Theta lite optical contact angle meter

The interfacial tension between the sample dispersion and sunflower oil was investigated using a Theta Lite optical contact angle meter (Biolin Scientific, Sweden) (Gomez-Luria, Vernon-Carter, Alvarez-Ramirez, & Cruz-Sosa, 2019 (link)). The sample (0.5 g) was added to 50 mL of distilled water, extracted under ultrasonication at 25 °C for 10 min, and then allowed to rest for 15 min. The supernatant was collected as the sample solution and loaded into a high-precision syringe. Then, to form the oil-water interface, a drop of sample solution was added to a cuvette containing sunflower oil. Then, the interfacial tension was calculated by recording the axisymmetrical drop shape and fitting it with the Young-Laplace equation.

The interfacial tension and contact angle measurements of the samples were determined using a Theta Lite optical contact angle meter (Biolin Scientific, Stockholm, Sweden) (Wei & Huang, 2019 (link)). The samples were pressed into a thin slice (diameter 2 cm, thickness 0.5 cm) using a tablet machine at a pressure of 15 MPa. The slices were then placed in a quartz vessel containing MCT, and 6 μL of ultra-pure water was dropped on the surface with a syringe. An image of the droplet was automatically recorded, and the corresponding contact angle was calculated using OneAttension software (Biolin Scientific, Stockholm, Sweden).
The excess sample was dispersed in water to prepare a saturated solution. Then, the pipette tip was inserted into MCT, extracting 25 μL of saturated sample solution, which was then emitted dropwise. The droplet morphology was continuously recorded, and the corresponding interfacial tension was calculated using OneAttension software.