Understanding the dependence of contact angles of commercially RO membranes on external conditions and surface features

The contact angles of three kinds of typically commercial reverse osmosis (RO) membranes (LP21, ULP21, and FR11) were firstly investigated. The relationships between the contact angles and external conditions were researched by well considering the effects of sample pretreatment, water-droplet volume, environmental humidity, water temperature and salinity. Furthermore, the surface features of these RO membranes, including functional groups, surface roughness, and zeta potentials, were also analyzed for exploring their influences on the contact-angle values, by using attenuate total reflectance infrared (ATR-IR) spectra, scanning electronic microscopy (SEM), and streaming potential instrument. The experimental results suggest that the sample pretreatment makes the hydrophilicity of RO membranes decrease, because of the part removal of physically coated hydrophilic aliphatic alcohols and protect agents introduced in the synthesis process. The water-droplet volumes have no obvious effect on the contact-angle measurement results. The contact-angle values can be gradually decreased with the enhancements of the environmental humidity, external temperature, and water salinity. Moreover, it was found that the enhancements on the density of modified hydrophilic functional groups, surface roughness and surface zeta potential are favorable for the decrease of contact angles.

► We investigated the effects of external conditions on RO-membrane contact angles.
► The relationships between surface features and contact angles were analyzed.
► The action mechanisms on contact angles were systematically reported.
► The contact angles of three RO membranes were first comprehensively reported.