Temperature Dependence of Diffusion in Mineral Oil-Based Polymer Gels

One application of polymer gels is for use as transdermal drug patches where the temperature of the gels would vary slightly depending on which part of the body the patch is applied to and the climate that the patient is living in. Therefore, it is important to consider the temperature dependence of diffusion of solutes through these gels. Additionally, studying diffusion allows for the determination of the activation energy of the diffusive process for a specific gel composition. Diffusion testing in temperature-controlled environments was conducted to find the diffusion coefficients of the gels at different temperatures. This testing determined the relationship between temperature and diffusion coefficient. Since diffusion coefficient is a temperature dependent property, it can be hypothesized that the relationship between these variables follows the Arrhenius Equation D(T) = D₀e^-E_a/(RT) where D(T) is diffusion versus temperature (T), R is the universal gas constant and E_a is the activation energy required to initiate the diffusion. Based on the results of this investigation, the change in diffusion coefficient as temperature changes for 20% SEBS polymer mineral oil-based gels is very strongly correlated to the above Arrhenius Equation. Additionally, the activation energy of the diffusion process for these gels was found to be 39.9 kJ/mol. This represents the minimum energy required to begin the process of diffusion of molecules out of this type of gel. Future projects can be conducted on polymer gels with different polymer concentrations or polymer species to determine the effect of these factors on temperature dependence of diffusivity.