Liquid Crystal–Ferrofluid Emulsions

Dispersing nanoparticles in liquid crystals (LCs) is used to tune liquid crystal properties, to add functionality, or to exploit the self-organization of the liquid crystals to transfer order onto dispersed particles. Dispersing ferrofluid droplets into liquid crystals (LCs) not only adds magnetic functionality to the LCs, but also produces unique systems. Magnetic functionality can be used to measure the anisotropic viscosities of the LCs on a microscopic scale when moving the ferrofluid inclusions through various thermotropic, lyotropic, and colloidal LCs using an external magnetic field. The magnetite nanoparticles of the ferrofluid form a boundary layer at the interface between the LC and the ferrofluid droplets. The viscosities are calculated using Stokes’ Law, together with the introduction of the boundary layer at the LC–ferrofluid interface. The viscosities for a variety of different liquid crystalline systems were measured as a function of changing environment, such as temperature, concentration, or pitch.

In nematic LCs, ferrofluid droplet chains are formed due to the topological defects in the LC induced by the dispersed ferrofluid droplets. The movement of these chains can be controlled by the external magnetic field. The velocities of water-based ferrofluid droplet chains in nematic 5CB, while varying factors such as the average size of the droplets, the number of droplets in the chain, and the external magnetic field strength, are reported. Adding a surfactant to the LC–ferrofluid emulsions enables the production of ferrofluid droplet chains encoated with a membrane in the LC. A comparitive study between the behaviour of the LC–ferrofluid emulsion with the addition of the surfactant polysorbate 60 (Tween-60) and uncoated ferrofluid droplet chains is reported. Different surfactants and lipids are used to produce membranes around the ferrofluid droplets to create a synthetic structure which mimics a magnetotactic bacterium.