Polymers simple charge neutralization

As mentioned earlier, polymers can exert a dramatic influence on colloidal stability. However, the description of particle interactions in the presence of polymers is complex, and even a qualitative estimation of conditions for attraction or repulsion has yet to be developed. Three theories have been proposed to explain flocculation of charged particles by oppositely charged polyelectrolytes bridging, simple charge neutralization, and charge patch neutralization. 

Simple Charge Neutralization and Charge Patch Neutralization Oppositely charged polyelectrolytes reduce the particle surface charge density such that particles may approach each other sufficiently closely so that the attractive van der Waals force becomes effective. Flocculation caused by this mechanism should not be sensitive to the molecular weight of the polymer. 

Runkana et al. [23, 25] developed population balance models (PBMs) for polymer-induced flocculation by two well-known mechanisms, simple charge neutralization [23] and bridging [25]. They assumed that polymer adsorption on oppositely charged particle surfaces is very fast and equilibrium conformation is achieved before collisions between particles take place. It was also assumed that polymer adsorbs uniformly and polymer surface coverage and adsorbed layer thickness are the same for all particles. The composite polymer-coated particle radius was estimated by adding adsorbed layer thickness to the soM particle radius. 

The formation of complexes is not restricted to mixtures of polyectrolytes and surfactants of opposite charge. Neutral polymers and ionic surfactants can also form bulk and/or surface complexes. Philip et al. [74] have studied the colloidal forces in presence of neutral polymer/ionic surfactant mixtures in the case where both species can adsorb at the interface of oil droplets dispersed in an aqueous phase. The molecules used in their studies are a neutral PVA-Vac copolymer (vinyl alcohol [88%] and vinyl acetate [12%]), with average molecular weight M = 155000 g/mol, and ionic surfactants such as SDS. The force measurements were performed using MCT. The force profiles were always roughly linear in semilogarithmic scale and were fitted by a simple exponential function ... 

Tanaka et al. studied the decay reactions of PVB radical anions produced by electron pulses in MTHF [47]. At low concentration ( < 0.05 base-mol dm - 3) of polymers the decay reaction followed a simple second-order kinetics. The charge neutralization reaction is responsible for the decay curve as is the case of biphenyl radical anions. However, the rate constant of the polymer anions was only a half or one-third of that of the biphenyl anion, because of the small diffusion coefficient of the polymer ion in solution. At high concentration of the polymer, a spike was observed in the time-profile of the PVB anion this was attributed to the retarded geminate recombinations within micro-domains where the polymers were entangled with each other. 

In any consideration of what is presently known regarding adsorption from aqueous solution it is necessary to distinguish between neutral species, simple ions, complex ions, surface active agents, polyelectrolytes, and charged and uncharged high polymers. Much of the data available in the literature relates to the adsorption of polymers and complex-... 

A simple model calculation of the folding transition in line with the above analysis has demonstrated that the degree of the remanent charge inside the folded part is a crucial factor for the transition manner (Fig. 3.12). If the folded part is completely neutralized by oppositely charged low molecular solvents, then the scenario developed for neutral semiflexible polymers can be applied. 

A simple way consists in testing two ATPS systems, dextran 40/PEG-8000 and dextran 500/PEG-8000, which lead to a relatively quick settling and allow reproducible results. For charged macromolecules, the two key parameters are the pH with regard to the isoelectric point of the product and the nature and concentration of the chosen salt. The composition in polymer has a smaller influence, except for some neutral compounds. 

If neutral and charged polymer brushes are exposed to solvents, a very interesting and rich phase behavior can be observed. As a consequence, such surface-attached brushes have become the focus of considerable theoretical efforts in studies on the structure and phase behavior of such polymer chains in contact with a solvent. The thickness of a neutral brush scales linearly with the degree of polymerization, N, which is in stark contrast to the well-known characteristics of free polymer chains in a good solvent, where the radius of the coils scales as R oc AT0 58. For neutral brushes the simple scaling... 

---