Polyelectrolyte mixture enables electrowetting liquid lens with large optical power tuning range

Abstract

Electrowetting liquid lenses have aroused considerable interest among researchers in a variety of industrial applications and wetting sciences. However, conventional electrowetting liquid lenses face significant limitations in their optical power tuning range due to contact angle saturation. To address this issue, our research introduces a polyelectrolyte mixture (PM) composed of ammonium polyphosphate and potassium chloride, which enables a broad optical power tuning range for electrowetting liquid lenses. Through a comprehensive analysis involving viscosity, Raman spectrum, and contact angle measurements, we offer additional insights into the interdisciplinary mechanism of the PM in enhancing the electrowetting effect. Our investigation elucidates how the conformation of the polyelectrolyte and the formation of hydrogen bonds at varying concentrations can impact the electrowetting gain. By optimizing the electrowetting concentration of the PM (12.5 wt. % ammonium polyphosphate and 7.5 wt. % potassium chloride), we achieve a liquid lens with an extensive tuning range (−37.97 to +18.71 D) at 0–45 V, featuring a substantial aperture (6.4 mm) and a low threshold voltage (10 V). This PM formulation effectively mitigates contact angle saturation, thereby offering promising applications and paving the way for the development of liquid lenses with a significantly enhanced optical power tuning capacity.