Development of a Low Stress Creep Rheometer

有许多实际上是弱凝胶的流体的例子，这是由于在材料中存在比分子尺寸大得多的长度尺度上的结构。 在某一临界屈服应力以下，这些结构化流体是固体，其特征在于模量。 在大多数情况下，该模量不能在市售流变仪器中测量，因为那些流变仪不能施加足够低的应力。 然而，通过简单地组合已经被证明在各种流变仪中工作的技术，可以构造能够施加比“最先进的”商业流变仪低三个数量级的应力水平的蠕变流变仪。 这种新的流变仪将允许应用低于屈服应力的应力，以测量未断裂结构的模量。 在屈服应力附近的应力的应用将允许在结构流体中的屈服的详细研究。 该信息对于结构化流体的流变学建模是必需的，因为整个流变学响应（即使在高应力下）是由于结构断裂。 我们目前正在研究的这种结构化流体的例子有：溶胀凝胶、液晶聚合物、嵌段共聚物、聚电解质-表面活性剂复合物、悬浮液、表面活性剂溶液和食品。 新的流变仪将导致我们对每一类材料的理解取得突破，因为它将首次允许表征线性响应和首次偏离线性响应。 因此，这款流变仪对于Penn State Rheology Group的长期研究和教育计划至关重要。%*

9802793ColbyThere are many examples of fluids that are actually weak gels due to the presence of structure in the materials on length scales much larger than molecular dimensions. Below some critical yield stress, these structured fluids are solids, characterized by a modulus. In most cases, this modulus cannot be measured in commercially available rheological instrumentation because those rheometers cannot apply low enough stresses. However, by simply combining technologies that have been proven to work in various rheometers, it is possible to construct a creep rheometer capable of applying three orders of magnitude lower stress levels than "state of the art" commercial rheometers. This new rheometer will allow application of stresses below the yield stress, to measure the modulus of the unbroken structure. Application of stresses in the vicinity of the yield stress will allow detailed studies of yielding in structured fluids. This information is needed for needed for modeling the rheology of structured fluids, as the entire rheological response (even at high stresses) is due to structure breaking. Examples of such structured fluids that we are currently studying are: swollen gels, liquid crystal polymers, block copolymers, polyelectrolyte-surfactant complexes, suspensions, surfactant solutions and foods. The new rheometer will lead to breakthroughs in our understanding of each of these classes of materials because it will allow, for the first time, characterization of the linear response and the first departures from linear response. This rheometer is, therefore, vital to the long-term research and education plans of the Penn State Rheology Group.%%%***