Role of α and δ’ phases in the piezoelectric response of in situ poled electrospun ferroelectric polyamide 11 fibers

Le résumé fourni par la source

In situ poling of amine dipoles in ferroelectric polyamide 11 (PA11) fibers directly obtained from electrospinning is demonstrated. The combined effect of thermal treatments and mechanical stretching on the crystalline phases and the crystals orientation in the electrospun fibers has been studied. The electrospun PA11 fibers exhibited oriented α and δ’ phases with Hermans orientation factor, f c , of 0.40 and 0.42, both contributing to the piezoelectric response under transverse mechanical stress (d 31 of 0.17 pC/N). Enhanced piezoelectric response was obtained when the PA11 sample was stretched at 15 % of strain ratio, that corresponds to its yield point. Once PA11 transits from elastic to plastic regime, an increase in the degree of crystallinity is observed (X c of 24.9 %), along with a transition from the triclinic phase (α) to the pseudo-hexagonal phase (δ’). The piezoelectric response was significantly increased once the material exceeded its yield point, at which a large piezoelectric coefficient d 33 of 0.37 pC/N had resulted. Thermal treatment at 100 °C of PA11 fibers also resulted in preferential crystallographic orientation α and of δ’ phase (f c of 0.47 and 0.44), which is favoured by both mechanical stretching and heat treatment. These findings reveal the strong correlation between the mechanical and thermal treatment, crystalline phases and piezoelectric performance of in situ poled electrospun PA11 fibers. • Electrospinning provides polarized PA11 fibers with in situ oriented α/δ’ phases. • A mechanism is proposed relating piezoelectricity and the α/δ’ phases roles. • Pre-stretching enhances piezoelectricity at the yielding mechanical point of fibers. • Thermal treatment improves the d 31 coefficient of PA11 electrospun fibers.

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