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September, 2018

Polymorphism, defined as the existence of several crystalline structures in a material, is of particular interest in piezoelectric polymers as functional properties may vary dramatically across different crystal phases. Crystal structure is crucial in determining the properties of piezoelectric polymers, particularly at the nanoscale where precise control of the crystalline phase is possible. In this work, we report the first microscopic mechanical and electrical characterization of Nylon-11 nanowires fabricated in distinct crystalline phases with precise control. Three different nanowire phases were prepared via the fine-tuning of a template-assisted nanoconfinement method. The mechanical and electrical properties of these nanowires were extensively explored using scanning probe microscopy techniques, namely quantitative nanomechanical mapping (QNM) and piezoresponse force microscopy (PFM), revealing differences in nanoscale properties across the different nanowires, and when compared to films with the same crystal structure. Stiff α-phase nanowires exhibited a low piezoelectric response, while relatively soft δ′-phase nanowires displayed an enhanced piezoelectric response.

This paper was featured in the 2018 Emerging Investigators Issue of Chemical Communications.

Figure: Crystal structure is crucial in determining the properties of piezoelectric polymers, particularly at the nanoscale where precise control of the crystalline phase is possible. Stiff α-phase nanowires exhibit a low piezoelectric response, while relatively soft δ′-phase nanowires displayed an enhanced piezoelectric response

Y. S. Choi, S. Kim, F. Williams, Y. Calahorra, J. A. Elliott & S. Kar-Narayan, “The effect of crystal structure on the electromechanical properties of piezoelectric Nylon-11 nanowires” Chemical Communications 54, 6863-6866 (2018)