Dual Structure Reinforces Interfacial Polarized MXene/PVDF-TrFE Piezoelectric Nanocomposite for Pressure Monitoring

Abstract

The emerging interfacial polarization strategy exhibits applicative potential in piezoelectric enhancement. However, there is an ongoing effort to address the inherent limitations arising from charge bridging phenomena and stochastic interface disorder that plague the improvement of piezoelectric performance. Here, we report a dual structure reinforced MXene/PVDF-TrFE piezoelectric composite, whose piezoelectricity is enhanced under the coupling effect of interfacial polarization and structural design. Synergistically, molecular dynamics simulations, density functional theory calculations and experimental validation revealed the details of interfacial interactions, which promotes the net spontaneous polarization of PVDF-TrFE from the 0.56 to 31.41 Debye. The oriented MXene distribution and porous structure not only tripled the piezoelectric response but also achieved an eightfold increase in sensitivity within the low-pressure region, along with demonstrating cyclic stability exceeding 20,000 cycles. The properties reinforcement originating from dual structure is elucidated through the finite element simulation and experimental validation. Attributed to the excellent piezoelectric response and deep learning algorithm, the sensor can effectively recognize the signals of artery pulse and finger flexion. Finally, a 3×3 sensor array is fabricated to monitor the pressure distribution wirelessly. This study provides an innovative methodology for reinforcing interfacial polarized piezoelectric materials and insight into structural designs.

1. Introduction

Piezoelectric materials play a critical role in sensing and actuating [1, 2]. Due to the flexibility, biocompatibility, and lightweight characteristics, polyvinylidene fluoride (PVDF) and its copolymers are widely utilized in wearable sensors, medical actuators and various flexible electronic devices [3–8]. Although PVDF exhibits reliable piezoelectricity and ferroelectricity, achieving these qualities requires intensive processing [9–13]. In comparison, poly(vinylidene fluoride-ran-trifluoroethylene) (PVDF-TrFE) features enhanced polarization capability, improved phase stability, and a higher piezoelectric coefficient, which can be attributed to the inclusion of TrFE units on the molecular chains [12, 14]. However, despite these advantages, substantial efforts are still required to further enhance the piezoelectric properties of PVDF-TrFE, as there remains a significant performance gap compared to ceramic piezoelectric materials.

Numerous studies have been dedicated to enhancing the piezoelectric properties of PVDF-TrFE. Traditional approaches include incorporating fillers with high piezoelectricity or high dielectric constant into the matrix, as well as employing preparation methods that utilize in situ fields—such as electrospinning, hot pressing, and electrohydrodynamic printing—to improve material performance [15, 16]. In principle, polarization enhancement is the critical approach for boosting piezoelectric properties [17–20]. Up to now, tremendous efforts have been focused on structural design at the molecular scale, including chemical modification [20, 21], component regulation [14], and doping with functional fillers [22, 23].

The method of templating polarization has been investigated to induce interfacial polarization via the interactions between nanofillers and PVDF-TrFE at the interface [24–27]. It turns out to be a prospective pathway to realize piezoelectric performance enhancement by interfacial polarization, emphasizing the crucial role of a well-defined polarized interface in material design [28–31]. MXene, a burgeoning two-dimensional material, features a high aspect ratio and significant specific surface area [32–34]. More importantly, MXene possesses abundant terminal functional groups that provide a polar surface, making it an ideal candidate for creating a large well-polarized interface within the matrix to boost piezoelectric performance [35]. However, the random distribution of MXene and the stochastic interface disorder remain challenges that need to be addressed.