Proposal No. CTS-0421043 Principal Investigator: H. Winter, University of Massachusetts Amherst
This grant is for the development of two novel instruments. An optical micro-rheometer and a filament stretching rheometer will be designed to simultaneously measure the evolution of stress and material structure as a function of time and accumulated strain in shear and in uniaxial extension. The optical micro-rheometer combines stress measurement with simultaneous observation of light scattering, microscopy, fluorescence, and birefringence from the sample. The filament stretching rheometer is capable of measuring the response of complex fluids to a transient extensional flow starting from an imposed initial microstructural deformation, alignment and morphology. Both instruments are designed for studies on very small samples that are required for collaboration with polymer chemists who typically prepare their most advanced materials as small samples only. Experiments with the proposed instruments will generate a deeper understanding of the behavior of complex materials such as liquid crystalline polymers under shear, crystallizing polymers as a function of molecular topology, phase separating polymer blends in shear, self assembling micellar systems in shear and extension, and particle topology in particle gels. The properties of these complex materials are strongly affected by the deformation and alignment of their microstructure in addition to their molecular composition. The study of rheology attempts to relate the local state of stress in such complex materials to the local deformation rate, elapsed time, and accumulated strain through a series of carefully designed experiments. Specifically for the new experiments, simultaneous measurement of stress and structure are expected to lead to conclusive information about flow-induced transitional states. Among the broader impacts of this work is to facilitate the development of new products, which depends on the availability of suitable materials. Therefore it is essential to develop new instruments that further our ability to create and understand new materials. In addition, the availability of the proposed instruments as a multi-user facility will have great impact on the education of all researchers involved. Once the instruments are completed, broader interaction and cross-fertilization of ideas will be enabled. Regular interdisciplinary research meetings will involve both graduate and undergraduate students. While the new instruments allow graduate students to perform their advanced research, undergraduate students will particularly profit from learning the proposed optical methods that will allow them to perform very advanced materials research on complicated topics through visual observation before their analytical skills have been developed to a comparable level. This will introduce students at an early state of their education to the excitement of discovery.
