Is There a Relationship between Surface Wettability of Structured Surfaces and Lyophobicity toward Liquid Metals?

Abstract

The liquid metal lyophobicity of a rough substrate was, in previous articles, found to be rather independent on the surface wettability. In this article, we scrutinize the impact of surface wettability of a structured (rough) surface on the liquid metal wettability and adhesion. As a model system, a structured diamond coating was synthesized and modified by air plasma. We show that surface wettability (surface free energy) does not play a prominent role for static contact angle measurements and for the liquid metal repelling properties of the diamond coating in droplet impact experiments. In contrast, roll off angles and repeated deposition experiments illustrate that the increased hydrophilicity impacts the long-term liquid metal repellency of our coating. Liquid metal adhered after around 50 deposition/removal cycles on the hydrophilic diamond coating, while no liquid metal adhesion was visible after 100 cycles on the hydrophobic diamond coating, illustrating the fundamental role for the adhesion of liquid metal. The effect of repeated deposition in conjunction with gentle applied force was employed for coating the liquid metal lyophobic (hydrophilic) diamond coating with a thin liquid metal layer. The observed effect may find application in flexible electronics and thermal management systems as a means to improve interfacing of the liquid metal with conductive non-metal coatings.

Surface Tension of the Oxide Skin of Gallium-Based Liquid Metals

“…The liquid metal was extruded at a speed of 2 mL/min and droplet volumes between 30 and 1000 μL were generated. The liquid metal was passed through a fluorocarbon syringe tip, led by a microfluidic tube equipped with a fluorocarbon finish (self-built) toward the substrate surface and deposited without an impact on different surfaces, such as glass slide, poly­(tetrafluoroethylene) (PTFE), or liquid metal-phobic (hydrophobic and structured) diamond coating (see refs , , and for synthesis, structure, and water and liquid metal wettability of the diamond-coated substrate).…”

“…The left image is the image taken using a contact angle microscope (droplet shape), the second image (middle) denotes the side view taken using a camera, and the right image is the top view taken with a camera. Droplets with volumes of (a) 30 surface tension of a liquid alloy depends on its composition and the composition at the surface, in particular. 45 Therefore, we envisage that the surface tension of the liquid metal oxide (predominantly gallium oxide) is lower than the surface tension of liquid gallium (values between 705 and 730 mN/m at 303 K 46,47 ) and also likely lower than that of galinstan (≈600 mN/m).…”

Ultrathin Diamond Nanofilms—Development, Challenges, and Applications

“…One of the biggest and most active fields of the diamond research community is the research on the conductive diamond in areas, such as high power, high frequency and high temperature electronics, [214,215] electrochemistry and electrochemical sensors, [32,[216][217][218][219][220][221][222][223][224][225] supercapacitors, [181,223,226,227] interface material for liquid metal, [1,228] photochemistry, [229] and optically transparent electrodes (OTEs). Recent reviews on conductive diamond coatings, their synthesis, properties, and applications are available.…”

“…[130,131] For example, such coatings endowed with electric conductivity are interesting for interfacing with the liquid metal for all-soft devices due to the chemical inertness of the diamond coating toward the liquid metal. [1,228]…”

Liquid Metal Based Nano-Composites for Printable Stretchable Electronics

“…Nevertheless, it still remains an on-going challenge to directly process or pattern LM materials [ 16 ]. For example, due to its high surface tension, LM is maintained as droplets or particles in most cases [ 17 ], which leads to the weak interface compatibility between liquid metal and substrates. The poor substrate adaptability of LM materials causes an obvious mismatch between the actual design pattern and a loss in the printing speed, and may damage the printed products.…”