Plasmon-Polariton Induced, from Surface RAFT Polymerization, as a Way toward Creation of Grafted Polymer Films with Thickness Precisely Controlled by Self-Limiting Mechanism

Plasmon-induced from surface reversible addition-fragmentation chain-transfer (RAFT) polymerization is reported for the first time. The gold grating surface, supporting the surface plasmon polariton excitation and propagation, is grafted with RAFT agent, immersed in the solution, containing the NIPAm monomer and AIBN and subsequently illuminated at a wavelength corresponding to plasmon absorption. The grafting of the polymer layer, its thickness, and morphology are characterized by several techniques (including the surface-enhanced Raman spectroscopy (SERS), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray photoelectron spectroscopy (XPS), nanomechanical atomic force microscopy (AFM) mapping, and goniometry). It is shown that the polymerization efficiently starts only under the surface plasmon-polariton excitation. The time-dependent SERS and XPS measurements indicate rather self-limiting nature of plasmon-induced from the surface PNIPAm growth, namely the reaction takes place up to a certain polymer thickness and is stopped despite a significant excess of polymerization initiator and monomer in the reaction solution. The present results provide the basis for designing further experiments on plasmonic catalysis in general and offer a new way of producing ultrathin polymer films with a defined structural dimension.