The Effect of Surface-active Block Copolymers on Two-phase Flow

Blending two thermodynamically immiscible polymers to create a material with desirable properties is an attractive alternative to synthesizing polymers from new monomers. The microstructure of the blend often determines its physical properties and thus its uses. It is therefore beneficial to control the microstructure during blending, and it is well known that compatibilizers (macromolecular surfactants) can alter the morphological evolution of polymer blends. This work aims to examine the effect of compatibilizers on flow phenomena in which interfacial tension plays an important role, i.e. two-phase flow during the morphological development of immiscible polymer blends. We study compatibilizer effects on the two-phase flow of polymers at two length scales: single drops and macroscopic blends. A key concern is the effects of compatibilizer on rheological properties.Experiments on the effect of surfactant on single drop dynamics in a PEO/PPO/Pluronic system showed complex and previously unknown and unusual behavior. We hypothesize that this unusual behavior was caused by the sample preparation protocol.For multi-drop systems, or blends, of a PIB/PDMS model system near phase inversion, we identify the key role of the compatibilizer as immobilizing the interface, and we also identify the effect of such immobilization on two-phase rheology and coalescence suppression. Also, the compatibilizer affected the morphological development by decreasing the drop size through a combination of a decreased interfacial tension and coalescence suppression. We attempted to exploit this coalescence suppression phenomenon as a mechanism of kinetically trapping the morphology in desired states. By varying the sequence of mixing, a double emulsion morphology was created. These double emulsion blends show complex relaxation behavior and an increase in viscosity due to the increased effective droplet volume fraction. We also attempted to exploit coalescence suppression to create a blend with a dispersed phase volume fraction exceeding 50%, but were unsuccessful, even with reactive compatibilization in a PA/PS system. New experimental work suggests it might be possible to use reactive compatibilizers that crosslink at the interface to effect large changes in two-phase morphology not possible with traditional compatibilizers