Phase Transitions in Disordered Polymers and Gels

这个实验和理论项目致力于研究各种无序聚合物和杂多聚合物凝胶的相和相变。这种情况下的无序包括序列的无序（当几种单体聚合在一起时，单体序列携带一些有用的信息）、分支的无序以及与结、连接和缠结相关的拓扑无序。在实验中，旨在探索各种无序聚合物在温度、溶剂选择等参数和制备条件控制下的相和相变，制备条件控制无序程度。它还旨在从设计的角度检查：(i)其他类型的无序聚合物，包括支链聚合物，结，和；（ii）当密度波动与冻结和设计相结合时，提供花型或胶束型结构的实际紧密程度；（iii）实际类型的相互作用，包括远距离库仑相互作用；（iv）部分平衡状态，这对折叠动力学很重要。在凝胶的研究中，第一个目标是观察聚合物凝胶中的冷冻相变。该领域的第二个目标是通过实验实现序列设计的思想，以允许生产能够冻结成至少显示所需构象的某些元素的状态的凝胶。这项理论和实验相结合的研究将揭示无序聚合物和凝胶相变背后的基本物理原理，并将对这些迷人材料的物理学以及它们在生物学，医学和技术方面的应用具有巨大的潜在重要性。这个实验和理论项目致力于研究一类被称为聚合物的材料，它是由重复的化学单元组成的极长的分子。感兴趣的问题涉及到这些物质质量的随机性或无序程度，以及这些物质最初处于液态的条件下可以冻结并变得刚性。在某些情况下，聚合物可以被认为是长而灵活的分子串，当它们溶解在液体溶剂中时，就像煮熟的意大利面在水中一样。这项工作将包括许多其他类型的聚合物，例如，包括那些有分支的聚合物。这项工作的核心问题之一是澄清导致从液体到刚性固体转变的条件，例如温度、溶剂类型和聚合物分子类型。例如，当环氧胶变硬时，会发生类似但不可逆的冻结转变，但该现象将在本项目中以非常基本和广泛的方式进行研究，其结果将对广泛的聚合物和条件具有预测价值。这项工作的结果可能包括生物学和医学以及技术方面的情况。＊＊＊

w:\decs\decs97\0formdec.doc Tanaka 9616791 This experimental and theoretical project is devoted to study of the phases and phase transitions of various disordered polymers and heteropolymer gels. Disorder in this context includes disorder of sequences (when several monomer species are polymerized together, with the sequence of monomers bearing some useful information), disorder of branches, and topological disorder that is related to knots, links, and entanglements. In experiment, it is intended to explore the phases and phase transitions of various disordered polymers as controlled by both parameters such as temperature, choice of solvent, etc, and also by the preparation conditions, which control the degree of disorder. It is intended also to examine from the point of view of design: (i) other types of disordered polymers, including branched polymers, knots, and ; (ii) realistic degrees of compactness, when density fluctuations are coupled to freezing and to design, providing for flower- or micelle-type structures; (iii) realistic types of interactions, including long-range Coulomb interactions; and (iv) states of partial equilibrium, important for folding kinetics. In work on gels, the first goal is to observe the freezing phase transition in a polymer gel. A second goal in this area is to experimentally realize the idea of sequence design, to allow the production of gels capable of freezing into a state which exhibits at least certain elements of the desired conformation. This combined theoretical and experimental study will shed light on basic physical principles behind phase transitions of disordered polymers and gels, and will be of great potential importance for the physics of these fascinating materials, as well as for their applications in biology, medicine, and technology. %%% This experimental and theor etical project is devoted to study of a class of materials known as polymers, which are extremely long molecules composed of repeating chemical units. The questions of interest relate to the degree of randomness or disorder in masses of such material, and the conditions under which such material, originally in a liquid state, can freeze and become rigid. Polymers in some cases can be thought of as long flexible molecular strings, which, when dissolved in a liquid solvent, resemble cooked spaghetti in water. This work will include many other types of polymers, including those in which branches occur, for example. One of the central questions in this work is to clarify the conditions, for example, temperature, the type of solvent, and the type of polymer molecules, which lead to a transition from a liquid to a rigid solid. A somewhat similar, but irreversible, freezing transition for example occurs when epoxy glue hardens, but the phenomenon is to be examined in this project in a very fundamental and broad manner, leading to results which will be of predictive value for a wide range of polymers and conditions. The utility of the results of this work may include situations in biology and medicine, as well as in technology. ***