Effect of Valence and Chemical Species of Added Electrolyte on Polyelectrolyte Conformations and Interactions

Counterion condensation and effective charge of poly(styrenesulfonate)

The effective charge of poly(styrenesulfonate) has been investigated by diffusion and electrophoresis nuclear magnetic resonance (NMR). While the electrophoretic mobility is determined in the electrophoresis NMR experiment, the hydrodynamic friction is determined from diffusion NMR using Einstein's formula. On the timescale of the NMR experiment a steady state is reached, which results from the force balance between the electric field and the hydrodynamic friction from that the effective charge is calculated without any further model. For the monomer and short polymers the effective charge is equal to the nominal charge, the difference increases with an increasing degree of polymerisation. Increasing the ionic strength of the solution leads to enhanced counterion condensation. If the dielectric constant of the solution is lowered, condensation of counterions is enhanced as well. A lowered effective charge results in reduced repelling forces along the polymer chain and thus in a more compact conformation of the polymer as reflected in the hydrodynamic size. The effective charge of poly(styrenesulfonate) has been studied experimentally as a function of the degree of polymerisation, of the ionic strength and the dielectric constant of the solution.

Online monitoring of polymerization reactions in inverse emulsions

Automatic continuous online monitoring of polymerization reactions (ACOMP) was adapted to the monitoring of acrylamide polymerization in inverse emulsions. This is the first application of ACOMP to heterogeneous phase polymerization. The conversion and reduced viscosity were monitored by continuously inverting and diluting the emulsion phase using a small reactor sample stream and a breaker surfactant solution, followed by UV absorption and viscometric detection. This inversion into a stable portion of the polymer/surfactant phase diagram is accomplished in tens of seconds, yielding dilute solutions containing acrylamide (Aam), polyacrylamide (PA), oil droplets, and small quantities of surfactant, initiator and other debris, and low molecular weight compounds. After establishing the means of making ACOMP measurements, a first application of the method is made to resolving some of the kinetic issues involved in emulsion polymerization, including the evolution of molecular mass, and the simultaneous action of an "intrinsic" initiator and an added chemical initiator.

Plant protein-polysaccharide interactions in solutions: application of soft particle analysis and light scattering measurements

The soft particle analysis theory was applied to plant proteins and polysaccharides in solution, to determine the charge density of these polymers and the depth of the layer accessible by counterions according to pH conditions. In addition to the macromolecule shape characterized by light scattering measurements, these properties are also correlated with the optimum coacervation condition, so as to establish the prevalent plant protein-polysaccharide interactions governing the coacervate formation. Globulin was found to be highly charged and spherically shaped. The best coacervation condition was obtained at the pH value, which corresponds to the protein conformation with a dense and compact accessible layer. On the contrary, for the alpha gliadin, bearing a lower charge, a more extended conformation seems to be more favourable. For the plant proteins studied, the coacervation seems to be controlled by the structure of the counter polyanion used: from our model, it turns out that the rod-like structure of arabic gum observed at acidic pH allows the interaction with plant proteins to form coacervates, contrary to the highly charged and spherical structure of alginate.

Phenomenon observed at the onset of micellization using static light scattering

A phenomenon was observed near the critical micelle concentration (cmc) of surfactants using static light scattering. This consists of an unexpected peak in light scattering as the concentration varies between zero and above the cmc. This work studied three different surfactants: the two ionic surfactants hexadecyltrimethylammonium bromide (CTABr) and sodium dodecyl sulfate (SDS) and the nonionic surfactant Triton X-100. Peaks were observed for all three under different conditions such as varying ionic strengths and different concentration paths. These peaks are real, are reproducible, and appear to have static properties.