One-step dynamic assembly of polyelectrolyte complex membranes

Abstract

During the past decades, layer-by-layer (LbL) assembly technique based on electrostatic adsorption of oppositely charged polyelectrolytes (PEs) has been one of the most frequently utilized processes for assembling ultra-thin film. However, LbL process is also recognized as a time-consuming process, especially for assembly of dense membranes. In this paper, a one-step dynamic assembly based on electrostatic adsorption was developed to prepare the PE complex membranes. The chitosan (CS), used as a model polycation, was dynamically deposited on a hydrolyzed polyacrylonitrile (PAN) support membrane with negative charges under a selected pressure to form a PE complex membrane for pervaporation separation of water–ethanol mixture. Compared with traditional dip-coating method, this new assembly process could offer some advantages such as the formation of selective layer with dilute solution, easily used for different membrane module types and suitable for large scale applications. The assembly conditions such as dynamic pressure, CS molecular weight, and CS concentration were investigated. The appropriate conditions for assembly were: dynamic pressure, 0.2 MPa; CS molecular weight, 82,000; and CS concentration, 0.5 wt.%. In the case of pervaporation of 95 wt.% ethanol/water mixtures, the separation factor and the permeate flux of the CS polyelectrolyte complex membranes were 422 and 230 g/(m 2 h) (60 °C), respectively. The cross-linking treatment with glutaraldehyde and sulfuric acid were subsequently performed. It was found that the separation performance was improved by the cross-linking treatment. Finally, inner skin hollow fiber PE complex membranes were also successfully explored using one-step dynamic assembly for pervaporation dehydration. The proposed process will offer a new approach to obtain a relatively integrated PE complex membrane.