Effect of Adsorbed Polymers

Effect of adsorbed polymer on the double-layer. Because of the presence of adsorbed train segments, the double layer is modified. The zeta-potential, , is displaced because the adsorbed polymer displaces the plane of shear. The parameters for describing adsorbed polymers are the fraction of the first layer covered by segments, 0, and the effective thickness, A, of the polymer layer, The insert gives the distribution of segments over trains and loops for polyvinyl alcohol adsorbed on silver iodide. Results obtained from double layer and electrophoresis measurements. 

Vincent, B. Adv. Coll. Interface Sci. 4 (1974) 193. The effect of adsorbed polymers on dispersion stability. 

In general, the adsorption of a surfactant on particles with previously adsorbed polymer can be influenced by (i) a reduction of surface area available for adsorption as a result of the presence of adsorbed polymer, (ii) possible interactions between polymer and surfactant in the bulk solution or in the interfacial region (that is, surfactant with loops, tails or trains of adsorbed polymer molecules), (iii) the steric effect of adsorbed polymer, preventing approach of surfactant molecules for adsorption at the surface, or (iv) possible electrostatic effects if polymer and/or surfactant are charged species. 

Zaitoun, A., Kohler, N., 1988. Two phase flow through porous media Effect of adsorbed polymer layer. Paper SPE 18085 presented at the SPE 63" Annual Technical Conference, Houston, 2-5 October. 

Effect of Adsorbed Polymer Conformation on Dispersion Characteristics... 

Hydrodynamic and solvation factors, emulsion stability, microemulsions, multiple emulsions, coagulation and flocculation theory, foam stability, demulsiflcation and defoaming, the effects of adsorbed polymers on stability and flocculation... 

Chapter in on colloidal dispersions. Electrostatics follows S.I. units. New section on characterization of colloidal dispersions. Section on effects of adsorbed polymer completely rewritten with new material. 

Brooks, D.E. (1973). Effect of Neutral Polymers on Electrokinetic Potential of CeUs and Other Charged Particles. 11. Model for Effect of Adsorbed Polymer on Diffuse Double Layer. J. Colloid Interface Sci., Vol. 43, pp. 687-699. 

Effect of adsorbed polymer on two-phase flow and relative permeabilities... 

A very similar effect of the surface concentration on the conformation of adsorbed macromolecules was observed by Cohen Stuart et al. [25] who studied the diffusion of the polystyrene latex particles in aqueous solutions of PEO by photon-correlation spectroscopy. The thickness of the hydrodynamic layer 8 (nm) calculated from the loss of the particle diffusivity was low at low coverage but showed a steep increase as the adsorbed amount exceeded a certain threshold. Concretely, 8 increased from 40 to 170 nm when the surface concentration of PEO rose from 1.0 to 1.5 mg/m2. This character of the dependence is consistent with the calculations made by the authors [25] according to the theory developed by Scheutjens and Fleer [10,12] which predicts a similar variation of the hydrodynamic layer thickness of adsorbed polymer with coverage. The dominant contribution to this thickness comes from long tails which extend far into the solution. 

The effectiveness of nonionic polymers as migrating clay stabilizers and the geometry of the adsorbed polymer - mineral complex may be substantially different for the nonionic polymers and the quaternary ammonium salt polymers. The observation that some quaternary ammonium salt polymers, while effective swelling clay stabilizers, are ineffective mineral fines stabilizers is consistent with a different adsorbed polymer - particle complex geometry on different mineral surfaces. 

Among the properties measured here, the settling rate is mainly a measure of the size of the floes and in later stages the compressibility of floes and floe networks, and the supernatant clarity is a measure of the size distribution of floes and size dependent capture of the particles and floes by the polymer. The sediment volume and the pulp viscosity on the other hand, are direct measures, not only of floe size and structure but also of adsorbed polymer layers. It is to be noted in this regard that it is this latter aspect which makes it possible to estimate the thickness of adsorbed polymer layers by measuring the viscosity of the medium and the suspension in the presence of polymers (20,21). This combination of effects is another reason one cannot always expect correlation between various flocculation responses. 

It has been assumed that the total surface area of a floe is proportional to the number of singlets in that floe, a reasonable assumption for small floes and open floe structures. The effective fractional surface coverage, 0k, is not necessarily equal to the fractional surface coverage at equilibrium for a given amount of adsorbed polymer. This will be discussed in some detail below. 

Decreased mobility of adsorbed chains has been observed and proved in many cases both in the melt and in the solid state [52-54] and changes in composite properties are very often explained by it [52,54]. Overall properties of the interphase, however, are not completely clear. Based on model calculations the formation of a soft interphase is claimed [51], while in most cases the increased stiffness of the composite is explained by the presence of a rigid interphase [55,56]. The contradiction obviously stems from two opposing effects. Imperfection of the crystallites and decreased crystallinity of the interphase should lead to lower modulus and strength and larger deformability. Adhesion and hindered mobility of adsorbed polymer chains, on the other hand, decrease deformability and increase the strength of the interlayer. 

Fig. 22. Molecular weight effect of synthetic polymer adsorption. Molecular weight (MW) distribution of poly(vinyl chloride) in solution and in the adsorbed layer at equilibrium. Note that the adsorbed material has a higher average MW than the bulk solution (from Ref.1001, p. 120)...

Before describing this theory, we outline the theory of Hoeve et al.41) formulated under the assumptions that the polymer chain is so long that end effects, i.e. tail formation, may be neglected and that the surface coverage is so low that the interaction of adsorbed polymer chains is negligible. 

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