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Automated method for measurement of dynamic contact angles of liquids

University of Sofia Department of Physical Chemistry mavramov@chem.uni-sofia.bg. M. Z. Avramov, I. Ivanov , B. Radoev. Automated method for measurement of dynamic contact angles of liquids. Motivation.

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Automated method for measurement of dynamic contact angles of liquids

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  1. University of Sofia Department of Physical Chemistry mavramov@chem.uni-sofia.bg M. Z. Avramov, I. Ivanov, B. Radoev Automated method for measurement of dynamiccontact angles of liquids

  2. Motivation • In some cases the measurement of contact angles with inclination plate are not easy to implement due to externaldisturbances. • The precise inclination and precision positioning of the camera require complicated mechanical equipment. • The drop is relatively complex object from point of view of geometry and description of the system.

  3. Concept • A three phase contact is formed if liquid is placed in a capillary. • By changing the angle of the capillary one can easily vary the hydrostatic force. • Different force applied on the menisci delivers different contact angles – “reseeding” and “advancing”. • In a thin capillary the shape of the meniscus is spherical (the gravitational deformation can be ignored).

  4. Force balance

  5. Finding of Radius of the meniscus

  6. Construction of the Device Image Processing Controller a) USB microscope b) Mirror c) Capillary d) Holder + Servomotor e) Acceleration Sensor

  7. Image Processing • Collect image of the meniscus at different angle • Preprocess the image (filter and edge detection) • Extraction of the coordinates of the meniscus

  8. Extraction of points • The extraction of points is based on an adaptive threshold algorithmwhich does in addition an integral estimation of each point. • The result is sub pixel resolution and this way higher precision

  9. Curvature and Radius • Due to multiple different surfaces involved in the system a significant distortion of the observed meniscus may appear. • One should take into account that the distortion is small on the axe of the capillary. • The used solution is to find the maximum observed meniscus curvature which corresponds to the best optical path (lowest distortion).

  10. Some Results • To evaluate the operation of the device a calculation of both curvatures vs. the inclination of the capillary is made. • The red dots are the experimental data (with regression line) • The dashed line is the expected line based on typical values for physical constants DH [m-1] sina

  11. Conclusion • The measurement of contact angles using a capillary provide a possibility for automation. • The simple geometry (cylindrical) of the capillary simplifies calculations but introduces some difficulties because of optical distortions. • Nevertheless reasonable results can be obtained for known system.

  12. Thank You for Your Attention This work has been supported by project FP7 Beyond Everest (contract No 1996 SRD department University of Sofia) and Metrologic Lab Of University of Sofia and BSS LTD

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