Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (8): 945-951.doi: 10.3866/PKU.WHXB201801292

Special Issue: Green Chemistry

• ARTICLE • Previous Articles     Next Articles

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

Xiaomeng CHENG1,Dongxia JIAO1,Zhihao LIANG1,Jinjin WEI1,Hongping LI1,*(),Junjiao YANG2,*()   

  1. 1 College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou 450001, P. R. China
    2 Beijing Key Laboratory of Environmentally Harmful Chemical Analysis, Beijing University of Chemical Technology, Beijing 100029, P. R. China
  • Received:2018-01-03 Published:2018-04-03
  • Contact: Hongping LI,Junjiao YANG E-mail:lihongping@zzu.edu.cn;yangjj@mail.buct.edu.cn
  • Supported by:
    This work was supported by the National Natural Science Foundation of China(21773215);This work was supported by the National Natural Science Foundation of China(J1210060);the Innovative Research Grant for Undergraduate Students of National/Zhengzhou University(201710459008)

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Abstract:

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.

Key words: CO2-expanded liquids, Colloidal aggregates, Morphology control, PS-b-P4VP, Self-assembly