Drop shape analysis system dsa100e

Surface tension and CA measurements were carried out by the use of a Drop Shape Analysis System DSA100E (KRÜSS GmbH, Germany, accuracy ±0.01 mN m⁻¹), at 25 °C. Temperature was controlled using a Fisherbrand FBH604 thermostatic bath (Fisher, Germany, accuracy ±0.1 °C). The surface tension was determined using the pendant drop method. This method consists of fitting the Young–Laplace equation to the digitized shape of a drop suspended from the end of a capillary tube. The image of the drop (6 μL) was taken from a charge coupled device (CCD) camera. The values of the critical micelle concentration (CMC) and the surface tension at the CMC (γCMC) were determined from the intersection of the two straight lines drawn in low and high concentration regions in surface tension curves (γ vs log C curves) using a linear regression analysis method.
The CA was measured using the sessile drop method (Young–Laplace), i.e. drop of liquid was deposited on a solid surface (paraffin). The drop was produced before the measurement and had a constant volume during the measurement. In this method the complete drop contour was evaluated. After the successful fitting of the Young–Laplace equation the CA was determined as the slope of the contour line at the 3-phase contact point.

The wettability was determined using the Drop Shape Analysis System DSA100E (KRÜSS GmbH, Hamburg, Germany, accuracy ±0.01 mN/m). The calculation method (Young–Laplace) is based on the static contact angles (the sessile drop method is the standard method for an accurate wetting test). The drop is produced before the measurement and has a constant volume (2 µL) during the measurement. After successful fitting of the Young–Laplace equation, the contact angle was determined as the slope of the contour line at the 3-phase contact point.
The surface free energy (σ_s) was determined with the Owens, Wendt, Rabel, and Kaelble method (OWRK), which is a standard method for calculating the surface free energy of a solid from the contact angle with several liquids – polar (water) and nonpolar (diiodomethane). The calculation of surface free energy (SEF) using the Young equations [42 (link)] (Equation (1)) and the Fowkes method [43 ] was carried out. The interfacial tension σ_sl is calculated based on the two surface tensions σ_s and σ_l and the similar interactions between the phases. These interactions can be interpreted as the geometric mean of a disperse part σ_D and a polar part σ_P of the surface tension or surface free energy (Equation (2)).
${\sigma }_s={\sigma }_{sl}+{\sigma }_l·\cos \theta$
${\sigma }_s={\sigma }_{sl}+{\sigma }_l-2\left(\sqrt{{\sigma }_s^D·{\sigma }_l^D}+\sqrt{{\sigma }_s^P·{\sigma }_l^P}\right)$

Contact angle measurements were carried out using a Drop Shape Analysis System DSA100E (KRÜSS GmbH, Germany, accuracy ±0.01 mN/m). The calculation method (Young-Laplace) is based on the sessile drop method, i.e., drops of liquid are deposited on a solid surface. The drop is prepared prior to the measurement and has a constant volume during the measurement. The Young-Laplace fitting is the most complicated, but theoretically also the most exactly accurate for calculating the contact angle. In this method, the complete drop contour is evaluated. The contoured fitting includes a correction that considers that the shape of the drop does not result solely from interfacial effects, but that it is also distorted by the weight of the liquid it contains. After the successful fitting of the Young-Laplace equation, the contact angle was determined as the slope of the contour line at the 3-phase contact point.