Abstract
The development of switchable adhesives for reversible bonding and debonding can overcome the problems associated with conventional adhesives in separating, recycling, and repairing glued surfaces. Here, a photoresponsive azobenzene-containing polymer (azopolymer) is developed for photocontrolled adhesion. The azopolymer P1 (poly(6-(4-(p-tolyldiazenyl)phenoxy)hexyl acrylate)) exhibits photoinduced reversible solid-to-liquid transitions due to trans-cis photoisomerization. Trans P1 is a solid that glues two substrates with a stiffness comparable to that of conventional adhesives. UV light induces trans-to-cis isomerization, liquefies P1, weakens the adhesion, and facilitates the separation of glued substrates. Conversely, visible light induces cis-to-trans isomerization, solidifies P1, and enhances the adhesion. P1 enables photocontrolled reversible adhesion for various substrates with different wettability, chemical compositions, and surface roughness. P1 can also be implemented in both dry and wet environments. Light can control the adhesion process with high spatiotemporal resolution when using P1 as a switchable adhesive. Photoinduced reversible solid-to-liquid transitions represent a strategy for materials recycling and automated production processes that require reversible bonding and debonding.
Highlights
Adhesives are materials that bind two separate surfaces together and resist separation
The development of switchable adhesives for reversible bonding and debonding can overcome the problems associated with conventional adhesives in separating, recycling, and repairing glued surfaces
Photoinduced reversible solid-to-liquid transitions represent a strategy for materials recycling and automated production processes that require reversible bonding and debonding
Summary
Letter strength of trans P1 was measured after the drying process, whereas the adhesion strength of cis P1 was measured after both the drying process and subsequent UV irradiation. The adhesion strengths of the trans and cis P1-glued quartz/paper were the highest for all tested samples. These experiments demonstrated again that the interaction within the P1 layer was weaker than those between P1 and the substrates These results coincide with the results in Figure 3c: When different substrates glued with P1 were separated, the failure was always within the P1 layer. The underwater adhesion of trans-P1-glued quartz was ∼0.93 MPa. UV irradiation reduced the underwater adhesion to ∼0.08 MPa. We further investigated the reversibility of underwater adhesion under light-assisted and solvent-assisted processes (see more details in the Supporting Information). Subsequent exposure to visible light (530 nm, 5 mW/cm[2, 15] min) solidified P1 and regenerated trans-P1-glued substrates, which had ∼46% of the original adhesion strength.
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