When liquid pesticides are sprayed, some of the product runs off the leaf instead of remaining on it. In order to keep this amount as small as possible, the solution to be sprayed should form small drops and wet the leaves thoroughly. As both objectives are linked to the surface tension, the composition of pesticides can be optimized with the help of our interfacial chemical measuring instruments.
Surface tension measurement for evaluating surfactants
Surfactants in pesticides improve wetting by reducing the surface tension of the solution. The droplet size also depends on this value, as a spray mist has a larger internal surface area which is easier to achieve with low surface tension.
Our tensiometers measure the value of the surface tension quickly and precisely. Together with measurements of the critical micelle concentration (CMC), they also help to assess the efficiency of the surfactant. The CMC specifies the surfactant content at which the maximum reduction in surface tension is achieved.
Spraying is a highly dynamic process for which the mobility of the surfactants is particularly important. The required reduction in surface tension must often be achieved within the fractions of a second which elapse between the generation of the droplet and the contact with the leaf. Our stationary and mobile Bubble Pressure Tensiometers – BP100 and BPT Mobile measure the dynamic surface tension even at surface ages of a few milliseconds.
Contact angle measurement for assessing wetting
The wetting on a particular type of leaf can be determined by measuring the contact angle. Our drop shape analysis instruments measure this precisely. Furthermore, a tilting table as an accessory measures the roll-off angle for a dispensed drop. The roll-off angle describes the inclination of the surface - in this case the leaf - at which the drop rolls or slides off the surface.