The characterization of structure-tailored plasma films deposited from the pulsed RF discharge

Abstract

Pulsed RF plasma polymerization using vinyl acetic acid as a prototype precursor was investigated in order to evaluate the applicability of the pulsed RF discharge to obtain plasma polymers with less cross-linked structure and high degree retention of the groups in the starting monomer. The chemical structure and the surface morphology of the polymerized vinyl acetic acid were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscope (XPS) and scanning electron microscope (SEM). At all other plasma parameters remaining constant, the chemical structure was observed to vary with the plasma duty cycles. The FTIR results showed that more carboxylic groups could be ‘retained’ with the decreasing of the duty cycles. The XPS results were consistent with the FTIR measurements. Surface energy measurements indicated that the plasma films were hydrophilic. The plasma polymerized films at continuous discharge mode show higher thermal stability than the films polymerized at pulsed discharge mode. But the later is less cross-linked. So it is possible to control the chemical composition of the plasma film with the same surface functional groups as its monomer being ‘retained’ by pulse plasma technologies. Some regular graft ‘lightning’ network patterns were interestingly found in the plasma films kept at room temperature for some time by SEM. It was estimated that the mechanism of the plasma polymerization is different along the ‘lightning’ network and on the valley of the pattern.