As I reach my 24th year in industry, I find myself reflecting on the changes I have seen. Although some of the changes have been painful, I am encouraged to see traditional areas of materials science reinvent themselves and find new roles. What gives me a real buzz at the moment is seeing the emergence of ‘structural materials underpinning functional materials’. Let me elaborate.
I have seen multinational companies move away from their traditional materials base and refocus on higher-added-value markets, which are not subject to cyclical changes. This has been a common theme throughout the chemical industry. What I would call ‘structural’ and ‘engineering’ polymer businesses have increasingly become commodity industries, with a focus on driving down costs and improving manufacturing efficiency. (This is a generalization and there are exceptions.) The research spend in industry and academia has mirrored this trend and the focus of cutting-edge research has shifted elsewhere. At the same time, the spend on ‘functional’ materials has increased. This feels right as, in my opinion, research funding should provide support where industry needs to be in the future, rather than where it has been in the past.
So much for the ‘old’ – now for the ‘new’. Over my time in industry, I have heard researchers present their early work on new families of materials, such as conjugated polymers, dendritic structures, and biomaterials. I can now see some of these areas begin to form embryonic industries. One area in which I am involved, and is a good example of where traditional materials can find a fresh role, is the electronics and display industry based on conjugated polymers. There is a revolution taking place, with a range of new start-up companies, such as Cambridge Display Technology, E Ink, Gyricon, Infineon Technologies, Plastic Logic, PolyIC, Polymer Vision, and Universal Display Corporation, challenging the Si-based world and the plasma and liquid-crystal display market. The flat-panel display business is huge and growing rapidly. However, large displays are still made by expensive photolithography techniques. A new manufacturing approach is needed to lower costs and open up new design opportunities.
Flexible displays offer substantial rewards by being thin, light, robust, conformable, and can be rolled away when not in use. In addition, plastic-based substrates, coupled with recent developments in the deposition and printing of organic light-emitting polymers and active matrix thin-film transistor arrays, open up the possibility of cost-effective, roll-to-roll processing in high volumes.
To replace glass, a plastic substrate needs to be able to offer the same properties, i.e. clarity, dimensional and thermal stability, solvent resistance, a low coefficient of thermal expansion, and a smooth surface. No plastic film offers all of these properties, so any candidate substrate will almost certainly be a multilayer composite structure. To illustrate this, let's look at the films that are currently being proposed as replacements for glass. These consist of first a base film; this will likely have good transparency, excellent dimensional stability, a thermal expansion coefficient as low as possible, and a smooth surface. The next layer may be a hard coat to prevent scratching during processing and provide solvent resistance. On top of this goes the barrier coating. The required barrier properties are several orders of magnitude better than can currently be achieved by a plastic film, as displays based on organic light-emitting diodes are extremely sensitive to oxygen and moisture. One approach, which has been pioneered by start-up company Vitex Systems, is to lay down a stack of alternating organic and inorganic coatings. The organic coatings planarize out surface defects that lead to pinholes, while the inorganic layers make the diffusion path for water and oxygen more tortuous. Finally, a conductive layer is deposited on top – at present this is likely to be inorganic but one day may be organic. At this stage, the process gets really complicated as circuitry is laid down. The display is built on top of this structure.
Clearly, the final structure is complex. In addition to choosing the right materials, one now has a new set of issues associated with the properties of multilayer structures. What will happen when the structure is flexed or dropped? Can it withstand thermal shock or exposure to the environment? Will it still retain the required barrier and conductive properties after this type of treatment? How do you turn the above steps into a roll-to-roll process? What you now start to see is a new area of materials science – structural materials underpinning functional materials. Some of the science required to address these issues is already in place, but much further research will be needed. I believe that this presents a new role for those of us coming from a traditional materials background. To fully engage, however, we need to recognize that the world of materials has changed. We need to focus on the exciting new challenges that the emerging functional materials industries will present to us.
[1] Bill A. MacDonald is a business research associate at DuPont Teijin Films, UK. The views expressed in this article are the author's own and do not necessarily reflect those of DuPont Teijin Films.