Surfactant-free Polystyrene Latex Research Articles

The influence of PEO/poly(vinyl phenol- co-styrene sulfonate) aqueous complex structure on flocculation

Colloidal suspensions were flocculated with complexes formed from high molecular weight polyethylene oxide (PEO) and a cofactor. Poly(vinyl phenol- co-potassium styrene sulfate) (PKS) or poly(styrene- co-styrene sulfonate) (PS- co-SSS) copolymers were used as the cofactors for this work. The larger the PEO/cofactor complex species, the better the initial flocculation. Factors such as increasing temperature or ionic strength that gave smaller complexes also gave poorer flocculation. Cofactor performance was sensitive to the balance of hydrophobic phenolic groups and hydrophilic styrene sulfonates. If there are too few phenolic groups, the PEO/PSK complexes are large but are too weak to give shear-resistant flocs, whereas complexes formed with high phenolic content PSK are relatively small, giving poorer flocculation but more shear-resistant flocs. Both phenyl and phenol groups are effective as the hydrophobic component in the cofactor. The hydrogen-bonding potential of phenolic cofactors does not seem to offer much advantage relative to phenyl groups. A crucial step in the flocculation is the adsorption of PEO/cofactor complex onto the target colloids. Thus, flocculation is sensitive to the target colloid surface chemistry. Positively charged precipitated calcium carbonate and surfactant-free polystyrene latex are particularly easy to flocculate because adsorption is driven by electrostatic and hydrophobic interactions, respectively. By contrast, the latex coated with hydrophilic poly( N-isopropylacrylamide) (PNIPAM) does not flocculate because the PEO/cofactor complex does not bind to PNIPAM. Finally, the flocculation of highly negatively charged, dextran sulfate coated calcium carbonate seems to be stimulated by the presence of soluble calcium ions that make the complex less soluble and more likely to adsorb.

Temperature Induced Hydrophobic Adsorption and Desorption of Linear Polymer Chains on Surfactant-Free Latex Nanoparticles

The adsorption of thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) on surfactant-free polystyrene latex was used as a model system to study the effect of chain hydrophobicity on the adsorption of protein on hydrophobic surface. PNIPAM is only soluble in water at lower temperatures with a lower critical solution temperature (LCST) of ∼32 °C. Using PNIPAM, we were able to continuously adjust the chain hydrophobicity and manipulate the adsorption by a simply temperature variation. A combination of static and dynamic laser light scattering was used to study the amount of the adsorption and the thickness of the adsorbed polymer layer. We found that there existed a hysteresis of the adsorption in the heating-and-cooling cycle, indicating an additional adsorption at temperatures higher than the LCST. We also found that the heating rate could greatly affect the adsorption. Our results revealed that the desorption accompanying the swelling of the adsorbed PNIPAM layer was logarithmically proportional to the desorption time, indicating a diffusion-controlled process.

Deposition of hairy latex particles onto a glass surface

Hairy latex particles are observed to deposit on a glass surface under conditions for which the DLVO theory predicts no deposition. From electrophoretic mobility and dynamic light scattering experiments it can be concluded that the surfactant-free polystyrene latex particles used in this study are “hairy”, with the length of the hairs being more than 5nm. It is speculated that the hairs can tunnel through the energy barrier and make contact with the glass since deposition occurs when the length of the hairs is comparable to the minimum distance of approach calculated from DLVO theory. Consistent with this model, it is found that the deposition rates increase with salt concentration, while the detachment rates decrease with salt concentration.

Flocculation of Polystyrene Latex with Mixtures of Poly(p-vinylphenol) and Poly(ethylene oxide)

Poly(p-vinylphenol) (PVPh) was evaluated in conjunction with high molecular weight poly(ethylene oxide) (PEO) as a flocculant for monodisperse surfactant-free polystyrene latex. PVPh was effective ...

Effect of electrolyte type on the electrophoretic mobility of polystyrene latex colloids

Electrophoretic mobility studies of surfactant-free polystyrene latex particles in various types of inorganic electrolytes are reported. The particles carry sulfate functional groups and cover a wide range of surface charge. The electrophoretic mobility curves of all latices exhibit a pronounced maximum as a function of 1:1 electrolyte (KCl) concentrations. With 2:1 and 3:1 electrolytes (CaCl 2 and LaCl 3 respectively), the electrophoretic mobility curves pass through a minimum followed by a maximum. The results are discussed in terms of models that have been previously proposed to explain these maxima in the mobility curves. Our results suggest that the increase of mobility with salt concentration may be attributed to the approach of co-ions close to the hydrophobic surface of the particles. It is also suggested that three competing processes at the interface determine the shape of the mobility curves.

Particle-macromolecule interactions in aqueous solution Part II: Adsorption and flow studies of polyvinylalcohol/polystyrene latex mixtures

The adsorption characteristics of PvOH on a surfactant free polystyrene latex surface have been determined from adsorption isotherm and zeta potential measurements. The concentration and shear dependence of the flow behaviour of surfactant free polystyrene latex alone, and together with PvOH, have also been obtained. The. data show that the marked increase in viscosity observed in polystyrene dispersions upon the addition of PvOH is satisfactorily accounted for by the excluded volume effect of an adsorbed monolayer of PvOH on the polystyrene surface.