Reversible Adhesion Switching Using Spiropyran Photoisomerization in a High Glass Transition Temperature Polymer

Abstract

Previous work has shown that photoisomerization of dopant molecules in a polystyrene film can either enhance or suppress its adhesion to a polar glass surface (MostafaviS. H. Mostafavi, S. H. Macromolecules20185123882394; MostafaviS. H. Mostafavi, S. H. Macromolecules20195263116317). In this paper, a different polymer host, Zeonex (ZX), is used in conjunction with the photochrome spiropyran. Nonpolar ZX has a higher glass transition temperature that makes it resistant to nanoscale mechanical deformations, while the spiropyran (SP) → merocyanine (MC) photoisomerization is a reversible reaction with a large polarity change. Ultraviolet light isomerizes SP to the polar MC form, increasing both the shear and pull-off adhesion forces to a clean glass surface by a factor of 5. Visible irradiation switches it back to the nonpolar SP form and returns the film back to its original weak adhesion, in contrast to the previously studied polystyrene films. The ability of visible light to switch off the polymer–glass adhesion is harnessed to make a light-controlled payload release device as well as to accelerate the polymer film delamination rate in water by a factor of 100. The kinetics of the water delamination, as well as the origin of residual adhesion after switching back to the SP form, are investigated. This work demonstrates how light-controlled noncovalent adhesion can be used as a solvent-free method to remove protective coatings or to disassemble structures.

Photoswitchable Adhesives of Spiropyran Polymers

“…The increases in the adhesion strength by UV light irradiation were 0.59 30 and 0.16 MPa, 56 and the decreases by visible light irradiation were 0.18 30 and 0.14 MPa. 56 The large increase by UV light irradiation 30 was due to the nanoscale morphological changes resulting from local heating by SP, i.e., the photothermal effect, which caused little reversibility by visible light irradiation. In other words, the adhesion between the adhesives and adherends was insufficient in the initial samples due to the process of sample fabrication, i.e., solvent casting.…”

“…51−53 The dipole moment (μ) drastically changes between 4−6 D for SP and 14−18 D for MC. 49,54 However, to the best of our knowledge, SP has been only used as additives in polymer adhesives 30,55,56 or as low-molecular-weight adhesives. 57 In the additive approach, there is a concern about phase separation between a polymer matrix and SP small molecules particularly after isomerization to MC due to the large difference in the polarity between them, which degrades the performance and undermines the reliability.…”

Photoreversible Order–Disorder Transitions in Block Copolymer/Ionic Liquid Solutions

“…Control over nanoscale morphology in block polymers has been an important aspect of technological development from selective patterning of microchips to separation membranes with improved transport properties. − Additionally, the ability to reverse such patterning and switch between morphologies could expand applications, for example in drug delivery and repositionable adhesives. − Numerous stimulus-responsive systems have been developed; common stimuli include heat, pH, and light. − Thermo-responsive behavior is the most well-studied, but not all applications are amenable to changes in the temperature. Light allows for a contactless stimulus with both excellent temporal and spatial resolution.…”

Rewritable Polymer Materials for Ultraviolet Laser Based on Photochromic Microcapsules

“…41 Moreover, polymers are used for photochromic and luminescent devices as gels, 17 latex, 19,42 films, 16,43,44 and functional monomers. 9,14,15,45 Polydimethylsiloxane (PDMS) contains a macromolecular network that is highly transparent and thermosettable and also has been utilized in photochromic composites for years. Usually, two ways were always employed to fabricate a photochromic device based on PDMS: (a) directly adding dyes in PDMS and thermocured as a dyedoped matrix 46 and (b) dye molecules grafted or terminated on molecular chains of siloxane, then cured as a functional PDMS.…”