(558h) Temperature Dependent Diffusion in Styrenic Block Copolymer Organogels

Solute diffusion through polymeric gels has been heavily focused on hydrogels due to their wide applicability including in drug delivery and tissue engineering. However, several studies have considered gels composed of styrenic triblock copolymer and aliphatic oil – referred to here as organogels – for transdermal drug delivery. Over the past few years, our group has worked to better understand the fundamental process of solute diffusion through styrenic block copolymer organogels. The current work specifically examines the effect of temperature on diffusion through these gels. In order to measure temperature dependent diffusion, we modified our previous experimental setup, which consists of a shaker table loaded with containers holding supernatant aliphatic oil and submersed gels, to include a thermostatted water bath with precise temperature control. This setup was used to measure the diffusivity of sodium bis(2-ethyl-1-hexyl) sulfosuccinate (AOT) reverse micelles through gels composed of of poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) copolymer (M_w = 158 kDa, f_S = 0.278) at various concentrations (6%-14% by mass) and at different temperatures (20 °C-50 °C). Furthermore, temperature-dependent diffusion through gels with the same set of parameters but containing unique aliphatic oils (with viscosities of 29 cP, 80 cP, and 153 cP at 25 °C) was characterized. The collective results from these experiments can be interpreted using a single physical model that considers the relevant molecular/formulation parameters, as well as, temperature via an Arrhenius contribution. This interpretation ultimately leads to extraction of the activation energy associated with AOT reverse micelle diffusion through styrenic block copolymer organogels.