Effect of Stretching on Crystalline Structure, Ferroelectric and Piezoelectric Properties of Solution-Cast Nylon-11 Films

Abstract

Compared to polyvinylidene fluoride (PVDF) and its copolymers, castor-oil-derived nylon-11 has been less explored over the past decades, despite its excellent piezoelectric properties at elevated temperatures. To utilize nylon-11 for future sensor or vibrational energy harvesting devices, it is important to control the formation of the electroactive δ′ crystal phase. In this work, nylon-11 films were first fabricated by solution-casting and were then uniaxially stretched at different stretching ratios (SR) and temperatures (Ts) to obtain a series of stretched films. The combination of two-dimensional wide-angle X-ray diffraction (2D-WAXD) and differential scanning calorimetry (DSC) techniques showed that the fraction of the δ′ crystal phase increased with the stretching ratio and acquired a maximum at a Ts of 80 °C. Further, it was found that the ferroelectric and piezoelectric properties of the fabricated nylon-11 films could be correlated well with their crystalline structure. Consequently, the stretched nylon-11 film stretched at an SR of 300% and a Ts of 80 °C showed maximum remanent polarization and a remarkable piezoelectric coefficient of 7.2 pC/N. A simple piezoelectric device with such a nylon-11 film was made into a simple piezoelectric device, which could generate an output voltage of 1.5 V and a current of 11 nA, respectively.

Polyvinylidene fluoride, an advanced futuristic smart polymer material: A comprehensive review

“…Thermoplastic materials such as resins and epoxy are the best examples of amorphous polymers. 38 At the same time,…”

“…The primary mechanism behind adding fillers is usually polar and capable of interacting with CH 2 groups of PVDF. 38,[135][136][137] The main advantage of two-phase materials is their low acoustic impedance and dielectric constant. value, making it more suitable for flexible sensors.…”

“…It was also reported that adding a few organic and inorganic nanofillers like Barium titanate, Zinc oxide (ZnO), graphene (Gr), and graphene oxide (GO) could also make the composite with two‐phase material. The primary mechanism behind adding fillers is usually polar and capable of interacting with CH 2  groups of PVDF 38,135–137 . The main advantage of two‐phase materials is their low acoustic impedance and dielectric constant.…”

“…Amorphous polymers are those, which do not exhibit any crystalline structures in X‐ray experiments. Thermoplastic materials such as resins and epoxy are the best examples of amorphous polymers 38 . At the same time, Semicrystalline materials such as PVDF have plenty of excellent melting points, which do not soften with rise in temperature and remain in solid form and change into low viscosity liquid by absorbing heat 39,40 .…”

Recent Progress of Wearable Piezoelectric Pressure Sensors Based on Nanofibers, Yarns, and Their Fabrics via Electrospinning

“…[ 188 ] Among these, nylon‐11 owns good piezoelectric performance with piezoelectric charge constant d31 ranging from 3 to 15 pC N −1 , [ 189 ] which can be modified via various strategies, such as poling, stretching, sintering. [ 190 ] The δ ′‐phase nylon‐11 fiber was first reported recently from a designed nylon‐11 solution via electrospinning. [ 42 ] Acetone was added to the nylon solution to promote the rapid exhaustion of the solvent during preparation, as the strong hydrogen bond can be formed between acetone and trifluoroacetic acid (TFA) with the bonding of nearly −10 kcal mol −1 .…”