When contact lines remember: Surface charge and the evolving interaction with defects

Abstract

The motion of contact line plays a crucial role in both natural phenomena and industrial processes. While it is well known that surface defects influence contact line dynamics, we demonstrate that their impact depends not only on geometry, size, and composition, but also on the history of fluid interaction with the surface. Using ultrafast, high-resolution reflection microscopy, we visualized the dynamics of the three-phase contact line as successive water droplets slid across a hydrophobic surface patterned with protrusions. We observed a growing attraction between the contact line and surface defects with increasing drop number. This effect arises from the spontaneous electrification that occurs during sliding: the droplets and the surface acquire opposite charges, generating electrostatic forces that significantly influence both advancing and receding contact lines. These forces contribute more than half of the total pinning force. Our findings reveal a previously overlooked factor in drop sliding and offer new insights into the dynamics of the contact line.

References

[1] Snoeijer JH, Andreotti B. Moving contact lines: scales, regimes, and dynamical transitions. Annu Rev Fluid Mech. 2013; 45: 269-292.

[2] Perrin H, Lhermerout R, Davitt K, et al. Defects at the nanoscale impact contact line motion at all scales. Phys Rev Lett. 2016; 116:184502.

[3] Marsh JA, Cazabat AM. Dynamics of contact line depinning from a single defect. Phys Rev Lett. 1993; 71: 2433.

[4] Daniel D, Vuckovac M, Backholm M, et al. Probing surface wetting across multiple force, length and time scales. Commun Phys. 2023; 6: 152.

[5] Reyssat M, Quéré D. Contact angle hysteresis generated by strong dilute defects. J Phys Chem B. 2009; 113: 3906-3909.

[6] Perrin H, Lhermerout R, Davitt K, et al. Thermally activated motion of a contact line over defects. Soft Matter. 2018; 14: 1581-1595.

[7] Lhermerout R, Perrin H, Rolley E, et al. A moving contact line as a rheometer for nanometric interfacial layers. Nat Commun. 2016; 7:12545.

[8] Rostami P, Hormozi MA, Soltwedel O, et al. Dynamic wetting properties of PDMS pseudo-brushes: four-phase contact point dynamics case. J Chem Phys. 2023; 158:194703.

[9] Tadmor R. Line energy and the relation between advancing, receding, and young contact angles. Langmuir. 2004; 20: 7659-7664.

[10] Nadkarni GD, Garoff S. An investigation of microscopic aspects of contact angle hysteresis: pinning of the contact line on a single defect. Eur Phys Lett. 1992; 20: 523.

[11] Saal A, Straub BB, Butt HJ, et al. Pinning forces of sliding drops at defects. Eur Phys Lett. 2022; 139:47001.

[12] Lohse D, Zhang X. Surface nanobubbles and nanodroplets. Rev Mod Phys. 2015; 87: 981-1035.

[13] Tadmor R. Open problems in wetting phenomena: pinning retention forces. Langmuir. 2021; 37: 6357-6372.

[14] Butt HJ, Berger R, De Coninck J, et al. Drop friction. Nat Rev Phys. 2025; 7: 425-438.

[15] Zhang J, Ding W, Hampel U. How droplets pin on solid surfaces. J Colloid Interface Sci. 2023; 640: 940-948.

[16] Neumann AW, Good RJ. Thermodynamics of contact angles. I. Heterogeneous solid surfaces. J Colloid Interface Sci. 1972; 38: 341-358.

[17] Schwartz LW, Garoff S. Contact angle hysteresis on heterogeneous surfaces. Langmuir. 1985; 1: 219-230.

[18] Ray S, Sedev R, Priest C, et al. Influence of the work of adhesion on the dynamic wetting of chemically heterogeneous surfaces. Langmuir. 2008; 24: 13007-13012.

[19] Priest C, Sedev R, Ralston J. A quantitative experimental study of wetting hysteresis on discrete and continuous chemical heterogeneities. Colloid Polym Sci. 2013; 291: 271-277.

[20] Yatsuzuka K, Mizuno Y, Asano K. Electrification phenomena of pure water droplets dripping and sliding on a polymer surface. J Electrostat. 1994; 32: 157-171.

[21] Helseth LE, Wen HZ. Evaluation of the energy generation potential of rain cells. Energy. 2017; 119: 472-482.

[22] Li X, Bista P, Stetten AZ, et al. Spontaneous charging affects the motion of sliding drops. Nat Phys. 2022; 18: 713-719.

[23] Wang K, Li J. Electricity generation from the interaction of liquid‒solid interface: a review. J Mater Chem A. 2021; 9: 8870-8895.

[24] Knorr N, Rosselli S, Nelles G. Electrostatic surface charging by water dewetting. Langmuir. 2024; 40: 14321-14333.

[25] Wu J, Zhang M, Wang X, et al. A simple approach for local contact angle determination on a heterogeneous surface. Langmuir. 2011; 27: 5705-5708.

[26] Xiang Y, Huang S, Lv P, et al. Ultimate stable underwater superhydrophobic state. Phys Rev Lett. 2017; 119:134501.

[27] Papadopoulos P, Deng X, Mammen L, et al. Wetting on the microscale: shape of a liquid drop on a microstructured surface at different length scales. Langmuir. 2012; 28: 8392-8398.

[28] Cheng Y-T, Rodak DE, Angelopoulos A, et al. Microscopic observations of condensation of water on lotus leaves. Appl Phys Lett. 2005; 87:194112.

[29] Nosonovsky M, Bhushan B. Patterned nonadhesive surfaces: superhydrophobicity and wetting regime transitions. Langmuir. 2008; 24: 1525-1533.

[30] Paxson AT, Varanasi KK. Self-similarity of contact line depinning from textured surfaces. Nat Commun. 2013; 4: 1492.

[31] Oliver JF, Huh C, Mason SG. The apparent contact angle of liquids on finely-grooved solid surfaces—a SEM study. J Adhes. 1976; 8: 223-234.

[32] Huang JY, Lo Y-C, Niu JJ, et al. Nanowire liquid pumps. Nat Nanotechnol. 2013; 8: 277-281.

[33] De Gennes PG, Brochard-Wyart F, Quéré D. Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls, Waves. Springer; 2004.

[34] Stetten AZ, Golovko DS, Weber SA, et al. Slide electrification: charging of surfaces by moving water drops. Soft Matter. 2019; 15: 8667-8679.

[35] Ratschow AD, Bauer LS, Bista P, et al. How charges separate when surfaces are dewetted. Phys Rev Lett. 2024; 132:224002.

[36] Li X, Ratschow AD, Hardt S, et al. Surface charge deposition by moving drops reduces contact angles. Phys Rev Lett. 2023; 131:228201.

[37] Sosa MD, D'Accorso NB, Martinez Ricci ML, et al. Liquid‒polymer contact electrification: modeling the dependence of surface charges and ξ-potential on pH and added-salt concentration. Langmuir. 2022; 38: 8817-8828.

[38] Sun Q, Xu B, Du J, et al. Interfacial electrostatic charges promoted chemistry: reactions and mechanisms. Adv Colloid Interface Sci. 2025; 339:103436.

[39] Xu W, Jin Y, Li W, et al. Triboelectric wetting for continuous droplet transport. Sci Adv. 2022; 8:eade2085.

[40] Robbins MO, Joanny JF. Contact angle hysteresis on random surfaces. Eur Phys Lett. 1987; 3: 729-735.

[41] Vinod A, Barak Y, Schmid SY, et al. Measuring surface energy of solid surfaces using centrifugal adhesion balance. Phys Rev E. 2024; 110:014801.

RIGHTS & PERMISSIONS

2025 The Author(s). Droplet published by Jilin University and John Wiley & Sons Australia, Ltd.