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ARS Home » Midwest Area » Wooster, Ohio » Application Technology Research » Research » Publications at this Location » Publication #66684
Title: A SYSTEM FOR DETERMINING DYNAMIC SURFACE TENSION, USING THE OSCILLATING JET TECHNIQUE

Author
item REICHARD, DONALD - FORMERLY ARS (DECEASED)
item COOPER, JANE - OSU/OARDC-ENTOMOL DEPT
item BECHTEL, STEPH EN - OSU-ENGINEERING MECH DEPT
item FOX, ROBERT

Submitted to: Atomization and Sprays
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/7/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Experiments have shown that spray droplets rebound readily from some leaf surfaces, with a time between impaction and rebound of less than 1 msec. Spray atomization is another process important to effective pesticide application, where large changes in surface area occur in less than 3 msec. Surface tension of the sprayed liquid affects both of these processes but static surface tension can not be used to accurately predict droplet rebound from leaves. Measuring dynamic surface tension of the spray mixture at short surface ages will enable more accurate prediction of spray droplet rebound. A low speed video system was used with an oscillating jet to develop a procedure to measure the dynamic surface tension of liquids at surface ages less than 1 msec. The procedure reported here allows us to measure wavelengths and maximum and minimum diameters of the jet waveform with greater accuracy than was possible in earlier studies. Two methods were used to calculate dynamic surface tension using waveform measurements. Values of surface tension of true solutions (ethanol and water mixtures) determined by both calculation methods were in good agreement with handbook values. The dynamic surface tension of spray mixtures measured with this method have been shown to have a greater correlation with droplet rebound from leaf surfaces than surface tension measured by other methods. The ability to measure critical properties of spray mixtures, such as dynamic surface tension will give pesticide formulators the tools to create pesticides with optimum properties for desired application methods. Applicators will be able to use these key spray properties to tune their mixtures for each weather, crop, and pest situation encountered.

Technical Abstract: A motion analysis system based on a low speed video system was used to develop a procedure for measuring the dynamic surface tension of liquids at short surface ages using the oscillating jet method. Bohr's equation and Bechtel's inverse method were used to calculate surface tension from measurements of the jet waveforms. Values of surface tension determined by both methods were in good agreement with handbook values. Surface tensions calculated from waveforms near the jet orifice were found to be similar to values calculated for waveforms further from the orifice. True solutions have the same surface tension at all surface ages, although several previous studies had reported higher surface tensions for waveforms near the orifice. Most agricultural sprays are mixtures of materials, not true solutions, and as such their surface tensions change with surface age. A method of measuring surface tensions at short surface times are essential for predictive models of the effect of adjuvants on the properties of agricultural sprays, especially droplet atomization and droplet rebound from plant surfaces; both of these processes are completed in less than 3 ms.