Evaporation and Electrowetting of Sessile Droplets on Slippery Liquid-Like Surfaces and Slippery Liquid-Infused Porous Surfaces (SLIPS)

Abstract

Sessile droplet evaporation underpins a wide range of applications from inkjet printing to coating. However, drying times can be variable and contact-line pinning often leads to undesirable effects, such as ring stain formation. Here, we show voltage programmable control of contact angles during evaporation on two pinning-free surfaces. We use an electrowetting-on-dielectric approach and Slippery Liquid-Infused Porous (SLIP) and Slippery Omniphobic Covalently Attached Liquid-Like (SOCAL) surfaces to achieve a constant contact angle mode of evaporation. We report evaporation sequences and droplet lifetimes across a broad range of contact angles from 105°−67°. The values of the contact angles during evaporation are consistent with expectations from electrowetting and the Young-Lippman equation. The droplet contact areas reduce linearly in time, and this provides estimates of diffusion coefficients close to the expected literature value. We further find that the total time of evaporation over the broad contact angle range studied is only weakly dependent on the value of the contact angle. We conclude that on these types of slippery surfaces, droplet lifetimes can be predicted and controlled by the droplet's volume and physical properties (density, diffusion coefficient, and vapor concentration difference to the vapor phase) largely independent of the precise value of contact angle. These results are relevant to applications, such as printing, spraying, coating, and other processes, where controlling droplet evaporation and drying is important.

Lens Evaporation on Immiscible Liquid Surface with an Interfacial Cooling Effect

“…In their study, the evaporation flux along the droplet surface was one of the most important boundary conditions. In recent years, due to its simplicity, the formula proposed by Picknett and Bexon has also been widely applied in the theoretical analysis of the droplet evaporation process on solid surfaces, slippery liquid-infused porous surfaces, , and other immiscible liquid surfaces. − However, this formula ignores the interfacial cooling effect caused by droplet evaporation and the uneven distribution of evaporation flux, so the theoretically calculated value of the droplet mass evaporation rate is greater than the experimental data. Therefore, an increasing number of studies have investigated the temperature field inside the droplet and the evaporative flux distribution on its surface.…”

Continuous Droplet-Actuating Platforms via an Electric Field Gradient: Electrowetting and Liquid Dielectrophoresis

“…8 Nevertheless, other electrode configurations are also possible. 9 Although EWOD has been widely studied, 10,11 the method is restricted by limitations such as contact angle saturation and actuation incompatibility with non-conductive liquids. 6,7,12 In contrast, DW has been gaining attention for overcoming the limitations of electrowetting.…”

“…Although EWOD has been widely studied, , the method is restricted by limitations such as contact angle saturation and actuation incompatibility with non-conductive liquids. ,, In contrast, DW has been gaining attention for overcoming the limitations of electrowetting. , The dominant mechanism for DW is liquid dielectrophoresis (L-DEP), which exploits the electric bulk force produced near the liquid–solid interface of a droplet by applying a non-uniform electric field . Droplet manipulation with L-DEP has attracted a great deal of research interest, notably in the fields of optofluidics and lab-on-a-chip microfluidics. − …”

Modeling of Wetting Transition of Liquid Metals on Organic Liquid Surfaces

“…Interestingly, there exists a mixed state between the Wenzel state and the Cassie state . Transitions between different states usually have energy barriers; external stimuli such as mechanical impact, compression, thermal perturbation, and Laplace pressure can trigger the wetting transition by overcoming the energy barrier. − Another way of changing the wetting behavior between a solid surface and a liquid is to coat the substrate with a second thin liquid film that is immiscible with the first one. , This form is named slippery liquid-infused porous surfaces (SLIPS), also known as lubricant impregnated surfaces, which completely remove contact line pinning and contact angle hysteresis . Suitable LIS could transport liquid droplets easily due to the absence of contact line pinning, enabling it to be used in a variety of exciting applications such as heat transfer, self-cleaning, , antifogging, and a lab-on-a-chip .…”

“…27,28 This form is named slippery liquid-infused porous surfaces (SLIPS), also known as lubricant impregnated surfaces, which completely remove contact line pinning and contact angle hysteresis. 29 Suitable LIS could transport liquid droplets easily due to the absence of contact line pinning, enabling it to be used in a variety of exciting applications such as heat transfer, 30 self-cleaning, 31,32 antifogging, 33 and a lab-on-achip. 34 At present, most of the papers focus on the properties of liquid with low surface tension, but the properties of a liquid metal droplet with high surface tension on a liquid interface have not been studied well yet.…”