Crystal Engineering of Molecular Solids as Temporary Adhesives

Abstract

Crystal engineering of temporary adhesion is important in diverse fields ranging from healthcare to manufacturing. Molecular solidsa broad class of crystalline materials characterized by discrete molecules with well-defined chemical and crystal structurescan be utilized as sublimable adhesives to achieve rapid adhesion, strong mechanical bonding, and facile on-demand release of surfaces. Through systematic investigation of the interfacial and bulk properties of molecular solids, this paper shows that this class of materials can exhibit remarkable mechanical strength (resistance to shear stress up to 2100 kPa and shear strain up to 37, as well as shear moduli up to 1000 kPa) yet enable on-demand (within minutes) release from adhesion through controlled sublimation without the application of solvents and/or mechanical force. Intermolecular interactions heavily influence the mechanical performance via preferential orientation of the solid relative to surfaces during the melt-bonding process. This research quantifies how chemical and crystal structures inform macroscopic mechanical properties of polycrystalline solids.

Stimuli-responsive temporary adhesives: enabling debonding on demand through strategic molecular design

“…Sublimable adhesives are a general class of compounds that can release bonded substrates through the direct solid-to-gas phase transition of the material without the application of solvent or external mechanical force. 31,32,162 While these materials respond to external pressure, they do not rely on pressure to bond the adhesive with a surface. Instead, a reduction in the ambient pressure, oen coupled with an increase in temperature, initiate sublimation of the adhesive materials and, consequently, release of adherends.…”

“…Our laboratory was the rst to quantitatively characterize sublimable adhesives. 31,32,162 For a proof-of-concept demonstration, we selected a series of polycyclic aromatic hydrocarbons (PAHs)-naphthalene, anthracene, pyrene, and multiple naphthalene derivatives-because their crystal structures, intermolecular interactions, and enthalpies of phase transitions were well characterized. Mechanical testing conrmed that all PAHs studied (Fig.…”

“…228 To overcome this obstacle, adhesives may be responsive to magnetic elds with ferromagnetic or conductive additives, such as iron-based powders, aluminum, Copyright 2020 American Chemical Society. 31,32,162 cobalt, or nickel. 38 Applying a magnetic eld elicits molecular motions, rotations, or vibrations, that transfers thermal energy to the adhesives, which can lead to debonding with the previously discussed mechanisms.…”

“…Continued investigations into fundamental structure-property relationships of stimuli-responsive temporary adhesives pave the way for next-generation technologies. 29,31,32,162,[234][235][236][237][238][239][240][241][242][243][244][245][246] These materials exhibit the conicting, yet simultaneous, properties of bonding, resistance to mechanical stress and strain, and on-demand debonding, delineating them from traditional permanent adhesives. Molecular design strategies enable the intentional perturbation of intermolecular interactions within these adhesives or at the interfaces they form with substrates through the strategic application of an external stimulus or stimuli.…”

“…While stimuli-responsive permanent adhesives, also known as structural adhesives, exist, [27][28][29][30] this perspective is concerned with stimuli-responsive temporary adhesives, a class of materials that exhibit the conicting properties of bonding, resistance to mechanical stress and strain, and on-demand debonding. 29,[31][32][33][34][35][36][37][38][39][40][41][42]162 All temporary adhesives are stimuli-responsive; once two surfaces are bonded, a temporary adhesive requires some form of energy input to debond. This energy input is delivered by an external stimulus or stimuli.…”