Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06511, USA.
J Am Chem Soc. 2010 Dec 15;132(49):17516-22. doi: 10.1021/ja107309p. Epub 2010 Nov 22.
The self-assembly of diblock copolymers provides a convenient route to the formation of mechanically robust films with precise and tunable periodic arrangements of two physically demixed but chemically linked polymeric materials. Chemoselective transport membranes may be realized from such films by selective partitioning of an active species into one of the polymer domains. Here, lithium ions were selectively sequestered within the poly(ethylene oxide) block of a liquid crystalline diblock copolymer to form polymer electrolyte membranes. Optimization of the membrane conductivity mandates alignment of self-assembled structures such that conduction occurs via direct as opposed to tortuous transport between exterior surfaces. We show here that magnetic fields can be used in a very simple and scalable manner to produce highly aligned hexagonally packed cylindrical microdomains in such membranes over macroscopic areas. We systematically explore the dependence of the ionic conductivity of the membrane on both temperature and magnetic field strength. A surprising order of magnitude increase in conductivity relative to the nonaligned case is found in films aligned at the highest magnetic field strengths, 6 T. The conductivity of field aligned samples shows a nonmonotonic dependence on temperature, with a marked decrease on heating in the proximity of the order-disorder transition of the system before increasing again at elevated temperatures. The data suggest that domain-confined transport in hexagonally packed cylindrical systems differs markedly in anisotropy by comparison with lamellar systems.
两亲嵌段共聚物的自组装为形成具有精确和可调的两种物理混合但化学连接的聚合物材料周期性排列的机械坚固的薄膜提供了一种方便的途径。通过将活性物质选择性分配到聚合物域之一中，可以从这种薄膜中实现化学选择性传输膜。在这里，锂离子被选择性地隔离在液晶两亲嵌段共聚物的聚氧化乙烯嵌段中，形成聚合物电解质膜。为了优化膜的电导率，需要对准自组装结构，以便通过直接而不是在外部表面之间的曲折传输来进行传导。我们在这里表明，可以非常简单和可扩展的方式使用磁场在这种膜中产生宏观区域上高度对准的六边形排列的圆柱形微域。我们系统地研究了膜的离子电导率对温度和磁场强度的依赖性。与非对准情况相比，在磁场最强的情况下，对准的膜的电导率会惊人地增加一个数量级。在接近体系的有序-无序转变的温度下，场对准样品的电导率表现出非单调的温度依赖性，在加热时会明显下降，然后在高温下再次增加。数据表明，与层状体系相比，六边形排列的圆柱形体系中的域限制传输在各向异性方面有明显的差异。
