PS latex

An important step in tire progress of colloid science was tire development of monodisperse polymer latex suspensions in tire 1950s. These are prepared by emulsion polymerization, which is nowadays also carried out industrially on a large scale for many different polymers. Perhaps tire best-studied colloidal model system is tliat of polystyrene (PS) latex [9]. This is prepared with a hydrophilic group (such as sulphate) at tire end of each molecule. In water tliis produces well defined spheres witli a number of end groups at tire surface, which (partly) ionize to... 

Figure C2.6.11. SEM of AB2 stmcture, fonned in aqueous mixtures of PS latex spheres witli <3 = 68 nm and a = 264 nm (courtesy of Prof R H Ottewill).

Polymer adsorption is important in the flocculation and stabilization of colloidal sols and has been reviewed by Vincent et al. (1) and Tadros (2). Polyvinyl alcohol (PVA) has been used in these studies because of its practical application in textiles, adhesives, and coatings. The adsorption of PVA has been studied on silver iodide by Fleer (3) and Koopal (4), and on polystyrene (PS) latex particles by Garvey (5). The adsorption isotherms reported by these workers extend up to 600 ppm PVA. The adsorption at... 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

Effect of PVA Molecular Weight on Adsorbed Layer Thickness. Figure 4 shows the variation of reduced viscosity with volume fraction for the bare and PVA-covered 190nm-size PS latex particles. For the bare particles, nre(j/ is independent of and the value of the Einstein coefficient is ca. 3.0. For the covered particles, rired/ t increases linearly with tp. Table IV gives the adsorbed layer thicknesses calculated from the differences in the intercepts for the bare and covered particles and determined by photon correlation spectroscopy, as well as the root-mean-square radii of gyration of the free polymer coil in solution. The agreement of the adsorbed layer thicknesses determined by two independent methods is remarkable. The increase in adsorbed layer thickness follows the same dependence on molecular weight as the adsorption density, i.e., for the fully hydrolyzed PVA s and... 

Effect of PS Latex Particle Size on PVA Adsorption. Figure 5... 

Effect of PS Latex Particle Size on Adsorbed Layer Thickness. Figure 6 shows the variation of reduced viscosity with volume fraction for 190, 400, and HOOnm-size bare and PVA-covered PS latex particles. The viscosity variation of the different-size bare particles was the same, with an Einstein coefficient of ca. 3.0. The... 

In a previous paper (15) the segment density of PVA adsorbed on PS latex in water was presented and it was noted that H Cgans was at the extremity of the s.a.n.s. profile. Calculating <5 assuming a value of a of 0.5 nm gives 13 nm in contrast to the experimental value of 18 nm. The discrepancy here is much smaller than in the case of PE0. This effect is difficult to interpret without further theoretical work but may be attributable to the fact that the PVA chain is less flexible than PEO and that the block structure (PVA is a random block copolymer of vinyl acetate. 12%, and vinyl alcohol) makes the formation of tails less likely. 

TADROS PS Latex Dispersions with Adsorbed PVA Layers... 

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