Controlling Pattern Formation in Polymer and Nanoparticle Assemblies via Programmed Flow-coating

We have developed a novel flow-coating method for assembling periodic polymer and nanoparticle line patterns with controlled spacing and width of lines. In flow-coating, a dilute polymer and/or nanoparticle solution is held by capillary forces under a stationary knife blade fixed at gap height above a substrate fixed to a translating stage. Upon translating the substrate, spontaneous formation of convective polymer and nanoparticle assemblies occurs at the three-phase contact line of the meniscus. We demonstrate that the width and spacing of deposited lines can be controlled over a wide range by using programmed velocity profiles for the translating stage. Deposition of solutes is induced when contact lines are ``stick'' at slow or zero velocity, while limited deposition occurs during ``slip'' at high velocity. We investigate the effect of gap height, concentration, and velocity on the pattern formation This new method provides an easy, robust, and lithography-free method to control the deposition of line pattern of polymers and nanoparticles for various applications.