Acquisition of Rheometers for Materials Characterization under Controlled Stress or Strain

9626307布雷迪 软材料中的一个核心问题是预测它们在加工过程中的行为，特别是它们在流动和/或化学反应过程中的结构演变。 随着材料研究这一领域活动的增加， 需要仪器来表征聚合物和胶体材料的流动行为。 加州理工学院的研究探索了广泛的复杂流体：新的生物医学材料，介观结构聚合物，胶体悬浮液和聚合物溶液-相转化膜的前体。 生物医用聚合物原位合成材料的开发需要测量反应体系粘弹性的快速变化。 建立有效的方法来控制有序的介观结构聚合物需要同时光学和力学表征其流动行为。 测试目前对胶体悬浮液的理解取决于除了剪切应力之外的第一和第二法向应力差的精确测量。 有必要研究所有这些系统在流动条件下的动力学，包括以固定速率剪切的开始，固定剪切应力下的蠕变，动态剪切，以及叠加的稳态和动态剪切。 %该赠款提供资金购买两台流变仪：一台用于受控剪切应变下的实验，另一台用于受控应力和应变实验。 ***

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. ***