白炭黑/聚醚悬浮体系的结构调控与非线性流变行为研究

The silica/polypropylene glycol (PPG) suspensions exhibit shear thickening characteristic thus show potentials in impact-absorbing equipment or high-performance liquid lithium-ion batteries. In view of the limitations of the existing theory for STe (ignoring the agglomerate structures and their evolution upon shearing) and the new findings in our early preliminary investigations (weak gel exhibiting STe effect, and strong gel after large-strain shearing exhibiting STe effect), this proposal is devoted to manipulate the solvation layer surrounding the nanoparticle aggregates to develop methods being able to regulate the STe behavior and to create a relationship between material composition, microscopic effect and macroscopic rheology of the suspensions. The researches will be focused on the STe behavior in relation to the thermodynamic (sol and gel structures) and dynamic structural evolution mechanisms (shear-induced structural variations and aging regeneration). The “two phase” model will be used for analyzing both the linear rheology and the steady-dynamic superposition flows to disclose the structural evolutions of sols and weak gels in the static state and during different flow stages including Newtonian flow, low-rate thinning, STe and high-rate thinning. For strong gels, the rheology behaviors will be investigated for clarifying structural evolutions responsible for the shear-induced STe and its aging. The investigations are expected to provide experimental and theoretical bases for regulating and optimizing the STe behavior for designing high-performance suspensions.

白炭黑/聚氧化丙烯(PPG)悬浮体系具有剪切增稠(STe)特性，在冲击吸收装置、高性能液体锂离子电池等领域具有潜在应用价值。针对现有STe理论的局限性(忽略粒子团聚体结构及其演化动力学行为)与前期研究的新发现(弱凝胶具有STe效应；强凝胶具有大剪切诱导STe效应)，本项目拟以纳米粒子聚集体溶剂化层的调控为纽带，围绕“材料组成-微观结构-流变行为关系”目标，发展白炭黑/PPG悬浮体系STe调控方法，从热力学(溶胶、凝胶结构)与动力学(剪切诱导结构变化及其老化再生)上阐明结构演化机制。项目将采用“两相”模型研究悬浮体系线性流变行为、稳态-动态叠加流变行为，揭示溶胶、弱凝胶在静态、牛顿流动、低速剪切变稀、STe、高速剪切变稀等阶段的白炭黑团聚体结构演化特征，阐明强凝胶应力诱导STe及其老化动力学机制，为实现STe行为的调控与优化提供依据，为高性能STe悬浮体系的设计、制备提供新方法和新思路。

在项目资助下研究了纳米粒子表面化学性质、基体分子量、粒子-高分子界面相互作用等对高分子纳米复合材料熔体线性和非线性流变行为、界面结构、基体链段弛豫与终端流动行为的影响。通过界面结构调控在白炭黑/聚醚复合体系中实现黏度跨越4个数量级的溶胶-凝胶转变，揭示了其粒子表面玻璃化层逾渗机理以及溶胶、弱凝胶、强凝胶流变特性与界面结构的关系，阐明了溶胶、弱凝胶复合体系低速剪切变稀(等应变能控制)、剪切增稠(等应变)、高速剪切变稀(等应力、等应变、等能)的产生机制，阐明了基体分子量及分子量分布对溶胶-凝胶转变的调控机制。基于纳米粒子的应变放大效应及基体分子链终端弛豫受限效应，修正课题组所提出的“两相模型”，揭示了受限基体流体动力学效应对非终端区流变行为的贡献，提出流体动力学区流变行为的时间-浓度叠加原理，首次揭示了高分子分子量、纳米粒子拓扑结构对补强、滞后行为的影响。研究了高分子纳米复合材料非线性流变行为，揭示了粒子种类、含量及分散性对非线性Payne效应的影响规律，提出非线性流变临界等微观应变原理(应变-浓度叠加原理)，阐明了粒子团聚、基体非理想交联网络、基体非橡胶组分等对弱应力过冲行为的影响，发现Payne效应的产生是由线形链或非理想交联网络线形链缺陷所决定的，证明Payne效应及其弱应力过冲行为与结合胶及粒子表面玻璃化层无关，证明流变三阶谐波非线性与粒子分散性无关，而是由基体微观应变所决定的。提出的时间-浓度叠加原理和应变-浓度叠加原理，突破了传统模型仅可描述补强而不能解释滞后行为的局限性，排除了长期以来关于“粒子逾渗导致液-固转变”以及“粒子团簇软化”、“粒子表面吸附链脱吸附-滑移”、“粒子表面玻璃层屈服”、“粒子网络破坏”等非线性流变原因的错误假设，为研究纳米复合材料中高分子动力学行为提供了重要、可靠的补充性方法，也为深入研究并调控高分子纳米复合材料补强、耗散行为奠定了坚实的基础。