OCAT

Instumentelle Analytik (Umwelt- und Bodenchemie)

Instrument

Video-Based Optical Contact Angle Measuring Device

Model

OCA15Pro (DataPhysics)

Description / Measuring Principle

The OCA 15Pro instrument is used in studying different properties of surfaces and liquids. The device consists of four main parts: light source, high-speed camera, movable (x,y and z) sample holding base and a dosing unit.

OCA15Pro measures the static and dynamic contact angles formed by a liquid at the three-phase boundary where the liquid, gas, and solid intersect. According to Young's equation, there is a relationship between the contact angle, the surface tension of the liquid, the interfacial tension between liquid and solid and the surface free energy of the solid.

 

OCA15Pro capturing the changes in the shape of a sessile drop placed on a substrate surface using a high speed camera. The camera can be tilted to examine the substrate and contains a 6-fold zoom lens and integrated focus. The substrate is placed on the measuring stage between the light source and the high speed camera. An electronically controlled syringe is attached to the instrument in order to dispense a liquid onto a substrate. The drop is illuminated from behind and its image captured as a solid shape of a single black color. The image of the drop can be recorded in short time intervals range down to milliseconds. The instrument is controlled by SCA20 software contained on the associated PC which provides the ability to measure dynamic and static contact angles on plane, convex, and concave surfaces based on four different calculation algorithms:

•    Circle fitting
•    Tangent leaning
•    Ellipse fitting
•    Young-Laplace Fitting

The SCA20 software internal database contains the properties of many different liquids. These liquid properties and the measured contact angles provide the user with the ability to calculate the surface free energy through an included software package using one of the known methods (Zisman, Fowkes, WORK etc.).

Technical data:

  • Measuring range (contact angles): 0—180° ± 0.1° measuring precision of the video system
  • Measuring range (surface & interfacial tensions): 0.01—2000 mN/m ± 0.01 mN/m resolution
  • Optics: 6-fold zoom lens (0.7 … 4.5 magnification) with integrated fine focus (± 6 mm)
  • Light source: LED-lighting with software controlled adjustable intensity without hysteresis
  • Video system: 1/2” USB-CCD camera max. Resolution 768 x 576 pixel, (123 images/s sample rate), Image distortion < 0.05%
  • Temperature control units -10—100 °C (2000006 TFC 100). Liquid temperature control unit for use with a liquid circulator for measurements below or above room temperature, e.g. for measuring of temperature coefficients, as well as under protective atmosphere (Inert gas inlet).
  • Single direct dosing system SD-DM with one electronic syringe units ES-D.
  • Gastight 500 µl precision syringe (6000005 DS 500/GT).
  • Two different size dosing needle:
    • (6000007 SNS 052/026, Outer-Ø 0.52 mm; Inner-Ø 0.26 mm; Length 51 mm) for sessile drop measurements and fluids with a viscosity up to 120 mPas (e.g. Dipropylene glycol).
    • (6000027 SNP 165/119, Outer-Ø 1.65mm; Inner-Ø 1.19 mm; Length 51 mm For pendant drop measurements and fluids with a viscosity up to 3000 mPas (e.g. Glycerol).