Theoretical and Experimental Investigation on Hydrophilicity of Polymeric Membrane

Abstract

The study employs nitrogen (N2) plasma for surface modification of a polymeric membrane to investigate the changes in its hydrophilic properties under diverse storage conditions. It is found that the hydrophobic recovery of cellulose nitrate membrane for 7 minutes of plasma treatment is moderate for water medium, high for atmospheric medium, and low for vacuum medium. For water medium, this process is governed by fixed dipole-dipole interactions, which dominate over London dispersion forces, limiting hydrophobic recovery. In the atmospheric medium, hydrophobic recovery accelerates due to variations in temperature and relative humidity. In the vacuum medium, hydrophobic recovery is slowed down due to the absence of reactive species influencing recovery. As a result, the diffusion-based theoretical model matched with experimental data for the water and atmosphere mediums but not for the vacuum medium. SEM analysis reveals significant pore enlargement and surface etching of the plasma-facing membrane surface after 7 minutes of plasma treatment compared to untreated membranes. EDX results showed increase in C/N ratio indicating the presence of nitrogen containing functional groups. Since the FTIR penetration depth exceeds the modification depth caused by plasma treatment, similar peaks were observed for both treated and untreated membranes. Several peaks were observed in both treated and untreated samples at 1643 cm-1 (C-C stretch), 1275 cm−1 and 1059 cm−1 (C-O stretch), and 834 cm−1 (C-H bend). AFM analysis shows a significant enhancement in surface roughness for plasma-treated membrane with respect to untreated membrane which is obtained as 32% more than that of untreated membrane.