Probing the micellization kinetics of pyrene end-labeled diblock copolymer via a combination of stopped-flow light-scattering and fluorescence techniques
Probing the micellization kinetics of pyrene end-labeled diblock copolymer via a combination of stopped-flow light-scattering and fluorescence techniques
复制标题
通过停流光散射和荧光技术的结合探讨芘末端标记的二嵌段共聚物的胶束化动力学
DOI：
10.1021/jp075018b
复制
发表时间：
2007-10-25
影响因子：
3.3
通讯作者：
Liu, Shiyong
中科院分区：
文献类型：
--
作者：
Zhang, Jingyan;Li, Yuting;Liu, Shiyong
以1-芘甲醇为引发剂，采用含氧阴离子聚合法合成了芘末端标记的双亲水性嵌段共聚物聚甲基丙烯酸二乙氨基乙酯-聚甲基丙烯酸二甲氨基乙酯（Py-PDEA-b-PDMA）。该二嵌段共聚物在水溶液中表现出可逆的pH响应性胶束化行为，在中性或碱性pH下形成由可溶性PDMA嵌段稳定的PDEA核心胶束。利用共价连接到PDEA嵌段末端的芘探针，通过停流光散射使用荧光检测器监测Py-PDEA-bPDMA的pH诱导胶束化动力学。当pH从4.0跳到9.0时，散射光强度和受激准分子/单体荧光强度比（I-E/I-m）最初突然增加，随后逐渐增加以达到平台值。有趣的是，IE/Im比在前10 ms内突然增加：需要三重指数函数来拟合相应的动态迹线，导致三个特征弛豫时间常数（tau（1，fluo）< tau（2，fluo）< tau（3，fluo））。另一方面，散射光强度的动态轨迹可以通过双指数函数很好地拟合：产生的时间常数tau（1，scat）和tau（2，scat）可以分别归因于准平衡胶束的形成和驰豫到其最终平衡状态。最重要的是，从停流光散射获得的tau（l，scat）与从停流荧光获得的tau（2，flu）大体一致。通过停流荧光检测到的最快的过程（τ（1，fluo）类似于4 ms）归因于仅包括几个链的小的瞬态胶束的突发形成，所述链太小而不能通过常规光散射检测到。这些新生胶束经历快速融合并生长成准平衡胶束，然后缓慢地接近其最终平衡状态。后两个过程可以通过这两种技术来检测。
A pyrene end-labeled double hydrophilic diblock copolymer, poly(2-(diethylamino)ethyl methacrylate)-bpoly(2-(dimethylamino)ethyl methacrylate) (Py-PDEA-b-PDMA), was synthesized by sequential monomer addition via oxyanionic polymerization using a 1-pyrenemethanol-based initiator. This diblock copolymer exhibits reversible pH-responsive micellization behavior in aqueous solution, forming PDEA-core micelles stabilized by the soluble PDMA block at neutral or alkaline pH. Taking advantage of the pyrene probe covalently attached to the end of the PDEA block, the pH-induced micellization kinetics of Py-PDEA-bPDMA was monitored by stopped-flow light scattering using a fluorescence detector. Upon a pH jump from 4.0 to 9.0, both the scattered light intensity and excimer/monomer fluorescence intensity ratios (I-E/I-m) increase abruptly initially, followed by a more gradual increase to reach plateau values. Interestingly, the IE/Im ratio increases abruptly within the first 10 ms: a triple exponential function is needed to fit the corresponding dynamic trace, leading to three characteristic relaxation time constants (tau(1,fluo) < tau(2,fluo) < tau(3,fluo)). On the other hand, dynamic traces for the scattered light intensity can be well-fitted by double exponential functions: the resulting time constants tau(1,scat) and tau(2,scat) can be ascribed to formation of the quasi -equilibrium micelles and relaxation into their final equilibrium state, respectively. Most importantly, tau(l,scat) obtained from stopped-flow light scattering is in general agreement with tau(2,flu) obtained from stopped-flow fluorescence. The fastest process (tau(1,fluo) similar to 4 ms) detected by stopped-flow fluorescence is ascribed to the burst formation of small transient micelles comprising only a few chains, which are too small to be detected by conventional light scattering. These nascent micelles undergo rapid fusion and grow into quasi-equilibrium micelles and then slowly approach their final equilibrium state. The latter two processes can be detected by both techniques.