Block copolymer molecular weight is a crucial factor influencing micelle fragmentation kinetics. In particular, it is not established how block length affects the fragmentation rate, and which block is more important. In this work, we studied the separate dependence of micelle fragmentation kinetics on core and corona block lengths, with temperature-jump experiments by dynamic light scattering. Two series of 1,2-polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) copolymers were prepared, both with fixed N_PB (degree of polymerization of the core block) and various N_PEO. In all, a total of nine narrow dispersity (D̵ < 1.1) polymers were used, with PB-b-PEO block molar masses (in kDa) of (9–6), (9–9), (9–12), (9–13), (9–19), (15–10), (15–14), (15–17) and (15–22). Micelles were initially prepared using direct dissolution of PB-b-PEO in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide [C₂MIM][TFSI], followed by fragmentation during thermal annealing at 170 °C. The relaxation time (τ) for micelle fragmentation exhibits a power-law correlation with both N_PB and N_PEO as τ ∼ N_core^1.4 × N_corona^0.6. Micelles were also characterized before and after fragmentation, by small-angle X-ray scattering and by liquid-phase transmission electron microscopy. Both analyses confirmed that all micelles were spherical, and the mean aggregation numbers before and after fragmentation could be extracted. The stronger τ dependence on N_core suggests a higher core elastic free energy penalty due to core chain extension in the transition state, compared to the contribution of corona crowding. These results are apparently not captured by any available theory of micelle fragmentation.

中文翻译：

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嵌段共聚物胶束的裂解动力学：核和冠嵌段长度的影响


嵌段共聚物分子量是影响胶束破碎动力学的关键因素。特别是，还没有确定块长度如何影响碎片率，以及哪个块更重要。在这项工作中，我们通过动态光散射进行温度跳跃实验，研究了胶束破碎动力学对核心和冠块长度的独立依赖性。制备了两个系列的1,2-聚丁二烯-b-聚环氧乙烷(PB -b -PEO)共聚物，均具有固定的N _PB (核心嵌段的聚合度)和不同的N _PEO 。总共使用了九种窄分散性 ( D̵ < 1.1) 聚合物，PB -b -PEO 嵌段摩尔质量（以 kDa 为单位）为 (9–6)、(9–9)、(9–12) 、(9–13)、(9–19)、(15–10)、(15–14)、(15–17) 和 (15–22)。胶束最初是通过将 PB- b -PEO 直接溶解在离子液体 1-乙基-3-甲基咪唑鎓双（三氟甲基磺酰基）亚胺 [C ₂ MIM][TFSI] 中，然后在 170 °C 热退火过程中裂解来制备的。胶束破碎的弛豫时间 (τ) 与N _PB和N _PEO均呈现幂律相关性，即 τ ∼ N _core ^1.4 × N _corona ^0.6 。还通过小角 X 射线散射和液相透射电子显微镜对破碎前后的胶束进行了表征。两项分析均证实所有胶束都是球形的，并且可以提取破碎前后的平均聚集数。 τ 对N_核心的依赖性更强，表明与电晕拥挤的贡献相比，由于过渡态核心链延伸而导致的核心弹性自由能损失更高。这些结果显然没有被任何可用的胶束破碎理论所捕获。