Study of Particles at Fluid-Fluid Interfaces

Particles are known to adsorb at fluid-fluid interfaces in small molecule systems such as oil/water emulsions. These particle stabilized emulsions are called Pickering emulsions. This thesis aims to extend the phenomenon of particle adsorption as observed in Pickering emulsions to polymer blends. Polymer blends are high viscosity analogs of emulsions. They present an economical way of obtaining a material with desired properties by blending two immiscible polymers. The goal of this work is to examine the effects of interfacial adsorption of particles in polymer blends.We examine the effect of the simultaneous adsorption of silica particles at two polymer-polymer interfaces in polyisobutylene/polydimethylsiloxane (PIB/PDMS) and polyethyleneoxide/polyisobutylene (PEO/PIB) blends, leading to the bridging of drops. Microscopically and rheologically, the particle mediated drop bridging is shown to result in the formation of clusters and networks of drops. This is reported to impart weak gel-like characteristics to the blend.A variety of commercially available particles viz. polytetrafluoroethylene (PTFE), iron (Fe), iron oxyhydroxide (FeOOH) and titanium dioxide (TiO2) are shown to be interfacially active at chemically different polyisoprene/polydimethylsiloxane (PI/PDMS) and not so different polyisoprene/polyisobutylene (PI/PIB) interfaces. This has led to the possibility of exploiting the phenomenon of interfacial adsorption of particles, as particulate compatibilizers, to suppress the drop coalescence in PI/PDMS blends. Rheology is presented as a microstructural tool to qualitatively probe the effect of interfacial activity of particles on the drop size. Our rheology and microscopy results with 0.5vol% of particles show that none of the particle types suppress coalescence of drops in the blends. Instead, PTFE and Fe particles promote coalescence of the drops in PI/PDMS blends.We also examine the stabilization of polymer foams, specifically polystyrene (PS) and polyisobutylene (PIB) by PTFE particles. Our experimental results show that PTFE particles can significantly enhance the stabilization of PS and PIB foams, making them stable for extended periods of time. We believe that this approach of using PTFE particles to stabilize PS and PIB foams may prove useful in a variety of other polymers as well, and may extend the range of polymers and processing conditions under which foaming can be conducted