[MUSIC] Hi, this is module five. In module five we're going to look at several case studies of applications of high throughput materials development. To actually successfully develop new kinds of materials. The first case study I'm going to take you through is a look at proton exchange membranes for fuel cells. So the outcomes are to examine the applications of high through put screening to proton exchange membranes and fuel cells. To understand the primary structure and components of what we call semi-interpenetrating network membranes. This is the kind of material we were looking at. And to understand the kinds of key figures of merit that we need to measure for screening these membranes. So I've shown this slide before, back in module four when we talk about electronic properties. The basics schematic of a cross section through a proton exchange membranes fuel cell. Essentially, we're carrying out an electrochemical oxidation of a fuel, in this case, the fuel was hydrogen. So there's an anode electrode, where there is a catalyst, the hydrogen is oxidized, each H2 loses two electrons and it forms two protons, H plus, and these protons have to diffuse and move across the membrane. The membrane is the electrolyte, the grayed out area in the middle, so this electrolyte is the critical component that we are trying to design in this application. It has to serve several functions, the membrane has to, essentially block the exposure of the hydrogen to the oxygen, so that they don't oxidize directly and actually combust. And it has to allow for fast transport of protons to the cathode. It also has to be relatively mechanically robust so that it doesn't crack and so that it can go through many cycles without forming any defects. So in our membranes we were looking at a relatively new concept and this was to combine two components through blending. The two components were an inert fuel resistant polymer, which we show in blue here, and a proton conducting polyelectrolyte polymer, which we'll show in red. These were blended in solution at various compositions and then there were cast on a substrate, heated and cured, and to the final membrane and then the membrane could be tested for its properties. So these membranes actually are called semi-interpenetrating network polymers, or SIPNs, the idea is that there will be a background of the blue inert polymer chains and in this background, there will be interconnected nanoscale channels of the red polyelectrolyte. And it's in these nanoscale channels of polyelectrolyte that the protons can actually transport through the membrane. So there was some experimental design here based on preexisting knowledge. Most notably, I was working with the company called Arkema and this company is one of the major manufactures of a polymer called polyvinylidene flouride or PVDF, so we were using PVDF as the inert phase. We also looked at a copolymer between PVDF and something called polyhexafluoropropylene or PHFP. These homopolymers, the pure PVDF and the copolymers between PVDF and HFP are sold under the trademark name Kynar, and in our study we looked at five types of Kynar. Two that were PVDF and three that were the copolymers. These differ in properties like, crystallinity, and melt viscosity, and they allow us to adjust the structure of the network that forms. So the proton conducting polyelectrolyte, we chose to use a copolymer of sulfonated ethyl methacrylate, SEM. So, 90% of the copolymer had this SEM molecule and it's the sulfonate groups that are actually responsible for transporting the protons. This is where the protons form. We also added 10% of a monomer called HEMA which is hidroxietil methacrylate. The HEMA was added because the Groups allow us to crosslink and form a solid stable structure. If we look at the final copolymers that were formed, we had mostly SEM groups with the occasional HEMA group in blue here. This triisocyanate molecule, this is a molecule available from a number of suppliers, it's commercially available. We would asked you to react with the HEMA hydroxyl groups, and it can joined three of those HEMAs together in one linkage to crosslink into a stable solid. So that's what's actually going on when we cure the film. So a common material of a high-throughput design was we looked at five types of Kynars and we also looked at eight loadings of the SEM HEMA copolymer as the poly-electrolyte. So this would be 40 combinations. We also looked at other kinds of poly-electrolytes, but I'll just tell you about one of them today. These were blended, and after blending we put them in high temperature, about 170 celsius for a set amount of time, and this formed the crosslinks which resulted in the cast solid membrane. So the complexity and the need for using high-throughput materials development really arises from the need to fine-tune the nanostructure and the connectivity within the ionic conducting channels. It turns out the Nano structure is sensitive to small changes and chemistry of the PVDF and the PVDF copolymer's with HFP and it's sensitive to small changes in the ionomer composition. It's also sensitive to the solvent that you use, the temperature, the presence of catalysts, and even after the solid membrane is formed, it's sensitive to the conditioning. We usually expose the membrane to acids to protonate it. So we looked at preparing libraries using the composition gradient technique that I talked about earlier in module two, where we had two rate controlled syringe pumps. These syringe pumps would essentially pump at different rates into a mixing chamber. This mixing chamber had a tube that was connected to a microchannel coating blade that would distribute the solution over a moving substrate, and so essentially the substrate would be coated, and the composition gradient would change as indicated by the blue to black here. Here's a photograph of the inside of the micro channel coding blade and there's a little hole in the middle about in the center, about the third of the way down. You can actually see that's the inlet hole, and then the solution would spread out in these rectangular bifurcating channels, and so it would spread out over the whole firm. And we would program the pumps to look like this. They would start pumping PVDF and the poly lectrolyte at the same rate, but then the polyelectrolyte would increase while the PVDF decreased, and we could produce nice composition gradients like this. It turns out that although we could make the nice films when we expose them to water which was necessary to coordinate the membrane and measure it's conductivity. It turns out the site of the membrane that was swollen with poly electrolyte SEM-HEMA, turned out to swell dramatically, whereas, the part rich with PVDF didn't swell much at all and this turned into the formal membrane. So we decided that because of the swelling issue, composition gradients weren't really that good of an idea and we decided to simply make many uniform samples. These could be rapidly prepared using the same coding system, so we created libraries that for each polyelectolyte and for each repetition had 40 miniature film samples. Next, we're going to talk about how we actually screen this for conductivity and other properties. Thank you. [MUSIC]