In Situ SAXS Study of the Formation of Aluminum Hydroxide-Based Hydrogels with Excellent Optical Properties

In this work, the mild and homogeneous alkalization strategy known as the epoxide route was employed for the synthesis of aluminum hydroxide-based hydrogels. The formation of such materials was in situ analyzed through pH and conductivity measurements and, particularly, careful analysis of the evolution of small-angle X-ray scattering patterns along the sol-gel transition. This study allowed a thorough understanding of the key aspects that control the hydrogel formation as well as the final structure at the micro/mesoscale. Particularly, it is proposed that the hydrogels are formed by aggregates of clusters with fractional internal dimensions due to the anisotropic interaction of nanoparticles. Moreover, the study on the effect of the synthetic initial conditions (e.g., the concentration, cosolvent, and ionic strength) allows the determination of the control over hydrogel properties, where well-transparent hydrogels can be obtained even under high ionic strength conditions (up to 100 mM KClO₄). Thus, these Al(OH)₃ hydrogels have promising features as matrices to build one-pot composites for applications in several fields.