Why Organosilicone Adjuvants Spread

Abstract

The use of certain organosilicone surfactants as agricultural adjuvants has come about as a result of their unusual ability to promote the rapid spreading of dilute solutions on hydrophobic leaf surfaces. The reason for this unique spreading is not well understood. The spreading of surfactant solutions, including the organosilicone surfactants, has recently been shown to exhibit a maximum in spreading rate as the surfactant concentration is increased, and as the substrate is made more hydrophobic. Certain organic surfactants promote spreading equally as rapid as the organosilicones on slightly less hydrophobic surfaces. Organosilicone surfactants, on the other hand, exhibit rapid spreading even on very hydrophobic surfaces. Some have attributed the rapid spreading of the organosilicone surfactants to their unique molecular shape, but the evidence does not support this. A correlation has been found between solubility or turbidity and spreading-those materials which form turbid dispersions seem to provide the most rapid spreading. In this case turbidity is due to the presence of a dispersion of bilayer vesicles. The presence of vesicles contributes to the low dynamic surface and interfacial tensions at short time scales, leading to the ability to spread more rapidly over more hydrophobic substrates.