of polystyrene with ethylene-propylene and the results agree well with dynamic light scattering measurements. Fluorescence anisotropy has been used to measure adsorption isotherms of labelled polymers to silica as well as segmental relaxation processes in solutions of acrylic polymers. In the latter case unusual interactions were indicated between the polymers and chlorinated hydrocarbon solvents. Fluorescence analysis of hydrophobically modifled cellulose have shown the operation of slow dynamic processes while fluorescence... 

Figure 15. Fractograms of chromatographic silicas identified (by letter) in Table 11 obtained by using (a) sedimentation FFF system Sed 1 and (b) flow FFF system Flow II. The diameter scale at the top is obtained by using a calibration process based on equation 10 and the measured retention times of polystyrene latex standards. For sedimentation FFF, density compensation is carried out by adjusting the spin rate for each support material in accordance with its density (20). The corresponding spin rates utilized are A, 465 B, 479 C, 425 D, 500 ...

In Fig. 6, we illustrate some different ways that the core-shell topology could be varied for silica and gold. So far we have considered the two normal core-shell structures. We now focus on the third example the assembly of Au Si02 nanoparticles onto spherical polystyrene latex colloids. The resulting spheres are also essentially different to continuous metal shells grown on colloid templates, which have been reported by Halas and colleagues [17] and by van Blaaderen and coworkers [18]. Such continuous shells display optical properties associated with resonances of the whole shell, and are therefore extremely sensitive to both core size and shell thickness, while in the system presented here... 

In recent years there has been an increasing interest in heteroflocculation in aqueous media, and at least qualitative agreement found between experiment and theory, although not in every case. Systems studied include chromium hydroxide with polyvinyl chloride latex of similar size, silica with larger-size polyvinyl chloride latex , aluminium oxide and haematite with a smaller-size carboxylated polymer latex, and two polystyrene latexes of the same size but different surface groups. ... 

A similar technique was used for the preparation of polystyrene (PS)-Si02 nanohybrids, where colloidal silica solutions were mixed with PS solutions by means of ultrasonic homogenization [60]. Also, latex-silica nanohybrid films were synthesized upon mixing aqueous colloidal suspensions of silica and nanolatex polymer beads [61-63], Other silica-based nanohybrid systems with poly(ethylene oxide) (PEO) [64, 65], polyfvinyl alcohol) (PVA) [66], PS [67], polybutylacrylate [68], or PMMA [69] can be prepared by using the same suspension blending method. 

Figure 6.17. Typical data generated by the Amherst Process Instruments Inc. Aerosizer for aerosol systems, and powders aerosolized prior to characterization smdies. a) Calibration using aerosols of standard latex spheres of known size, b) Characterization of a mixture standard of polystyrene latex spheres, c) Characterization of a sample of 5 micron silica microspheres mixed with a small number of 10 micron microspheres. D) Glass spheres used in reflective paint (ballotini). E) Two oil mists diatacterized by direct injection into the Aerosizer .

Practically, the addition of a nonadsorbing polymer to a dispersion can induce flocculation of dispersed particles due to the depletion attraction. This was first observed by Cowell, Lin-In-On, and Vincent [1434]. When large amounts of poly (ethylene oxide) are added to an aqueous dispersion of hydrophilized polystyrene latex particles, the particles start to flocculate. For an organic dispersion, namely, hydrophobized silica particles in cyclohexane, de Hek and Vrij [1435] observed depletion-induced flocculation when dissolved polystyrene was added. Other combinations of particles and polymers followed [1436]. Phase diagrams for different particle-solvent-polymer systems were successfully drawn using the depletion potential of Asakura as interaction potential between dispersed spheres [1437] and for dissolved polymers using statistical mechanics [1438]. 

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