Spray Layer-By-Layer Assembled Composite Thin Films As Selective Layers in Reverse Osmosis Membranes

Development of novel, inexpensive, and highly-selective membranes for use in continuous-flow reverse osmosis (RO) processes can reduce both the capital and operating costs for modern desalination and wastewater treatment operations.  The flexibility of the spray layer-by-layer (spray-LbL) assembly process enables the deposition of composite polyelectrolyte/clay thin films on porous hydrophilic substrates to serve as a selective layer in a RO membrane.  This technique is particularly well-suited because large asymmetric films can be deposited orders of magnitude faster than with traditional dip-LbL assembly.  The composition and physical properties of spray-LbL assembled composite films can be fine-tuned by manipulating the film assembly conditions such as spray time and pH of the film components as well as the number of layers deposited.  Using mathematical modeling on data collected from dead-end permeation cells, permeability coefficients for water and salt through selective layers of varying film composition were calculated.  Experimental data have confirmed the viability of using composite polyelectrolyte-clay films deposited on commercially-available nanofiltration membranes as novel RO systems.