Researchers from Pennsylvania State University have unraveled a custom made 3D photolithography method, which is similar to stereolithography, to print out micro patterned membranes which can exchange ions. These membranes have been patterned thus for enhanced performance that can potentially improve many fields, such as the energy sector, desalination and purification of water, food processing, etc. Ion exchange membranes are essentially flat, sheet like substances that can transport solvent dissolved ions through a polymeric conductive membrane. These are used for various purposes across the energy sector. In fact, these membranes transfer ions of one solution to another. These membranes can be employed in certain batteries, fuel cells, food processing, desalination and water purification, etc. At Pennsylvania State University, researchers from the Department of Materials Science and Engineering have developed one of these membranes, yet with the help of 3D printing processes that enhance the membrane’s hydrodynamic properties. This can help improve transportation of ions and facilitate fouling.
In order to enhance the properties of these membranes in the most efficient way, they have to be made profiled or patterned. Traditionally, this is accomplished painstakingly by etching silicon molds with the required pattern, pouring the polymer in and waiting for the plate to harden. Even after so many painful steps, the end product would always be time consuming and cost ineffective. This is also a single type of pattern, which tells us about the limited choices in the membrane’s function if made traditionally.
The current membrane made at Penn State might look like an ordinary piece of kitchen plastic wrap at first glance, but these ion exchange membranes have their uses in several practical processes. These flat, thin sheets of polymer can be used in batteries and fuel cells, while their use in removing heavy metals, purification of water and food processing are also some potential benefits from the membrane. Traditionally though, they were made smooth and flat, without any kind of texture. Scientists now know otherwise. Today, scientists have found out that when 3D patterns are created on the surface of these membranes, some rather interesting hydrodynamic properties are seen in the polymers.
The primary function of the membranes in transportation of ions, with the help of these 3D patterns this property is made even better. A common problem faced in the exchange of ions is fouling, which can also be prevented by adding 3D patterns to the membranes. Today, there happens to be a better technology more advanced than the needle used to etch patterns. With the help of 3D printing, scientists can now easily impose patterns on the membranes accurately. The researchers studying the anion exchange membranes recognized that they could, in fact, put 3D printing to use in order to create the complex 3D structures as impressions on the exchange membranes. Associate Professor Michael Hickener from Material Science and Engineering Department of Penn State said that the research team thought of finding a quicker process of fabricating their own custom synthesized membranes for ion exchange. The process used in this regard is similar to stereolithography. It uses a light projector, curing a mix of ionic polymers to create a base layer. More polymer is added as required and finally a new pattern is projected onto the material to create the three dimensional serrated structure on the membrane. Tests conducted on the 3D printed ionic membranes showed that the new patterns in fact, increased the conductivity factor significantly. Hickner explains that membranes are to ions as resistors are to fuel cells or battery. When resistance is lowered by a factor of 2 or 3, something useful can be obtained from the result.
Even though other scientists have had their share of experiments with 3D patterned ion exchange membranes, researchers of Penn State believe that the research they conducted employed 3D printing in this purpose for the first time ever. Jiho Seo, a lead author of the paper and a PhD student explains that this happens to be the first examples of these structures being 3D printed, and also the first model that truly elaborates why the resistance decreased, in a quantitative approach. This can be explained by a simple parallel resistance model, describing the effect of this pattern on bringing down the resistance of the membranes. This insight is valuable to give them a design tool, which they can continue to improve and prepare new patterns for further advancement along with the changing internal chemistry of the membrane. Rapid prototyping helps to make models of these resistance plates, hence the researchers have ample opportunity to print out new models and decide which ones work best. Bridging the fundamental engineering and material science, the researchers hope to find better applications for their technology in order to benefit the related industries in a constructive manner.
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