Interplay between Interfacial Energy, Contact Mechanics, and Capillary Forces in EGaIn Droplets

Abstract

Eutectic gallium−indium (EGaIn) is increasingly employed as an interfacial conductor material in molecular electronics and wearable healthcare devices owing to its ability to be shaped at room temperature, conductivity, and mechanical stability. Despite this emerging usage, the mechanical and physical mechanisms governing EGaIn interactions with surrounding objectsmainly regulated by surface tension and interfacial adhesionremain poorly understood. Here, using depth-sensing nanoindentation (DSN) on pristine EGaIn/GaO x surfaces, we uncover how changes in EGaIn/substrate interfacial energies regulate the adhesive and contact mechanic behaviors, notably the evolution of EGaIn capillary bridges with distinct capillary geometries and pressures. Varying the interfacial energy by subjecting EGaIn to different chemical environments and by functionalizing the tip with chemically distinct self-assembled monolayers (SAMs), we show that the adhesion forces between EGaIn and the solid substrate can be increased by up to 2 orders of magnitude, resulting in about a 60-fold increase in the elongation of capillary bridges. Our data reveal that by deploying molecular junctions with SAMs of different terminal groups, the trends of charge transport rates, the resistance of monolayers, and the contact interactions between EGaIn and monolayers from electrical characterizations are governed by the interfacial energies as well. This study provides a key understanding into the role of interfacial energy on geometrical characteristics of EGaIn capillary bridges, offering insights toward the fabrication of EGaIn junctions in a controlled fashion.

Interfacial interaction-induced super-wettability of gallium-based liquid metals: a review

“…Notably, some tools 118 can be used to analyze and compare the wetting behavior of both pure LM and LM covered with the oxide layer. In the absence of the oxide layer, EGaIn easily deforms and develops capillary force when contacting with the solid substrate, resulting in a high adhesion of EGaIn on the solid substrate.…”

Smart Eutectic Gallium–Indium: From Properties to Applications

“…[50] Recently, Amini et al investigated the physical and mechanical interactions of EGaIn with its native Ga 2 O 3 layer by depth-sensing nanoindentation (DSN). [61] They found that the oxide layer is repeatedly ruptured and reformed during the flow, and its existence and chemical properties are directly related to the environment (air or various water environments) and strongly influence the mechanical and interfacial adhesion responses of EGaIn.…”

Charge Transport across Proteins inside Proteins: Tunneling across Encapsulin Protein Cages and the Effect of Cargo Proteins

“…. The EGaIn surface is coated with a thin, few nm-thick GaO x layer that provides stability to the junction [50,51]. All the protein structure schemes are made with Chimera software [52] based on the structure of Tm encapsulin (PDB 3DKT) [42].…”

“…(g) Equus ferus caballus spleen apoferritin cage structure Illustration of a complete EncH{FLP} tunneling junction with Enc immobilized on Au through lipoic acid linker SAM and EGaIn top contact of the form Au/SAM//EGaIn (where '/' and '//' re sent covalent and van der Waals interactions, respectively). The EGaIn surface is coated with a thin, few nm-thick GaOx layer that provides stability to the junction[50,51]. All the protein stru ture schemes are made with Chimera software[52] based on the structure of Tm encapsulin (P 3DKT)[42].…”