Morphological transitions in polymer vesicles upon bilayer swelling with small hydrophobic molecules in water

Parmenter, Christopher D.J. and Chen, Rong and Cheung, David and Bon, Stefan A.F. (2013) Morphological transitions in polymer vesicles upon bilayer swelling with small hydrophobic molecules in water. Soft Matter, 9 (29). pp. 6890-6896. ISSN 1744-6848 (https://doi.org/10.1039/C3SM50184A)

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Abstract

We show that when unilamellar polymer vesicles dispersed in water made from a blockcopolymer, in this case poly((ethylene oxide)45-block-(methyl methacrylate)164), poly((ethylene oxide)45-block-(methyl methacrylate)170), or poly(n-butyl methacrylate)81-block-(2-(dimethylamino)ethyl methacrylate)20, are exposed to small hydrophobic molecules, here methyl methacrylate as well as n-butyl methacrylate, they can undergo morphological transitions. Upon swelling, the polymersomes lose their original simple bilayer morphology and transform into more complex coil-like and patchy colloidal structures, as investigated experimentally by cryogenic electron microscopy (cryo-EM). Dissipative particle dynamics (DPD) simulations on a model flat bilayer indeed show that transitions can occur upon bilayer swelling, which is accompanied by a change in the mechanical bilayer properties. The transition involves the formation of water pockets in the interior regions of the bilayer. Co-existence of the various morphologies in the experiments suggests an activation barrier towards morphological changes and a possibility of multiple meta-stable states. The latter indeed is supported by the existence of multiple minima in the surface tension as a function of bilayer area, as found in the simulations.

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