第3讲 高分子链的柔性和溶液热力学1015F.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 溶解过程 The solution process (linear Polymer) This process is usually slower compared with small molecules, and strongly dependent on the chemical structures and condensed states of the samples. * Swelled Sample Polymer Solution 高分子特点：先溶胀，后溶解 Crosslinked polymers: only can be swelled 交联高分子：有溶胀，无溶解 Crystalline polymers 结晶高分子：先熔融，后溶解 Crystalline PE: dissolve at the temperature approached to its melting temperature. Crystalline Nylon 6,6: dissolved at room temperature by using the solvent with strong hydrogen bonds. (热力学判据) Criteria of Polymer Solubility Solubility occurs only when the DGmix is negative. (DE/v) cohesive energy density (内聚能密度) d =(DE/v)1/2 : solubility parameter (溶度参数) 1-1 + 2-2 1-2 + 1-2 1. Hildebrand enthalpy of mixing (混合焓) 1: solvent; 2: polymer P12 Molar mixture volume 由化学结构（重复单元）决定！ △Gmix= △Hmix- T△Smix Gibbs free energy of mixing 高分子溶液热力学理论Flory-Huggins theory ，Lattice Model (格子模型) 体系中有N1个溶剂分子 + N2个链段数为x的高分子 总格子数: N=N1+xN2 已有j个高分子放入, 剩下N-xj个空格, 求第j+1个高分子的放置方式Wj+1 ??? 1. 放置第j+1个高分子的第1个链段的概率 N-xj 2. 放置第j+1个高分子的第2个链段的概率 Z(N-xj-1)/N 3. 放置第j+1个高分子的第3个链段的概率 (Z-1)(N-xj-2)/N …. (Z-1)(N-xj-x+1)/N x. 放置第x个链段的概率 * Thermodynamics of Polymer Solutions Huggin’s 混合热 Enthalpy of mixing Mixing process: Different pairs in solution: solvent-solvent molecule: [1-1], e11 solute-solute segment: [2-2], e22 solvent-solute: [1-2], e12 Flory-Huggins parameter: (interaction parameter) volume fraction of solvent ~ Possibility of the cell occupied by solvent. cells surrounding a polymer number of polymers P12 total pairs of [1-2] and N1 N2 Thermodynamics of Polymer Solutions混合熵 (1) Entropy of mixing for ideal solution (2) Entropy of mixing for polymer solutions 体积不变 The lattice model assumes that the volume is unchanged during mixing. 各占一格 Each r