Polyhedral oligomeric silsesquioxane/polyamide bio-nanocomposite membranes : structure-gas transport properties

A series of bio-nanocomposite membranes based on different loadings of polyhedral oligomeric silsesquioxane (POSS) and dimer fatty acid polyamide was prepared by a facile solution casting method and their gas-transport properties were evaluated using oxygen, nitrogen and carbon dioxide. Intactness of POSS molecules in the polyamide was confirmed by 29Si CP/MAS NMR and FT-IR experiments. The formation of effective H-bonding interactions between POSS and polyamide was confirmed by FT-IR. The surface morphological features of the membranes prepared were analyzed using TEM, SEM and AFM techniques. TEM images revealed excellent dispersion of POSS into the membranes and it (POSS) was found to be in the range of 10 to 20 nanometers size. SEM images showed no agglomeration, even at a high content of POSS. AFM 3-D images of the membranes indicated a slight increase in surface roughness with increased POSS content. The hydrophilic/hydrophobic nature and the surface free energy of the nanocomposite membranes prepared were analysed by contact angle measurements using the Sessile drop method. Considerable influence of POSS on the glass transition temperature of the bio-nanocomposite membranes was observed. Increasing the POSS content decreased the free volume and increased the density of the membranes. These properties can be used to determine the permeability and selectivity of the membranes prepared.