Vanadium Pentoxide Sol and Gel Mesophases

Colloidal suspensions of V₂O₅ ribbon-like particles display optical textures typical of lyotropic nematic phases. Tactoids (small nematic droplets) and then isotropic phases are formed as these systems are diluted. Nematic suspensions can be oriented by applying a magnetic or an electric field. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsion should also be responsible for the stabilization of the nematic phases. Anisotropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. X-ray diffraction patterns of such coatings exhibit a series of 00l harmonics due to the turbostratic stacking of the oxide particles. Dehydration is reversible and fluid mesophases are again obtained via a swelling process when water is added to the xerogel.