From Trans to Cis Conformation: Further Understanding the Surface Properties of Poly(m-phenylene isophthalamide)

Controlling the membrane surface properties such as hydrophobicity and hydrophilicity is critical to achieving desirable performance. For a long time, the difference between the surface wettabilities of superhydrophilic poly(m-phenylene isophthalamide) (PMIA) electrospun nanofibrous membranes (ESMs) and the superhydrophobic parent material is believed to arise from the poling effect induced by the electrospinning process and wicking caused by the porous membrane structure. In this study, the short-term poling effect was eliminated using a reference, centrifugally spun nanofibrous membrane that has a similar fiber morphology and specific surface area to those of the ESM; consequently, we investigated the changes in the surface properties of the ESM in detail. Chemical analysis by angle-resolved X-ray photoelectron spectroscopy revealed that the N and O concentrations are greater at the surface of the ESM. In addition, analysis of the membranes by attenuated total reflectance Fourier-transform infrared spectroscopy and Raman spectra revealed that large amounts of cis conformations of the amide bonds appeared on the surface of ESM after the electrospinning process. The results indicate that the remarkable surface properties of PMIA ESMs mainly arise from the change in the conformation of the amide groups from the stable trans form to the cis form. This change was confirmed by the subsequent in situ growth of Pt nanoparticles and the excellent dye adsorption capacity of the membrane.