Fabrication and Characterisation of Amine-Rich Organic Thin Films: Focus on Stability

Thin films, rich in primary amines (C-NH2), were deposited from nitrogen (N-2) or ammonia (NH3) and ethylene (C2H4) with different gas mixture ratios, R, using three different methods: atmospheric-pressure- or low-pressure plasma polymerisation (PP), and vacuum-ultraviolet photo-polymerisation. They are designated H-plasma-polymerised ethylene (PPE):N, L-PPE:N and ultraviolet-polyethylene (UV-PE):N, respectively. Of interest in cell-culture and tissue engineering, all three coating-types were examined with regard to stability in air and solubility in water, compared with other deposits in the literature that were obtained from single precursors such as allylamine (AA) or n-heptylamine (HA), PP-AA and PP-HA, respectively. The three types of deposits, prepared using comparable R values, were characterised by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy and found to vary significantly among themselves in regard to their [N]- and [NH2] concentrations, and their chemical stabilities during long-term exposures to air or aqueous solvents. UV-PE:N and L-PPE:N films were found to compare very favourably with their best PP-AA and PP-HA counterparts; we conclude that the additional important fabrication parameter (the gas mixture ratio, R) is a major asset for preparing stable NH2-rich organic coatings with optimal properties.