The effect of micellar size on the chain exchange kinetics in spherical micelles consisting of poly(methyl methacrylate)-block-poly(n-butyl methacrylate) (PMMA-b-PnBMA) in a mixture of ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI], and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BMIM][TFSI]) was investigated using time-resolved small-angle neutron scattering (TR-SANS). Two spherical micelles with different core sizes were prepared from a single block copolymer by using different protocols. In one case the micelles were formed in the presence of a cosolvent, while in the other a polymer thin film was directly dissolved in the ionic liquid. Interestingly, the micelle core size prepared from the latter method is ∼30% larger than that obtained in the former case. TR-SANS experiments reveal that the rate of single chain exchange in the micelles with a larger core size is slowed down by ∼3 times compared to the smaller core radius. This can be possibly attributed to the smaller interfacial area per chain, and larger corona density, for micelles with a larger core dimension. These geometrical factors can potentially lead to changes in both the attempt time and activation barrier for chain expulsion during the unimer exchange process. Our results clearly suggest that, in addition to the molecular characteristics of the block copolymer and solvent, the geometrical structure of the micelle plays an important role in the unimer dynamic exchange processes in block copolymer micelles.

中文翻译：

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两种尺寸的胶束中单嵌段共聚物的交换动力学

-胶束尺寸对在球形胶束由聚（甲基丙烯酸甲酯）链交换动力学的影响块-聚（Ñ丁基丙烯酸甲酯）（PMMA- b-PnBMA）在离子液体（1-乙基-3-甲基咪唑双（三氟甲基磺酰基）酰亚胺，[EMIM] [TFSI]和1-丁基-3-甲基咪唑双（三氟甲基磺酰基）酰亚胺，[BMIM] [TFSI]的混合物中）是使用时间分辨小角中子散射（TR-SANS）进行研究的。通过使用不同的方案，由单一嵌段共聚物制备具有不同芯尺寸的两个球形胶束。在一种情况下，胶束是在助溶剂存在下形成的，而在另一种情况下，聚合物薄膜则直接溶解在离子液体中。有趣的是，用后一种方法制备的胶束核心尺寸比前一种方法大约30％。TR-SANS实验表明，与较小的核半径相比，具有较大核尺寸的胶束中的单链交换速率减慢了约3倍。对于核心尺寸较大的胶束，这可能归因于每条链的界面面积较小，电晕密度较大。这些几何因素可能会导致单体交换过程中链排出的尝试时间和激活障碍发生变化。我们的结果清楚地表明，除了嵌段共聚物和溶剂的分子特性外，胶束的几何结构在嵌段共聚物胶束的单体动态交换过程中也起着重要作用。