Thermally Fast-Curable, "Sticky" Nanoadhesive for Strong Adhesion on Arbitrary Substrates

Demand of adhesives that are strong but ultrathin with high flexibility, optical transparency, and long-term stability has been rapidly growing recently. Here, we suggest a thermally curable, "sticky" nanoadhesive with outstanding adhesion strength accomplished by single-side deposition of the nanoadhesive on arbitrary substrates. The sticky nanoadhesive is composed of an ionic copolymer film generated from two acrylate monomers with tertiary amine and alkyl halide functionalities, formed by a solvent-free method, initiated chemical vapor deposition (iCVD). Because of the low glass transition temperature (T_g) of the copolymer (-9 °C), the ionic copolymer shows a viscoelastic behavior that makes the adhesive attachable to various substrates, regardless of the substrate materials. Moreover, the copolymer film is thermally curable via a cross-linking reaction between the alkyl halide and tertiary amine functionalities, which substantially increased the adhesion strength of the 500 nm thick nanoadhesive greater than 25 N/25 mm within 5 min of curing at 120 °C. The adhesive thickness can further be reduced to 50 nm to achieve greater than 35 N/25 mm within 30 min at 120 °C. The nanoadhesive layer can form uniform adhesion in a large area substrate (up to 130 × 100 mm²) with the deposition of the adhesive only on one side of the substrates to be laminated. Because of its ultrathin nature, the nanoadhesive is also optically transparent as well as highly flexible, which will play a critical role in fabrication and the lamination of future flexible/wearable devices.