Surfactant and temperature effects on paraben transport through silicone membranes

This study investigates the effects of two surfactants (one anionic and one non-ionic) and controlled
modifications in temperature (298–323 K) on the permeation of two structurally similar compounds
through a silicone membrane using a Franz diffusion cell system.
In all cases the presence of an anionic surfactant, namely sodium dodecyl sulphate (SDS), reduced the
permeation of both compounds (methylparaben and ethylparaben) over a period of 24 h. The degree
of permeation reduction was proportional to the concentration of surfactant with a maximum effect
observed, with an average reduction of approximately 50%, at the highest surfactant concentration of
20 mM. Differences were seen around the critical micelle concentration (CMC) of SDS implying the effect
was partially connected with the favoured formation of micelles. In contrast, the presence of non-ionic
surfactant (Brij 35) had no effect on the permeation of methylparaben or ethylparaben at any of the
concentrations investigated, both above and below the CMC of the surfactant. From these findings the
authors conclude that the specific effects of SDS are a consequence of ionic surfactant–silicone interactions
retarding the movement of paraben through the membrane through indirect modifications to the
surface of the membrane.
As expected, an increase in experimental temperature appeared to enhance the permeation of both
model compounds, a finding that is in agreement with previously reported data. Interestingly, in the
majority of cases this effect was optimum at the second highest temperature studied (45 ◦C) which
suggests that permeation is a temperature-dependent phenomenon.