The nature of the transition between worm-like and spherical micelles in block copolymer dispersions varies between systems. In some formulations, heating drives a transition from worms to spheres, while in other systems the same transition is induced by cooling. In addition, a sphere-worm interconversion can be accompanied either by an increase or a decrease in the core solvation, even if the direction of the temperature dependence is the same. Here, self-consistent field theory is used to provide a potential explanation of this range of behaviour. Specifically, we show that, within this model, the dependence of the transition on the incompatibility χ_BS of the solvophobic block B and the solvent S (the parameter most closely related to the temperature) is strongly influenced by the incompatibility χ_AB between B and the solvophilic block A. When χ_AB is small (χ_AB < 0.1), it is found that increasing χ_BS produces a transition from worm-like micelles to spheres (or, more generally, from less curved to more curved structures). When χ_AB is above 0.1, increasing χ_BS drives the system from spheres to worm-like micelles. Whether a transition is observed within a realistic range of χ_BS is also found to depend on the fraction of solvophilic material in the copolymer. The relevance of our calculations to experiments is discussed, and we suggest that the direction of the temperature dependence may be controlled not only by the solution behaviour of the solvophobic block (upper critical solution temperature-like versus lower critical solution temperature-like) but also by χ_AB.

中文翻译：

---

共聚物溶液中胶束形状转变的温度依赖性：嵌段间不相容性的作用

嵌段共聚物分散体中蠕虫状胶束和球形胶束之间的转变性质因系统而异。在一些配方中，加热驱动从蠕虫到球体的转变，而在其他系统中，相同的转变是通过冷却引起的。此外，即使温度依赖性的方向相同，球体-蠕虫相互转化也可能伴随着核心溶剂化的增加或减少。在这里，自洽场论用于为这一系列行为提供潜在的解释。具体来说，我们表明，在该模型中，转变对疏溶剂嵌段 B 和溶剂 S（与温度最密切相关的参数）的不相容性χ _BS的依赖性受到B 和溶剂 S 之间的不相容性χ _AB的强烈影响。当χ _AB较小时 ( χ _AB < 0.1)，发现增加χ _BS会产生从蠕虫状胶束到球体的转变（或者更一般地，从不太弯曲的结构到更弯曲的结构）。当χ _AB高于 0.1 时，增加χ _BS会驱动系统从球体变为蠕虫状胶束。还发现是否在χ _BS的实际范围内观察到转变取决于共聚物中亲溶剂材料的分数。讨论了我们的计算与实验的相关性，并且我们建议温度依赖性的方向不仅可以通过疏溶剂块的溶液行为（类似上临界溶液温度与下临界溶液温度）来控制，还可以通过通过χ _AB。