Experimental and Theoretical Studies of Shear-Thickening in Associating Polymer Solutions

本研究的目的是发展对缔合聚合物溶液中剪切增厚和流动诱导凝胶的基本理解。提出了一种协调的、三管齐下的方法，包括新的功能化聚合物的合成、流变和剪切引起的结构变化的测量和理论。高度单分散的聚合物，具有明确的分子量，将被合成，并将定量端盖功能基团，旨在促进聚合物之间的联系。官能团将以四种构型中的一种放置：(1)在每条链的一端或(2)在链的两端或(3)在链主链的中间或(4)在链的两端和长度的中间。用不同配位数的金属离子控制物理交联的支化程度。缔合的程度（或缔合的寿命）将通过加入作为缔合基团“毒药”的助溶剂来控制。除了对剪应力和正应力进行广泛的流变学测量外，还将使用紫外/可见吸收光谱法作为剪切速率的函数进行现场直接测量。流动诱导聚合物排列的原位测量将使用双折射进行。静结构因子S(q)作为剪切速率函数的小角和大角光散射测量将用于跟踪流动引起的结构变化。利用新开发的光散射显微镜技术跟踪剪切诱导凝胶在剪切流下的生长。实验工作将与密集的理论研究计划密切配合。理论和实验研究将从模型聚合物溶液的工作开始，其中每个链包含单个末端连接的贴纸，并向更复杂的贴纸放置以及网络形成和凝胶化的问题发展。缔合聚合物溶液在工业应用中广泛用作粘度调节剂、防雾或防飞溅剂、涂料中的混凝剂和采油中的堵剂。这些系统的实用性源于许多重要的物理特性，包括通过添加极少量的聚合物显著提高溶液粘度的能力，控制甚至逆转粘度随温度降低的能力（这种能力对许多润滑剂很重要），抑制雾和飞溅的能力，以及在某些条件下的凝胶能力。本研究计划的目的是了解决定这些系统物理特性的分子因素，以便设计这些系统用于实际工业应用。＊＊＊

9870128 Pine The objective of this research is to develop a fundamental understanding of shear thickening and flow-induced gelation in associating polymer solutions. A coordinated, three-pronged approach is proposed which involves the synthesis of new functionalized polymers, measurements of rheological and shear- induced structural changes, and theory. Highly monodisperse polymers, with well defined molecular weights, will be synthesized and will be quantitatively end-capped with functional groups designed to promote associations between polymers. The functional groups will be placed in one of four configurations: (1) at one end of each chain or (2) at both ends of the chains or (3) halfway along the backbone of the chains or (4) at both ends and halfway along the chain length. The degree of branching at the physical crosslinks will be controlled using metal ions with different coordination numbers. The degree of the association (or lifetime of associations) will be controlled by the addition of cosolvents which serve as "poisons" for the associating groups. In addition to extensive rheological measurements of shear and normal stresses, in situ direct measurements of the degree of association will be performed as a function of shear rate using uv/vis absorption spectroscopy. In situ measurements of flow-induced alignment of polymers will be performed using birefringence. Small and large angle light scattering measurements of the static structure factor S(q) as a function of shear rate will be used to follow flow-induced structural changes. The growth of the shear-induced gel under shear flow will be followed using the newly developed light scattering microscopy technique. The experimental work will be closely coordinated with an intensive program of theoretical research. Theoretical and experimental studies will commence with work on a model polymer solution in which each chain contains a single, terminally-attached sticker and progress towards more complex sticker placement as well as issues of network formation and gelation. %%% Associating polymer solutions find wide use in industrial applications as viscosity modifiers, anti-misting or anti- splatter agents, coagulants in coatings, and blocking agents in oil recovery. The utility of these systems stems from a number of important physical properties, including their ability to significantly enhance solution viscosity with the addition of very small amounts of polymer, their ability to control and even reverse the reduction of viscosity with temperature (this capability is important for many lubricants), their ability to suppress misting and splatter, and their ability to gel under certain conditions. The purpose of this research program is to develop an understanding of the molecular factors which determine the physical properties of these systems in order to engineer these systems for practical industrial applications. ***