Gallium liquid metal alloys (GaLMAs) are room temperature fluidic conductors that have recently been used to create a variety of paradigm shifting concepts in stretchable and reconfigurable electronics[1-3]. They serve as an alternative to mercury based systems because of the non-toxic nature of GaLMAs. Like many other metals, a thin native oxide skin forms spontaneously on the surface. Unlike most other metals at room temperature though, the underlying metal remains fluid with the skin serving as a viscoelastic solid which allows remarkably unprecedented fluidic structures to be constructed[4]. This oxide also has detrimental effects to fluidic behavior in microchannels because it tends to adhere to the channel walls. Traditional solutions to mitigate this adhesion behavior have been to utilize strongly acidic or basic co-fluids to continuously react with the oxide [5]. This approach results in the need to replenish the chemical reactants as well as remove byproducts from the surface, not to mention limiting application of these fluids as electronic materials. Our work takes two approaches to mitigate these effects. The first approach is to utilize an ion exchange polymer to serve as the interface to the GaLMA fluid to both deliver minute concentrations of reactant to the surface and remove undesired byproducts[6]. The second approach utilizes surface modification of the gallium oxide surface with phosphonic acids to allow molecular control of the surface chemistry and control the interfacial chemistry at a molecular level. To date, phosphonic acid treatment has only been used on solid oxide thin films such as ITO and ZnO to modify the work function for thin film electronics[7]. We leverage these surface chemistries to control the GaLMA work function and the fluidic properties simultaneously. Detailed surface spectroscopy verifies the presence of the phosphonic acid linkers on the liquid surface and AFM is used to characterize mono and multilayer film growth. [1] M. Kubo, et al. Advanced materials 2010, 22, 2749. [2] E. Palleau, S. et al. Advanced materials 2013, 25, 1589. [3] B. L. Cumby, et al., Applied Physics Letters 2012, 101, 174102. [4] M. D. Dickey, ACS Applied Materials & Interfaces 2014, 6, 18369. [5] G. Li, et al., Lab on a Chip 2014, 14, 200. [6] N. Ilyas, et al., Advanced Materials Interfaces Submitted. [7] P. J. Hotchkiss, et al., Accounts of Chemical Research 2012, 45, 337.

Surface modification of gallium liquid metal alloy interfaces

251st National Meeting (2016)

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