Fabrication with magnetic-spin coating: Influence of magnetic-inertia energy ratio on gold-pickering ferrofluid droplet assembly morphology

Abstract

Magnetic self-assembly of nanoparticles is a well-known technique for creating thin-film array-patterned functional microstructures. However, an uncontrollable hierarchical assembly formation of magnetically stimulated particles has hindered the desired formation of free-standing two-dimensional (2D) array patterns in thin-film layers. In this study, we proposed a fluidic shearing effect from spin coating to reduce the magnetically stimulated particles’ disarrayed and complex chain formations. This would thus promote linear array formations, even as the film becomes thinner. A series of tests were conducted on a gold-pickering ferrofluid emulsion (GPFE) dispersed in 15.2 mPas aqueous polyvinyl alcohol (PVAh) under varying spin speeds and magnetic setups such as single (SI), compound (CC), and concentric (CR). These setups were chosen to observe the influence of magnetic field strength and distribution on the generated pattern profile from microscopic binary images of the resulting thin films. The aim was to quantify the formed chain thickness (ChT), chain gaps (ChG), and chain lengths (ChL) to capture the morphology and geometrical features of the formed patterns. Our results showed that the quantified values of these profiles and their dimensionless relationships were significantly influenced by the ratio between the applied magnetic packing energy and the centrifugally controlled fluidic energy, Q_PD. This investigation showed that ChT/ChG for a corresponding Q_PD value is 98.6% the same for all configurations, and CR was the best setup going forward, as it yielded the lowest array quality defectivity of 14%. Therefore, we assert that this fabrication method offers flexibility, cost-effectiveness, and expandability in generating linear array patterns that contain graduating variability in grating order dimensions within a single cast that can serve efficiently as a substrate for biomolecules under enhanced Raman and Infrared spectroscopies.