(De)bonding on Demand with Optically Switchable Adhesives

Abstract

nature of polymer-based adhesives prevent their easy removal and stifle or complicate debonding, rebonding, (end-of-life) recycling, and repair. In this context, the development of debonding-on-demand (DoD) adhesive technologies is attracting rapidly growing interest. Indeed, DoD techniques have already entered commercial exploitation in applications such as easily removable wound dressings, [2,3] temporal fixation in semiconductor manufacturing, [4][5][6] and the repair, replacement, or recycling of components. [7][8][9] While many debonding technologies employ heat to reduce the adhesive strength by imparting physical property changes of the adhesive, [10][11][12][13][14] light-induced debonding technologies represent an emerging field and have been much less explored. Photoirradiation is an attractive alternative to thermal debonding as it allows an efficient, contactless, remote stimulation that can be temporally and spatially controlled. [15][16][17][18] Moreover, factors such as the irradiation wavelength, intensity, and time can easily be tuned and it is often possible to focus the energy entry to the adhesive and minimize or avoid exposure of (sensitive) substrates. Of course, the approach requires that at least one of the substrates to be bonded is sufficiently transparent.The design of a light-debondable adhesive system is strongly related to the adhesive type and the requirements imparted by the application(s) for which the adhesive is designed. For instance, pressure-sensitive adhesives (PSAs), such as used in adhesive tapes, need to efficiently adhere under ambient conditions with only a brief application of pressure, they should withstand the (comparably small) loads experienced while bonded, and they must also be easily removable, ideally without leaving any residues on the substrate. [19,20] PSAs are therefore normally based on lightly physically or chemically cross-linked rubbery polymers such as natural rubber, styrene butadiene block copolymers, and acrylics. These materials provide a balance between adhesive and cohesive performance, i.e., adequate stiffness and strength to resist deformation and cohesive failure, and appropriate elasticity in order to establish adequate contact with the substrate. [1] On the other hand, structural adhesives must be able to effectively transmit large loads across the bonded joint and the high strength and high rigidity required for this function are usually achieved by the formation of glassy networks. Examples of such materials include cross-linked epoxy resins, which may possess shear strengths of >35 MPa, cyanoacrylates (superglues), acrylics, and polyurethanes. [19] Adhesives that enable bonding and especially debonding on demand (DoD) have attracted rapidly growing interest in the last decade, as these capabilities greatly improve the functionality of adhesives, particularly in connection with temporal fixation, repair, and recycling. Indeed, DoD techniques have already entered commercial exploitation in applications such as easily removable wound dressin...

Supramolecular adhesive materials from small‐molecule self‐assembly

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25] The reversibility of noncovalent interactions enables the dynamic modulation of intermolecular interactions by external stimuli, including light, temperature, pH, chemical redox, and microenvironments. 48,49 The related studies about macromolecular adhesives and coatings have emerged over the past two decades, which have been well summarized in several outstanding reviews. 22,[35][36][37] Thus, the topic of macromolecular adhesives will not be involved in this review.…”

Rapid and continuous regulating adhesion strength by mechanical micro-vibration

“…Considering that the apparent adhesion strength can be influenced by the real contact area, the contact region size 17 , and the adhesion work 20 , adhesion switching has been proposed by either controlling the load path and failure mode of the interface or constructing a "smart" interface such as a phase transition interface 6,20 . The adhesion switching triggers, such as mechanical 12,15,[21][22][23][24][25][26][27][28][29][30] , electro/magnetic 14,16,31 , light [32][33][34] , fluid [35][36][37][38] , and thermal [39][40][41][42][43][44] stimulations, have been suggested. However, at present, there have been only a few attempts to provide promising methods to tune the adhesion strength continuously and rapidly, for example, gecko-inspired directional adhesion 12,13,15,16,[45][46][47][48][49][50] and debonding/peeling speedregulated adhesion [24][25]…”

Bonding and Debonding on Demand with Temperature and Light Responsive Supramolecular Polymers

“…Several studies addressed the debonding on demand of supramolecular adhesives based on hydrogen bonding, [52,53] as well as host-guest interactions [49,50,54,55] by means of simple heating, but also via exposure to molecules that disassemble the binding motifs or irradiation with UV-light. [30,42,43,45,56,57] We here report on the rheological behavior and adhesive properties of supramolecular polymers assembled with the help of the hydrogen-bonding motif isophthalic acid-pyridine (IPA-Py). [57][58][59] Despite the fact that the IPA-Py binding motif exhibits a very low association constant (K a ≈ 500 m −1 ), [60] hydrogenbonded supramolecular polymer networks assembled from a telechelic poly(ethylene-co-butylene) (PEB) based building block that was end-functionalized with isophthalic acid groups and bipyridines display mechanical properties that are comparable to those of similar polymers made with much stronger-binding motifs.…”

“…While the intrinsically reversible nature of supramolecular adhesives has been investigated in many studies, it was not until recently that researchers started to investigate such polymers as adhesives with on demand debonding capability in a systematic manner. Several studies addressed the debonding on demand of supramolecular adhesives based on hydrogen bonding, as well as host–guest interactions by means of simple heating, but also via exposure to molecules that disassemble the binding motifs or irradiation with UV–light …”

“…[17][18][19] Several approaches to achieve debonding on demand have been introduced in recent years, including the combination of thermoset adhesives with shape memory polymers that reduce the bonding area on demand and in turn facilitate debonding, [20][21][22][23] the use of reversible covalent chemistry to thermally depolymerize cross-linked adhesives, [24] the use of magnetically responsive fillers that locally increase the temperature as a response to an electromagnetic field, [25] and the development of polymers that change their mechanical properties in response to changes in temperature or pH, [26][27][28] among others. [29,30] Another recently proposed general concept is the utilization of supramolecular polymers, as these materials present an attractive combination of adequate mechanical and adhesive properties and fairly low melt viscosity, [31,32] which roots in the stimuli-responsive nature of dynamic, noncovalent interactions through which the monomeric units of supramolecular polymers are held together. [33] Unlike "traditional" covalent polymers, supramolecular polymers are formed by monomers that are linked through hydrogen bonds, metal complexes, host-guest interactions, or other noncovalent, dynamic interactions.…”