Formation of well-ordered finger-like structures on pre-cast thin films

Abstract

In this work, we developed a simple method to construct well-ordered finger-like structures on pre-cast polymer films for the first time. Confining a droplet between a tilt carbon rod and a pre-cast poly(methyl methacrylate) film and limiting the evaporation of the droplet, a gradient finger-like surface structure consisting of multiple arc-segments and line-segments was formed. The wavelength of the arc-segments first decreases, reaches a minimum, and then increases with the increase of the distance to the tip of the gradient finger-like structure. The geometric characteristics of the finger-like surface structures are dependent on the droplet volume and the tilt angle. Using this approach and a “four-rod” template, a “cross” surface pattern, which consists of 4 finger-like structures, was constructed. In addition, this method was used to form surface structures on polystyrene (PS) films. The surface structures consisted of slightly undulating lines and disconnected beads in contrast to the continuous ridges formed on PMMA films.