Fine Particle 2D Crystals Prepared by the Dynamic Thin Laminar Flow Method

A novel method to make 2D crystals of fine particles is proposed. It is based on the hydrodynamic properties of thin laminar flow. To explore the possibilities of this method, we chose two variables, the particle diameter and the surface charge density. The spherule diameter varied from 6 μm to 53 nm, and its calculated surface charge density from 1134 to 4 μC/cm2. In every case, we easily obtained a rate of monolayer preparation up to 1 mm/s. Moreover, 2D crystals were always observed. The subphase ionic condition was the key parameter providing an adsorption window wide enough to allow a controlled particle−air/water interface adsorption, while maintaining particle−particle repelling electrostatic forces strong enough to avoid fractal formation during the surface compression. This report demonstrates that the DTLF method is an efficient way of producing monolayers and 2D crystals of colloids and that it could be developed to work in a continuous mode.