The diffusion of three polydisperse [H-3]ethoxylated octylphenols (5,
10 and 16 EO) through isolated plant cuticles was studied using diffus
ion half-cells and droplet application. The diffusion half-cells were
used to determine the influence of ethylene oxide (EO) content and of
surfactant concentration on the diffusion of the surfactants across th
e cuticle at a relatively constant concentration gradient. The influen
ce of EO content, of temperature and of surrounding relative humidity
on diffusion of the surfactants across the cuticle was determined with
droplet application. Measurements in diffusion half-cells showed that
flux was lowest for OP16 in comparison to OP5 and OP10. Diffusion coe
fficients were 0.92, 3.17 and 2.18 x 10(-12) cm2 s-1 for OP5, OP10 and
OP16 respectively in pepper fruit cuticles. Flux of OP10 across peppe
r fruit cuticles increased with surfactant concentration in the donor
cell (from 5 to 40 g litre-1), the diffusion coefficient of OP10 in th
e cuticle rising from 3.79 to 21.3 x 10(-12) cm2 S-1. Surfactant penet
ration through pepper fruit and rubber-plant leaf cuticles was initial
ly very rapid after droplet application, decreasing gradually after 24
h. Flux of OP16 across cuticles of both species was lower than for th
e other two octylphenols. Penetration of OP10 and OP16 through pepper
fruit cuticles was greater at low (40%) than at high (95%) relative hu
midity. Transfer of OP10 increased considerably as temperature increas
ed from 5-degrees-C to 30-degrees-C. The value obtained for the diffus
ion activation energy was - 70.3 kJ mol-1. The experimental results ar
e discussed in the light of the free-volume theory with respect to dif
fusion of organic molecules in polymers.