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September 2007

Relaxation Measurements

The analysis of surface tension relaxation contributes to the understanding of different physical mechanisms in or around the surface. This type of study is conducted by making one or more sudden changes (steps) to the drop volume of a pendant or sessile drop while dynamically measuring the surface tension. The steps can be positive or negative.

Researchers have used relaxation studies to better define the viscoelastic properties of solutions and surfactant monolayers. The relaxation of the surface after a sudden change in volume can also measure the kinetics of absorption and desorption. 

Cicciarelli, Hatton, and Smith1 demonstrate dynamic surface tension behavior in a photoresponsive surfactant system. In their referenced study, they measured dynamic surface tension under different illumination scenarios. They found that under UV lighting, the surface tension of their samples exhibited a sharp drop in initial surface tension, followed by a plateau of constant surface tension, and then finally ending with a second relaxation. They concluded that the behavior can be explained by competitive absorption between various isomers present in their test liquids.

1 Langmuir, 23 (9), 4753 -4764, 2007. 10.1021/la062814k S0743-7463(06)02814-9

DROPimage Advanced v2.2
This month we announce the release of v2.2 of DROPimage Advanced. Earlier in the year we released v2.1 which is now compatible with Windows Vista operating system. DROPimage Advanced v2.2 now includes new tools for conducting relaxation studies. Note that a ramé-hart Automated Dispensing System is required to use this feature.

The following changes have been made: First, the methods editor has been enhanced to now include the number of steps, or pulses, in a relaxation experiment. Other measurement types include "constant volume" and "oscillation". Note that the existing event file editor can also be used to define a relaxation study.

The key parameters to a relaxation experiment are: step volume and number of steps. If a negative step volume is specified, then volume is retracted from the drop. Typically the step volume may be in the 2-4μL range. The number of steps should be even; four is a good place to start. The time interval is also set (say 1 second).

Additionally, DROPimage Advanced v2.2 now includes a Relaxation Calculation tool as shown above. The calculation and graphing tool requires the log file from a previously run relaxation experiment. The data can be added and removed from the graph easily one step at a time -- or all at once.  The Calc buttons are used to calculate the following  values:

Please contact us if you are interested in obtaining more information on the relaxation support in DROPimage Advanced v2.2. Upgrades are available; however, this version will require a digital camera. If you are currently running DROPimage v1.5 or older, you may need our analog to digital upgrade kit (p/n 400-22-F1). Note that all new Model 250-F1 and 500-F1 goniometer orders will begin shipping this month with v2.2. DROPimage Standard has also been upgraded to v2.2 and supports Windows Vista but does not include any support for relaxation.



Carl Clegg
Director of Sales
Phone 973-448-0305
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