Determination of the receding contact angle of sessile drops on polymer surfaces by evaporation

H. Yildirim Erbil, Glen McHale, S. Michael Rowan, Michael Newton

Research output: Contribution to journalArticlepeer-review

157 Citations (Scopus)

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 0r 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.

Original languageEnglish
Pages (from-to)7378-7385
Number of pages8
JournalLangmuir
Volume15
Issue number21
DOIs
Publication statusPublished - 12 Oct 1999

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