A good chemical analysis is essential to offer quality products and services. Concentrol continuously increases its technical capacity. An example is a tool that allows the company’s laboratories to measure dynamic surface tension.

The surface tension of a liquid is defined as the energy required to increase its surface by a given area. It is a measure of the intermolecular attractive forces between the different molecules of a liquid at the surface of the liquid: liquids with strong intermolecular attractive forces have a high surface tension.

There are different methods for measuring surface tension. One of the most common is the Du Noüy ring, which allows the static surface tension of the liquid to be measured. However, for industrial processes where there is a rapid generation of new surfaces, such as roller application or printing, it is interesting to measure the dynamic surface tension. To obtain this measure, the dynamic bubble pressure method can be used. This instrument produces bubbles at different frequencies through a capillary immersed in the analyzed liquid, and measures the pressure required to form a bubble of the radius of the capillary (maximum pressure). The pressure required to form the bubble is directly related to the surface tension.

The surface tension value of a pure liquid is independent of the bubble lifetime. However, the surface tension in fluids in the presence of surface-active additives depends on the lifetime of the bubble. When a new surface is generated, the surfactant molecules diffuse towards this new surface and orient themselves, this process takes time and depends on the mobility of the surfactant in solution. For this reason, the dynamic surface tension value depends on the bubble lifetime.

Recently, Concentrol has acquired a bubble pressure tensiometer for the R&D laboratories. This equipment allows the measurement of dynamic stresses from a bubble time of 15 milliseconds to 100,000 milliseconds (100 seconds), where the values obtained are considered almost static. This equipment helps us in the development of new wetting additives, since it allows us to observe differences in behavior between different additives, as in the following comparison between two additives from the ORDISOL SWT range.

Surface tension measurements have been made in distilled water using the maximum bubble pressure method. Continuous readings have been acquired from 15 milliseconds to 50 seconds of bubble time. The dose of wetting additive has been set at 0.1%.

Surface tension values at bubble time of 50 seconds can be considered as a quasi-static tension value.

 

Results

Wetting additive Bubble time (s) Surface tension (mN/m))
ORDISOL SWT-31 48.483 38.3
ORDISOL SWT-33 50.075 39.9
Table 1: Quasi-static measurements of surface tension with a bubble time of 50 seconds.

The graph of surface tensions measured at the different bubble times for each additive is shown below. Two well-differentiated zones can be observed in the graph: the first (from 0.025 to 10 seconds) shows a strong decrease in the surface tension values as the bubble time increases. This zone corresponds to the region of dynamic surface tension. After 10 seconds, it is observed how the surface tension stabilizes, decreasing the slope of the curve. This zone corresponds to the quasi-static surface tension region.

 

Expansion of the dynamic region: the area of the dynamic region of the previous graph is enlarged. It can be seen how ORDISOL SWT-31 has a faster dynamic surface tension decrease behavior than ORDISOL SWT-33, obtaining lower dynamic tension values for each bubble time.

 

This new tool exemplifies Concentrol’s will to develop new solutions for its clients, as well as to maintain the best quality in its products. The company’s laboratories are in continuous research, proof of this is the continuous that it generates and is finally applied in new leading solutions in the sector.