Effect of Surrounding Solvents on Interfacial Behavior of Gallium-Based Liquid Metal Droplets

Abstract

Gallium-based liquid metal (GaLM) alloys have been extensively used in applications ranging from electronics to drug delivery systems. To broaden the understanding and applications of GaLMs, this paper discusses the interfacial behavior of eutectic gallium-indium liquid metal (EGaIn) droplets in various solvents. No significant difference in contact angles of EGaIn is observed regardless of the solvent types. However, the presence or absence of a conical tip on EGaIn droplets after dispensing could indirectly support that the interfacial energy of EGaIn is relatively low in non-polar solvents. Furthermore, in the impact experiments, the EGaIn droplet bounces off in the polar solvents of water and dimethyl sulfoxide (DMSO), whereas it spreads and adheres to the substrate in the non-polar solvents of hexane and benzene. Based on the dimensionless We number, it can be stated that the different impact behavior depending on the solvent types is closely related to the interfacial energy of EGaIn in each solvent. Finally, the contact angles and shapes of EGaIn droplets in aqueous buffer solutions with different pH values (4, 7, and 10) are compared. In the pH 10 buffer solution, the EGaIn droplet forms a spherical shape without the conical tip, representing the high surface energy. This is associated with the dissolution of the “interfacial energy-reducing” surface layer on EGaIn, which is supported by the enhanced concentration of gallium ion released from EGaIn in the buffer solution.

Eutectic Gallium–Indium Nanoparticles for Photodynamic Therapy of Pancreatic Cancer

“…As the hours of incubation increased, the pH 9 had a steady release in BPD and peaked at 24 h with 69% of total BPD being released. This could be due to the reduction of gallium oxide to gallium ions by the basic buffer solution prompting the release of BPD . On the other hand, pH 6 and 7.4 did not have significant BPD release till 6 h and had 32 and 26% drug release at 24 h, respectively.…”

“…The AFM methodology is considerably different than SEM as it provides a 3D topographical image, which is used to determine the height as the diameter in the z -direction. − One of the main factors that may explain the size difference is that AFM analysis of EGaPs is done by selecting particles individually, while the SEM software measures the diameter of all particles within an image without individual selection. Another factor is that EGaPs might be flattened (wetting the surface of the substrate) due to the presence of the oxide layer, which would reduce the height and increase the width . One potential issue with SEM is that as x – y distances are used for particle diameter calculation, the lateral magnification becomes important.…”

“…Another factor is that EGaPs might be flattened (wetting the surface of the substrate) due to the presence of the oxide layer, which would reduce the height and increase the width. 68 One potential issue with SEM is that as x – y distances are used for particle diameter calculation, the lateral magnification becomes important. On AFM, lateral magnification is not an important factor since dimensions (height) are measured on the z -axis, and with lower levels of noise and higher resolution, it is a better measurement technique for nanoparticles of any size.…”

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

“…We observed a significantly different indentation response when EGaIn droplets were immersed in 0.2 M NaOH (pH = 13.3), as shown in Figure 1c. NaOH was selected because it dissolves the oxide skin at a pH of >10, 14,37,38 resulting in "skin-free" liquid EGaIn. In this case, a large "jump-in" instability occurred upon approach because of attraction forces between the liquid EGaIn and the spherical tip.…”

Transportable, Endurable, and Recoverable Liquid Metal Powders with Mechanical Sintering Conductivity for Flexible Electronics and Electromagnetic Interference Shielding

“…Generally, EGaIn micro/nanodroplets can be fabricated by sonication, microfluidic, nebulization, and shearing, which can be utilized in patterning on various substrates (e.g., polyethylene terephthalate (PET), cellulose, glass, and elastomers). Nanometerization of LMs in organic fluids or aqueous solutions can promote the deposition of LMs’ droplets onto substrates and later sintering to recover its conductivity. − Usually, EGaIn micro/nanodroplets were coated with shells (monolayer, biological macromolecule, or polymers) via chemical bonds, coordination, or polymerization to enhance the colloidal stability. However, these LMs’ nanodroplets still lack enough oxidation resistance due to the active metal atoms on their dynamic surfaces, resulting in chemical instability in various solvents …”