Electron Microscopy of Modified Aluminum Alkoxide Microstructures on Freeze–Drying

Direct imaging of microstructures in chelated aluminum alkoxide systems subjected to freeze–drying and freeze–thaw–drying is reported using cryo-scanning electron microscopy (SEM) and SEM techniques. Aluminumsec-butoxide was chelated with a β-diketoester in different molar ratios. This system was gelled by hydrolysis under intense sonication. The sonogels formed were subjected to cryo-SEM. Samples for cryo-SEM were made by freezing the chelated alkoxide samples in liquid nitrogen and freeze–fracturing them inside the cryo-SEM and monitoring the apparent morphological changes on exposure to the cryo-SEM environment including intentional sample heating. Microstructures of unchelated, 1:1 chelated and 1:2 chelated (alkoxide:chelate) sonogels after freezing, thawing, and drying were also imaged by SEM techniques. Heterogeneity introduced by chelation of alkoxide is proposed as the cause for the formation of flakes in freeze–thaw–dried chelated alkoxide gels. Microstructures of 1:1 chelated freeze dried alkoxide were compared with the freeze–thaw–dried gels. The absence of flakes in the chelated samples when subjected toin situfreeze–drying indicated reversible nature of the gels.