Researchers discover new insights into how water filter membranes work

Scientists have known for years that membranes can do things such as act as a filter for saltwater. When salty ocean water is moved through a membrane, clean water comes out the other side that can be used for agriculture and drinking, among other things. While pushing water through a membrane is a simple enough process, the exact method that allowed water filtration membranes to work was unknown until now.

A group of researchers, including scientists from Penn State, the University of Texas at Austin, Iowa State University, Dow Chemical Company, and DuPont Water Solutions, have now published a study showing key findings and how membranes filter minerals from water. Researcher Enrique Gomez, professor of chemical engineering and materials science and engineering at Penn State, research lead, says that the team found that how the density distribution of the membrane is controlled at the nanoscale is important for water production performance.

The team used multimodal electron microscopy in the study, allowing them to combine atomic-scale detailed imaging techniques to rebuild the chemical composition to determine that desalination membranes are inconsistent in density and mass. Researchers mapped density variations in polymer film using three dimensions with a spatial resolution of approximately one nanometer. Gomez says that we can see differences in density and the surface of the coffee filter using the eye.

However, in filtration membranes, it may look even with the naked eye, but at the nanoscale, it may not be. How material distribution is controlled is very important for water filtration performance. Researchers originally thought the thicker the membrane was; the less water was produced during filtration. The scientists found that thicker membranes were more permeable.

Researchers found that thickness doesn't matter as much as avoiding highly dense nanoscale regions, dubbed "dead zones." Essentially, density throughout the membrane is more important than thickness for maximizing water production. Scientists believe their findings could increase membrane efficiency by 30 to 40 percent.