May 2011

The featured Product of the Month for May is our Model 190. This entry-level instrument is easy to setup and easy to use. Despite its simplicity, the Model 190 uses the same powerful algorithms to detect drop profiles and calculate contact angles that its bigger siblings use. Model 190 is also highly upgradeable. For example, the Manual Tilting Base can be added to do advancing and receding contact angle measurements using the tilting base method. Software upgrades are also available which add surface energy and surface tension measuring capabilities.

ramé-hart Model 190 (p/n 190-F2)

Most of our Model 190 customers choose this instrument for its affordability and for doing exactly what it was designed to do: measure static contact angles. However, with a little effort, Model 190 can also perform more sophisticated measurements. Even without any additional options, you can measure advancing and receding contact angles using the add/remove volume method. The procedure for doing so is detailed in the next section below and includes videos showing how this works.

If you are in the market for a versatile yet easy-to-use contact angle goniometer, Model 190 is hard to beat. For a quotation or for more information, please contact us today.
 

If you are a user of any edition of DROPimage and would like to add and remove drop volume to measure the advancing and receding contact angles, you will want to use the Right Line Option. This feature allows the user to filter out a needle or tip which remains embedded in the drop while contact angle measurements are being taken.

In the video below (or click here: http://www.youtube.com/watch?v=QkWa4lQ3wyE) DROPimage CA (included with Model 190) is being used to measure advancing and receding contact angles. First, enable the right line option in the Options menu. After setting the baseline, form a pendant drop. Before lowering it onto the surface, set the two vertical lines on each side of the needle (using the left and right mouse buttons for the respective lines). Then lower the pendant drop but leave the needle in the drop. Next, add volume while taking measurements to capture the advancing contact angle. Then remove volume to capture the receding contact angle. Finally, remove the needle and take a static contact angle measurement. The advancing contact angle in this experiment measures 120.4°. The receding contact angle is 74.1°. The static contact angle is 91.1°.

Critics of this add/remove volume method point out that while the advancing angle is accurately captured, the receding angle can measure high due to perturbation of the needle. One way to overcome this for some applications is to remove the needle and then allow the drop volume to decrease naturally through evaporation. This takes much longer and some liquids don't evaporate. Another solution is to use the tilting base method which is both fast and accurate and does not require the needle to stay in the drop. More on the tilting method can be found in our July 2010 Newsletter.

The right line option should not be confused with the red line option. While the right line is vertical and used - as shown in the video above - to filter out a needle or tip, the red line option is horizontal and is used to filter out anything above it - such as a needle which is detached from the drop but still in the image window. More on the red line option will follow in a future newsletter. Stay tuned.