Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto, Japan.
J Phys Condens Matter. 2011 Jul 20;23(28):284105. doi: 10.1088/0953-8984/23/28/284105. Epub 2011 Jun 27.
The collapse of a poly(N-isopropylacrylamide) (PNIPAM) chain upon heating and the phase diagrams of aqueous PNIPAM solutions with a very flat lower critical solution temperature (LCST) phase separation line are theoretically studied on the basis of cooperative dehydration (simultaneous dissociation of bound water molecules in a group of correlated sequence), and compared with the experimental observation of temperature-induced coil-globule transition by light scattering methods. The transition becomes sharper with the cooperativity parameter σ of hydration. The reentrant coil-globule-coil transition and cononsolvency in a mixed solvent of water and methanol are also studied from the viewpoint of competitive hydrogen bonds between polymer-water and polymer-methanol. The downward shift of the cloud-point curves (LCST cononsolvency) with the mol fraction of methanol due to the competition is calculated and compared with the experimental data. Aqueous solutions of hydrophobically modified PNIPAM carrying short alkyl chains at both chain ends (telechelic PNIPAM) are theoretically and experimentally studied. The LCST of these solutions is found to shift downward along the sol-gel transition curve as a result of end-chain association (association-induced phase separation), and separate from the coil-globule transition line. Associated structures in the solution, such as flower micelles, mesoglobules, and higher fractal assembly, are studied by ultra small-angle neutron scattering with theoretical modeling of the scattering function. Dynamic-mechanical modulus, nonlinear stationary viscosity, and stress build-up in start-up shear flows of the associated networks are studied on the basis of the affine and non-affine transient network theory. The molecular conditions for thickening, strain hardening, and stress overshoot are found in terms of the nonlinear amplitude A of the chain tension and the tension-dissociation coupling constant g.
基于协同脱水（一组相关序列中结合水分子的同时离解）理论，研究了聚 N-异丙基丙烯酰胺（PNIPAM）链在加热时的坍塌以及具有非常平坦低临界溶液温度（LCST）相分离线的水溶液 PNIPAM 溶液的相图，并通过光散射方法与实验观察到的温度诱导的无规卷曲-球粒转变进行了比较。随着水合协同参数 σ 的增加，转变变得更加陡峭。还从聚合物-水和聚合物-甲醇之间的氢键竞争的角度研究了混合溶剂中水和甲醇中的再进入无规卷曲-球粒-无规卷曲转变和共溶剂。由于竞争，计算并比较了由于竞争导致的浊点曲线（LCST 共溶剂）向甲醇摩尔分数的向下移动，并与实验数据进行了比较。对两端带有短烷基链的疏水改性 PNIPAM（端基 PNIPAM）的水溶液进行了理论和实验研究。发现这些溶液的 LCST 由于末端链缔合（缔合诱导相分离）沿着溶胶-凝胶转变曲线向下移动，并与无规卷曲转变线分离。通过超小角中子散射并用散射函数的理论模型研究了溶液中的缔合结构，如花状胶束、介球和更高的分形组装。基于仿射和非仿射瞬态网络理论，研究了缔合网络的启动剪切流中的动态力学模量、非线性稳态粘度和应力建立。根据链张力的非线性幅度 A 和张力离解耦合常数 g，找到了增稠、应变硬化和应力过冲的分子条件。
