Variations in thermal stability and hydrophilicity of multiple polyampholyte membranes with unique structural compositions

Polyampholytes are polymers that have randomly distributed sequences of both positively and negatively charged monomeric units. Polyampholytes show excellent anti-fouling properties because of the oppositely charged components along their chains. Therefore, they are ideal candidates for the fabrication of filtration membranes. In this study, we used a random polyampholyte amphiphilic copolymer (r-PAC) that is composed of monomer units that are hydrophobic in addition to the positively and negatively charged components in various compositions. The r-PAC membranes were prepared by doctor blading, and thin films were prepared by spin casting. The doctor-bladed membranes were characterized using thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). Sessile drop contact angle measurements were performed on spin-cast thin films. TGA showed that r-PACs degrade via a multistep process and FTIR confirmed that the cationic group degrades first. Sessile drop contact angle measurements showed that as the negatively charged components increased, the surface of the material became more hydrophobic. With increased hydrophobicity, these materials possess excellent mechanical and chemical stability while the hydrophilicity of the charged components preserves their anti-fouling properties.