Effect of Changing Interfacial Tension on Fragmentation Kinetics of Block Copolymer Micelles
Effect of Changing Interfacial Tension on Fragmentation Kinetics of Block Copolymer Micelles
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DOI：
10.1021/acs.macromol.2c02158
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发表时间：
2023-02
期刊：
影响因子：
5.5
通讯作者：
Supriya Gupta;T. Lodge
中科院分区：
文献类型：
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作者：
Supriya Gupta;T. Lodge
研究了嵌段共聚物胶束在离子液体（ILs）中的胶束碎裂现象，这是胶束动力学平衡的关键机制之一。特别是，胶束破碎的驱动力的作用进行了研究，通过改变溶剂qualityaftermicelle制备，相当于一个跳跃的界面张力γ之间的溶剂和胶束核心。1，2-聚丁二烯-b-聚环氧乙烷（PB-b-PEO）共聚物（Mn= 17.5kDa，fPEO = 0.38）在离子液体[C2mim][TFSI]中的直接溶解导致大胶束的形成，其平均粒径为68 nm，分散度为1.27。然后通过小心添加具有较低γ的第二离子液体[C10 mim][TFSI]与胶束核心稀释所制备的胶束的溶液，使得胶束保持不受影响。通过稀释度控制γ，从而控制溶剂混合物的质量。第二溶剂的选择是基于使用悬滴试验进行的一系列具有1-2-聚丁二烯均聚物的[Cxmim][TFSI] IL的γ测量。通过添加另一种具有较低γ的离子液体来稀释胶束倾向于减小平衡胶束尺寸，这反过来又增强了较大的制备胶束的破碎驱动力，表现为聚集数Q/Qeq的比率增加。使稀释的胶束溶液经受温度跳跃至170 °C，随后进行热退火，导致所制备的胶束破碎以达到近平衡状态。胶束的特征在于使用原位动态光散射（DLS）技术，观察平均胶束尺寸的时间演变，从其中得到的弛豫时间。此外，小角X射线散射（SAXS）和低温透射电子显微镜（TEM）测量进行，以获得胶束核心的大小和分布在胶束溶液之前和之后的碎片。通过控制低γ溶剂的量实现的驱动力的增强导致更快的碎裂;特征碎裂时间随着尺寸比Q/Qeq从1.2增加到5而单调减小。
Micelle fragmentation, one of the key mechanisms responsible for equilibration of kinetically trapped micelles, is investigated for block copolymer micelles in ionic liquids (ILs). In particular, the role of driving force for micelle fragmentation is studied by altering the solvent qualityaftermicelle preparation, amounting to a jump in interfacial tension γ between solvent and the micelle core. Direct dissolution of a 1,2-polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) copolymer (Mn= 17.5 kDa andfPEO= 0.38) in the ionic liquid [C2mim][TFSI] results in large micelles with average size ⟨Rh⟩o≈ 68 nm and dispersityĐ≈ 1.27. The solution of the as-prepared micelles is then diluted by the careful addition of a second ionic liquid [C10mim][TFSI] having lower γ with the micelle core, such that the micelles remain unaffected. The γ and hence the quality of the solvent mixture were controlled by the degree of dilution. The choice of the second solvent is based on the measurement of γ for a series of [Cxmim][TFSI] ILs with 1-2-polybutadiene homopolymer, carried out using a pendant drop test. Diluting the micelles by adding another ionic liquid with lower γ tends to decrease the equilibrium micelle size, which, in turn, enhances the driving force for fragmentation of the bigger as-prepared micelles, represented by increase in the ratio of aggregation numbersQ/Qeq. Subjecting the diluted micellar solution to temperature-jump to 170 °C followed by thermal annealing leads to fragmentation of the as-prepared micelles to attain a near-equilibrium state. The micelles are characterized using anin situdynamic light scattering (DLS) technique to observe the time evolution of average micelle size, from which the relaxation time is obtained. Additionally, small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (TEM) measurements were carried out to obtain the micelle core size and distribution in the micellar solutions before and after fragmentation. The enhancement in the driving force achieved by controlling the amount of low γ solvent resulted in faster fragmentation; the characteristic fragmentation time decreases monotonically on increasing the size ratioQ/Qeqfrom 1.2 to 5.