| Popis: |
The study of interactions within complex formulations is essential for the understanding of stability in colloidal dispersions and in particular the use of adsorbed polymers. Instability of dispersions caused by the displacement of the stabiliser is a well-known problem in industry, especially when two particles compete for the same stabiliser. Most experiments in this thesis involve the adsorption of poly(vinyl pyrrolidone), PVP, onto silica. Although a particle size dependency was observed, all measured silica diameters gave an NMR solvent relaxation rate enhancement upon PVP adsorption. Competition between PVP and poly(ethylene oxide), PEO, was investigated. When there is excess polymer, the PVP will replace the PEO at the silica/water interface. Small-angle neutron scattering measurements were used to complement the NMR data and provide detailed information on the structure of the polymer layer. The competition between particles for polymer adsorption was studied; silica and PVP were used, in competition with either alumina-modified silica or titanium dioxide. The ability for the solvent relaxation NMR technique to measure a population weighted average of the relaxation environments allowed predictions to be made for the relaxation rate in a number of polymer adsorption scenarios. These were compared to the experimental data to reveal that, in both situations, the PVP preferentially adsorbed onto silica. An experiment using SANS indicated that polymer competition may also be studied with the use of contrast-matching methods. Finally, the use of solvent relaxation NMR to study the kinetics of processes such as pigment sedimentation, polymer adsorption and competition was investigated. For the PVP/PEO system, it appeared that the adsorption of the polymers to Si02 was very rapid after sample agitation and displacement occurred in a timescale of minute |
