Light-Activated Adhesion and Debonding of Underwater Pressure-Sensitive Adhesives

Abstract

Pressure-sensitive adhesives (PSAs) such as sticky notes and labels are a ubiquitous part of modern society. PSAs with a wide range of peel adhesion strength are designed by tailoring the bulk and surface properties of the adhesive. However, designing an adhesive with strong initial adhesion but showing an on-demand decrease in adhesion has been an enduring challenge in the design of PSAs. To address this challenge, we designed alkoxyphenacyl-based polyurethane (APPU) PSAs that show a photoactivated increase and decrease in peel strength. With increasing time of light exposure, the failure mode of our PSAs shifted from cohesive to adhesive failure, providing residue-free removal with up to 83% decrease in peel strength. The APPU-PSAs also adhere to substrates submerged underwater and show a similar photoinduced decrease in adhesion strength.

Photoswitchable Adhesives of Spiropyran Polymers

“…Meanwhile, as represented by marine plastic pollution, global environmental problems are worsening, and material recycling is strongly required. − In this context, switching of adhesives between strong bonding during use and on-demand debonding by external stimuli is a key technology to achieve both development of complex architectures and material recycling. , In particular, light is an ideal stimulus that can minimize effects on adherends due to the high spatiotemporal resolution and easy, precise control of the intensity and wavelength . To date, photoswitchable adhesives have been developed by utilizing a variety of photoresponsive systems including large structural changes of azobenzenes, − conjugation changes of diarylethenes, , dimerization of anthracenes, − photothermal effects of supramolecular motifs and dyes, − and other reactions. − Reversibly switchable polymer adhesives are particularly attractive because of their strong adhesion and recyclability. Similarly, large polarity changes in the photoisomerization between noncharged spiropyran (SP) and zwitterionic merocyanine (MC) seem highly suitable for photocontrol of adhesion (Figure a) , because molecular polarity and related interactions between adhesives and substrate surfaces are dominant factors to generate adhesion force. − The dipole moment (μ) drastically changes between 4–6 D for SP and 14–18 D for MC. , However, to the best of our knowledge, SP has been only used as additives in polymer adhesives ,, or as low-molecular-weight adhesives .…”

Supramolecular Polymeric Pressure-Sensitive Adhesive That Can Be Directly Operated at Low Temperatures

“…New design strategies should be applied to construct supramolecular adhesives with low-temperature direct adhesion. Pressure-sensitive adhesives ( PSA s) are less widely used in supramolecular adhesion. − PSA s realize a strong adhesion effect via pressure-induced solid–liquid transition, instead of heating-induced phase transition. Therefore, compared with hot-melt adhesives, PSA s are relatively insensitive to the operation temperature and have the potential to directly realize supramolecular adhesion at low temperatures.…”

Rational design of adhesives for effective underwater bonding

“…Another functional group is the isocyanate. This group is highly reactive, and widely used in the synthesis of polyurethane (PU) materials ( Tseng et al, 2021 ; Xia et al, 2021 ; Yan et al, 2022 ). Due to the high reactivity, the isocyanate-containing adhesives can react with the interfacial water, and then form multiple bonds or interactions with the underwater substance, achieving strong underwater adhesion.…”