Determination of the Receding Contact Angle of Sessile Drops on Polymer Surfaces by Evaporation

Abstract

The receding contact angles of water drops on PMMA and PET surfaces were determined by using video microscopy to follow the time-dependent evaporation of sessile drops. Depending on the initial drop size, receding angles of θr = 54−64° for PMMA and θr = 64−66° for PET were found with an average hysteresis of 23.5 ± 1.5 and 19.5 ± 1.5°, respectively. Advancing and receding angles, θa and θr, were also determined by the needle-syringe and the inclined plane methods for comparison. The discrepancies from the mean of the maximum and minimum contact angle results of both the needle-syringe and the inclined plane methods were larger than expected for all the polymer surfaces. A general trend was seen with samples giving a larger hysteresis also producing a larger discrepancy for all the samples. The major cause of this discrepancy is the variation of the rate of liquid introduction and withdrawal with the syringe in the needle-syringe method and the drop size effect in the inclined plane method. In this respect the drop evaporation method allows a rate of liquid withdrawal which minimizes (or standardizes) the linear rate of retreat effect on receding contact angle measurement. The literature values are also given for comparison. A discrepancy of 11−15% from the mean for θa and 27−32% for θr is reported in the literature for these polymers. This is approximately five times more than the previously claimed 2−3% deviation from the mean for θa on the same clean homopolymer samples.

Selective adsorption of L1210 leukemia cells/human leukocytes on micropatterned surfaces prepared from polystyrene/polypropylene-polyethylene blends

“…In addition, we measured both advancing (Â adv ) and receding (Â rec ) water contact angles (WCA) on the sample surfaces by increasing the volume of the droplets from 3 to 8 L and decreasing from 8 to 4 L respectively through the needle by using the automatic dispenser while the needle was kept within the liquid droplet. Â rec were also measured by drop evaporation method for better precision [43,44].…”

Effect of contact angle hysteresis on the removal of the sporelings of the green alga Ulva from the fouling-release coatings synthesized from polyolefin polymers

“…30 The precise measurement of receding contact angles is a difficult process and r can be determined by following the time dependent drop evaporation measurements with a videomicroscopy technique in comparison with the static needlesyringe sessile drop method. 31,32 Contact angle hysteresis, CAH, is defined as the difference between the advancing and receding contact angles, CAHϵ a − r . This hysteresis is due to the system under investigation not meeting the ideal conditions.…”

Evaporation of Sessile Water Droplets in Presence of Contact Angle Hysteresis

“…(2.18) and (2.20) are validated against available experimental data extracted from literature sources [5,7,45]. The characteristic time of the process can be calculated using Eq.…”

“…Water on PET [45] Theory (θ ad =1.486; t ch =760 s) Figure 8. glass, the estimation showed that the average temperature of the droplet surface, T av , appeared to be higher than the ambient temperature, T ∞ , what is in contradiction with the physics of the phenomenon.…”

“…Hence, Water on polished epoxy surface [5] Water on corning glass 7740 [7] Water on PMMA [45] Water on PET [45] Theory …”