(421c) Surface Nano-Structuring by Atmospheric Pressure Plasma Induced Graft Polymerization for the Synthesis of Low Fouling and Scaling Ro/nf Membranes

Rapid population growth and limited potable water resources are generating an increasing demand for water desalination. One of the leading methods of desalination is through the use of reverse osmosis (RO) membranes. However, the major problem associated with desalination through RO is membrane surface scaling by mineral salt, organic and biological fouling. Membrane surface modification has been widely employed to mitigate salt scale formation and biofouling problem. However, traditional RO membrane surface modification methods have been shown to reduce the intrinsic membrane permeability and involve complex chemical steps that are problematic for scale-up commercial production. In the present study, a novel atmospheric pressure plasma-induced graft polymerization method was developed for surface nano-structuring of RO and NF membranes with the goal of synthesizing RO and NF membranes with a highly dense, covalently-bound permselective grafted polymer brush layer. The chemical and physical features of the grafted polymer film were established for the selected monomer by tuning the reaction conditions to achieve unique surface architectures that are optimized for low fouling/scaling RO membrane synthesis. The properties of the graft polymerized surfaces, such as surface topography and surface feature uniformity, were evaluated by Atomic Force Microscopy (AFM), and the surface chemistry was elucidated by Fourier Transform Infrared (FTIR) Spectroscopy. A Quartz Crystal Microbalance (QCM) flow cell was used to investigate the effect of the grafted polymer layer topography on scale formation and the surface scaling/fouling kinetics (e.g., onset of mineral scaling, surface scale coverage) of surface nano-structured RO membranes with typical commercial RO membrane surfaces to determine the impact of the polymer brush layer properties (i.e., polymer chain density, chain length, and monomer chemistry) on surface fouling/scaling. The sensitivity of QCM allowed for the detection of surface scale and protein formation/adsorption in the ng/cm² range. The QCM system enabled direct measurements of the kinetics of mineral scaling and organic/biological fouling on the surface nano-structured membranes. The implications of the results from the present study for the development of a new class of RO/NF membranes of low bio-fouling and mineral scaling propensities will be discussed with specific reference to the structural surface properties.