A team of researchers from the University of Hyderabad (UoH) claim to have developed an optically transparent flexible composite material that could be utilized for the development of future transparent wearable sensors and biomedical devices.

Optically transparent flexible materials possessing high dielectric constant have tremendous applications in a wide range of applications such as flexible electronics devices, micro-electromechanical systems(MEMS), wearable sensors and biomedical devices.

A crucial issue in the fabrication of the flexible composite materials is the uniform dispersion of the filler material in the polymer matrix. As a consequence of the poor distribution of the filler material in the polymer matrix, defects and cracks are induced in the composite which in turn degrades the flexibility of the material. Since most of the MEMS and sensors generally require higher repeatability and reversible electromechanical response for higher performance and efficiency, a highly flexible material is required.

Furthermore, maintaining the optical transparency and electrical properties together is a big challenge since a higher volume percentage of the filler material is generally required for enhancement in the electrical properties. As a result, the optical transparency of the flexible material degrades.

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A team of researchers led by Dr. Raj Kishora Dash, an assistant professor at the Advanced Materials and NEMS Lab., School of Engineering Sciences and Technology, University of Hyderabad has for the first time fabricated and developed an optically transparent flexible composite material with almost 88% optical transparency and high dielectric constant. The material is very flexible and it could be easily bent, twisted and stretched. Gunda Rajitha, research scholar, who has recently submitted her Ph.D. thesis under Dr. Dash supervision is co-contributor for this work.

The researchers have used a simple and facile approach to fabricate a flexible high dielectric constant composite material by employing a very low vol. % chemically treated reduced graphene oxide (RGO) as a filler material in the PDMS matrix. Using the process they obtain a uniform distribution of the RGO in the PDMS matrix and demonstrate that this composite could be utilized for the development of capacitive-based transparent flexible sensor.

“For most of the flexible composite materials, a very low optical transparency has been reported. However, the new flexible composite material shows 88% optical transparency with high dielectric constant. We are very excited about this development and our group is actively working in this area to fabricate transparent wearable sensors for different applications like transparent keyboard, switches, transparent touch sensor, bio-medical sensors and more to come”, said Dr. Dash.

This work has been published online in Sensors and Actuators A: Physical 2018,https://doi.org/10.1016/j.sna.2018.04.040