Effect of the angle of wedge-shaped hydrophilic patterns on drop evaporation and contact line behaviour: A lattice Boltzmann study

Abstract

Hypothesis:Angular hydrophilic patterns can manipulate the drop morphology for applications like inkjet-printing. It is hypothesized that such patterns can also affect the contact line behaviour and evaporation rate of drops in a dynamic way, further affecting the quality of depositions. Here, the effect of the angular region is quantified using a wedge-shaped pattern. Experiments:The pseudo-potential multicomponent lattice Boltzmann (LB) model is used for the diffusion-limited (isothermal) evaporation of pinned liquid drops from wedge-shaped hydrophilic patterns. Findings:The contact line unpins the earliest at the apex region of the smallest wedge angles due to a pronounced difference between the local and overall contact angles. The difference reduces linearly with increasing wedge angles, leading to their delayed unpinning. The evaporative flux along the contact line is initially independent of the contact angle but reduces sharply near the unpinning angle. The variation of flux across wedge angles depends more on unpinning timings, as maximum flux values did not differ significantly. The evaporation rate is dynamic, with the smaller wedge angles initially exhibiting a higher evaporation rate because of larger drop surface areas, while the larger wedge angles dominate later owing to the delayed unpinning and retaining larger drop surface areas.