The effect of polymer additives on polyolefin crystallization and homopolymer droplet emulsification

The impact of polymer additives on the crystallization of polyolefins and the emulsification of immiscible polymers in polymer blends were investigated in this dissertation. The crystallization of isotactic poly(1-butene), mixed with low molecular weight modifiers was quantified by calorimetry and optical microscopy. Two modifiers were used: oligomeric plasticizer, designated HOAO and oligomeric tackifier, designated HOCP. Modifiers decreased the nucleation rate, crystal growth rate, and final crystallinity of each blend.;Using rheo-optical techniques, we investigated the impact of interfacial wetting of symmetric diblock copolymers (BCPs) on the emulsification of polydimethylsiloxane (PDMS) droplets in polyethylene-propylene (PEP). Molecular weights of these components were varied to ensure that the inner block of the copolymer inside the droplet was collapsed, whereas the outer block was stretched. Droplet coalescence and interfacial surface tensions were measured using rheo-optical experiments. The BCPs mitigated shear-induced coalescence at lower shear stresses. Increased BCP stretching was inferred from surface tension measurements, which indicate that BCP stretching causes the droplet surface to saturate at lower BCP coverage. Droplet aggregation was detected with further reductions in shear stress. The aggregates form when attractive forces dominate the forces related to shearing flow.;The coalescence efficiency of the PDMS/PEP blends was measured with BCP volume fractions up to one percent by volume. Shear rate, surface tension, as well as the molecular weights and viscosities of all components are all hypothesized to impact coalescence. Within a PEP matrix, the coalescence efficiency was found to vary with a power law with respect to strain, where the amount of copolymer did not change the power law relationship.;Small amplitude oscillatory shear experiments (SAOS) experiments were used to measure the storage modulus (G') of the polymer blends. The frequency-dependent storage modulus shows a single relaxation for uncompatibilized blends, a characteristic of droplet relaxation. In comparison, two relaxations were observed for compatibilized formulations, corresponding to droplet relaxation as well interfacial relaxation. With increases in copolymer concentration, the shape relaxation shifts toward lower frequencies, signifying slower relaxation times. Further, shape and interfacial relaxations diminish with copolymer concentrations around one percent.