Fundamentals of co-crystallization of polyoxacyclobutane and water

在晶格内由两种不同分子组成的晶体（共晶体）被称为笼形物、主客体化合物、金属间的金属间化合物或水合物（如果包括水的话）。有机共晶的一个众所周知的例子是由甲烷和水的共晶形成的天然气水合物。聚合物，长链有机分子，与小分子的共结晶是不寻常的，与水的共结晶尤其罕见。本研究项目的重点是研究一类罕见的基于聚合物聚氧环丁烷（POCB）和水的共晶。研究人员将研究POCB水合物可以形成的相类型以及形成速率。了解POCB水合物的独特行为是很重要的，因为它可以应用于不涉及膜的热脱盐过程。该项目将包括培训研究生和本科生进行最先进的研究，以及与项目主题相关的一些课程开发。研究人员还将围绕分子形状和分子间相互作用的主题，特别是在天然气水合物及其与能源相关的背景下，对大学预科学生进行外展活动。POCB可以与水共结晶形成水合物，加热到37摄氏度以上就会融化。熔化后的产物要么是均匀的液相，要么是富水和富聚合物的两相混合物。POCB水合物具有独特的性质：(1)共晶的熔点超过两种纯晶；(2)共结晶既可以发生在液-液平衡状态，也可以发生在均相液体溶液中；(3)水合物对盐高度不敏感；(4)水合物的熔点碰巧与人体温度几乎完全一致。这种特性的组合使得POCB不仅在聚合物中，而且在所有材料中都是独一无二的。我们对POCB水合物所知甚少。即使是最基本的信息，如水合物在高分子量极限下的熔点或其熔合热，也没有。本研究项目将探索POCB水合物的热力学和结晶动力学，并研究聚合物与溶剂共结晶过程中LLE与结晶之间的耦合。POCB独特的相行为可以用于不需要真空或压力、不需要制冷和不需要膜的纯热脱盐过程。这种方法可以使废热脱盐和高盐度水脱盐成为可能。这个研究项目将为这一过程提供第一个原理证明和初步的技术经济评价。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Crystals composed of two distinct molecules organized within a lattice (co-crystals) are variously known as clathrates, host-guest compounds, intermetallic compounds amongst metals, or hydrates if water is included. A well-known example of an organic co-crystal is the gas hydrate formed from the co-crystallization of methane and water. The co-crystallization of polymers, very long chain organic molecules, with small molecules is unusual, and those with water are especially rare. The focus of this research project is to study a rare class of co-crystals based on the polymer, polyoxacyclobutane (POCB), and water. The researchers will investigate the types of phases that POCB hydrate can form as well as the rates of formation. Understanding the unique behavior of POCB hydrate is important, because it could be applied to a thermal desalination process that involves no membranes. The project will involve training graduate and undergraduate students in state-of-the-art research, as well as some curriculum development related to the topic of the project. The researchers will also perform outreach activities to pre-college students around the topic of molecular shapes and intermolecular interactions, especially in the context of gas hydrates and their relevance to energy. POCB can co-crystallize with water to form a hydrate, which melts upon heating above 37 degrees Celsius. Melting yields either a homogeneous liquid phase, or a water-rich and a polymer-rich two-phase mixture. The properties of the POCB hydrate are unique: (1) the melting point of the co-crystal exceeds that of the two pure species; (2) co-crystallization can occur either from a liquid-liquid equilibrium (LLE) state or from a homogeneous liquid solution; (3) the hydrate is highly insensitive to salt; and (4) the hydrate melting point fortuitously happens to be almost exactly at human body temperature. This combination of properties makes POCB unique not just amongst polymers, but amongst all materials. Very little is known about the POCB hydrate. Even the most basic information, such as the melting point of the hydrate in the high molecular weight limit or its heat of fusion, is missing. This research project will explore the thermodynamics and crystallization kinetics of POCB hydrate and examine the coupling between LLE and crystallization in which the polymer co-crystallizes with the solvent. The unique phase behavior of POCB could be used for a purely-thermal desalination process that requires no vacuum or pressure, no refrigeration, and no membrane. Such a process may enable waste-heat-based desalination and the desalination of high salinity waters. This research project will provide the first proof-of-principle and a preliminary technoeconomic evaluation of such a process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.