Viscosity-Dependent Janus Particle Chain Dynamics

Abstract

Iron oxide (Fe3O4) Janus particles assemble into staggered chains parallel to the field lines in an ac electric field. Subsequent application of an external magnetic field leads to contraction of the staggered chains into double chains. The relation between the viscosity of the surrounding solution and the contraction rate of the iron oxide Janus particle chains is studied. Further, the influence of particle size and chain length (i.e., number of particles in chain) on the contraction rate is investigated. The base material for the Janus structure is silica (SiO2) with particle sizes of 1, 2, and 4 μm, and the cap material is Fe3O4. Addition of increasing amounts of glycerol to the aqueous system reveals that the contraction dynamics strongly correlate with the viscosity of the solution. The average chain contraction rate for each particle size can be fitted in the low viscosity range from 1 to 30 mPa·s with a power function of the form A/μ(0.9) - B/μ, in which the coefficients A and B are particle size, electric field, and magnetic-field-dependent constants. Using this function, the viscosity of an unknown solution can be determined, thereby pointing to the potential application of these Janus particle chain assemblies as in situ microviscometers.

Actuating Soft Matter with Magnetic Torque

“…In addition to driving optical assemblies, janus particles have also been used to monitor local properties in fluids (e.g., pH, viscosity) . Anker and Kopelman developed magnetically modulated optical nanoprobes (MagMOONs) consisting of a fluorescent polystyrene microsphere containing a ferromagnetic material, with a portion of the hemisphere coated with a metal (aluminum or gold) .…”

Janus nanoparticles inside polymeric materials: interfacial arrangement toward functional hybrid materials

“…In this regard, external field-assisted alignment techniques may offer economical alternatives for fabricating highly ordered composite nanostructures. For example, various groups have already incorporated magnetic NPs or magnetic/metallic caps to investigate the self-assembly behavior of Janus NPs in magnetic [96][97][98][99][100][101][102][103] or electric fields. 104,105 A fluid-fluid interface is a natural platform for obtaining monolayer self-assembled structures of Janus NPs.…”

Dynamics of a Pair of Paramagnetic Janus Particles under a Uniform Magnetic Field and Simple Shear Flow

“…For isotropic particles, chains or flails can form with spherical and elliptical microparticles [19,20]. For anisotropic particles under a magnetic field, staggered chains, double chains, or clusters can be constructed [4,[21][22][23][24]. Colloidal superstructures can also be formed under a rotating magnetic field when programmed magnetic Janus particles rotate on their long axis and are used as building blocks with other particles [14].…”