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Contact angle module:

The Syringe is fixed on top of the goniometer.
It can be moved in x,y,z- direction.

The most recent extension is the contact angle module. The contour of a sessile drop is analyzed and fitted to the Young-Laplace equation. The module uses many existing hardware components of The Multiskop such as framegrabber, CCD-camera, sample stage, computer etc. and is therefore a consequent extension of its capabilities.
A contact angle measurement requires the precise determination of the location of the three phase contact point. Many commercial programs demand further user input to solve this task but not our program CAM. The implemented contour tracing algorithm is smart enough to distinguish between drop and mirror image. The contact angle is then calculated at the intersection of mirror and drop contour. This is fast, accurate and user friendly.

Download the demoversion of the Contact Angle Measurement software CAM!

sample cell with illumination.

The sample cell can be hooked up to a thermostat and minimize evaporation effects.
A diode array provides a uniform illumination of the droplet. The array is fixed on one side of the cell.

The Multiskop system enables novel measurement schemes which are advantageous for the measurement of contact angles on rough or heterogeneous solid surfaces. In this case the three phase contact line possesses irregularities and a contact angle determined by the tangent at the three phase contact point is of dubious value. The better strategy relies on an analysis of the top view of the drop. The contact angle is then calculated on the basis of the drop volume and average drop diameter leading to reliable results due to an averaging over the drop contact area.

Future Developments: Drop analysis from above

Measurements of flat sessile drops with low contact angles, say below 15° are diffcult to perform. The accuracy in the determination of contact angles decreases under these circumstances since it becomes increasingly diácult to acquire accurate coordinate points along the edge of the drop profile. In this case the better choice is to view the drop from above and determine the contact angle on the basis of the contact diameter.

Many real samples are actually inhomogenous or rough. The drop adopts then an irregularshape. In this case it is again advantageous to analyze the drop from above. The aim is to determine the average diameter of the drop. The contact angle can then be calculated provided that the drop volume is known.

The usefulness of averaging over irregularities in the three phase contact line proved to be such an asset that it became desirable to use it as well for larger contact angles. It can even be used for contact angles exceeding 90°. In this case the contact line is not visible from above but nevertheless it is possible to calculate the average contact angle using an algorithm called Axisymmetric Drop Shape Analysis-Maximum Diameter (ADSA-MD).

All these methods require imaging from above: the CCD-camera is placed above the sample. This can be achieved with the Multiskop. The required routines are in the testing stage and about to be integrated in the Software CAM.

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