Remarkable crystallization morphologies of poly(4-vinylpyridine) on single-walled carbon nanotubes in CO2-expanded liquids

Abstract

Poly(4-vinylpyridine) (P4VP) is a widely studied polymer for applications in catalysis, humidity sensitive and antimicrobial materials due to its pyridine group exhibiting coordinative reactivity with transition metals. In this work, the non-covalent functionalization of single-walled carbon nanotubes (SWCNTs) with P4VP in CO2-expanded liquids (CXLs) is reported. It is found that P4VP stabilized SWCNTs show good dispersion in both organic solvent and aqueous solution (pH = 2). The ability to manipulate the dispersion state of CNTs in water with P4VP will likely benefit many biological applications, such as drug delivery and optical sensors. Furthermore, the structure and morphology of P4VP/SWCNTs composite are examined, with the focus on molecular weight of P4VP (MW-P4VP), the pressure of CXLs and the concen- tration of P4VP. It is amazing that the P4VP15470 wrapping patterns undergo a notable morphological evolution from dot- like crystals to bottle brush-like, then to compact kebab-like, and then to widely-spaced dotted kebab patterns by facile pressure tuning in the higher polymer concentration series. In other words, the CXLs method enables superior control of the P4VP crystallization patterns on SWCNTs. Meanwhile, the CXL-assisted P4VP crystal growth mechanism on SWCNT is investigated, and the dominating growth mechanism is attributed to 'size dependent soft epitaxy' in P4VP15470/SWCNTs composites. We believe these studies would reveal great potential for P4VP in building up functional structures in CXLs that are responsive to environmental stimuli.