Structure-Property Relationships in Clay/Polymer Dispersions: Characterizing Bulk and Nanoscale Changes.

Abstract

Colloids and polymers are often used in industrial applications such as pharmaceuticals, food, paints, cosmetics and drilling fluids to achieve the desired properties. The work presented in this thesis focuses on the study of aqueous dispersions of Laponite®, a synthetic clay mineral, and how the addition Pluronic F127®, a triblock copolymer (PEO-PPO-PEO), changes the structure and properties of these dispersions.

The first part of the work presented shows that solution interactions between F127 molecules and Laponite particles have a significant effect on the room temperature properties of these systems and can interfere with gel forming abilities of Laponite. We also demonstrate a significant change in the microstructure of these materials using rheology and microscopy. In the second part, we focus on the thermal response of F127/Laponite dispersions. We show that these materials exhibit thermally reversible gel formation. At 3.6wt% F127, the presence of Laponite is essential for thermal gel formation while at 10wt% and 25wt% F127, the addition of Laponite delayed the onset of gel formation. The structure and thermally induced changes were probed using small angle x-ray scattering (SAXS). We show that F127 adsorbed onto the surface of the particles collapse as temperature increases allowing particle aggregation and gel formation.

Finally, we demonstrate the ability to produce a photogel forming system by adding a light active component to the formulation. Photorheology data indicates that gelation kinetics depend strongly on the formulation compositions using photo-rheology. Time-resolved UV-SAXS was used to track structural changes during UV irradiation and obtain direct evidence of particle restructuring. Finally, by comparing the structure changes with photo-rheology data, structure changes and bulk gel formation were found to occur on similar time scales. The data presented demonstrates that this process occurs in three fairly distinct regimes of interaction.