Unlocking Energy Harvesting Strategies from Size Tunable Pvdf Microspheres Via Microfluidics Technology: An Interplay between Flow Rate and Electroactive Phase

Polyvinylidene fluoride (PVDF), a semi-crystalline polymer in its electroactive phase (EA), exhibits great potential due to its promising piezo-, ferro- and pyroelectric properties, making it highly suitable for extensive applications. Among various processing techniques for producing microspheres of PVDF, microfluidics stands out due to its advantages in size and shape adjustability, simplicity, and greater efficiency. Microfluidic-based techniques, specifically droplet-microfluidics, have emerged as an optimal choice, offering precise manipulation of droplet dimensions and efficient heat dissipation. This article focuses on the processing of PVDF microspheres using a microfluidic flow focussing device (MFFD) with thermal initiated off-chip polymerization technique. The MFFD is utilized to disperse uniform droplets into an oil bath, initiating the polymerization process and resulting in microspheres ranging from 126 to 754 µm in size. By fine-tuning the flow rates, we achieve precise regulation of microparticle uniformity, monodispersity, size, and shape. Furthermore, by optimizing the reaction temperature (Toil), the EA phase of PVDF microspheres is significantly enhanced, with the highest achieved fraction of 82.05% observed at Toil = 60°C. The resulting microspheres are characterized for their 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 phase of PVDF microspheres. These microspheres exhibit characteristics suitable for various applications, including surface-sensitive biological applications, energy harvesting, and energy storage devices. To demonstrate its viability, a flexible piezoelectric device made from PVDF microspheres was fabricated and tested for its electrical outputs in response to finger and foot tapping movements. Promising outcomes, such as an open circuit voltage of ~23.5V, suggest its potential utility as self-powered wearable sensors and devices. Overall, this article highlights the potential of combining microfluidics, polymer science, and artificial intelligence to advance the field of smart materials.