Macroscopic patterning via dynamic self-assembly and wrinkling instability

Abstract

My PhD work focuses on developing new methods to create the macroscopic patterns in a simple, robust, and versatile way. For macroscopic pattern formation, we first use flow coating as an assembly technique, uniquely balancing two driving forces: (i) evaporative deposition of nonvolatile solutes at a three-phase contact line and (ii) precision movement of a confined meniscus layer. This balance leads to the formation of line-based patterns that range in height and width from nanometers to microns, with lengths greater than centimeters. Moreover, we couple this deposition methodology with functional ligand chemistry on the nanoparticle surface, which allows us to create complex nanoparticle structures. By lifting crosslinked nanoparticle ribbons and ropes, exceptionally intriguing structures emanate from this process. The nanoparticle ribbons and ropes demonstrate a leap forward in nanomaterials fabrication, since the nanoscale properties are embedded within a macroscale object that can be manipulated with conventional methods and engineered into advanced technologies Using mechanical instability, we fabricate a simple, robust stimuli-responsive surface with periodic structures over a large area based upon osmotically-driven surface wrinkling. Although surface wrinkling has received considerable attention in the scientific literature, only a handful of papers have shown the ability to harness perhaps the greatest potential attribute of surface wrinkles: their active reversible nature. The ability to precisely control surface topographic morphologies in accordance with established scaling relationships opens a wide array of advanced materials applications, which do not rely upon cost-limiting fabrication techniques. Specifically, the surfaces respond to solvent exposure by developing well-defined topographic structures over laterally extensive areas due to osmotically-driven differential strains between a surface layer and underlying soft substrate. The observed wrinkling occurs spontaneously, forming hierarchical morphologies with controlled dimensions, and vanishes upon removal of the solvent driving force. The combined responsiveness and reversibility of wrinkling allow for the realization of functional devices, such as smart windows, smart microlens arrays, reversible channels in microfluidic devices. Moreover, by using thermal and osmotic approaches, we study the influence of geometry and material properties on surface instability such as cracking and wrinkling in a trilayer system consisting of a thin film on a soft foundation supported by a rigid substrate.