Presidential Young Investigator Award: Sub-Triple Liquids and Crystallization in Supercritical Fluids

研究综述：亚三重液体(低于其三相点的亚稳液体)：该项目包括同时沸腾和结晶的相变(亚三重液体所特有的)的实验研究，完成拉伸不稳定性(拉伸强度损失)的理论研究，以及密度异常(加热时收缩的液体)的分子起源的研究。由等电点得到了拉伸不稳定性与密度反常之间的关系。超临界流体中的结晶：该项目的这一部分包括完成设备建造和初步实验，在这些实验中，连续的沉淀形成一种可以独立控制温度、压力和组成的流体。新奇/创新：亚三重液体是一种未被探索的物质状态(这个术语是由圆周率创造的)。它们的行为包括拉伸不稳定性(随着温度的降低，拉伸强度下降，这是由等电点最先解释的实验观察到的异常)，以及涉及快速结晶和沸腾的相变，以及液体消失，这是自然界其他地方没有的现象。超临界流体结晶是制备均一晶体和单分散聚合物粒子的一种新方法。这个项目中最具创新性的概念是在流体中实现均匀、可控的条件，其中成核通过控制压力而不是温度来发生。压力扰动以音速传播，因此确保了整个流体介质的一致性，并应用于临界点附近的高度可压缩流体，从而导致密度和溶剂功率的巨大变化。技术影响/实际意义：当脱气液体在刚性容器内冷却时产生的张力非常适合于对平板表面的附着力进行无损测试。这是微芯片制造中的一个至关重要的问题(例如，光刻胶附着力测试)。实验观察到的亚三重液体和晶体的平衡表明，产生均匀应力的固体的新想法。由于固体不可能承受各向同性拉伸，这一过程(拉伸结晶)可能导致产生具有独特性能的材料。

Research Summary: Sub-triple liquids (metastable liquids below their triple point): This project includes an experimental study of the phase transition (unique to sub-triple liquids) involving simultaneous boiling and crystallization, completion of a theoretical study of tensile instability (loss of tensile strength), and investigation of the molecular origin of density anomalies (liquids which contract when heated). The connection between tensile instability and density anomalies was derived by the PI. Crystallization in supercritical fluids: This portion of the project involves completion of equipment construction and preliminary experiments in which continuous precipitation occurs into a fluid whose temperature, pressure, and composition can be independently manipulated. Novelty/Innovation: Sub-triple liquids are an unexplored state of matter (the term was coined by the PI). Their behavior includes tensile instabilities (a decrease in tensile strength as the temperature is lowered, an experimentally observed anomaly first explained by the PI) and a phase transition involving rapid crystallization and boiling coupled with liquid disappearance, a phenomenon not to be found elsewhere in nature. Crystallization from supercritical fluids is a novel method for the production of uniform crystals and monodisperse polymer particles. The most innovative concept in this project is the attainment of uniform, controllable conditions within the fluid where nucleation occurs through a manipulation of pressure instead of temperature. Pressure perturbations travel at the speed of sound, thus guaranteeing uniformity throughout the fluid medium and are applied to a highly compressible fluid near its critical point, thus giving rise to large changes in density and hence solvent power. Technical Impact/Practical Significance: Tension generated when a degassed liquid is cooled inside a rigid container is ideally suited for the non-destructive testing of adhesion on flat surfaces. This is a problem of vital importance in microchip manufacture (e.g., photo-resist adhesion testing). The experimentally observed equilibrium of a sub-triple liquid and a crystal suggests the novel idea of creating solids which are uniformly stressed. Since it is otherwise impossible to subject a solid to isotropic tension, this process (tension crystallization) could lead to the production of materials with unique properties.