Opto-Mechanical Scission of Polymer Chains in Photosensitive Diblock-Copolymer Brushes

Abstract

In this paper we report on an opto-mechanical scission of polymer chains within photosensitive diblock-copolymer brushes grafted to flat solid substrates. We employ surface-initiated polymerization of methylmethacrylate (MMA) and t-butyl methacrylate (tBMA) to grow diblock-copolymer brushes of poly(methylmethacrylate-b-t-butyl methacrylate) following the atom transfer polymerization (ATRP) scheme. After the synthesis, deprotection of the PtBMA block yields poly(methacrylic acid) (PMAA). To render PMMA-b-PMAA copolymers photosensitive, cationic azobenzene containing surfactants are attached to the negatively charged outer PMAA block. During irradiation with an ultraviolet (UV) interference pattern, the extent of photoisomerization of the azobenzene groups varies spatially and results in a topography change of the brush, i.e., formation of surface relief gratings (SRG). The SRG formation is accompanied by local rupturing of the polymer chains in areas from which the polymer material recedes. This opto-mechanically induced scission of the polymer chains takes place at the interfaces of the two blocks and depends strongly on the UV irradiation intensity. Our results indicate that this process may be explained by employing classical continuum fracture mechanics, which might be important for tailoring the phenomenon for applying it to poststructuring of polymer brushes.

Manipulation of small particles at solid liquid interface: light driven diffusioosmosis

“…One can, for instance, trigger compaction and decompaction of a DNA molecule by light in a reversible way2021222324252627282930, or remotely control the size of microgels by applying periodically UV and blue irradiation313233. One can modify polymer brushes with these molecules and make them photoresponsive with respect to topography and surface energy343536. Geared towards applications in microfluidics, it was shown that a Marangoni-type flow can be induced by cis-trans isomerization of azobenzene solutes at the liquid-air or liquid-liquid interface; this effect has been used to steer oil droplets on an aqueous subphase37.…”

High‐Density Liquid‐Crystalline Polymer Brushes Formed by Surface Segregation and Self‐Assembly

“…Grafting of polymer chains on substrate surfaces is primarily formed by chemical attachment achieved using the preformed polymer chains ("grafting-to"), surfaceinitiated (SI) polymerization ("grafting-from"), [1,2] and, more recently,p olymerization using surface attached monomers ("grafting-through"). [4][5][6][7] Thet hermal and mechanical properties of the high-density polymer brushes were significantly different compared with the unconstrained polymer chains in the spincast film. [4][5][6][7] Thet hermal and mechanical properties of the high-density polymer brushes were significantly different compared with the unconstrained polymer chains in the spincast film.…”

Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

“…154 Applying UV intensity interference patterns to diblock copolymer brushes covalently attached to flat solid substrates and ionically complexed with azobenzene, it was found that the local variation in azobenzene photoisomerization leads to the formation of SRG patterns accompanied by optomechanical scission. 155 One interesting SRG-forming azobenzene-containing BCP is a polyelectrolyte block copolymer composed of two different poly(ferrocenylsilane) blocks, one of which contains azobenzene. 69 This material exhibited a cylindrical microphaseseparated structure, with the azobenzene-containing block forming the continuous phase.…”