Optical system for surface property measurements

Supervisors: Federico Veronesi, Davide Gardini

The optical system for surface property measurements allows to observe the behavior of suspended or sessile drops.

A software-controlled syringe dispenses drops in a reproducible manner. The lighting system projects the drop profile on the camera lens, then the software detects such profile and fits it according to the chosen mathematical model. Image acquisition can be adjusted to maximize the resolution.

Such system allows to characterize properties like:

• Contact angle of sessile drops on a surface, calculated as the angle between the baseline and the tangent to the fitted drop profile in the liquid-solid-air triple contact point. It is possible to measure static contact angles with the sessile drop method, as well as “dynamic” contact angles like the advancing and receding contact angles or the sliding angle;
• Surface tension of liquids, calculated with the pendant drop method;
• Surface energy of solids, calculated from the contact angle values obtained with different liquids according to one of the available mathematical models (Zisman, OWRK, and others).

CNR-ISTEC owns to optical systems for surface property measurements:

• Drop Shape Analyzer DSA 30S (Krüss GmbH)
• Optical Contact Angle OCA15plus (DataPhysics Instruments GmbH)

DSA 30S Krüss Optical system

• LED lighting
• Camera with acquisition speed up to 2000 fps
• Accuracy of 0.3° for contact angle measurements, 0.3 mN/m for surface tension measurements
• Maximum sample size 320 mm × ∞ × 275 mm (width x depth x height) (132 mm × 132 mm × 27 mm for measurements in the TC40 chamber)
• Two PT100 probes to monitor the temperature on the surface and in the syringe
• Possibility to establish automated measurement and dispensing routines
• Equipped with a tilting table for sliding angle measurements
• Equipped with a TC40 chamber with a Peltier cell for measurements at temperatures ranging from -25 to 150°C

OCA15plus DataPhysics Optical system

• Camera with acquisition speed up to 50 fps
• Accuracy of 0.1° for contact angle measurements, 0.05 mN/m for surface tension measurements
• Maximum sample size 330 mm × ∞ × 60 mm