Song Shaofei, Jiang Jingjie, Nikbin Ehsan, Howe Jane Y, Manners Ian, Winnik Mitchell A
Department of Chemistry, University of Toronto Toronto Ontario M5S 3H6 Canada
Department of Materials Science and Engineering, University of Toronto, 184 College Street Toronto Ontario M5S 3E4 Canada.
Chem Sci. 2021 Dec 2;13(2):396-409. doi: 10.1039/d1sc05937h. eCollection 2022 Jan 5.
Self-assembly of crystalline-coil block copolymers (BCPs) in selective solvents is often carried out by heating the mixture until the sample appears to dissolve and then allowing the solution to cool back to room temperature. In self-seeding experiments, some crystallites persist during sample annealing and nucleate the growth of core-crystalline micelles upon cooling. There is evidence in the literature that the nature of the self-assembled structures formed is independent of the annealing time at a particular temperature. There are, however, no systematic studies of how the rate of cooling affects self-assembly. We examine three systems based upon poly(ferrocenyldimethylsilane) BCPs that generated uniform micelles under typical conditions where cooling took pace on the 1-2 h time scale. For example, several of the systems generated elongated 1D micelles of uniform length under these slow cooling conditions. When subjected to rapid cooling (on the time scale of a few minutes or faster), branched structures were obtained. Variation of the cooling rate led to a variation in the size and degree of branching of some of the structures examined. These changes can be explained in terms of the high degree of supersaturation that occurs when unimer solutions at high temperature are suddenly cooled. Enhanced nucleation, seed aggregation, and selective growth of the species of lowest solubility contribute to branching. Cooling rate becomes another tool for manipulating crystallization-driven self-assembly and controlling micelle morphologies.
结晶-无规线团嵌段共聚物（BCPs）在选择性溶剂中的自组装通常是通过加热混合物直至样品看起来溶解，然后让溶液冷却回室温来进行的。在自种晶实验中，一些微晶在样品退火过程中持续存在，并在冷却时促使核-结晶胶束生长。文献中有证据表明，在特定温度下形成的自组装结构的性质与退火时间无关。然而，对于冷却速率如何影响自组装，目前还没有系统的研究。我们研究了基于聚（二茂铁基二甲基硅烷）BCPs的三个体系，这些体系在典型条件下（冷却时间为1-2小时）能生成均匀的胶束。例如，在这些缓慢冷却条件下，其中几个体系生成了长度均匀的细长一维胶束。当进行快速冷却（几分钟或更短时间内）时，会得到分支结构。冷却速率的变化导致了所研究的一些结构的尺寸和分支程度的变化。这些变化可以用高温下单体溶液突然冷却时发生的高度过饱和来解释。增强的成核、晶种聚集以及最低溶解度物种的选择性生长导致了分支。冷却速率成为控制结晶驱动的自组装和胶束形态的另一种手段。
