Fumed alumina-in-nematic liquid crystal suspensions under shear and electric field

We study rheology, microstructure, and response to an applied electric field (E) in suspensions of fumed alumina (Al <inf>2</inf> O <inf>3</inf> ) nanoparticles in a nematic liquid crystal (NLC) made of N-(4-methoxybenzylidene)-4-butylaniline (MBBA). Fumed Al <inf>2</inf> O <inf>3</inf> /MBBA suspensions exhibit flowability with nanoparticle volume fraction (ϕ) = 0.001 and 0.007, and become solid-like gels at a nanoparticle ϕ = 0.014 and beyond. The dynamic rheology of gel-like suspensions follows the soft glass rheology (SGR) model. The effective noise temperature remains close to 1 for these Al <inf>2</inf> O <inf>3</inf> /MBBA suspensions, which serves as an indication of the presence of glassy dynamics. Further, the optical microscopy and the differential scanning calorimetry (DSC) reveal that the incorporation of fumed Al <inf>2</inf> O <inf>3</inf> nanoparticles causes a significant depression in the nematic-isotropic phase transition temperature (T <inf>NI</inf> ). The gel-like suspensions are less sensitive to pre-shear and show a large structural recovery after shear when compared to Al <inf>2</inf> O <inf>3</inf> /silicone oil suspensions. At and above a critical nanoparticle ϕ = 0.005, the suspensions exhibit a reversible nematic-isotropic phase transition under the application of E.