Electrowetting on swollen dielectric-hydrophobic composite PDMS film for digital microfluidics

Abstract

Polydimethylsiloxane (PDMS), a commonly used material, serves as both a dielectric layer and a hydrophobic surface in digital microfluidics (DMF) systems. However, its low dielectric constant results in suboptimal electrowetting-on-dielectric (EWOD) performance, limiting its application in DMF systems. In this study, a novel dielectric-hydrophobic integrated film, termed swollen composite PDMS (S-CPDMS), was developed. This film was fabricated by combining the ferroelectric polymer Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) with PDMS and enhancing surface hydrophobicity and smoothness through the application of silicone oil as a liquid lubricant. Experimental results demonstrated that the S-CPDMS film exhibits excellent hydrophobicity, high optical transparency, anti-biofouling properties, and smooth sliding performance. The effects of film composition, applied voltage frequency, and vertical placement time after silicone oil injection on its EWOD behavior were systematically investigated. The findings revealed that the S-CPDMS film achieves optimal EWOD performance when the P(VDF-TrFE) to PDMS ratio is 3:1. Furthermore, under a 1 kHz square wave alternating current (AC), the droplets on the film exhibited strong EWOD responsiveness and high reversibility. Using the S-CPDMS film, a DMF device was constructed, successfully enabling droplet manipulation in both open and closed environments. Finally, glucose colorimetric reactions were successfully performed in the DMF device utilizing the S-CPDMS film. This dielectric-hydrophobic integrated film offers a simple and cost-effective solution for integrating dielectric and hydrophobic layers in DMF systems, opening new possibilities for developing lab-on-a-chip platforms.