Chloro-silane vapor assisted in-plane delamination of liquid metal films for unconventional heterogeneous wettability

Abstract

Numerous complex methods have been reported to generate heterogeneously wettable surfaces in the literature. These surfaces are well-sought in energy, water, health care, separation science, self-cleaning, biology, and other lab-on-chip applications. While most of the demonstrations of heterogeneous wettability rely on a series of complex fabrication protocols, we reveal an unconventional approach to achieving heterogeneous wettability through three simple steps (i.e., patterning, silanizing, and rinsing). Here, we show heterogeneous wettability on a planar substrate harnessing (a) the wetting and dewetting behavior of nano-textured conductive surface patterns of Gallium alloys and (b) interfacial chemical reactivity of the native surface oxides of these alloys in the presence of chloro-silane vapor. Alloys of Gallium (eGaIn and others) have emerged as one of the most promising soft metals for the fabrication of soft functional devices harnessing their surface oxides, mostly Gallium Oxide (Ga2O3). These alloys can be 2D patterned utilizing the wetting behavior of the Ga2O3, which seems impossible due to the high surface tension of the bare metal. We utilized such 2D metal patterns on the planar glass surface and exposed the patterns in chloro-silane vapors to begin our study. Chloro-silanes can alter the surface energy of different substrates (i.e., glass, silicon wafer) to offer hydrophobicity and releases Chlorine vapors which etch Ga2O3 that induces the delamination. A simple DI water rinsing operation reveals a thin hydrophilic layer on the pre-patterned area that we utilized for an open-ended microfluidic demonstration, as well. We confirmed hydrophilicity through contact angle measurements; elemental compositions, and Chlorine's presence through energy dispersive spectroscopic (EDS) analyses. We believe such an unconventional approach of achieving heterogeneous wettability has the potential for fundamental studies related to bioinspired and biomimetic applications.