Theory and Simulation of Liquids, Solutions, and Nucleation Processes

熔体或溶液结晶成核是一个重要的过程，在我们周围的环境中几乎无处不在。冰晶在液态水中的成核，以及溶液中食盐如NaCl（岩盐）的成核是本建议考虑的重要例子。水的正常冰点是0℃，但纯水在结冰前可以过冷到接近-35℃。这意味着基本上地球上或大气中所有冰的成核都是通过与异物接触而促进的。这个过程被称为非均相成核，这种异物被称为冰核。非均质冰成核是大气中的一个重要过程，因为大气气溶胶的冰成核导致冰云，而冰云反过来又影响全球气候。尽管非均相冰核长期以来一直是研究的主题，但人们对良好冰核的微观性质知之甚少。这种知识的缺乏主要是因为与成核有关的小尺寸和快时间，目前的实验不容易获得。拟议的研究将采用计算机模拟来检验这些问题。计算机模拟可以看作是对真实系统的代表性模型的“实验”，它使我们能够在分子水平上跟踪物理过程。这是一种非常有力的方法，它产生了对物理现象的微观理解，这是其他方法无法获得的。我们将使用分子动力学模拟来研究特别重要的大气气溶胶，如粘土和其他矿物颗粒，以及对影响非均质冰成核的一般因素有更深入的了解。我们还将采用分子模拟来研究溶液中盐和其他分子固体的结晶。目的是再次探讨晶体诞生的潜在机制，并确定促进或抑制晶体成核和生长的晶体和溶液性质。******许多物理和生物系统的状态和功能取决于与水相互作用有利的部分（亲水）和不与水相互作用的部分（疏水）之间的平衡。同时具有亲水部分和疏水部分的分子称为两亲分子。我们将探讨相互竞争的亲疏水相互作用如何影响含有两亲性溶质的几种模型溶液的纳米级结构。这项工作有望对为什么一些小分子作为蛋白质变性剂的功能比其他小分子更有效提供新的见解。变性剂是一种分子，它能使蛋白质在水溶液中改变结构，使其变得不那么紧密（未展开）。**

Crystal nucleation from melts or solution is an important process that occurs practically everywhere in our surrounding environment. The nucleation of ice crystals in liquid water, and of common salts such as NaCl (rock salt) from solution are important examples considered in this proposal. The normal freezing point of water is 0 oC, but pure water can be supercooled to near -35 oC before freezing occurs. This means that essentially all ice nucleation on earth or in the atmosphere is facilitated by contact with a foreign body. This process is called heterogeneous nucleation, and the foreign body is termed an ice nucleus. Heterogeneous ice nucleation is an important process in the atmosphere because ice nucleation by atmospheric aerosols results in ice clouds, which in turn influence the global climate. Although heterogeneous ice nucleation has long been a subject of investigation, little is known about the microscopic nature of a good ice nucleus. This absence of knowledge is mainly because the small sizes and fast times relevant to nucleation are not easily accessible by current experiments. The proposed research will employ computer simulations to examine these questions. Computer simulations can be viewed as "experiments'' on representative models of real systems, which allow us to follow physical processes at the molecular level. This is a very powerful approach which yields a microscopic understanding of physical phenomena that is not otherwise available. We will use molecular dynamics simulations to examine particularly important atmospheric aerosols, such clays and other mineral particles, as well as to obtain a deeper understanding of the general factors that influence heterogeneous ice nucleation. We will also employ molecular simulation to investigate the crystallization of salts and other molecular solids from solution. The purpose is again to probe the underlying mechanisms of crystal birth, and identify the crystal and solution properties which enhance or inhibit crystal nucleation and growth. ******The state and function of many physical and biological systems depends on a balance between moieties that interact favourably with water (hydrophilic) and those that do not (hydrophobic). Molecules that have both hydrophilic and hydrophobic parts are called amphiphilic. We will explore how competing hydrophilic and hydrophobic interactions influences the nanoscale structure of several model solutions containing amphiphilic solutes. This work promises new insight into why some small molecules function more effectively than others as protein denaturants. Denaturants are molecules that cause proteins to change their structure to a less compact (unfolded) state in aqueous solution. **