Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, P.O. Box 1129, Hefei, Anhui, People's Republic of China.
J Phys Chem B. 2012 Nov 15;116(45):13411-5. doi: 10.1021/jp306531b. Epub 2012 Nov 6.
Gaining control over precise and predictable structures of colloidal systems and understanding the abundant dynamic behaviors remains a formidable challenge. In this study, low-frequency mechanical spectroscopy was applied to investigate the dynamics of aqueous solutions of N-isopropylacrylamide-acrylic acid (NIPAM-AA) copolymers with three different AA contents. A mechanical loss valley was found for the solution with low molar fraction of AA (f(AA)), f(AA) = 25 and 50 mol %, and a loss peak was shown for the solution with f(AA) = 75 mol %. The former is suggested to be due to the particle glass phase of repulsive micelles above the low critical solution temperature, whereas the latter is associated with the α relaxation behavior of NIPAM-AA/water mixture at high concentrations. The relaxation time of the α relaxation seems to follow a simple Arrhenius temperature dependence. The activation energy H is ∼53 kJ/mol, and the larger H value is suggested to be due to multiple strong hydrogen bonds in the copolymer solution. The present work demonstrates that by controlling the proportion of ingredients in the colloidal systems the systems can exhibit distinct dynamic behaviors, which is helpful in the design and fabrication of colloids.
控制胶体系统的精确和可预测结构并理解丰富的动态行为仍然是一个艰巨的挑战。在这项研究中，低频机械光谱学被应用于研究三种不同 AA 含量的 N-异丙基丙烯酰胺-丙烯酸（NIPAM-AA）共聚物水溶液的动力学。对于摩尔分数 f(AA)为 25 和 50 mol %的 AA 的溶液，发现了机械损耗谷，而对于 f(AA)为 75 mol %的 AA 的溶液，发现了损耗峰。前者被认为是由于在低临界溶液温度以上的排斥胶束的粒子玻璃相，而后者与 NIPAM-AA/水混合物在高浓度下的α弛豫行为有关。α弛豫的弛豫时间似乎遵循简单的 Arrhenius 温度依赖性。活化能 H 约为 53 kJ/mol，较大的 H 值被认为是由于共聚物溶液中存在多个强氢键。本工作表明，通过控制胶体系统中成分的比例，可以使系统表现出明显的动态行为，这有助于胶体的设计和制造。
