Experimental Study of Gravitation Effects on Liquid Crystal Phase Transitions in Polydisperse Aqueous Suspensions of Mg 2 Al Layered Double Hydroxide

Effects of gravity on liquid crystal phase transitions (LCPT) in polydisperse aqueous suspensions of Mg 2 Al layered double hydroxide (LDHs) were studied under normal gravity condition. Samples with different suspension concentration (SC) were tested for 15 days and the relevant changes in samples were observed through crossed polarizers. Our results showed: (a) the samples were still isotropic (I) when SC < 23 wt%; (b) when 23 wt% < SC < 30 wt%, a shear-induced birefringence appeared after preparation, and finally coexistence of four phases was reached, including an opaque isotropic top phase, a birefringent middle phase, a faint birefringence phase and a sediment layer of larger platelets resulting from the high polydispersity; (c) when SC > 30 wt%, the suspensions were in a gel state, and the gel network slowed down the LCPT. The above different behavior of phase transitions is apparently due to the concentration gradient and fractionation caused by gravity. This study provides guidance on how to select samples of LDHs suspensions for LCPT used in the upcoming experiment in the space program SJ-10 satellite.