胶体与湿颗粒体系的聚集行为及其结构转变的力学谱研究

Investigation on aggregation behaviors and structural changes of complex systems such as colloids and granular matters is one of the frontier areas in soft condensed physics. The liquid-solid transition of colloidal and granular systems usually occurs at a certain volume fraction or packing density. However, the aggregation behaviors and the relaxation characteristics and mechanism of colloidal and granular systems under the environmental conditions are still not well understood. Therefore, based on the previous work, we have proposed a project to study the aggregation behaviors as well as dynamics and cooperative mechanism of liquid-solid transition in colloidal (hard sphere and soft sphere) and wet granular systems by mechanical spectroscopy. Through the measurements of mechanical properties such as modulus and mechanical loss of the systems with increasing volume fraction/packing density, temperature, frequency and amplitude, the effects of different factors such as the sizes, shapes and elastic coefficient of particles on the aggregation behaviors and the liquid-solid transition of colloidal and wet granular systems will be investigated. The origin of mechanical loss will be analyzed and a quantitative or semi-quantitative relationship between mechanical loss and material parameters of different systems will be obtained. Based on the coupling model, the coupling behaviors and variation rules of liquid-solid transition of colloidal and wet granular systems will be obtained, and the aggregation behaviors and cooperative mechanism and intrinsic connection of the liquid-solid transition for these two systems will be clarified. This research will have important implications for deeply understanding the glass transition, and develop the research field of internal friction.

复杂体系（胶体、颗粒物质等）的聚集行为及其结构转变研究是软凝聚态物理的前沿领域之一。胶体和颗粒物质在一定的体积分数/堆积密度下会发生液-固转变。然而，关于胶体和颗粒物质在外界因素诱导下的各种聚集行为及其液-固转变的弛豫特征与机制的研究进展较为缓慢。本课题在前期工作基础上，基于内耗技术研究胶体（硬球、软球）以及湿颗粒体系的聚集行为及其液-固转变的动力学特征与耦合机制。通过测量体系的力学性质（模量和力学损耗）随体积分数/堆积密度、温度、频率与应变振幅的变化曲线，探讨粒子大小、形状与弹性系数等因素对体系的聚集行为及其液-固转变的影响。分析力学损耗的具体来源，获得其对研究体系具体材料参数的定量或半定量的依赖关系。基于耦合模型获得胶体与湿颗粒体系液-固转变的耦合特征与规律，揭示这两种体系的聚集行为及其液-固转变的耦合机制和内在关联。该项目对深入理解玻璃化转变有重要意义，同时拓展了内耗学科的研究领域。

研究软物质（胶体、颗粒物质等）的聚集行为及其结构转变对理解其基本规律及其工程应用具有重要的意义。本项目利用内耗技术研究胶体与颗粒物质的聚集行为及其液-固转变的动力学特征与机制。此外，还将内耗技术拓展用于研究非晶药物的结构转变。项目的主要研究内容和结论如下：1）研究了高分子聚N-异丙基丙烯酰胺（PNIPAM）微凝胶体系在高浓度下的相转变行为，构建了体系在不同交联度、温度和浓度下的相图。发现了两种异常的结构转变，即排斥玻璃—凝胶态转变和凝胶态—吸引玻璃转变，并基于粒子间相互作用的方向性我们给出合理解释。2）研究了双亲三嵌段共聚物聚氧乙烯-聚氧丙烯-聚氧乙烯（PEO80-PPO30-PEO80，F68）在水溶液中的相行为。发现其随温度变化的相转变过程并揭示了其胶团形成过程中的动力学行为。3）研究了颗粒体系力链弹性性质及堵塞转变机制，发现颗粒链的共振频率随形变量等因素之间存在一个普适的标度关系，它不依赖于颗粒的种类及外加压强等条件。低频微剪切振动下颗粒链间的力学性质主要由非线性Hertz定律决定。揭示了颗粒体系随颗粒大小、浸入深度及外加压力下流动态-堵塞态-冻结态转变过程及其机制。4）研究了湿颗粒体系的能量耗散规律与机制，发现沙水混合体系中能量耗散-水体积分数曲线上存在一个具有一阶相变特征的内耗峰，初步认为该峰与湿颗粒体系在某一体积分数下形成的复杂结构有关。不同水分浓度下的NaCl颗粒系中观察到一个结构转变过程，它与体系的堵塞转变以及颗粒间毛细液桥力有关。5）研究了非晶药物盐酸维拉帕米（Verapamil Hydrochloride）的离子σ弛豫与ɑ弛豫之间的关联性，发现一种反常的现象，即ɑ弛豫的温度依赖性要弱于σ弛豫，这与通常在非晶离子导体中观测到的趋势相反。基于耦合模型（Coupling Model）对该反常现象给予理论解释。在本基金的资助下已发表论文6篇（标注资助号），申请人在第十七届国际内耗与力学谱学术会议上作主题邀请报告。