Rheometer for the study of structured soft materials

流体和固体的宏观性质由微观相互作用决定。在我的研究计划中，我研究自组装胶体系统的结构和动力学。胶体悬浮液是颗粒在流体中的悬浮，其中颗粒足够小，以至于它们不断地被周围流体中的分子碰撞。这就是布朗运动--1905年，爱因斯坦假设胶体中的布朗运动确实证明了流体的分子性质。微观的胶体结构改变了流体的宏观流动特性。番茄酱是一种胶体流体，表现出粘弹性：在没有剪切的情况下更像固体，但在有剪切的情况下变稀。尽管即使是胶体流体也会表现出对剪切的复杂响应(“流变性”)，但人们预计，接近无定形固体(“玻璃”)相的方法的特点是打破了微观观察到的扩散系数和宏观粘性之间的经典关系，即斯托克斯-爱因斯坦关系。当结晶被抑制时，胶体悬浮液可能会表现出玻璃性行为。然而，在外加电场的作用下，胶体悬浮液形成包括结晶胶体相在内的许多各向异性结构。这种微观现象伴随着类似固体的流变响应的增加：固体在极限应力以下不屈服，这种材料被称为电流变流体。在胶体玻璃化转变和电流变效应的研究中，主要目的是了解微观机制以及微观结构和宏观性能之间的关系。流变仪将能够在存在和不存在外电场的情况下研究散体胶体悬浮液的粘弹性特性，并将提供微观和宏观特性之间的关键联系。流变仪作为一种有价值的研究和培训工具，将使其他研究界成员受益。

Macroscopic properties of fluids and solids are determined by microscopic interactions. In my research programme, I study structure and dynamics in self-assembling colloidal systems. Colloidal suspensions are suspensions of particles in a fluid where the particles are small enough that they are constantly kept jostling by the molecules in the surrounding fluid. This is termed Brownian motion - in 1905 Einstein postulated that Brownian motion in colloids was indeed a proof of the molecular nature of the fluid.Microscopic colloidal structure modifies the macroscopic flowing characteristics of the fluid. Tomato ketchup is a colloidal fluid that exhibits viscoelastic properties: more solid-like in the absence of shear but thinning in the presence of shear. While even colloidal fluids can exhibit a complex response to shear ("rheological behaviour"), it is expected that the approach to an amorphous solid ("glass") phase is characterized by a breakdown of a classic relationship, known as the Stokes-Einstein relation, between microscopically observed diffusion coefficients and the macroscopic viscous properties.Colloidal suspensions can exhibit glassy behaviour when crystallization is suppressed. However, colloidal suspensions form many anisotropic structures including crystalline colloidal phases in the presence of external electric fields. This microscopic phenomenon is coupled with an increase in solid-like rheological response: the solid does not yield below a limiting stress, and such a material is termed an electrorheological fluid. In the study of both the colloidal glass transition and the electrorheological effect, the primary goals are the understanding of microscopic mechanisms and the relationship between micro-structure and macroscopic properties. A rheometer will enable the study of viscoelastic properties of bulk colloidal suspensions in the presence and absence of an external electric field, and will provide the crucial link between microscopic and macroscopic properties.The rheometer will benefit other members of the research community as a valuable research and training tool.