Spontaneous charge separation at receding contact lines causes contact angle hysteresis

Contact angle hysteresis is one of the most important phenomena in wetting. Despite many known contributions and corresponding theories, some observations still remain unexplained. In recent years, slide electrification – the spontaneous charge separation at receding contact lines – has sparked increased interest. Here, we show that electrostatic interactions between the liquid surface and the deposited surface charge on the dewetted substrate can decrease the receding contact angle and thus cause contact angle hysteresis exceeding 10°. This occurs even for grounded liquids and can thus not be explained by electrowetting. We propose an analytical model for this mechanism and experimentally confirm the predicted dependency on drop size. We further demonstrate this universal effect for various salt solutions and substrates. Our results uncover electrostatic interactions at receding contact lines as a fundamental and until now overlooked phenomenon in wetting.