pH刺激响应水凝胶微观结构动力学的超快红外光谱研究

本文合成了甲基丙烯酸二甲氨基乙酯/丙烯酸共聚水凝胶，并在不同pH条件下表征其宏观溶胀行为. 以硫氰酸根阴离子作为局部红外探针，结合傅里叶变换红外光谱和超快红外光谱学研究了pH刺激响应水凝胶的微观结构动力学. 超快红外光谱数据表明，当水凝胶体系的pH从2.0变为12.0时，硫氰酸根探针的振动弛豫时间常数从(14±1) ps增加到(20±1) ps. 转动各向异性测量结果进一步表明，硫氰酸根探针的转动受到水凝胶中形成的三维网络结构的限制. 尤其是在pH为7.0时，SCN探针的旋转不会衰减到零.

Ultrafast Infrared Spectroscopic Study of Microscopic Structural Dynamics in pH Stimulus-Responsive Hydrogels

Hydrogels show versatile properties and are of great interest in the fields of bioelectronics and tissue engineering. Understanding the dynamics of the water molecules trapped in the three-dimensional polymeric networks of the hydrogels is crucial to elucidate their mechanical and swelling properties at the molecular level. In this report, the poly(DMAEMA-co-AA) hydrogels were synthesized and characterized by the macroscopic swelling measurements under different pH conditions. Furthermore, the microscopic structural dynamics of pH stimulus-responsive hydrogels were studied using FTIR and ultrafast IR spectroscopies from the viewpoint of the SCN? anionic solute as the local vibrational reporter. Ultrafast IR spectroscopic measurements showed the time constants of the vibrational population decay of SCN? were increased from 14±1 ps to 20±1 ps when the pH of the hydrogels varied from 2.0 to 12.0. Rotational anisotropy measurements further revealed that the rotation of SCN? anionic probe was restricted by the three-dimensional network formed in the hydrogels and the rotation of SCN? anionic probe cannot decay to zero especially at the pH of 7.0. These results are expected to provide a molecular-level understanding of the microscopic structure of the cross-linked polymeric network in the pH stimulus-responsive hydrogels.