Thin-film stability in the formation of polymeric blends, foams, and nanostructured materials

The present study experimentally investigates the mechanisms involved in the coalescence process related to the formation of polymer blends (flow-induced coalescence of two equal-sized drops) and that related to the formation of polymeric foams (viscous coalescence of expanding low-viscosity drops). The effect of surface-active block-copolymer and the interfacial activity of polymer-coated gold nanoparticles are also studied.; Head-on collision experiments have been designed with a time-dependent force mimicking the force-history during the interaction of two droplets in a glancing collision. The (near)axisymmetric film drainage process, achieved by a head-on collision, has been proven to provide a good approximation to the real non-axisymmetric glancing collision. The same approach was used in the presence of block-copolymers (adding another non-linearity due to copolymer convection/diffusion from the external flow and thin-film drainage). The same qualitative results were obtained, emphasizing the sensitivity of the film drainage process and the evolution of the film geometry to the details of the force-history.; Similarly, an experimental device for the study of the interaction of two equal-sized inviscid expanding drops was designed, in order to mimic the interactions of two expanding bubbles during the formation of polymeric foams; to the best of our knowledge, this is the first experimental device that allows the study of the viscous thin-film drainage and coalescence of expanding drops. A simple scaling theory was developed, based on the drainage of two approaching flat disk-like interfaces; in contrast to the flow-induced drop coalescence, the thin film radius will expand throughout the interaction, as the volume of the drops increases.; Finally, the interfacial activity of polymer-coated gold nanoparticles was studied using the capabilities of the four-roll mill. The nanoparticle locality within the polymeric domains (bulk or interface) was accomplished with the design and synthesis of tailored PDMS and PBd ligands. The formation of nanoparticles was determined via TEM imaging and their interfacial activity was manifested with a reduction in the interfacial tension and inhibition of coalescence. The effect of the interfacial concentration of nanoparticles on the interfacial tension and drainage time for coalescence was also studied.