Contact angle and volume retention effects from capillary bridge evaporation in biochemical microplating

Biochemical microplating in resource-limited venues presents a challenge with important outcomes. The feasibility of using capillary bridges developed in schemes that apply transparencies and samples between rods with EGFP samples to interrogate wetting via the contact angle and to retain volumes for longer under evaporation was investigated here. The experiments with capillary bridge evaporation between two flat silicone surfaces found a steep contact angle reducing rate in the early stage followed by a more gradual reducing rate later. The steep process was attributed to the liquid–vapor interface accommodating for thermodynamic entropy changes during evaporation. The initial convex meniscus also resulted in faster volume reduction from Kelvinʹs relation on escape tendency. With the same volume, the two silicone surfaces extended the retention time of the sessile drop by over 5 times. This unexpected effect was attributed to the initial convex to concave meniscus change in a confined space that resulted in a more saturated vapor pressure nearer to the interface. This finding portends the favorable use of hydrophobic surfaces in transparency microplating. Its use in contact angle measurements however will be subject to the evaporation mechanics at confined areas. It is also limited by rupture. With capillary bridge between three rods, this occurred at higher angles. This approach did not improve volume retention from evaporation much and was prone to wetting not being constant along the bridge length. Higher fluctuations in the contact angle trend were found which made attempts to estimate volume based on geometry subject to large levels of uncertainty. Nevertheless, the geometrical equations and approximated parameter changes showed the length change to be above two times the cross sectional area change during evaporation. The results indicate that creating capillary bridges for the transparency microplates offer the best ability to retain volumes while allowing the contact angle to be interrogated.