Speaker
Description
Huiling Ong1, Nurul A. Mazlan2, Glen McHale1 and Nan Gao2
1School of Engineering, The University of Edinburgh, UK
2Department of Mechanical Engineering, The University of Birmingham, UK
Low pinning surface coatings are important for smooth motion of contact lines in capillaries and microfluidics. One approach is to use slippery liquid-infused porous surfaces (SLIPS) to create a continuous liquid-lubricating layer [1]. However, these layers tend to be hydrophobic, and the infused liquid lubricant can leak or deplete over time, or cause toxicity issues depending on the lubricant. Recently, Cho et al. have presented a novel method for fabricating permanently substrate-bound molecularly mixed Slippery Covalently Attached Liquid-like Surfaces (SCALS) capable of being tuned from hydrophilic to hydrophobic over a contact angle range 40o-103o whilst retaining low contact line pinning [2]. These layers possess liquid-like behaviour with flexible polymer chains anchored only at one end to the substrate, behaving like a permanent layer of liquid lubricant, and are stable and non-toxic. Here we optimise this new approach to functionalizing surfaces and report sessile droplet contact angle and contact angle hysteresis measurements, and static and kinetic friction force measurements based on a previously reported cantilever-type experiment [3]. This approach allows the direct measurement of friction and adhesion forces in the micro-Newton (µN) range, where the water droplets were translated across the fabricated surfaces at controlled velocities spanning two orders of magnitude (0.1 to 10 mm/s). The friction force is interpreted within a strong dilute defects model [4,5]. This provides a robust platform for designing surfaces for various applications such as in medical devices, biological equipment, and marine applications.
Acknowledgments. Professor Chiara Neto and Dr. Isaac Gresham (The University of Sydney) for advice on the manufacture of mixed SCALS and The Leverhulme Trust for funding (Research Project Grant RPG-2024-339).
References
1. Wong, T.-S., Kang, S. H., Tang, S. K. Y. Y., Smythe, E. J., Hatton, B. D., Grinthal, A., & Aizenberg, J. (2011). Bioinspired self-repairing slippery surfaces with pressure-stable omniphobicity. Nature, 477(7365), 443–447.
2. Cho, J. H., Gresham, I. J., Katselas, A., McHale, G., & Neto, C. (2025). Design of mixed PDMS-mPEG Slippery Covalently Attached Liquid-Like Surfaces. ACS Applied Materials & Interfaces, 17(20), 30316–30326.
3. Gao, N., Geyer, F., Pilat, D. W., Wooh, S., Vollmer, D., Butt, H.-J., & Berger, R. (2018). How drops start sliding over solid surfaces. Nature Physics, 14(2), 191–196.
4. Reyssat, M., & Quéré, D. (2009). Contact Angle hysteresis generated by strong dilute defects. Journal of Physical Chemistry B, 113(12), 3906–3909. https://doi.org/10.1021/jp8066876
5. Hu, R., McHale, G., Barrio-Zhang, H., Neto, C., & Wells, G. G. (2025). Understanding contact angle hysteresis: The case of slippery micropatterned biphilic liquid-Like surfaces. Langmuir, 41(42), 28579–28591.