Tunable hydrodynamics and restricted motions: probing dynamics and the mechanisms of self-organization in soft matter

微观结构和相互作用以及宏观行为之间的关系是几乎所有科学领域的核心。在软材料和生物材料中常见的胶体领域，由于两两的静电相互作用和多体流体动力相互作用，多个长度和时间尺度共存，简单的积木块形成复杂的结构。 我们将使用软材料-胶体悬浮液、表面活性剂、蛋白质-来构建纳米和微尺度的模型系统，用来解决凝聚态物理中的基本问题。共格结构是如何形成的是一个重要的问题：晶体是如何生长的？结晶什么时候会停止？在被驱动的系统中，也可能形成不连贯的结构，如星团和云。我们将通过填充分数控制熵排除体积相互作用，并调整远程静电和流体相互作用。在这样做的过程中，我们的目标是更好地理解潜在的机制：连贯和不连贯的结构是如何形成的，以及最终如何接近活着的有机体的复杂性。 我们用光学显微镜研究微米尺度的结构形成，用核磁共振研究纳米结构的动力学。流变学测量材料中的应力和应变，并用于表征宏观性能。到目前为止，我们的战略一直非常富有成效，我们的战略是创建一个系统，在这个系统中，管理互动可以通过一个外部场来控制和改变。 相干的微尺度晶体结构可以很容易地在外力的作用下进行控制，可以用来制造新型的场响应(或智能)材料。对于基本过程的研究来说，制造功能材料可能是一个非常令人满意的终点，因为它可以真正测试我们对基本物理的理解程度。然而，在其他情况下，新材料的发现是偶然的，潜在的机制尚不清楚，应用材料科学的方法可以在凝聚态物理中产生有趣的新的基本问题。这项研究计划旨在适应这两种可能的情况。

The relationship between microscopic structure and interactions, and macroscopic behaviour is central to almost all fields of science. In the colloidal domain, which is common to soft and biological materials, several length- and time-scales coexist and complex structures emerge from simple building blocks due to both pairwise electrostatic interactions and many-body hydrodynamic interactions. We will use soft materials - colloidal suspensions, surfactants, proteins - to construct nano- and micro-scale model systems with which to address fundamental questions in condensed matter physics. How coherent structures form is an important question: How do crystals grow? When does crystallization get arrested? In driven systems, incoherent structures such as clusters and clouds can also form. We will control entropic excluded volume interactions via packing fraction, and tune long-range electrostatic and hydrodynamic interactions. In doing so, we aim to better understand underlying mechanisms: how coherent and incoherent structures form, and eventually, how to approach the complexity of living organisms. We use optical microscopies to study structure formation on the micrometer scale and nuclear magnetic resonance to study dynamics of nanoscale structures. Rheology measures stresses and strains in materials and is used to characterize macroscopic properties. Our strategy, which has been very fruitful thus far, is to create systems where the governing interactions can be controlled and varied via an external field. Coherent micro-scale crystalline structures can be easily controlled with external forces, and can be used to make novel kinds of field responsive (or smart) materials. Making functional materials can be a very satisfying end point for a study of fundamental processes, as it can really test the degree to which we understand the basic physics. In other cases, however, where the discovery of a new material is serendipitous, and underlying mechanisms are unclear, application of a materials science approach can yield interesting new fundamental problems in condensed matter physics. This research program is designed to accommodate both eventualities.