Nucleation and glassy dynamics in liquids and nanoparticles

水是一种奇怪的物质，这种液体沐浴着我们的星球，对生命来说是必不可少的。例如，与简单物质相比，它的热膨胀系数、比热和可压缩性都表现出反常的行为，后两者在低温下似乎发散。一种解释水的反常行为的假说听起来更奇怪：存在两种不同的亚稳液体形式的水，由一级转变线分隔，这条线终止于液-液临界点(LLCP)，该临界点被认为存在于压力在50-200 mpa和温度低于-50°C之间。尽管越来越多的实验证据与这一假说一致，而且越来越多的计算机模拟水模型展示了这种奇异现象，但还没有实验直接显示液-液转变。由于没有人成功地避免了快速结晶，这阻碍了对所提议的LLCP温度和压力范围内的液态的研究。LLCP假说是液态物理学丰富的象征。另外两个对材料科学至关重要的液态现象是玻璃化转变，即液体粘度的急剧增加，直到它成为无定形固体，以及晶体成核，这是启动液体向有序结晶固体转变的过程。我研究的主要目标是使用计算机模拟来更好地了解LLCP、玻璃动力学、晶体成核以及它们之间的联系。*一个提议的想法是研究水纳米液滴，其表面张力和小半径可以在LLCP建议的范围内产生高内压。它们是微型压力室。纳米水滴中的成核作用也被抑制，因此它们可能被证明是在迄今仍无法达到的条件下研究液态水的理想实验探测器。在统一我们对水、二氧化硅和相关网络形成液体的理解方面，我们希望继续在将它们的性质映射到四价胶体系统方面取得进展，四价胶体系统具有相对简单、可调节的相互作用，更容易理解。我们想进一步发展我们对一种模型材料的惊人发现，这种材料具有在冷却时熔化的潜在有用性质，这与人们通常预期的完全相反，并找到在真实的胶体系统中复制这种行为的方法。最后，在成功地将为液体研究开发的统计机械和模拟技术应用于鱼来源抗菌肽、肺表面活性蛋白和抗细胞增殖药物候选的跨学科工作的基础上，我们建议研究磁性纳米颗粒以及它们如何用于组织修复。

Water, the liquid that bathes our planet and is essential for life, is a strange substance. For example, its thermal expansion coefficient, specific heat and compressibility all show anomalous behavior compared to simple substances, the latter two appearing to diverge at low temperature. A hypothesis that accounts for water's anomalous behaviour sounds stranger still: the existence of two distinct metastable liquid forms of water separated by a line of first order transitions that terminates in a liquid-liquid critical point (LLCP) thought to exist at pressures between 50-200MPa and temperatures below -50°C. Despite an increasing body of experimental evidence consistent with this hypothesis and a growing number of computer simulations of water-like models that exhibit this exotic phenomenon, no experiment has directly shown the liquid-liquid transition, since none has successfully avoided the rapid crystallization that prevents the study of the liquid state in the temperature and pressure range of the proposed LLCP.******The LLCP hypothesis is emblematic of the richness of liquid state physics. Two other liquid state phenomena of fundamental importance to materials science are the glass transition, the dramatic increase in viscosity of a liquid until it becomes an amorphous solid, and crystal nucleation, the process that initiates the transformation of a liquid to an ordered, crystalline solid. The overarching goal of my research is to use computer simulations to better understand the LLCP, glassy dynamics, crystal nucleation, and the connections between them.******One proposed idea is to study water nanodroplets, the surface tension and small radii of which can produce high internal pressures in the range proposed for the LLCP. They are miniature pressure chambers. Nucleation is also suppressed in nanodroplets, so they may prove to be ideal experimental probes to study liquid water at conditions that so far have remained out of reach. In terms of unifying our understanding of water, silica, and related network-forming liquids, we want to continue our progress in mapping their properties onto tetravalent colloidal systems, which have relatively simple, tunable interactions that are easier to understand. We want to further develop our surprising discovery of a model material with the potentially useful property of melting on cooling, the exact opposite of what one typically expects, and find ways of replicating the behaviour in real colloidal systems. Finally, building on success in applying the statistical mechanical and simulation techniques developed for the study of liquids to interdisciplinary work on fish-derived antimicrobial peptides, a lung surfactant protein and an anti-cell-proliferative drug candidate, we propose to study magnetic nanoparticles and how they can be used in tissue repair.