Diffusion of dextran probes in a self-assembled fibrous gel composed of two-dimensional arborols

Two-dimensional arborols are bolaform amphiphiles in which a central, hydrophobic spacer separates twin hydrophilic ends. Under appropriate conditions, these relatively small molecules assemble into very long fibers; subsequently, the system gels if the arborol concentration is sufficiently high. The diffusion of linear or slightly branched dextran probes in 3 and 6% arborol gels, as determined by fluorescence photobleaching recovery, resembles that of dextrans in water, suggesting a highly open network structure. Melting the gels produces almost no change in diffusion of the dextran probes. Small-angle X-ray scattering (SAXS) of wet arborol gels at different concentrations and temperatures reveals the diameter of the repeating unit of the fibers to be 8.26+/-0.68 nm. This dimension, which is independent of concentration and temperature, exceeds the length of a single arborol molecule by about a factor of 3. Rheological investigation identifies the linear response regime of the gels and permits an examination of the weak correlation between dextran probe diffusion and gel viscoelasticity.