对聚合物纳米复合材料非爱因斯坦行为的探索

Einstein predicted that the viscosity of a particle suspension should always increase as the volume fraction of the particles increases. While broadly observed, this prediction was recently refuted by several studies of polymer-nanoparticle composites. According to popular views, the non-Einstein behavior could be caused by the nanoparticles acting as a plasticizer, or it may be due to the constraint release they may bring to the polymer’s reptation motion. While both suggestions are plausible, it has not been verified if one or both effects actually take place. Furthermore, the interactions between nanoparticles and polymer worsen matters and may suggest different rules governing the non-Einstein behavior than the ones contemplated before. In this proposal, we outline a program to address these questions. We shall design a system of polymer smooth nanoparticles composites to investigate the relative significance of the diluent and constraint release mechanisms within the effect of entanglement. We shall contracture a model system based on polymer hydrodynamics with controllable particle/polymer interface to explore the physical origin of the non-Einstein behavior through investigations of the bulk rheology and the effects of particles and interfaces on the particle mobility and the single-chain dynamics of host polymer. The outcome of the proposed studies with simulations will help develop a model that would enable us to further understand how particle inclusions modify the rheology of a fluid, a subject highly relevant to polymer nanomaterials processing and petroleum.

据爱因斯坦预测，颗粒悬浮液的黏度应随颗粒体积分数的增加而增加；但聚合物纳米材料黏度降低的现象广泛存在。目前对该黏度降低现象的机理解释主要为塑化剂作用和约束释放作用。尽管二者皆具合理性，可到底是其中一种或者两种因素同时作用，尚未被证实；当纳米粒子与聚合物基质相互渗透时，界面作用可能使问题更为复杂。针对以上难题，本项目先基于高分子链缠结理论从粒子粒径和聚合物基质回转半径角度来验证聚合物光滑纳米粒子复合材料非爱因斯坦行为的塑化剂和约束释放作用；再根据高分子流体动力学构建纳米粒子/聚合物基质界面特性可控的聚合物纳米复合体系，从粒子扩散和高分子单链动力学方面定量分析纳米粒子与聚合物基质间的相互作用进而研究复合体系宏观流变行为以深入理解非爱因斯坦行为这一普遍现象的物理机制。最后将根据以上研究，建立一个系统模型用于理解和预测聚合物纳米复合体系流变行为，为高分子纳米复合材料加工和原油开采运输提供理论指导。

据爱因斯坦预测，颗粒悬浮液的黏度应随颗粒体积分数的增加而增加。与此相反，聚合物纳米复合材料体系的黏度降低现象却广泛存在。目前对该黏度降低现象的机理解释主要为塑化剂作用和约束释放作用。尽管二者皆具合理性，可到底是其中一种或者两种因素同时作用，尚未被证实；当纳米粒 子与聚合物基质相互渗透时，界面作用可能使问题更为复杂。针对以上难题，本工作从粒子扩散和高分子单链动力学方面定量分析纳米粒子、塑化剂（表面活性剂）与水性聚合物基质间的相互作用进而研究复合体系宏观流变行为以深入理解非爱因斯坦行为这一普 遍现象的物理机制；同时，运用分子动力学模拟研究水性聚合物和金属纳米粒子复合体的粘度变化与流变行为。主要研究成果有以下三方面：一、水性聚合物体系的粘度除受聚合物自身结构影响外，还受到外界剪切力的影响，在一定剪切粘度下，聚合物链形成网状结构，提升体系粘度，但剪切粘度过大时，聚合物链段会因剪切作用而受到破坏，使体系粘度降低;同时，聚合物链段可吸收、存储和释放湍流能量。二、在水相中，水性聚合物可与有机分子表面活性剂相互作用，形成复配体，该复配体的抗剪切性能明显增强，可在较高剪切下保持良好的网络结构，稳定体系粘度，且有望应用于管道流动减阻。三、通过调控聚合物与纳米粒子的相互作用，提升聚合物纳米粒子的界面相互作用，提升相应复合材料的疏水性和力学相应性能，进而开发出长寿命、高稳定性和良好耐水性的聚合物基传感器。