By: Prof Giridhar Madras
The next generation of electronic devices is likely to be made of organic polymers, instead of the brittle, inorganic material that is being used today. Besides being inexpensive, organic or carbon-based polymers have the advantage of being flexible and ductile, and are therefore less prone to degradation.
Until now, metals and semi-conductors have been preferred for manufacturing devices because of their ability to conduct electrical charge. However, some organic polymers with electricity-conducting properties have also been synthesised recently. These materials are suitable for the development of flexible electronics.
But the problem with organic devices is that they are vulnerable to moisture and oxygen. Therefore, when conducting polymers are exposed to the atmosphere, they get oxidised due to the moisture, resulting in the failure of the devices.
This prompted us to create a moisture barrier in between the device and the environment. One of the best options is to use glass. But the flexibility of the device is compromised, which is the biggest advantage of an organic instrument.
It was this problem that we (Assistant Prof Praveen C Ramamurthy, Ph.D candidate Sindhu Seethamraju, ME student Gayathri N Kopanati and I), at the Indian Institute of Science, have been working on. We have now developed a barrier that is not rigid and does not allow the water vapour to come in contact with the organic material either. We looked at the compounds that can react with water molecules and, by sacrificing themselves, protect the device from environmental moisture.
We worked on the innovative design of polymer nanocomposite barrier materials that are a mixture of polymers and nanosized reactive materials.
In this project, we used a polymer called Surlyn while Magnesium Oxide (MgO) was the nanosized material. Magnesium Oxide reacts with water to form Magnesium Hydroxide Mg(OH)2. Magnesium oxide was synthesised and blended with Surlyn to fabricate the barrier.
This barrier material did its job with excellent efficiency. With this film, we have limited the permeation rates of water vapour to one by ten thousandth of a gram per square metre of surface per day. This is at least a thousand times better than the currently available commercial polymers. The water vapour transmission rates through normal plastic are about one to hundred gram per square metre per day. The tetra packs that are used to store perishable food items allow one by a hundredth of a gram per square metre per day.
Under extensive laboratory ageing conditions (95 per cent humidity, which is much higher than the ambient atmospheric conditions), the efficiency of the fabricated device sealed with this barrier film reduced by only 50 per cent after one hour of continuous exposure to water vapour. We are further working on the development of better barrier materials to ensure the primary objective of protecting the organic devices for at least 10,000 hours of exposure to moisture under ambient environmental conditions.
Prof Giridhar Madras, Department of Chemical Engineering, Indian Institute of Science, Bangalore
Madras can be reached at