Industrial block copolymer surfactants: Diversity of associative forms and interaction with carbon nanomaterial

Abstract

• Upon copolymer micellization alteration of micelle shape and hydrodynamic size takes place. • Hypothesis about the double-stage nature of copolymer micellization was proposed. • Diversity of associative forms of MWCNT-block copolymer complexation was revealed. • Interaction of block copolymers can results in liquid crystal structuring. In this work, we studied self-association/micellization of several block copolymers based on PEO and PPO blocks – two poloxamers and reverse-sequential poloxamine in aqueous solutions and dispersions of multi-walled carbon nanotubes (MWCNTs). To study this process the number of NMR experiments was used, such as self-diffusion measurements and spectral analysis including alterations of chemical shift and resonance line width. The absence of strictly defined critical micelle concentration, when micelles of constant size start forming, was found. The obtained results proved that amphiphilic copolymers alter micelle shape and hydrodynamic size upon the growth of polymer concentration. The hypothesis about the double-stage nature of copolymer molecules association/micellization has been proposed. At the first stage the polymers hydrophobic blocks connect into cord-like associates/micelles and then these associates join into spherical micelles or liquid-crystalline domains. The transmission electron microscopy of block copolymers revealed a variety of their associative forms. The interaction peculiarities of various associates for different block copolymers with MWCNTs were considered. In poloxamers/MWCNTs dispersions the central hydrophobic blocks of poloxamers can be adsorbed on the hydrophobic surface of MWCNTs, isolating a part of the nanotube surface, thereby preventing their sticking. For the X-shaped diproxamine another mechanism of interaction with carbon surface was proposed, which makes it possible to explain the opposite NMR effects in the presence of MWCNTs. The transmission electron microscopy revealed a variety of associative forms of block copolymers studied.