arXiv 2403.143672024-03-21cond-mat.soft

嵌段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

Temperature dependence of micelle shape transitions in copolymer solutions: the role of inter-block incompatibility

M. J. Greenall, M. J. Derry

AI总结：

本文用自洽场理论解释嵌段共聚物胶束形状转变的温度依赖性，发现转变方向由嵌段间不相容性$χ_{AB}$与$χ_{BS}$共同决定，为实验中加热或冷却引起蠕虫状与球形胶束相互转化的现象提供理论依据。

摘要：

嵌段共聚物分散体系中蠕虫状与球形胶束之间转变的本质因系统而异。在某些配方中，加热驱动从蠕虫状向球形的转变，而在其他系统中，相同的转变由冷却引起。此外，球形-蠕虫状相互转化可能伴随溶剂化核心的增加或减少，即使温度依赖的方向相同。本文使用自洽场理论为这一系列行为提供潜在解释。具体而言，我们展示在该模型中，转变对溶剂疏性嵌段B与溶剂S的不相容性$χ_{BS}$（与温度最相关的参数）的依赖性，受B与溶剂亲性嵌段A间不相容性$χ_{AB}$的强烈影响。当$χ_{AB}$较小（$χ_{AB}\le 0.1$）时，增加$χ_{BS}$产生从蠕虫状胶束向球形（或更一般地，从低曲率到高曲率结构）的转变。当$χ_{AB}$高于0.1时，增加$χ_{BS}$驱动系统从球形向蠕虫状胶束转变。是否在现实$χ_{BS}$范围内观察到转变也取决于共聚物中溶剂亲性材料的分数。我们讨论了计算与实验结果的相关性，并建议温度依赖的方向可能不仅由溶剂疏性嵌段的溶液行为（上临界溶液温度与下临界溶液温度）控制，还由$χ_{AB}$控制。

英文摘要：

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 solvation of the core, 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 ($χ_{AB}\le 0.1$), 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 experimental results 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 versus lower critical solution temperature) but also by $χ_{AB}$.

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