Guo Rong H, Hsu Chih H, Hua Chi C, Chen Show A
Department of Chemical Engineering, National Chung Cheng University , Chiayi 621, Taiwan, Republic of China.
J Phys Chem B. 2015 Feb 19;119(7):3320-31. doi: 10.1021/acs.jpcb.5b00575. Epub 2015 Feb 2.
A practical valuable amorphous conjugated polymer, poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV), has been revealed to foster an abundance of micrometer-sized colloidal aggregates at relatively low concentration (below 1 wt %) in a hybrid-solvent medium that contains a nonsolvent, and the solution turned into gel by colloidal bridging after one-day aging at 30 °C. In contrast with typical polymer gels fostered by (anisotropic) chain cross-linking or planar packing on selective interacting sites, the MEH-PPV gel has been revealed (via dynamic light scattering, small-angle light scattering, time-sweep dynamic modulus and optical microscope) to first develop featureless aggregate clusters in solution and, as the solvent quality worsens with reduced system temperature, bridge themselves to form gel through a one-dimensional (1-D) to three-dimensional (3-D) kinetic pathway. Combined dynamic/static light scattering analyses, along with supporting scanning electron microscope image and molecular dynamics simulation, indicated a concomitant structural reorganization within the colloidal aggregates, where spontaneous chain packing was perceived to form local fiber-like materials that are elastic by nature (i.e., a q-independent decay rate). The near coincidence of the above-mentioned microscopic and macroscopic phase alterations led us to contend that similar fibrous materials have served as the exterior bridging agent to fabricate colloidal strands upon gelation. The present findings clarify previously enigmatic, much speculative, gelation phenomena of MEH-PPV, and shed light on the prospect of capitalizing on specific polymer-solvent interactions to incubate desirable colloidal aggregates and gels in room-temperature processing of practical valuable conjugated polymers.
一种实用且有价值的无定形共轭聚合物，聚（2-甲氧基-5-（2'-乙基己氧基）-1,4-亚苯基亚乙烯基）（MEH-PPV），已被发现在含有非溶剂的混合溶剂介质中，在相对较低浓度（低于1 wt%）时会形成大量微米级胶体聚集体，并且在30°C下老化一天后，溶液通过胶体桥连变成凝胶。与通过（各向异性）链交联或在选择性相互作用位点上的平面堆积形成的典型聚合物凝胶不同，MEH-PPV凝胶（通过动态光散射、小角光散射、时间扫描动态模量和光学显微镜）已被发现首先在溶液中形成无特征的聚集体簇，并且随着系统温度降低溶剂质量变差，通过一维（1-D）到三维（3-D）的动力学途径自身桥连形成凝胶。动态/静态光散射分析相结合，以及辅助的扫描电子显微镜图像和分子动力学模拟表明，胶体聚集体内同时发生结构重组，其中自发的链堆积被认为形成了本质上具有弹性的局部纤维状材料（即与q无关的衰减率）。上述微观和宏观相变化的近乎巧合使我们认为，类似的纤维状材料在凝胶化时充当了外部桥连剂以形成胶体链。本研究结果澄清了之前关于MEH-PPV的神秘且多为推测的凝胶化现象，并为利用特定的聚合物-溶剂相互作用在实用有价值的共轭聚合物的室温加工中培育理想的胶体聚集体和凝胶的前景提供了启示。
