Block Copolymer Self-Assembly: Morphologies, Thermo-mechanical Behaviors and Kinetic Pathways

由于嵌段共聚物作为纳米技术材料的巨大前景，以及它们作为自组装复杂流体模型系统的内在科学兴趣，我们将利用统计力学技术对涉及自组装嵌段共聚物纳米结构的一些主题进行系统的理论研究。其中一些主题涉及的现象有望应用于大类两亲体系，而其他主题则是嵌段共聚物所特有的。对嵌段共聚物有序纳米结构的热机械性能进行了研究。通过纳入机械应力或应变，为自组装复杂流体的研究增加了一个新的维度。重点将放在有序纳米结构受到各向异性应力或应变时发生的各种热机械不稳定性和相变上。其中一些不稳定性和转变是有序嵌段共聚物纳米结构所特有的，是长度尺度依赖于有序的表现。在单体尺度上表现为类流体行为，在聚合物长度尺度上表现为类固体行为。此外，还将研究二嵌段共聚物中有序-无序和有序-有序转变的动力学途径，并采用时间相关的金兹堡-朗道方法。重点将放在系统参数突然变化后的各种过渡期间可能出现的非平凡中间状态。特别令人感兴趣的是所谓的伪稳定状态的存在，它对应于自由能表面上的鞍点。这些状态将在动态和平衡中进行探索。最后，将利用自洽场技术研究ABC三嵌段共聚物的相行为和纳米结构。与研究得更好的AB双嵌段相比，这里有一个根本的新特征，即形态结构和相行为不仅取决于每个嵌段的比例和总分子量，而且关键取决于链中嵌段的顺序以及三个不同嵌段对之间相互作用的相对强度。这个新奖项是用来支持嵌段共聚物的纳米结构和相变的理论研究。这项研究特别关注了这类重要聚合物在受到机械力作用时的行为。除了提供对聚合物物理学基本问题的见解外，研究结果还将有助于这类聚合物的实际应用。＊＊＊

9531914 Wang Motivated by the high promise of block copolymers as materials for nanotechnology, and by their intrinsic scientific interest as model systems for self-assembling complex fluids, a systematic program of theoretical investigations will be undertaken on a number of topics involving self-assembled block copolymer nanostructures using statistical mechanical techniques. Some of these topics deal with phenomenologies that are expected to apply to a large class of amphiphilic systems, while others are unique to block copolymers. The thermo-mechanical properties of ordered nanostructures of block copolymers will be studied. By including mechanical stress or strain, a new dimension is added to the study of self-assembling complex fluids. Focus will be on various thermo-mechanical instabilities and phase transitions that occur when an ordered nanostructure is subjected to anisotropic stress or strain. Some of these instabilities and transitions are unique to ordered block copolymer nanostructures and are manifestations of length- scale dependent ordering,i.e., fluid-like behavior on the monomer scale and solid-like on the polymer length-scale. Also to be studied will be kinetic pathways of order- disorder and order-order transitions in diblock copolymers using a time-dependent Ginzburg-Landau approach. Focus will be on possible non-trivial intermediate states during the various transitions after a sudden change in the system parameters. Of special interest will be the existence of the so-called pseudo-stable states which correspond to saddle points on the free energy surfaces. These states will be explored both dynamically and in equilibrium. Finally, the phase behavior and nanostructures of ABC triblock copolymers will be studied using self-consistent field techniques. In contrast to the better studied AB diblocks, a fundamentally new feature here is that the morphological structures and phase behaviors depend not only on the fraction of ea ch block and the overall molecular weight, but also crucially on the sequence of the blocks in the chain and on the relative strengths of the interactions between the three unlike pairs of blocks. %%% This new award is to support theoretical research on nanostructure and phase transitions in block copolymers. The research particularly looks at the behavior of this important class of polymers when subjected to mechanical forces. In addition to providing insight into fundamental issues in polymer physics, the results will also be useful in applications of this class of polymers for practical use. ***