Nanoparticle induced self-assembly

Abstract

Self-assembly has for the large part focused on the assembly of molecules without guidanceor management from an outside source. However, self-assembly is in principle by no meanslimited to molecules or the nanoscale. A particularly interesting method to theself-assembly of micro- to millimetre sized components is the use of the ‘magnetic hole’effect. In this method, nonmagnetic particles can be manipulated by external magneticfields by immersing them in a dispersion of colloidal, magnetic nanoparticles, denotedferrofluids. Nonmagnetic particles in magnetized ferrofluids are in many ways ideal modelsystems to test various forms of particle self-assembly and dynamics. When microspheresare confined to a monolayer between two parallel plates and subjected to static oroscillating magnetic fields they show a variety of dynamical behaviours and assemblages,depending on the frequency and direction of the external fields. A single pair of magneticholes oscillating in a ferrofluid layer may be used to measure the viscosity of tiny volumesof the fluid. We have also observed ordering of dilute dispersions of macromolecules andnanoparticles in magnetized ferrofluids. The self-assembly at this length scale resultsfrom structural correlations between these nanostructures and ferrofluid particlesrather than from the macroscopic magnetostatic effect for the magnetic holes.