Optical Contact Angle Measurement Considering Spreading, Evaporation and Reactive Substrate

Effect of gravity on the spreading of a droplet deposited by liquid needle deposition technique

“…If the injection mass flow rate is high enough then there will be formation of jet from the needle instead of a droplet 32 . On the other hand, if the injection of mass flow rate is low, it will grow at drop-medium interface rather spreading at the three-phase contact line and the evaporation of liquid can also take place during the slower drop generation 37 . Considering all the adverse effects of existing drop deposition method in microgravity, a jet-based drop deposition method, also known as liquid needle method 29 , 38 , 39 , is proposed here.…”

“…It is proven that, on terrestrial conditions, a reproducible sessile drop volumes with the same equilibrium contact angles can be produced with this deposition technique 38 , 39 . It is also proven that if the ratio of the diameter of the jet to the diameter of the drop is 0.2 or less, the adverse effect of kinetic energy 38 , 39 on the reproducibility of the recently advanced contact angle can be minimized 37 . Therefore, considering all the shortcomings of traditional droplet deposition techniques and other approaches, we have decided to extend the utility of a jet-based drop deposition technique 29 , 39 to deposit or generate the droplet onto the substrate under reduce gravity condition.…”

Double-Emulsion Drop Evaporation and Formation of a Daughter Droplet

“…As observed for saturated environment wettability studies, 49 the saturated vapor not only maintains the contact angle closer to theoretically predicted Young's angle but also circumvent the decrements in the contact angle due to evaporation. 49,50 During the outer water drop evaporation, the surrounding medium for the inner drop gets saturated with the water vapor, which further gets adsorbed on the solid surface. Once the outer liquid cushion is evaporated, the inner drop is suddenly exposed to a modified surface energy interface that results in another marginal decrease in the contact angle, Δθ ≈ 5°(inset of Figure 2b) with a sudden increase in the base diameter, ΔΦ ≈ 0.1 mm (inset of Figure 2c) of the inner drop.…”