Biomimetic Engineering of Patterned Surfaces to Control Crystallization: From Colloids to Ice

Abstract

Numerous natural organisms use chemical and structural patterning to manipulate complex crystal growth and control their aqueous environment. Structural templates such as vesicles and cell walls aid in the growth of nano- and micro-patterned single crystal structures seen in sea urchins, brittlestars, and sea cucumbers. Patterned surface chemistry is used by the Namib dessert beetle for water collection and by the lotus leaf to fend off raindrops. Taking inspiration from natural organisms, structural and chemical patterning is used to achieve extended functionality and better control over the properties of self-assembled colloidal crystals and anti-icing water-repellent surfaces. The first system involves the use of self-assembled colloidal crystals (Part I) as patterned structural templates for synthesizing porous inverse opals (with applications in photonics, tissue engineering, sensing, catalysis). Controlling colloidal crystal assembly poses a technological challenge and Chapter 1 explores how assembling colloids together with a matrix material (silica sol-gel) results in large-scale, ordered, crack-free inverse opal structures. It also discusses the mechanical and optical properties of these large-scale films and investigates the different aspects of this assembly mechanism. Chapter 2 demonstrates several methods for altering the surface chemistry and composition of co- assembled inverse opals in order to add new functionality. Chapter 3 explores how patterned micro- topography can be used to alter direct and inverse opal growth and make novel hierarchical structures. The second system involves using structurally patterned water-repellent (superhydrophobic) surfaces to control condensation and ice crystallization (Part II). Materials that control ice formation are important to aircraft efficiency, highway and powerline maintenance, and building construction. Chapter 1 explores how superhydrophobic materials can be designed to prevent or control impact ice accumulation by limiting the time and area of contact of a droplet with a cold surface. Chapter 2 discusses how our structured, water-repellent surfaces respond to high humidity conditions and condensation. Chapter 3 discusses how localized chemical patterning on various superhydophobic surface geometries can be used to spatially control water condensation and freezing.