American researchers have come up with a new 3D printing technique to create polymer membranes that have been patterned for improved performance.
Michael Hickner, associate professor of materials science and engineering at Penn State University, said ion exchange membranes are a focus of their research.
Used in many types of energy applications, from fuel cells to water purification, most of these membranes are thin, flat sheets, however, recent work has shown that by creating 3D patterns on top of the 2D membrane surface, interesting hydrodynamic properties emerge that can improve ion transport or mitigate fouling, a serious problem in many membrane applications.
"We thought if we could use 3D printing to fabricate our custom-synthesised ion exchange membranes, we could make any sort of pattern and we could make it quickly," said Hickner.
Using a custom 3D photolithographic printing process similar in concept to stereolithography, the team developed a photocurable mixture of ionic polymers and exposed the mixture under a light projector to harden the base layer. They then added more polymer to the base layer and projected a pattern on the new material to selectively harden the surface. This surface pattern increases the conductivity of the membrane by as much as a factor of two or three.
"Membranes act like a resistor in a battery or fuel cell," he said. "If you can lower the resistance by a factor of two or three, you've really got something useful."
The team believes this is the first 3D printed example of these structures and the first model that really explains the resistance decrease in a quantitative way. A simple parallel resistance model describes the effect of the pattern on lowering the resistance of these new membranes. This insight gives us a design tool to continue to innovate and create new patterns for further improvements along with changing the intrinsic chemistry of the material.
They now plan to continue optimising the geometry and chemistry of the membranes they print, as well as learn to print new materials, both for membranes and beyond, that have never been printed heretofore.
"We want to bridge the fundamental chemistry and materials science that we do with the engineering and rapid design iterations that the 3D printing industry is really good at," said Hickner.
[Membranes printed with the technique. Photo: Penn State]
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