Conversion of Polymer Surfaces into Nonwetting Substrates for Liquid Metal Applications

Abstract

Liquid metal-based applications are limited by the wetting nature of polymers toward surface-oxidized gallium-based liquid metals. This work demonstrates that a 120 s CF4/O2 plasma treatment of polymer surfacessuch as poly­(dimethylsiloxane) (PDMS), SU8, S1813, and polyimideconverts these previously wetting surfaces to nonwetting surfaces for gallium-based liquid metals. Static and advancing contact angles of all plasma-treated surfaces are >150°, and receding contact angles are >140°, with contact angle hysteresis in the range of 8.2–10.7°, collectively indicating lyophobic behavior. This lyophobic behavior is attributed to the plasma simultaneously fluorinating the surface while creating sub-micron scale roughness. X-ray photoelectron spectroscopy (XPS) results show a large presence of fluorine at the surface, indicating fluorination of surface methyl groups, while atomic force microscopy (AFM) results show that plasma-treated surfaces have an order of magnitude greater surface roughness than pristine surfaces, indicating a Cassie–Baxter state, which suggests that surface roughness is the primary cause of the nonwetting property, with surface chemistry making a smaller contribution. Solid surface free energy values for all plasma-treated surfaces were found to be generally lower than the pristine surfaces, indicating that this process can be used to make similar classes of polymers nonwetting to gallium-based liquid metals.

Acoustic wave-driven oxide dependant dynamic behavior of liquid metal droplet for inkjet applications

“…There have been a few methods to remove the oxide layer to have the non-wetting property recovered or overcome the wetting problem, such as making a lyophobic and non-wettable surface against the oxidized liquid metal [22][23][24][25]. Most representative method to have a non-wetting property of gallium-based liquid metal is to treat Hydrochloric acid (HCl) to the oxide layer of liquid metal [26].…”

1000 °C High-Temperature Wetting Behaviors of Molten Metals on Laser-Microstructured Metal Surfaces

“…Recently, molten metals have also been proposed to be potential novel materials in various fields, such as newly developed batteries and nuclear fusion. − The wetting of molten metals on various substrate surfaces has a great impact on related processes and applications, significantly affecting the processing feasibility and product performance. However, only few literature studies focused on the wettability of molten metals at high temperatures (e.g., 1000 °C) compared with the wettability studies on more common liquids under more gentle conditions, such as water and low-melting-point liquid metals at room temperature. − Various simulations have been performed to predict the probable wetting behaviors of molten metals on various substrates, − but practical observations remain scarce due to the availability of materials and the strict environmental requirements. Among the restricted experimental work, researchers prefer to improve the wettability of molten metals with several kinds of solid surfaces for better performance in welding, brazing, metal-based composite formation, and lithium battery preparation. − ,− For example, Wu et al proposed a method to enhance the wettability of a kind of room-temperature gallium-based liquid metal on polyacrylate surfaces for a better connection, Fan et al modified the wetting and spreading behaviors of Sn on the SiC surface by changing the content of the alloying element Cr, Li et al enhanced the wettability of molten high manganese steel with Ni–Co-coated ZTA ceramic particles to strengthen the abrasive wear resistance of the composites, and Sui et al studied the wetting ability of molten Ce and Cu–Ce alloy on various carbon materials.…”

Controlling the oxidation and wettability of liquid metal via femtosecond laser for high-resolution flexible electronics

“…Building wetting/dewetting surfaces by an ultrafast laser is utilized for forming and transferring liquid metal patterns ( Joshipura et al, 2018 ; Pan et al, 2018 ; Zhang et al, 2020b ; Yong et al, 2020 ), which not only owns remarkable flexibility but also presents high resolution. Controlling the surface morphology is the key to realizing a wetting/dewetting surface for liquid metal ( Kramer et al, 2014 ; Babu et al, 2021 ; Johnston et al, 2022 ). For instance, Joshipura et al (2018) proposed a rough spray-coating and laser scanning method to form liquid metal patterns.…”