Temperature dependent diffusion in block copolymer organogels*

Organogels made with styrenic block copolymers are recently being studied for their potential use in transdermal drug delivery which requires an extensive investigation of diffusion behavior through these gels. To completely characterize diffusion of solutes through these gels, examining temperature dependence of diffusion is crucial along with other factors including gel concentration, polymer molecular weight, and nanostructure. In this work, the temperature dependent transport of a solute, namely sodium bis(2-ethyl-1-hexyl) sulfosuccinate (AOT) reverse micelles, is determined for several unique gels. These gels consist of the same organic solvent (Hydrobrite 200) and one of three different styrenic triblock copolymers ( triblock1: 158 kg/mol and ƒS = 0.278; triblock2: 248 kg/mole, ƒS = 0.297; triblock3: 421 kg/mol, fS = 0.291) at concentrations in the range of 6 to 14%. Diffusivity values for AOT reverse micelles are determined over a temperature range of 20 to 50°C. To confirm the validity of this somewhat narrow experimental temperature range, temperature dependent transport of triblock1 copolymer organogels varying in solvent viscosity (29, 80, 153 cP at 25°C) is also analyzed. Results from these experiments will be compared with theoretical models of temperature dependent solute diffusion.