A building unit(defined as SBU) synthesized from 1,2,4,5-benzene tetracarboxylic acid and 4-hydroxy pyridine was used as the gelator with low molecular weight to form supramolecular hydrogels at various concentrations.The dried hydrogels(xerogels) were observed by scanning electron microscope(SEM).The results indicate that the xerogels possess network structures composing of intertwined fibers and the dimension of the fibers can be regulated by the concentration of SBU.Powder X-ray diffraction(XRD) analysis indicates that the fibers are connected by SBU building units.The reversible sol-gel transition of the supramolecular system with the change of temperature was also noticed.
A new hydrogelator,2,6-di[N-(carboxypropylcarbonyl)amino] pyridine (defined as DPAP) was synthesized from 2,6-diaminopyridine and glutaric anhydride by a one-step procedure.Self-supporting supramolecular hyrogels were formed through cooling DPAP aqueous solution and DPAP mixed solution of 1,4-dioxane and water with 1,4-dioxane content no more than 15 wt%.However,only fiber-like crystals were obtained in pure 1,4-dioxane system.SEM observation of the xerogels indicated that the gelator molecules assembled into large sized sheet-like aggregates.The powder XRD diagrams indicated that the xerogel samples possess onset diffraction at 5.6°(2θ),corresponding to a d spacing of 1.580 nm.Such a length corresponded well with DPAP molecular length of 1.895 nm if considering the aggregating chain tilting with respect to the normal to the layer plane.So the hydrogen bonded molecular chain direction represents the main aggregating direction.Meanwhile,the xerogel samples have another preferred diffraction at 16.64°(2θ) due to the preferred arrangement of molecules under the help of hydrophobic association,therefore resulting in two-dimensional aggregating structure.
