A Fourier transform infrared spectroscopy-based method for tracking diffusion in organogels

Abstract

Organogels possess characteristics that make them promising materials for enhancing our understanding of nanostructure-diffusion relationships in gels and for use in diffusion-centered applications including drug delivery and nanoreactor media. Unlike hydrogels, however, there are no well-recognized techniques for measuring the fundamental diffusion parameter of diffusivity, D, in organogels. The present work establishes a technique for measuring D based upon Fourier-transform infrared spectroscopy. Physically crosslinked gels composed of poly[styrene-b-(ethylene-butylene)-b-styrene] and aliphatic mineral oil are used to showcase the new technique's capability. Diffusivity of unimers—oleic acid—and reverse micelles—sodium dioctyl sulfosuccinate (AOT)—within as-prepared and preswollen gels is quantified and resultant values are commensurate with studies of unimer and micelle diffusion in hydrogels. The case of AOT diffusion is further validated through small-angle X-ray scattering analysis, which is in close agreement (<20% difference).