Exploiting flow manipulation to engineer the electroactive phase for improved piezo response in size tunable PVDF microspheres via microfluidic technology

Abstract

Polyvinylidene fluoride (PVDF), a semi-crystalline polymer with remarkable piezo-, ferro-, and pyroelectric properties in its electroactive phase (EA), holds significant potential. Microfluidic-based techniques, particularly droplet-microfluidics, have become a preferred method for producing PVDF microspheres, offering advantages like size and shape adjustability, simplicity, efficiency, and effective heat dissipation. This article focuses on employing a microfluidic flow focussing device (MFFD) with thermal initiated off-chip polymerization to process PVDF microspheres. The MFFD disperses uniform droplets into an oil bath, initiating polymerization and yielding microspheres ranging from 126 to 754 µm. Fine-tuning flow rates achieves precise control over microparticle uniformity, monodispersity, size, and spherical shape. Optimization of reaction temperature (Toil) significantly enhances the EA phase, reaching 82.05 % at Toil = 60 °C. The resulting microspheres are comprehensively characterized for structure, morphology, composition, phase, hydrophobicity, biocompatibility, thermal, and piezoelectric properties. Additionally, machine learning analysis is employed to predict the mean diameter as well as the EA and β-phase of PVDF microspheres. A flexible piezoelectric device made from PVDF microspheres, demonstrating an open circuit voltage of ∼23.5 V in response to finger and foot tapping movements, showcases potential for self-powered wearable sensors and devices. This study underscores the synergy of microfluidics, polymer science, and artificial intelligence in advancing smart materials.