A newly developed technology in the form of a piezoelectric nanogenerator is regarded as a promising energy harvesting device. From previous studies, piezoelectric materials with perovskite structures or polyvinylidene fluoride polymers have shown good device efficiency in terms of output signals and piezoelectric response.
However, at higher temperatures, piezoelectric polymeric materials in particular are susceptible to melting or possess low electromechanical responses, leading to a need for developing piezoelectric materials that can provide high output signals and responses at a wider temperature range of operation.
A new research led by Dr. Sohini Kar-Narayan and published in the journal, Advanced Functional Materials, discusses the development of Nylon-11 nanowires by a capillary wetting process in the confines of anodized aluminum oxide templates.
They developed Nylon-11 nanowire arrays from Nylon-11 pellets via a template wetting process followed by characterization and study of morphological features of the released and template-protected Nylon-11 nanowires. The fabrication of the nanogenerator was also discussed.
The authors with the aid of scanning electron microscopy images discovered that during the capillary wetting process of Nylon-11 solution in formic acid, an optimum solution concentration of 10 wt% possessed the highest growth length of Nylon-11 nanowires within the anodized aluminum oxide templates. Some of the Nylon-11 nanowire arrays were detached easily from the template using phosphoric acid and they rolled into flexible mats, aiding in the further characterization of these nanowire arrays.
Results from differential scanning calorimetry showed two peaks of melting temperature for both the released and template-protected Nylon-11 nanowires compared to the parent Nylon-11 pellets which had a single melting temperature peak. During cooling, the Nylon-11 nanowires maintained a higher crystallization temperature, indicating their functionality in a wider temperature range of operation.
The authors when observing the temperature dependence of dielectric permittivity of the Nylon-11 nanowires showed no dielectric anomaly up to their melting temperature peak, thereby erasing any possibility of Curie transition that would be detrimental to piezoelectric performance.
The Nylon-11 nanowire-based nanogenerator, when lightly impacted at an amplitude and frequency of 0.5mm and 5Hz respectively, had an output open circuit voltage of 1V and short-circuit current of 100nA. An increase in output power density was also visualized as a result of increase in applied frequency and amplitude. It also had high thermal stability when tested up to temperatures of 150°C. This piezoelectric nanogenerator with Nylon-11 nanowires maintained its responsive performance despite being cooled controlled back to room temperature (20°C).
The Nylon-11 nanogenerators also possessed good fatigue performance as no changes were observed in the open circuit voltage and structural features of the Nylon-11 nanowires over prolonged use. An intrinsic energy conversion efficiency of 11.5% was also attained by the template-grown Nylon-11 nanowires. Dr. Kar-Narayan comments that “the realization of highly crystalline Nylon-11 nanowires using a simple template-wetting process and their integration into piezoelectric energy harvesters that can operate over a significant temperature span and with good device reliability opens up the prospect of using these devices in many practical situations at relatively low cost, for example in future electronic textiles or wearable electronics”.
In this study the authors were able to develop a low-cost polymer-based piezoelectric generator for energy harvesting devices that can certainly operate efficiently at high temperatures.
Datta, A., Choi, Y.S., Chalmers, E., Ou, C., Kar-Narayan, S. Piezoelectric Nylon-11 Nanowire Arrays Grown by Template Wetting for Vibrational Energy Harvesting Applications, Advanced Functional Materials 27 (2017) 1604262.
Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK.Go To Advanced Functional Materials