Dropwise deposition and wetting of nanoparticle suspensions

The wetting and spreading behavior of micron-sized colloidal nanoparticle suspension ('nanoink') droplets upon deposition on a flat substrate is investigated experimentally and numerically and compared to the behavior of the pure liquid solvent. Toluene containing gold particles is used as a reference working liquid, deposited either on a copper or a glass substrate. The experiments undertaken with a high-speed camera record the dynamic impact and spreading process and the results are used to calibrate a numerical model based on the Navier-Stokes equations in Lagrangian coordinates. The model accounts for wetting and the motion of a representative number of computational particles according to the relevant form of Newton's second law. The presence of the particles reduces spreading up to about 30%. The simulation using the particle model suggests that recirculation flow patterns during oscillatory recoiling phases lead to a particle pre-structuring in the vicinity of the substrate, providing an additional mechanism for the development of the characteristic trough shape encountered during the drying of printed colloidal suspension droplets