多分散性高分子/胶体碟片体系的液晶相变动力学研究

The platelet-like colloid and polymer, such as the clay, gibbsite and blood red cells, can exhibit the richer liquid crystalline phase behaviors than other materials with geometric anisotropy. There are few explicit theories, however, to study the dynamics of liquid crystalline phase transition driven by the external conditions in the polydisperse systems of the colloidal/polymer platelets. In this proposal, we shall theoretically study the dynamics of liquid crystalline phase transition in systems of the platelet-like colloid and polymer with polydispersity under the sedimentation or the evaporation. Using Onsager variation principle as a framework, we plan to derive the non-equilibrium evolution equations (with the moving boundary conditions) for the phase transition in the different kinds of platelet systems, and the self-adaptive numerical methods will be utilized to ensure the efficient and stable solutions of these equations. In a consequence, the concentration profiles of each component, the profiles of oriented order parameter and the demixing state diagrams are all able to be obtained and discussed. Besides, we shall also build up the local analytical models to describe the motions of crystalline interface. Combining the numerical computations and the analytical models, we can fully analyze the mechanisms that either the sedimentation or the evaporation approach drives the platelet-like colloid/polymer systems with the polydispersity to evolve the complex crystalline phase configurations, for instance the inverted or floating crystalline phases, and the coexistence of multi-crystalline phase configurations. Meanwhile, the roles these two approaches play in the gel-crystal phase transition in the systems of polymer-based platelet composites will be also investigated. All these studies are able to provide the clearly theoretical predictions and guidance for the experimental researches and the applications of the new multi-composite platelet-like colloid/polymer liquid-crystal materials.

碟状胶体或高分子（如黏土、水铝矿、血红细胞）较其他几何各向异性材料具有更丰富的液晶相行为，然而未有明确的理论能够研究多分散性碟片材料体系在外界条件驱动下的液晶相变动力学。本项目开展对沉降或蒸发驱动多分散性高分子/胶体碟片体系的液晶相变动力学理论研究。以Onsager变分原理为理论框架，针对不同体系推导出非平衡态下的液晶相变演化方程组（带有动态边界条件），采用自适应数值计算方法对模型进行高效稳定地求解以获取各组分的浓度、取向序参及各组分间分层状态等的演变图像，同时拟建立液晶界面运动的局部解析模型。结合数值计算与解析模型来分析沉降或蒸发条件驱动上述研究目标体系演化出诸如倒转/浮动液晶相、交替/多晶相共存等复杂晶相结构的不同机制，及两种条件在调控高分子复合碟片体系的凝胶-液晶相转变中的作用。这些研究能为新型多复合碟状胶体/高分子液晶材料的实验研究与应用提供清晰的理论预测和指导。

本项目利用理论建模，如离散液晶取向原理、扩散-力学耦合机制、昂萨格变分原理，以及数值计算方法，如自适应有限差分、有限体积和独创的软格子方法（Soft-Cell Approach）等，针对（1）外场（如溶剂蒸发）诱导碟状胶体颗粒液晶相变动力学；（2）及其与水凝胶智能软材料交叉应用等问题展开研究。我们考察限域通道内定向蒸发诱导纳米碟片悬浮液的液晶相变动力学，探讨了溶剂蒸发速率、通道几何约束和碟片横纵比如何影响向列相（N）液晶薄膜的生长。研究表明，碟片液晶相在蒸发端处形成并生长，蒸发速率越高，液晶相形成的越快，液晶相前锋（N相界面）出现的越早，液晶膜内碟片包装密度越高，但最终长度越短。通道约束强化可促使碟片液晶相的生长，以获得更宽的液晶薄膜。我们证明碟片形成的致密液晶相的保水能力要明显优于球形胶粒形成的渗透性无序包装结构。在与水凝胶软材料交叉应用研究中，我们首先报道了胶态凝胶宏观塌缩下的团簇网络内部溶剂回流水动力学的作用。在壁面约束下，凝胶平均沉降速度非单调地依赖于初始胶粒浓度，且与凝胶的弹性常数相关。其次，我们利用扩散-力学耦合机制对水凝胶溶胀动力学建模，详细分析了水凝胶溶胀表面上碟片纳米液晶薄膜自生长过程，证明水凝胶溶胀诱导胶体颗粒或大分子的相变（自组装）来制备（生物）功能性纳米薄膜具有材料工程学上优越性。研究表明，溶胀表面的纳米薄膜自生长动力学完全由水凝胶基底的溶胀力学行为决定，而与周围溶液中的溶质相变类型无关，如溶液-凝胶相变，向列相液晶相变。水凝胶的溶胀准平衡态对预判纳米薄膜何时达到最大厚度有实际意义。最后，我们理论分析水凝胶渗透诱导溶胀/消溶胀时宏观弹性形变引起的主动溶剂水动力学对在生命微环境中的药物递送过程影响。理论证明了水凝胶因其内部水动力学和物质扩散的协同耦合性而作为释药递送的先进软载体，具有极大的研发潜能。本人作为唯一独立作者发表SCI论文4篇，包括Phys. Rev. E，Phys. Chem. Chem. Phys.，Phys. Fluids等期刊。

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