The effects of stress on soft glasses and biological membranes

我们研究的软无序材料，如聚合物熔体和生物膜的应力的影响，使用理论建模和计算机模拟。一个优先事项是了解什么可能是一种治疗软眼镜的新方法。玻璃，可以看作是液体冻结成他们的配置之一，总是老化，也就是说，在很长的时间，他们演变成较低的能量配置，其特征是较长的弛豫时间。它已被观察到在软胶体玻璃实验，并通过计算机模拟在冷却的聚合物熔体（我们的工作），即，当受到应力，弛豫时间的变化在非平凡的方式，特别是可以显着增加。从目前已知的情况来看，受压的“过度老化”玻璃不像自然老化的玻璃。它更均匀，并表现出增加的有序性，但不一定是较低的能量。 了解过时效的起源以及这些无序系统的微观结构和机械性能的变化可能会导致更好的方法来制备玻璃。 第二个优先事项是控制形成细胞壁的脂质双层的破裂。这种双层通过脂质尾部不愿与水分子接触而保持在一起，称为它们的疏水性。 当这个双层破裂时，细胞失去其内容物。 由渗透压差或电场的应用触发，这种破裂由孔隙的形成介导。 孔也可以通过吸收肽形成，这些肽被细菌和细胞本身用来破坏细胞。破裂并不一定是一个不受欢迎的实验结果。 例如用于包封药物的小的单分散囊泡是通过将大的多层囊泡挤出穿过纳米尺寸的孔而获得的，在纳米尺寸的孔中，囊泡在通过期间破裂。 挤出的片段改革成较小的囊泡，其尺寸理想地是单分散的。了解破裂过程提供了巨大的医学潜力，在保护细胞免受攻击，并在开发靶向药物输送方法。

We study the effects of stress on soft disordered materials, such as polymer melts and biological membranes, using theoretical modeling and computer simulation. One priority is to understand what may turn out to be a new way to treat soft glasses. Glasses, which can viewed as liquids frozen into one of their configurations, always age, that is over long times, they evolve into lower energy configurations characterized by longer relaxation times. It has been observed experimentally in soft colloidal glasses, and through computer simulations in a cooled polymer melt (our work), that, when subjected to stress, the relaxation times change in non-trivial ways, and in particular can be increased significantly. From what is known at this point, the stressed "overaged" glass, is not like a naturally aged glass. It is more homogeneous and exhibits increased ordering but not necessarily a lower energy.  Understanding the origins of the overaging and the changes in the microstructure and mechanical properties of these disordered systems may lead to better ways to prepare glasses.   A second priority is controlling the rupture of lipid bilayers, which form the walls of cells. This double layer is held together by the reluctance of the lipid tails to be in contact with water molecules, known as their hydrophobicity.  When this bilayer ruptures the cell loses its content.  Triggered by osmotic pressure differences or the application of electrical fields, this rupture is mediated by the formation of pores.  Pores can also form through the absorption of peptides, which are used by bacteria and cells themselves to rupture cells. Rupture is not necessarily an unwelcome outcome of an experiment.  Small monodisperse vesicles used for instance for encapsulating drugs are obtained by extrusion of large multi-lamellar vesicles, through nanometer size holes, where they rupture during passage.  The extruded fragments reform into smaller vesicles, whose size ideally would be monodisperse. Understanding the rupture process offers great medical potential, in protecting cells against attack, and in developing methods for targeted drug delivery.