Photoresponsive Polymersomes Formed by Amphiphilic Linear-Dendritic Block Copolymers: Generation-Dependent Aggregation Behavior
Photoresponsive Polymersomes Formed by Amphiphilic Linear-Dendritic Block Copolymers: Generation-Dependent Aggregation Behavior
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DOI：
10.1021/ma301251s
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发表时间：
2012-09-11
期刊：
影响因子：
5.5
通讯作者：
Tsao, Heng-Kwong
中科院分区：
文献类型：
--
作者：
Lin, Yung-Lung;Chang, Hung-Yu;Tsao, Heng-Kwong
最近合成了不同代数的含偶氮苯的线性树枝状嵌段共聚物（LDBC）。这种光敏LDBC由线性亲溶剂嵌段(R)和亲溶剂树枝状体组成，其外围附有疏溶剂线圈棒二嵌段(B-Y)。通过耗散粒子动力学探索自组装及其光响应转变。根据代数、聚合物浓度、嵌段长度和杆嵌段之间的 pi-pi 相互作用，聚集体表现出丰富多样的形态构象，包括球形胶束、蠕虫状胶束、圆柱形胶束、汉堡包状胶束、纳米片、纳米碗和囊泡。一般来说，代数较大的 LDBC 会形成聚合物囊泡，而代数较小的 LDBC 会形成纳米纤维和纳米片。在紫外线照射下，偶氮苯发生光诱导的反式异构化为顺式异构化，膜变得扭曲、起皱，甚至破裂。还观察到通过聚合物囊泡膜的水渗透率显着增加。这些模拟结果与实验观察结果一致。通过改变聚合物浓度以及 R 和 B 嵌段的长度，可以获得所得聚集体的形态相图和内部结构。随着聚合物浓度的增加，观察到从纳米片或纳米碗到聚合物囊泡的转变。当R-嵌段长度减少时，聚合物囊泡开始形成的代数减少。另一方面，纳米片往往会形成较长的 R 嵌段长度。这一预测也与实验观察结果一致。还可以以较低的代数形成足够长的B嵌段长度的聚合物囊泡。由于疏水层厚度的增加，膜对水渗透的阻力随着 B 嵌段长度的增加而增加。最后，随着 pi-pi 强度的增加，整体形态从聚合物囊泡、纳米碗到纳米片发生变化。因此，由于偶氮棒之间的高度排列相关的阻碍，只有当 pi-pi 强度足够弱时，才会形成聚合物囊泡。
Azobenzene-containing linear dendritic block copolymers (LDBC) with varied generation numbers were synthesized recently. This photosensitive LDBC consists of a linear solvophilic block (R) and solvophilic dendrons of which the periphery is attached with a solvophobic coil rod diblock (B-Y). The self-assembly and its photoresponsive transformation are explored by dissipative particle dynamics. Dependent on the generation number, polymer concentration, block lengths, and pi-pi interaction between rod blocks, the aggregate exhibits a rich variety of morphological conformations, including spherical micelle, worm-like micelle, cylindrical micelle, hamburger-like micelle, nanosheet, nanobowl, and vesicle. In general, polymersomes take shape for LDBCs with large generation number while nanofibers and nanosheets develop for LDBCs with small generation number. Upon UV illumination, the photoinduced trans-to-cis isomerization of azobenzene takes place and the membrane becomes distorted, wrinkled, and even ruptured. A significant increase in water permeation through the polymersome membrane is also observed. These simulation findings are consistent with experimental observations. By varying polymer concentration and lengths of R- and B-blocks, morphological phase diagrams and internal structures of the resulting aggregates are obtained. Transformation from nanosheet or nanobowl to polymersome is observed as polymer concentration grows. When the R-block length decreases, the generation number at which polymersomes start to form declines. On the other hand, nanosheets tend to form for long R-block length. This prediction is also consistent with experimental observations. Polymersomes can also be formed for long enough B-block length at lower generation number. The membrane resistance to water permeation grows with increasing B-block length because of the increment of the hydrophobic layer thickness. Finally, as the pi-pi strength is increased, the overall morphologies vary from polymersome, nanobowl, to nanosheet. Therefore, polymersomes are formed only when the pi-pi strength is weak enough due to the hindrance associated with high degree of alignment among azo-rods.