Wetting Behaviour of Superhydrophobic Membranes Coated with Nanoparticles in Membrane Distillation

Abstract

The field of membrane distillation (MD) is currently enjoying a great deal of interest and its possible fields of application are being explored. However, penetration of liquid feed in membrane pores (wetting phenomenon) has caused in the lack of overall attention in the MD processes. Even though commercial polymeric membranes (e.g., polyvinylidene fluoride (PVDF), polypropylene (PP), and polytetrafluoroethylene) show intrinsic hydrophobicity, the pore wetting may still take place for treatment of solutions with surface tensions lower than water. Depositing nanoparticles (nPs) on membrane surface to form a microstructure on top of macrostructure (physical property rather than a chemical property of surface) as it is in natural superhydrophobic surfaces such as lotus leaf can increase water repelling effect of membranes.In this paper, membrane pore wetting behavior is investigated by depositing/grafting SiO2 nanoparticles on the surface of commercially available polypropylene membrane. Dip coating method is used to deposit nPs for increasing the membrane surface roughness, water contact angle and consequently reducing membrane wettability. The effect of experiment parameters on the superhydrophobicity and permeability of nano-coating membranes are examined herein to explore the optimum preparing conditions. Atomic force microscope (AFM) and contact angle goniometry measurements are applied to study the influences of surface coating on the surface structure and performance of the original and coated membranes.Moreover, membrane distillation tests are performed for modified and virgin flat sheet PP membranes. By comparing the performance of the original and modified membranes in direct contact membrane distillation experiments in the presence of a surfactant (sodium dodecyl sulphate, SDS), the influence of coating on membrane pore wetting and contamination degree of permeate with a surfactant is shown.