Multi-substrate adhesion enabled by initiated chemical vapor deposited gradient nano-coatings

Achieving reliable adhesion across chemically diverse substrates remains a central challenge in adhesive science, because interfacial bonding and stress transfer depend strongly on substrate surface chemistry. Here, a multi-substrate strategy combines an optimized UV-curable thiol–ene adhesive with a gradient adhesion-promoting layer deposited by initiated chemical vapor deposition (iCVD). Among adhesives modified with a polysulfide oligomer (G4), the 10 wt% formulation shows the most balanced rheological and mechanical behavior, giving a lap-shear strength of 2.94 ± 0.20 MPa on glass. A nanoscale gradient copolymer, poly(1-vinylimidazole-grad-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane-grad-allyl methacrylate), deposited by iCVD. Three monomers give three regions with distinct functions, namely an imidazole-rich base that anchors the coating to the substrate, a V4D4-containing region that is crosslinked during deposition, and an allyl-rich surface. Stage-wise spectroscopy supports the programmed compositional gradient, FTIR and control experiments are consistent with thiol–ene coupling at the adhesive–coating interface, and nanoindentation reveals a corresponding mechanical gradient. The coating improves adhesion across all substrates, raising lap-shear strength from 1.87 to 2.55 MPa on aluminum, 2.22 to 3.15 MPa on stainless steel, 1.92 to 2.55 MPa on polycarbonate (PC), 1.18 to 2.24 MPa on poly (methyl methacrylate) (PMMA), and 0.17 to 0.47 MPa on polytetrafluoroethylene (PTFE), while retaining high visible-range transmittance. This solvent-free approach offers a practical platform for UV-curable adhesives, microelectronics packaging, and transparent device assembly.