Amphiphilic diblock copolymer modification of carbon nanotubes in CO2-expanded liquids

Abstract

Poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) is an ideal amphiphilic diblock copolymer for potential applications in emulsion polymerization, colloid stabilization and microreactors, and the self-assembly ability also helps P4VP-b-PS to find wide applications in nanolithography, catalysis, molecular templating, and drug delivery. In this work, the non-covalent functionalization of single-walled carbon nanotubes (SWCNTs) with P4VP-b-PS in CO2-expanded liquids (CXLs) is reported. It is found that P4VP-b-PS stabilized SWCNTs showed better dispersion in organic solvent. Raman spectra indicated that there exist interactions between SWCNTs and P4VP-b-PS chains. Furthermore, the structure and morphology of P4VP-b-PS/SWCNTs composite were examined, focusing on P4VP-b-PS concentration and the pressure of CXLs. It is found that the P4VP-b-PS wrapping patterns undergo a remarkable morphological evolution from dotted coating crystals to compact kebabs, and then to helical patternings by facile pressure tuning in the high polymer concentration series. In other words, the CXLs method enables superior control of the P4VP-b-PS crystallization patternings on SWCNTs. What is more, the CXL-assisted P4VP-b-PS crystal growth mechanism on SWCNT is investigated. The crystal growth exhibited a pressure-switchable mechanism, i.e., the dominating mechanism switches from “soft epitaxy” (kebabs) at pressures below the threshold pressure to “normal epitaxy” (helicals) at higher pressure above the threshold value. We believe these studies would reveal great potential for P4VP-b-PS in building up functional structures in CXLs that are responsive to environmental stimuli.