Chemical structure and surface morphology of plasma polymerized-allylamine film

Abstract

In this study, we conducted the plasma polymerization of allylamine using radio frequency (RF) glow discharge with continuous wave (CW) in order to make an organic thin film with an amine functional group retained. Allylamine as a monomer was deposited on a glass in a bell-jar type plasma reactor and polymerized to plasma-polymerized allylamine (PPAa). The parameter to control the property of plasma polymer was input power at other conditions remaining constant. The chemical structure and the surface morphology of plasma-polymerized allylamine (PPAa) film were characterized by contact angle measurement, Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM). The property of PPAa film was highly dependent upon the plasma input power. The input power, which determines the plasma density, results in a property of PPAa thin film such as hydrophilicity, high retention of functionality of PPAa’s surface. Surface energy calculated by contact angle measurement indicated that increasing input power (from 30W to 90W) decreased the hydrophilic property of PPAa due to loss of amine functional group and high cross-linking. The increase of the energy causes the films to be harder. ATR-FTIR and XPS results showed that high input energy fragmented the amine group from monomer with increasing nitrogen atomic content and nitrile group. The high retention of amine groups seems mainly favored by low input power (<30 W). From thickness measurement usingα-stepper, the deposition rates were 0.43, 0.83, 1.11, 1.37 nm/s at 30, 50, 70, 90W, respectively. The change of surface morphology of plasma-polymerized thin films was investigated after soaking the PPAa film into ethanol. Due to weak adhesion with substrate and internal stress in plasma polymer film, the surface morphology of PPAa film revealed some irregular network pattern.