Alladi Ramakrishnan Hall

Mixtures of liquid crystals and magnetic nanoparticles: hybrid materials with tunable flow properties

Gaurav Prakash Shrivastav

TU Vienna

Composites of liquid crystals (LC) and magnetic nanoparticles (MNP) have attracted significant research attention in the past few years. These stimuli-responsive and adaptive hybrid materials are extremely interesting in terms of advancing new functionalities. While the equilibrium self-assembly of these systems is well explored, this is not yet the case for the dynamics and flow properties. Motivated by this lack, we present an extensive molecular dynamics simulation study on the equilibrium dynamics and rheology of a hybrid system composed of magnetic colloids doped inside a liquid crystalline matrix. We demonstrate that the anisotropic environment provided by the LC matrix strongly affects the equilibrium translational dynamics of the MNPs. This effect is reflected in the form of a subdiffusive regime at intermediate times in the mean square displacement of the MNPs which gets extended as the strength of the dipolar coupling is increased. When the external shear is applied, the mixture shows a shear thinning behavior. A transition from the Newtonian to non-Newtonian behavior is observed at a critical shear rate. The extent of the non-Newtonian regime increases as the strength of the dipolar coupling among the magnetic particles is increased. The microstructure of the mixture is highly affected by the shear which is reflected in the shear-induced isotropic to nematic ordering in both the species at large shear rates. These studies on the equilibrium dynamics and rheological properties of the LC-MNP mixture are interesting as these provide a pathway to design complex fluids with tunable flow properties.