Highly flexible smart electronic devices are susceptible to electromagnetic interferences effects, cyclic fatigue, corrosion and contamination, that requires urgent countermeasures not only to enhance their functionality but also to reduce their risk on the human health and environment at large. To this end, researchers have developed numerous materials such as metal nanowires to overcome these problems. In particular, silver nanowire films have been intensively investigated owing to their excellent optical, electrical and mechanical properties. However, silver nanowires experience numerous drawbacks when used as highly conducting materials attributed majorly to poor conductance between themselves and weak attachment to the substrate. This hinders their overall efficiency and fabrication and thus alternative strategies should be put in place to address these issues.
In recent research, Jong Han Choi (Research scientist) and Dr. Sang Woo Kim from the Korean Institute of Science and Technology in collaboration with Kwan Young Lee from the Korean University investigated the feasibility of using ultra-bendable and durable graphene-urethane composites/silver nanowires in flexible transparent electrodes for effective electromagnetic interference shielding. These materials with a high figure of merit ware fabricated on a polyethylene terephthalate substrate via wet sintering of silver nanowires and hydrophobic silane-functionalized graphene urethane rubber coat. The characteristics of these nanowire films in terms of cyclic bending electromagnetic interference shielding effectiveness and durability were investigated. Their work is published in the research journal, Composites Part B: Engineering.
Results showed that the sintered silver nanowires exhibited a significantly small threshold radius of curvature, 17 times lower than that of indium tin oxide, highly suitable for foldable displays. Consequently, hydrophobic-silane functionalized graphene nanoflake-embedded urethane composite overcoat reported a reduced threshold radius of curvature of 0.43mm and a corresponding increase in the cyclic-bending durability purportedly due to the improved adhesion between the substrate and the nanowire.
A bending test involving 300,000 cycles at a threshold radius of curvature of 2 mm was performed. The authors observed no change in the electrical resistance of the hydrophobic silane/ graphene-urethane/ sintered silver nanowires (HS/G-UR/SSN) film with a 25-µm thick PET substrate. The contact angle also remained constant due to hydrophobic silane-functionalized composite coat. Furthermore, the electromagnetic interference shielding effectiveness of the fabricated film also improved after the bending test cycles. The optoelectronic performance of the nanowire films was evaluated by calculating the figure of merit based on the sheet resistance and transmittance in the bulk region and was found to be better than those previously reported conducting materials.
In a nutshell, the scholars successfully fabricated transparent polymer composite/ silver nanowire films with improved nanowire networking and hydrophobic graphene-urethane composite coating highly desirable for durable repetitive bending and humidity. With excellent flexibility, transparency, electromagnetic interference shielding effectiveness, humidity and bending durability properties, the HS/G-UR/SSN films are a promising strategy for developing highly flexible devices suitable for use in transparent electrodes and/ or electromagnetic interference shields. Dr. Sang Woo Kim, the lead author in a statement to Advances in Engineering noted that the study is versatile and the approach can be used in other conductive transparent materials.
Choi, J.H., Lee, K.Y., & Kim, S.W. (2019). Ultra-bendable and durable Graphene–Urethane composite/silver nanowire film for flexible transparent electrodes and electromagnetic-interference shielding. Composites Part B: Engineering, 177, 107406.