Influence of Nanosize Silica Particles on the Rheological Behaviour of Lyotropic Cubic Phase of Glucopone (APG) Surfactant

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The effect of nanosize silica particle on the stability, structures and rheological behaviours of cubic liquid crystalline phases of Glucopone/water/heptane system were investigated. Small-angle X-ray scattering (SAXS) and polarizing microscope were used for phase identification and structure characterization. SAXS scattering profile was characteristic to cubic phase before and after the addition of silica particles. The cubic samples showed several diffraction peaks and can be assigned to the Ia3d space group. The area per surfactant molecule was found to increase as the silica concentrations was increased. Moreover, the rheological study on the cubic phase with different silica concentration was performed. The frequency-dependent storage and loss modulus were found to be characteristic of the cubic phase in the linear viscoelastic region. The cubic samples behave as solid-like material with storage modulus G’~ 0.7106 Pa typical of cubic lyotropic materials. The elasticity of cubic samples was found to increase with silica concentration. The increase in the elasticity was ascribed to the network and the formation of smaller structure as indicated by SAXS measurements. As temperature was further increased a decreased in the elasticity was observed confirming the structural change as indicated by the change in slopes of G’ and G”. The cubic samples exhibited shear thinning behaviours, with the dynamic viscosity being affected by the silica particles concentrations and the effect of silica particles on the rheological behaviours was quite noticeable as the concentration increased. The results showed strong correlation between rheology and microstructural changes in the dispersion of nanoparticle silica in the cubic phase system.