Facile fabrication of high thickness hydrophilic polymer brushes via Surface-Initiated Microliter-Scale copper mediated PhotoATRP toward antifouling surfaces

Abstract

The recent development of sustainable chemistry motivates scientists to develop economically favourable, highly efficient, and environmentally friendly polymerization techniques. This contribution demonstrates a facile fabrication of hydrophilic polymer brushes via surface-initiated photochemically induced atom transfer radical polymerization using a copper catalyst in low concentrations and microlitre volume of polymerization mixture (SI-μL-CuPhotoATRP). The fabrication proceeds by sandwiching of μL reaction solution between a Si-wafer modified with ATRP-initiator and a glass slide under atmospheric and ambient conditions. Optimization of reaction conditions was realized on hydrophilic monomer such as 2-hydroxyethyl methacrylate (HEMA). Effect of various experimental parameters such as light intensity, solvents, ligands, the volume of the reaction solution, size of the Si-wafers, amount of CuBr2, and CuBr2/ligand ratio in kinetics, linear increase of polymer layer thickness, final thickness and profile of unmodified edges were investigated. The successful fabrication of hydrophilic polymer brushes is confirmed via Fourier transfer infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), profilometry and water contact angle. A linear thickness increase with time up to at least 300 nm was achieved, compared to polymethacrylate layers with thickness up to approximately 100 nm previously published by using photoATRP. The general applicability of the optimized conditions for SI-μL-CuPhotoATRP was further proved for two additional hydrophilic monomers, such as glycidyl methacrylate and 2-hydroxypropyl methacrylate. Furthermore, sequential homo and block copolymerization demonstrated the living character of fabrication conditions, permitting facile fabrication of well-controlled tetra block homo/copolymer brushes with a pyramid-like pattern on Si-wafer. Poly(2-hydroxyethyl methacrylate) (PHEMA) brushes-grown surfaces exhibit excellent antifouling properties and long-term structural stability. The facile, affordable, and environmentally friendly SI-μL-CuPhotoATRP approach provides avenues for various surface modifications, such as biomedical, soft robotic, and coating applications.