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Intelligent processing for customized polymer blends

Model systems were set up in order to study how the morphology of polymer blends is affected by processing, so that final properties can be predicted and improved. The model systems consisted of molten polymers at room temperature, selected with appropriate refractive indices, and a potential variation in viscous and elastic properties. At least one was in the liquid crystalline phase. The two main model systems studied were the polydimethylsiloxane/aqueous hydroxypropylcellulose solution and a mixture of two molten polymers with or without a copolymer (a system which is closer to industrial polymer blends), polydimethylsiloxane/polyisobutylene.

Light scattering was effectively used for morphology measurements (size distribution on droplet morphologies, use of transient morphologies to evaluate size and interfacial tension). High resolution optical microscopy/image analysis was developed and rheological tests used to measure morphology size. Drop deformation was monitored in shear by many different techniques (optical microscopy, light scattering, dichroism, shear stress, first normal stress difference, oscillatory rheology). Drop deformation was modelled and the results were successfully compared with experiments. An improved model of drop retraction was produced, giving a better estimate of interfacial tension. Stress predictions were obtained with an affine model and the Napoli model. The relative contributions of morphology breaking and coalescence were assessed and the direct evidence of these two mechanisms was shown in transient rheology and rheo-optics. There is a good understanding of break-up at rest and during flow at low concentrations. An extensive set of data on coalescence was generated. No measurable influence of the liquid crystalline character of one phase on interfacial tension or morphology was seen.

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