典型物理凝胶化体系的统计特征及物理凝胶的动态响应研究

The physical gelation system is referred to a complex system where the most important interaction between particles is the physical association such as hydrogen bonds, hydrophobic and hydrophilic forces, dipole force as well as depletion force. Such systems are usually inhomogeneous and multi-scale because of clusters formed by "physical bonds" with various sizes, and as a result, physical gelation is an interesting phenomenon resulting from the connectivity due to physical associations. In a physical gelation system, the interplay between geometrical phases and thermodynamic phases results in rich phase behaviors and complex structural properties. In this proposal, the principle of statistical mechanics is employed to study some fundamental properties of typical physical gelation systems such as hydrogen bonding fluid, patchy particle and antigen-antibody system. In detail, starting with kinetic equations for the growth of clusters, the free energy and the law of mass action concerning physical association process are obtained. A relationship between the association degree and the binding energy, functionality and temperature are explicitly given. Meanwhile, the size distribution of clusters together with averaged molecular weights and spatial dimension are explicitly calculated. Moreover, the sol-gel transition will be investigated from the thermodynamic viewpoint with the generalized scaling law for describing this kind of phase transition being presented. In order to find the relationship between the geometrical phases and thermodynamic phases, the effect of the relevant factors on the phase behavior is discussed by means of the phase diagrams. Interestingly, it is found that in the physical gelation systems, the percolation of treelike bonds corresponds to the sol-gel transition, while the percolation of cyclic bonds corresponds to the physical gelation. Accordingly, in terms of the structural parameters that characterize the network structure of physical gel, it is pointed out that cyclization in the postgel regime plays an important role in the stabilization of physical gel. With the network structural parameters, the dynamical response property of physical gel is analyzed. Furthermore, for physical gelation systems under various geometrical restrictions, the density functional theory for classical fluids is used to study the phase equilibria, spatial correlation and the dependences of the local and global structures on the association degree. The main attempt is twofold: one is to deepen the understanding of the physical gelation and reveal the influences of physical associations on the aggregated structures and properties of systems, and another is to promote the applications of physical gel materials in related fields.

物理凝胶化体系是典型的多尺度、非均相体系,其中的几何相变和热力学相变相互耦合,呈现丰富的相态结构.本项目基于统计力学原理研究体系的联结特征,导出自由能和质量作用定律,得到交联度与内外因素间的解析关系,给出团簇的数量分布函数、平均分子量和空间尺度.进而从热力学角度研究"溶胶-凝胶"相变,获得相应的广义标度律.为了揭示几何相与热力学相的关系,通过相图研究各种因素对相态特征的影响,指出体系中的树键逾渗与"溶胶-凝胶"相变对应,而环键逾渗则与物理凝胶化对应.进一步计算凝胶网络的网络结构参数,指出环结构的协同作用是物理凝胶稳定化的重要机理,研究内外因素对于物理凝胶结构及其动态响应性的调控.同时,利用密度泛函理论研究典型几何约束下体系的相平衡特征,指出物理交联对体系局部和整体结构的影响.研究旨在深化对物理凝胶化的认知,揭示物理凝胶化的本质,为物理凝胶材料的开发提供理论线索.

本项目以物理凝胶化现象为出发点, 集中探讨物理凝胶化的相变本质以及物理凝胶材料的动态响应问题. 在研究中, 主要针对凝胶结构单元之间因物理联结作用所致的聚集态结构和相态结构问题. Patchy胶体粒子和氢键流体是最具代表性的两类物理凝胶化体系, 有鉴于此, 我们基于统计力学原理研究了体系的联结特征,导出相应的自由能和质量作用定律,得到交联度与内外诸因素间的解析关系,给出团簇的数量分布函数、平均分子量和空间尺度..在此基础上, 从热力学角度研究溶胶-凝胶转变和流体-固体转变两类相变过程, 揭示出几何相与热力学相的关系, 通过相图研究各种因素对相态特征的影响, 指出体系中的树键渗流与溶胶-凝胶相变对应, 而环键渗流则与物理凝胶化对应. 进一步分析物理凝胶的拓扑结构, 指出了环结构的协同作用是物理凝胶稳定化的重要机理, 研究内外因素对于物理凝胶结构及其动态响应性的调控. 同时, 制备了典型的自修复凝胶, 探讨了相应的自修复机制及其动态响应性. 此外, 基于动态键型自修复凝胶的格气模型指出其自修复行为在本质上是一种相变过程, 并根据自修复过程中的比热变化予以证明. .此外, 利用经典流体的密度泛函理论研究了在典型几何约束下氢键流体的相平衡特征, 结合Kirkwood-Buff(KB)理论指出物理交联对体系局部和整体结构的影响. 同时, 将KB理论用于Yukawa流体和氢键流体的研究中, 指出了流体局域结构和宏观特征之间的关联. 研究旨在深化对物理凝胶化的认知、阐释其本质, 为物理凝胶材料的开发和应用提供可靠的理论线索.