pH-induced deswelling kinetics of sterically stabilized poly(2-vinylpyridine) microgels probed by stopped-flow light scattering.
pH-induced deswelling kinetics of sterically stabilized poly(2-vinylpyridine) microgels probed by stopped-flow light scattering.
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DOI：
10.1021/la8014282
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发表时间：
2008-07
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影响因子：
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通讯作者：
Jun Yin;D. Dupin;Junfang Li;S. Armes;Shiyong Liu
中科院分区：
文献类型：
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作者：
Jun Yin;D. Dupin;Junfang Li;S. Armes;Shiyong Liu
采用乳液聚合法合成了近单分散、空间稳定的聚2-乙烯基吡啶（P2 VP）微凝胶。这些颗粒在水溶液中表现出完全可逆的pH响应性溶胀/去溶胀行为。采用停流光散射研究了高度稀释分散体中pH诱导的去溶胀动力学。当pH从2跳变到各种最终溶液pH值（>或=5.4）时，1，960 nm微凝胶的水性分散体的散射光强度表现出突然的初始增加，随后逐渐降低到最终平衡值。整个微凝胶到胶乳去溶胀过程发生在约0.5-1.0 s的时间尺度上，这比胶乳到微凝胶溶胀的动力学慢得多。微凝胶去溶胀动力学取决于最终pH，较高的最终pH导致更快的收缩速率。在早期阶段（<0.2s）期间对去溶胀动力学的仔细检查揭示了初始微凝胶塌陷发生在约50 ms内，当目标为更高的最终pH值时，观察到更快速的转变。外加盐的加入显著加速了去溶胀的动力学。系统研究了一系列的六个近单分散P2 VP颗粒（溶胀微凝胶直径范围从1270到4230 nm）的微凝胶到胶乳的转变也进行了研究。初始微凝胶塌陷的特征去溶胀时间，τ deswell，与初始溶胀微凝胶半径，R，与田中方程一致。此外，凝胶网络的集体扩散系数D（由τ deswell- R（2）曲线的斜率计算）为10（-7）cm（2）s（-1）的数量级。
Near-monodisperse, sterically stabilized poly(2-vinylpyridine) (P2VP) microgels were synthesized by emulsion polymerization. These particles exhibited completely reversible pH-responsive swelling/deswelling behavior in aqueous solution. Stopped-flow light scattering was employed to investigate the kinetics of pH-induced deswelling in highly dilute dispersions. Upon a pH jump from 2 to various final solution pH values (>or=5.4), the scattered light intensity of an aqueous dispersion of a 1,960 nm microgel exhibited an abrupt initial increase, followed by a gradual decrease to the final equilibrium value. The whole microgel-to-latex deswelling process occurred over time scales of approximately 0.5-1.0 s, which is much slower than the kinetics for latex-to-microgel swelling. The microgel deswelling kinetics depends on the final pH, with a higher final pH leading to a faster rate of shrinkage. Close inspection of the deswelling kinetics during the early stages (<0.2 s) revealed that initial microgel collapse occurred within approximately 50 ms, with more rapid transitions being observed when higher final pH values were targeted. Addition of external salt significantly accelerates the kinetics of deswelling. Systematic studies of the microgel-to-latex transition for a series of six near-monodisperse P2VP particles (with swollen microgel diameters ranging from 1270 to 4230 nm) has also been investigated. The characteristic deswelling time for initial microgel collapse, tau deswell, correlated fairly well with the initial swollen microgel radius, R, in agreement with the Tanaka equation. Moreover, the collective diffusion coefficient of the gel network, D, calculated from the slope of the tau deswell- R (2) curve, was of the order of 10 (-7) cm (2) s (-1).