Polymer adsorption effect, stability

H. Yoneyama, Y. Murao, and H. Tamura, Effect of attachment of trimethylchlorosilane and polymer adsorption on stability of silicon photoelectrodes in aqueous solutions, I. Electroanal. Chem. 108, 87, 1980. 

The various regimes and effects obtained for the interaetion of polymer solutions between two surfaces have recently been reviewed [55]. It transpires that force-microscope experiments done on adsorbed polymer layers form an ideal tool for investigating the basic mechanisms of polymer adsorption, colloidal stabilization, and flocculation. 

If only electrostatic effects are responsible for polymer adsorption and flocculation, our results can be explained according to the same scheme as that used by Furusawa et Al.(20) to interprete the destabilization of negatively charged latex by a cationic polymer. In a first step, the adsorption of the polymer leads to the neutralization of the particles which are no more stabilized by electrostatic repulsions and there is flocculation (we have not studied this step since in our experiments polymer was always in large excess with respect to Al(0H)3). In a second step the adsorption inverses the charge and (we have indeed measured by... 

In this paper some of the current thinking in three closely-related areas is highlighted polymer adsorption the effect of polymer on the pairwise interaction between particles and the effect of polymers on dispersion stability. 

Polymer Adsorption at the Lower Critical Solution Temperature and Its Effect on Colloid Stability... 

Among the various branches in colloid and interface science, polymer adsorption and its effect on the colloid stability is one of the most crucial problems. Polymer molecules are increasingly used as stabilizers in many industrial preparations, where stability is needed at a high dispersed phase volume fraction, at a high electrolyte concentration, as well as under extreme temperature and flow velocity conditions. 

Understanding how polymer functions as a stabilizer and flocculant is obviously a problem of polymer adsorption and its conformation at the particle/liquid interface(l, 2). The process of polymer adsorption is fairly complicated the behavior depends on many factors, e.g., the nature of the adsorbent, the molecular weight of the polymer, the temperature, the effect of the solvent,... 

This entropic force is important where adsorption of polymers occnrs on colloidal particles. This is due to interaction between polymer chains on the interacting particles As the particles approach each other to the point where the polymer chains of the two particles interact, there is an decrease in entropy due to confinement of the chains, in an analogous manner to the solution species discussed earher, with the same result— repulsion. This is the basis of polymeric stabilization of colloids it is generally undesirable in CD, since adhesion and aggregation are preferred in this case. However, in view of the fact that the presence of such polymers (and other stabilizing adsorbates) may prevent the aggregation needed to build up a CD layer, it is important to be aware of the effect. 

Polymer molecules are often employed to stabilize colloids [1]. In most theoretical treatments of the effect of polymer adsorption [2-5], only the steric force is taken into account, and the steric force and the traditional double-layer force for particles devoid of hairs are assumed to be additive. The steric force is a short-range interaction which acts only when the chains on the surfaces of the two particles interpenetrate [6-8]. However, in addition to this short-range interaction, a hairy surface can also generate another effect, because it can change the dielectric constant in the vicinity of the surface. 

Ringenbach, E., Chauveteau, G., and Pefferkom, E.. Effect of soluble aluminum ions on polyelectrolyte-alumina interaction. Kinetics of polymer adsorption and colloid stabilization. Colloids Surf. A, 99, 161, 1995. 

Furusawa, K., Shou, Z., and Nagahashi, N., Polymer adsorption on fine particles the effect of particles size audits stability. Colloid Polym. Sci., 2IQ, 212, 1992. 

Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

Tadros, T.F. (1981) Polymer adsorption and dispersion stability, in The Effect of Polymers on Dispersion Properties (ed. T.F. Tadros), Academic Press,... 

Table 11 shows that PVP was an effective stabilizer if used with MMT prior to addition of the polymerizing monomers (ANI and PY) and the oxidants. Apparently, this procedure would help surface adsorption of the available polymeric stabilizer particles by the precipitating polymers. 

The colloidal stabilization of aqueous dispersions by polymer surfactants is believed to be a result of the adsorption of the amphiphilic macromolecules on the particle surface. This adsorption results in the formation of mono- or multi-layers of certain structure and thickness which provide sterical and/or electrostatic stabilization effects [1-5], Polymer adsorption from aqueous solution on a particle surface is a result of specific interactions of various active sites on the particle surface with corresponding sites (groups) of the macromolecule. Therefore the adsorption behaviour and the colloidal stabilization may be used as a sensitive approach (tool) to elucidate the effects of the polymers structural differences on their behaviour on the liquid-solid interface [6-9],... 

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