On the Structure and Dynamics of Polyelectrolyte Gel Systems and Gel-surfactant Complexes

• Main Author: Råsmark, Per Johan
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Fysikalisk-kemiska institutionen 2004
• Subjects: Physical chemistry; polyelectrolyte gel; microgel; dynamic light scattering; Raman spectroscopy; periodic boundary conditions; percolation; hypersphere; Monte Carlo; Brownian dynamics; Fysikalisk kemi
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4652; http://nbn-resolving.de/urn:isbn:91-554-6083-6

This thesis describes the results of experimental work on polyelectrolyte gels and their interaction with oppositely charged surfactants, and presents two new algorithms applicable to the simulation of colloid and polymer systems. The model systems investigated were crosslinked poly(acrylate) (PA) and poly(styrene sulphonate) (PSS), and the surfactant was dodecyl trimethylammonium bromide (DoTAB). Pure gel materials were studied using dynamic light scattering. It was shown that the diffusion coefficient (D) increases with increasing degree of swelling and the concentration dependence is larger than predicted by scaling arguments. For gels at swelling equilibrium D increases with increasing degree of crosslinking. In subsequent studies on gel particles in DoTAB solution, Raman spectra were recorded at different positions in the gel. For both types of gels two distinct regions could be observed. For PA the surfactant is localised in the outer phase without any surfactant in the core, while for PSS the surfactant was distributed such that it had the same concentration relative to the polymer throughout the gel. In a second experiment, the kinetics for the deswelling of microscopic PSS particles in DoTAB solution was studied. It was found that the final volume varied linearly with the DoTAB concentration, and the rate of volume decrease could be fitted to a single exponential indicating stagnant layer diffusion to be the rate limiting process for the deswelling of the PSS particles. In the second part, I first describe an algorithm showing an efficient way to detect percolation in simulations, with periodic boundary conditions, using recursion. Spherical boundary conditions is an alternative to periodic boundary conditions for systems with long-range interactions. In the last part, the possibility to use the surface of a hypersphere in four dimensions for simulations of polymer systems is investigated, and algorithms for Monte Carlo and Brownian dynamics simulations are described.