聚苯乙烯-聚4-乙烯基吡啶两亲嵌段共聚物在CO2膨胀液体中的组装行为

嵌段共聚物的自组装行为和其组装形成的胶束聚集体的形貌因在生物医学、药物传输和催化等方面的潜在应用而引起了科学家们的极大兴趣。本工作报道了利用二氧化碳膨胀液体(CXLs)对嵌段共聚物聚苯乙烯-聚4-乙烯基吡啶(PS-b-P4VP)的自组装聚集体(SAA)进行组装结构调控的初步探索。研究发现利用CXLs的抗溶剂效应可以成功调节共聚物PS-b-P4VP的自组装行为。研究结果表明，CXLs的压力及共聚物的组成是影响SAA结构的主要外部因素，CXLs的抗溶剂效应及其对共聚物溶剂化构型的影响是控制SAA形貌转变的主要内在因素。不同组成的共聚物，在CXLs中其SAA的结构形貌均表现出了对压力的显著响应特性。共聚物PS₁₆₈-b-P4VP₄₂₀的自组装聚集体的结构由常压(0.1 MPa)下以球形胶束为主转变为高压下(6.35 MPa)以互联棒状胶束结构为主,而PS₇₉₀-b-P4VP₂₆₃的SAA结构则由常压下的小型囊泡过渡到6.35 MPa下的大复合囊泡(LCVs)。但是对于PS₁₅₃-b-P4VP₁₅₃₀，随着压力的调节，其SAA的结构由常压(0.1 MPa)下的大复合胶束(LCMs)转变为6.35 MPa下的大复合囊泡(LCVs)。特别是，我们发现在本工作考察的实验条件下，在常规溶剂甲苯中控制SAA结构的主要因素是共聚物的组成；而在CXLs条件下，PS壳链与溶剂CXLs间的接触面积随压力调节而发生的改变，可能是控制SAA形貌转变的主要因素。此外，随着CXLs压力升高而引起的PS与P4VP嵌段间双亲性差别的减小，会引起P4VP核-PS壳的界面间的表面张力发生改变，这也是触发SAA形貌转变的诱因之一。本工作充分显示了CXLs方法有助于可控调节自组装聚集体(SAA)的形貌和组装行为，为研发复合纳米材料开辟了一条崭新的绿色途径。

Self-Assembly Behavior of Amphiphilic Diblock Copolymer PS-b-P4VP in CO2-Expanded Liquids

The self-assembly behavior of block copolymers and their assembled micellar morphologies have attracted considerable attention because of their potential applications in biomedicine, drug delivery, and catalysis. Herein we report that CO₂-expanded liquids (CXLs) facilitate the morphology control of the self-assembled aggregates (SAAs) of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) formed in CO₂-expanded toluene. It is found that the anti-solvent effect of CXLs can successfully regulate the self-assembly behavior of the copolymer PS-b-P4VP. The difference in amphiphilicity between PS and P4VP block is reduced with increasing pressure of CO₂-expanded toluene owing to the anti-solvent effect of CO₂. In addition, this diminished difference may influence the interfacial tension at the P4VP core-PS corona interface, which triggers a morphological change of the aggregate. The SAA structures are dependent on both CXL pressure and copolymer composition under the experimental conditions implemented in this work. The morphological evolution of the SAAs in CXLs exhibits remarkable pressure dependence. As the pressure increases, the SAA structure of PS₁₆₈-b-P4VP₄₂₀ transits from primarily spheres (0.1 MPa) to mostly interconnected rods (6.35 MPa), the SAA of PS₇₉₀-b-P4VP₂₆₃ evolves from small vesicles (0.1 MPa) to large compound vesicles (LCVs, 6.35 MPa), whereas the PS₁₅₃-b-P4VP₁₅₃₀ counterpart switches from large compound micelles (LCMs, 0.1 MPa) to mainly large compound vesicles (LCVs, 6.35 MPa). Moreover, transmission electron microscopy (TEM) data on constant copolymer composition implies that the packing parameter p of the SAAs increases with the CXLs pressure. Especially, under the experimental conditions employed in this work, we find that the major factor controlling the SAA shape in conventional toluene is the copolymer composition, while in CO₂-expanded toluene, the dominant factor controlling the SAA morphology might be the varying contact area between shell-forming segment PS and the CXLs with increasing pressure. This work proves that the CXL method facilitates the modulation of morphology of the SAAs, and opens a green route for the development of new nano-functional materials.