Shear-induced alignment of block copolymer worms in mineral oil

Abstract

Poly(stearyl methacrylate)–poly(benzyl methacrylate) [PSMA–PBzMA] diblock copolymer worms were synthesized directly in mineral oil via reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization at 90 °C. Free-standing gels were obtained from this polymerization-induced self-assembly (PISA) formulation when targeting PSMA13–PBzMA65 dispersions at 5% w/w to 20% w/w copolymer concentration. Gel permeation chromatography (GPC) studies indicated that almost identical copolymer chains were obtained in all cases, while transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) studies confirmed that highly anisotropic worms were formed with mean cross-sectional diameters of 11.9–13.1 nm. These worms undergo a thermoreversible worm-to-sphere transition on heating up to 150 °C. Rheological studies were conducted to characterize the shear rate- and concentration-dependent behaviour caused by this change in copolymer morphology, where the initial shear-thinning worm gels form spheres (i.e. a Newtonian fluid) on heating up to 150 °C. Complementary shear-induced polarized light imaging (SIPLI) experiments confirmed the formation of aligned linear worms under applied shear between 80 °C and 110 °C, with high-viscosity dispersions of branched worms being obtained at 20–60 °C and low-viscosity spheres being produced at 150 °C. This study informs the use of such block copolymer worms as rheology modifiers for non-polar oils, which is of potential interest for the automotive industry.

Graphical abstract: Shear-induced alignment of block copolymer worms in mineral oil

Supplementary files

Article information

Article type
Paper
Submitted
09 Jul 2021
Accepted
14 Sep 2021
First published
15 Sep 2021
This article is Open Access
Creative Commons BY license

Soft Matter, 2021, Advance Article

Shear-induced alignment of block copolymer worms in mineral oil

M. J. Derry, O. O. Mykhaylyk and S. P. Armes, Soft Matter, 2021, Advance Article , DOI: 10.1039/D1SM01011E

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