Controlling the micellar morphology of binary PEO-PCL block copolymers in water-THF through controlled blending.
Controlling the micellar morphology of binary PEO-PCL block copolymers in water-THF through controlled blending.
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DOI：
10.1039/c0sm00938e
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发表时间：
2011-01
期刊：
影响因子：
3.4
通讯作者：
Peter Schuetz;M. Greenall;Julian Bent;S. Furzeland;D. Atkins;Michael F. Butler;T. McLeish;D. Martin;A. Buzza
中科院分区：
文献类型：
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作者：
Peter Schuetz;M. Greenall;Julian Bent;S. Furzeland;D. Atkins;Michael F. Butler;T. McLeish;D. Martin;A. Buzza
我们从实验和理论两方面研究了二元聚己内酯-聚环氧乙烷（PCL-PEO）嵌段共聚物在稀溶液中的自组装，其中自组装是通过将溶剂从常用的良溶剂THF改变为选择性溶剂水来触发的，并且其中两种物质在水中各自形成囊泡和球形胶束。我们发现，在水中，这些嵌段共聚物的胶束间交换极其缓慢，使得所得的自组装结构处于局部而非全局平衡（即，它们是非遍历的）。这开辟了控制胶束形态的化学和动力学。具体来说，当两种物质在混合和自组装之前首先分子溶解在THF中时，（“预混合”）通过用水稀释，发现所形成的结构的形态取决于两种物质的混合比，逐渐沿着从囊泡通过中间状态的胶束减少表面曲率的路线进行。球状的棒，环，Y-结，并最终球形胶束，因为我们增加的比例的“球形成者”。另一方面，如果两种物质在混合和进一步自组装（“中间混合”）之前首先部分自组装（通过溶剂与水的部分交换），则出现新的亚稳态结构，包括纳米级的“袋”。这些实验结果证实了自洽场理论（SCFT）的计算再现的序列中看到的预混合实验的形态。SCFT还揭示了聚合物组合物和聚集体曲率之间的明确耦合，正曲率和负曲率的区域分别通过球体形成者的富集和耗尽而稳定。我们的研究表明，嵌段共聚物的热力学和动力学共混是有效的设计参数，以控制所得的结构，并使我们能够获得比单峰嵌段共聚物溶液更丰富的纳米形态。
We study both experimentally and theoretically the self-assembly of binary polycaprolactone–polyethylene oxide (PCL–PEO) block copolymers in dilute solution, where self-assembly is triggered by changing the solvent from the common good solvent THF to the selective solvent water, and where the two species on their own in water form vesicles and spherical micelles respectively. We find that in water the inter-micellar exchange of these block copolymers is extremely slow so that the resultant self-assembled structures are in local but not in global equilibrium (i.e., they are non-ergodic). This opens up the possibility of controlling micelle morphology both thermodynamically and kinetically. Specifically, when the two species are first molecularly dissolved in THF before mixing and self-assembly (‘pre-mixing’) by dilution with water, the morphology of the formed structures is found to depend on the mixing ratio of the two species, going gradually on a route of decreasing surface curvature from vesiclesvia an intermediate regime of micelles in the shape of ‘bulbed’ rods, rings, Y-junctions and finally to spherical micelles as we increase the proportion of the “sphere formers”. On the other hand, if the two species are first partially self-assembled (by partial exchange of the solvent with water) before mixing and further self-assembly (‘intermediate mixing’), novel metastable structures, including nanoscopic ‘pouches’, emerge. These experimental results are corroborated by Self-Consistent Field Theory (SCFT) calculations which reproduce the sequence of morphologies seen in the pre-mixing experiments. SCFT also reveals a clear coupling between polymer composition and aggregate curvature, with regions of positive and negative curvature being stabilized by an enrichment and depletion of sphere formers respectively. Our study demonstrates that both thermodynamic and kinetic blending of block copolymers are effective design parameters to control the resulting structures and allow us to access a much richer range of nano-morphologies than is possible with monomodal block copolymer solutions.