Driven, directed or crowded: dynamics of soft matter near and far from equilibrium

理解非平衡物理的统一框架并不存在。在这个研究项目中，我们将研究三类不平衡的实验模型系统的动力学，这三类系统解决了非平衡行为的互补方面：能量注入和耗散，粒子间相互作用的修改和环境的作用。 第一个目标是创造动态响应的材料。首先，我们希望大量制造微米级、单分散、不对称的布朗设计者液滴。制造复杂的胶体结构用于相行为研究是具有挑战性的。我们的假设是，远离平衡的驱动系统，在这种情况下，通过电动流体动力液滴破碎，将使我们能够创造出更小的结构。其次，活细胞中的自驱动运动(称为活动)本质上是纳米级的；然而，所有活性物质的胶体类似物都是微米级和二维的。我们将设计一种纳米级的光激活马达，使用嵌入在脂质双细胞中的细菌视紫红质(一种光激活的质子泵)，并通过在非生物模型系统中的实验来检验活动在指导生命系统中组织方面的作用。 第二个目标是研究胶体团的形成动力学。相互竞争的胶体相互作用可以导致中等有序的结构：例如，长程静电斥力和短程耗尽力的组合产生了团簇、凝胶和玻璃态。我们将首次研究耗尽和各向异性偶极力的组合。通过这一点，我们希望解决一个长期存在的问题：偶极气液转变是否存在？然后，我们将打开和关闭偶极相互作用，以定量研究团簇形成的动力学。与此平行的是，我们将研究已观察到但未被理解的特殊聚集现象。我们将检验我们的假设，即这种聚集是电荷调节的结果，电荷调节可以在均匀的胶体体系中引起自发电荷不对称。 第三个目标是了解拥挤环境对活细胞中分子动力学和构象的影响：这被称为大分子拥挤。虽然已经出现了一些关于其性质的定性见解，但即使在简单的模型系统中也无法实现真正的定量理解。使用合成聚合物作为Crowder和Probe分子，我们将使用各种实验工具研究电荷、多分散性和流体动力相互作用的作用。我们将比较合成的聚合物探针分子与真实的蛋白质，以及合成的聚集体与真实的细菌细胞材料。 胶体自组装的控制带来了根本性的进步和新材料的出现。我们的愿景是，将自组装的研究扩展到远离平衡的系统，在那里直觉往往会失败，这将带来新的基本见解。

A unifying framework for understanding non-equilibrium physics does not exist. In this research program we will study dynamics in three classes of experimental model systems that are out of equilibrium which address complementary aspects of non-equilibrium behavior: energy injection and dissipation, modification of interparticle interactions and role of environment. The first objective is to create dynamically responsive materials. First, we wish to make micron-scale, monodisperse, asymmetric Brownian designer droplets in large quantities. Making complex colloidal structures for phase behavior studies is challenging. Our hypothesis is that driving systems far from equilibrium, in this case via electrohydrodynamic drop breakup, will enable us to create smaller structures. Second, self-driven motion in living cells (termed as activity) is inherently nanoscale; however, all colloidal analogs of active matter have been micron-scale and 2-dimensional. We will devise a nanoscale light-activated motor, using bacteriorhodopsin (a light-activated proton pump) embedded in a lipid bicelle, and examine, using experiments in a non-living model system, the role of activity in directing organization in living systems. A second objective is to study kinetics of colloidal cluster formation. Competing colloidal interactions can result in structures of intermediate order: e.g., the combination of long-range electrostatic repulsions and short-range depletion forces gives clusters, gels, and glassy states. We will examine, for the first time, the combination of depletion and anisotropic dipolar forces. With this, we hope to address the long-standing question: does the dipolar gas-liquid transition exist? We will then switch dipolar interactions on and off to study kinetics of cluster formation quantitatively. Parallel to this, we will examine peculiar clustering phenomena that are observed but not understood. We will test our hypothesis that this clustering is a consequence of charge regulation, which can give rise to spontaneous charge asymmetries in a homogeneous colloidal system. A third objective is to understand the effect of the crowded environment on molecular dynamics and conformations in living cells: this is referred to as macromolecular crowding. While several qualitative insights have emerged as to its nature, a true quantitative understanding is not achieved even in simple model systems. Using synthetic polymers both as crowder and probe molecule, we will examine the role of charge, polydispersity, and hydrodynamic interactions using a diverse set of experimental tools. We will compare synthetic polymer probe molecules with real proteins, as well as synthetic crowders with real bacterial cell material. Control of colloidal self-assembly has led to fundamental advances and to new materials. The vision is that extending the study of self-assembly to systems far from equilibrium, where intuition often fails, will lead to new fundamental insights.