Acquisition of Rheometers for Materials Characterization under Controlled Stress or Strain

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9626307 Brady A central issue in soft materials is the prediction of their behavior during processing, especially the evolution of their structure during flow and/or chemical reaction. With the increasing activity in this area of materials research, there is a concomitant increase in the need for instrumentation to characterize the flow behavior of polymeric and colloidal materials. Research at the California Institute of Technology probes a wide range of complex fluids: new biomedical materials, mesostructured polymers, colloidal suspensions and polymer solution-precursors of phase-inversion membranes. Development of materials for in-situ synthesis of biomedical polymers demands measurement of rapid changes in the viscoelasticity of reacting systems. Establishing efficient methods to control order in mesostructured polymers requires simultaneous optical and mechanical characterization of their flow behavior. Testing current understanding of colloidal suspensions depends upon precise measurements of both the first and second normal stress differences, in addition to the shear stress. It is necessary to examine the dynamics of all these systems under flow conditions that include inception of shearing at a fixed rate, creep under fixed shear stress, dynamic shearing, and superposed steady and dynamic shear. %%% This grant provides funds for the purchase of two rheometers: one for experiments under controlled shear strain and the other optimized for controlled stress and strain experiments. ***