Electrowetting-on-dielectric behavior of micro-nano hierarchical SiO2 layers decorated with noble metals

Abstract

The performances of electrowetting-on-dielectric (EWOD) devices were investigated using micro-nano hierarchical structures of pristine and noble metal-decorated SiO2 layers, with the entropy wetting model. The SiO2 layers were prepared by an electrospray technique, and noble metals were decorated by UV irradiation. In addition, a thin Teflon coating was applied to enhance their initial hydrophobicity. The initial water contact angle (WCA) value of the Pd-decorated SiO2 (Pd-SiO2) and Ag-decorated SiO2 (Ag-SiO2) layers was 165 degrees, while that of the Au-decorated SiO2 (Au-SiO2) and pristine SiO2 layers was 154 degrees. Different external voltages (up to 200 V) were used to investigate the EWOD behavior of the fabricated layers. In all cases, the WCA decreased with increasing applied voltage. Under 200 V (maximum applied voltage), WCA values of 129, 120, 115, and 102 degrees were measured for pristine SiO2, Pd-SiO2, Ag-SiO2, and Au-SiO2 layers, respectively. Moreover, the EWOD properties of the noble metal-decorated layers were studied in the presence of dodecane oil. At 200 V, the WCAs of the Pd-SiO2, Ag-SiO2, Au-SiO2, and layers were 134, 97 and 100 degrees, respectively. Finally, we applied the entropy wetting model to further understand the results of the EWOD experiments.