RESEARCHERS have developed a method of 3D printing that will allow faster design, prototyping and testing of polymer membranes that can be patterned for improved performance.
Ion exchange membranes are used in energy applications, such as fuel cells and certain batteries, plus in water purification, desalination, removal of heavy metals and food processing.
Current techniques for making patterned membranes involve etching a silicon mould with the desired pattern, pouring in the polymer and waiting until it hardens. This is a time consuming process that only results in one pattern. However, recent developments have shown creating 3D patterns on top of the 2D membrane surface helps improve ion transport or reduce the build-up of unwanted materials that foul the membrane.
A team from Penn State University, US have developed a custom 3D photolithographic printing process similar in concept to a current 3D process called stereolithography, which will allow the team to modify the membrane patterns easily to test for improved performance.
The team used a photocurable mixture of ionic polymers and exposed the mixture under a light projector to harden the base layer. They then added more raw polymer to the base layer and projected a changeable pattern of light onto the new material to selectively harden the surface. The surface pattern increases the conductivity of the membrane by up to three times.
Michael Hickner, associate professor of materials science and engineering at Penn State, said: “Membranes act like a resistor in a battery or fuel cell. If you can lower the resistance by a factor of two or three, you've really got something useful.”
Hickner told The Chemical Engineer that current lithography techniques take up to two days to fabricate a patterned mould and another day to cast the membrane into one shape, and subsequent shapes would have to be designed to change the pattern. He said with 3D printing, 10 different patterns can be made in one day.
The team say the printed membranes allow them to model the resistance decreases quantitatively, and parallel resistance models allow the team to see the effects the patterns are having on membrane performance. The team says the insight gives them a design tool to innovate new patterns that will continually improve performance and change the intrinsic chemistry of the material.
The next stage for the team will be to continue to optimise the geometry and the chemistry of the membrane patterns and print new materials that have never been 3D printed before.
“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,” continued Hickner.
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