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Autonomous Thermal-Oxidative Composition Inversion (TOCI) and Texture Tuning of Liquid Metal Surfaces Joel Cutinho, Boyce S. Chang, Stephanie Oyola-Reynoso, Jiahao Chen, S. Sabrina Akhter, Ian D. Tevis, Nelson J. Bello, Andrew Martin, Michelle C. Foster, and Martin M. Thuo ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.8b01438 • Publication Date (Web): 12 Apr 2018 Downloaded from http://pubs.acs.org on April 12, 2018
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ACS Nano
Autonomous Thermal-Oxidative Composition Inversion (TOCI) and Texture Tuning of Liquid Metal Surfaces Joel Cutinho1, Boyce S. Chang1, Stephanie Oyola-Reynoso1, Jiahao Chen1,2, S. Sabrina Akhter3, Ian D. Tevis1, Nelson J. Bello3, Andrew Martin1, Michelle C. Foster3, Martin M. Thuo1,2,4*
1
Department of Materials Science and Engineering, Iowa State University, 2220 Hoover Hall,
Ames, IA 50011 USA 2
Micro-electronic research center, Iowa State University, 133 Applied Sciences Complex I, 1925
Scholl Road, Ames, IA 50011 USA 3
Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Blvd., Boston,
MA 02169 USA 4
Biopolymer and Bio-composites Research Team, Center for Bioplastics and Bio-composites,
Iowa State University, 1041 Food Sciences Building, Ames, IA 50011 USA
1 ACS Paragon Plus Environment
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ABSTRACT Droplets capture an environment-dictated equilibrium state of a liquid material. Equilibrium, however, often necessitates nanoscale interface organization especially with formation of a passivating layer. Herein, we demonstrate that this kinetics-driven organization may predispose a material to autonomous thermal-oxidative composition inversion (TOCI) and texture reconfiguration under felicitous choice of trigger. We exploit inherent structural complexity, differential reactivity, and metastability of the ultra-thin (~0.7-3 nm) passivating oxide layer on eutectic gallium-indium (EGaIn, 75.5 % Ga, 24.5% In w/w) core-shell particles to illustrate this approach to surface engineering. Two tiers of texture can be produced after ca. 15 minutes of heating with the first evolution showing crumpling while the second is a particulate growth above the first uniform texture. The formation of tier 1 texture occurs primarily due to diffusiondriven oxide build-up which, as expected, increases stiffness of the oxide layer. The surface of this tier is rich in Ga, akin to the ambient formed passivating oxide. Tier 2 occurs at higher temperature due to thermal triggered fracture of the now thick and stiff oxide shell. This process leads to inversion in composition of the surface oxide due to higher In content on the tier 2 features. At higher temperatures (≥800 °C), significant changes in composition leads to solidification of the remaining material. Volume change upon oxidation and solidification leads to a hollow structure with a textured surface and faceted core. Controlled thermal treatment of liquid EGaIn, therefore leads to tunable surface roughness, composition inversion, increased stiffness in the oxide shell, or a porous solid structure. We infer that this tunability is due to structure of the passivating oxide layer that is driven by differences in reactivity of Ga and In, and requisite enrichment of the less reactive component at the metal-oxide interface. KEYWORDS 2 ACS Paragon Plus Environment
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ACS Nano
passivating oxide, Composition inversion, surface engineering, liquid metal, thermal oxidation, TOCI, nano-interface
The shape and surface of liquid droplets are, by definition, a manifestation of a thermodynamically equilibrated state of fluid material(s).1-2 Mechanical equilibrium, however, requires that pressure in the droplet be higher than its environment—the so-called Laplace pressure jump condition3 which is size dependent (∆P=2γint/r; where γint =interfacial surface tension, r =radius).3 In a homogeneous non-reactive liquid, the nature of the interface is dominated by this pressure jump condition. For high vapor pressure homogeneous liquids, these interfaces are binary; that is, liquid dominates across the Gibbs dividing plane hence a positive interface excess, Γi, ≥0. Similarly, in low vapor pressure liquids, Γi
