Preparation of hydrogels on solid surfaces is of great significance for a number of reasons such as changing the interfacial properties, increasing hydrophilicity, etc. Such films strongly improve mechanical and hydrodynamic properties of the surfaces. Creating nano-layers of hydrogel thin films has been an attractive subject in advanced academic research for past few years. Due to the relatively high water absorption capacity of hydrogels, the hydrogel coatings have critical applications including biological detectors, drug delivery, contact lenses, artificial blood veins, and biocompatible implants such as stents in heart and ears. In this study, free radical polymerization was initiated by electron transfer from a metallic substrate (stainless steel) to a redox-active initiator in NaNO3 containing electrolyte, using electro-polymerization method. The resulted electro-polymerized polyacrylamide hydrogel nano-films with a typical thickness of 30 to 150 nm were examined and globule-like microstructures on the surface were observed in field emission scanning electron microscopy (FE-SEM) images. The formation of these globules in the early stages of reaction could be due to the disproportionate distribution of radicals, disproportionate growth in specific area, local gelation of film, and an increase in propagation rate constant of reaction on nano-film surface. Also many nano-tracks were observed on the surface and it refers to the morphological instability of surface attached hydrogels. Finally, atomic force microscopy (AFM) images were studied and monomer concentration introduced as an effective parameter on average roughness of the nano-film surface.

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