Contact Angle

Contact angle measurement characterizes the surface energy of a solid surface.

EAG Laboratories performs optical contact angle measurements and drop shape analysis using a Dataphysics OCA25 instrument. The main application of contact angle measurement is determination of the wetting behavior of a solid surface with a specific liquid. Water drops are used to measure hydrophobicity or hydrophilicity. With individual drops of 2, 3 or more different liquids, the free energy of a surface can be calculated. A common method of surface free energy calculation is the OWRK model, which splits free energy in two contributions: a polar and a dispersive component.

In another application on the same instrument, the surface tension of unknown liquids in air (or in other media) can be measured by analysis of the shape of pendant drops, elongated by gravity.

Ideal Uses of Contact Angle and Drop Shape Measurement

  • Wetting behavior of coatings
  • Hydrophobic/hydrophilic properties
  • Investigate the effect of cleaning and other surface treatments
  • Surface tension of unknown liquids
  • Quality assurance and quality control

Strengths

  • Non-destructive
  • Quantitative
  • Surface tension can be measured on (nearly) all surfaces with (nearly) all liquids
  • Fast and easy: no sample or instrument preparation, no vacuum

Limitations

  • Minimum measurement area: 1–3 mm diameter for standard droplets, 0.1-0.3 mm for nanodrops
  • Strongly absorbing materials
  • Region of interest must be visible in grazing light
  • Maximum sample size is 20 cm in one direction, no limit in transverse
  • Minimum sample volume (for measurement of a liquid’s surface tension) is ~1 ml

Contact Angle Technical Specifications

  • Manual 3-axis positioning
  • 6.5x zoom lens
  • Camera acquisition for very fast processes
  • Electronic positioning and dosing of 3 syringes
  • Nanoliter dosing system to generate very small droplets down to 10 nl

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