Surfactant effects on cuticular penetration of neutral polar compounds: dependence on humidity and temperature

Effects of poly(ethylene glycol) (PEG 400) and polydisperse fatty alcohol ethoxylates ("Genapols") on methylglucose penetration across cuticles of Pyrus communis were studied under different humidities and temperatures. All surfactants increased methylglucose penetration better than PEG 400. The efficacy was proportional to their own penetration. Genapol C-100 (C12.5E8.4; C, average number of carbon atoms in the alkyl chain; E, average number of ethoxy groups) effects were strongly concentration dependent (0.2-5 g/L). At 2 g/L distinct differences between surfactants were observed. Effects of Genapol C-050 (C12.5E5.8) did not depend on humidity (11-93% RH) and temperature (15-35 degrees C). They were maximal after application but decreased rapidly due to surfactant penetration. Genapol C-200 (C12.5E17) effects increased strongly with humidity and temperature both of which prevented its solidification. Genapol C-100 was superior under most conditions and never failed to increase penetration. There was no simple relationship between ethylene oxide content and surfactant effect.