Design and fabrication micro/nano patterned surfaces using fluid-based techniques

Micro/nano patterned surfaces have found increasing applications in various emerging technologies, thanks to their interesting functionalities related to wetting, self-cleaning, adhesion, acoustics, and interactions with biological entities. However, the task of developing practical techniques to fabricate large area of such surfaces in a well-controlled and cost-effective manner still remains challenging. This project investigates the feasibility of techniques driven by capillary fluids for fabrication of functional polymeric surfaces with patterns ranging from microscale down to nanoscale. The ultimate goal here is to reproduce the complex bactericidal nanostructures that appear on the wings of insects, such as cicada and dragon flies through biomimicry approaches. The technical and scientific developments offered in this PhD project span over multiple fields of science and engineering, such as fluid mechanics, material and polymer science, micro- and nanotechnology, and mechanical and chemical engineering.

Relative to other fabrication tools, such as micro- and nano-etching, fluid-based techniques are energy-efficient and inexpensive, and can be used to process a variety of different polymeric materials. Moreover, fluid-based patterning approaches rely on natural self-organising forces, and thus can be implemented over significantly larger-area of substrates. Capillary fluid techniques start with a soft polymeric solution coating and employ micro/nano bubbles or droplets as temporal templates to create a final uniform pattern on the polymer. During the drying process of the polymer, the bubbles collapse and droplets evaporate, providing a self-organised hexagonally packed micro/nano patterned solid surface. Two main approaches are to be investigated for producing micro bubbles and droplets as templates in this project: (i) condensation in humid environments to produce water droplets and (ii) microfluidics to generate foams with well/controlled bubble size and packing.

The structure and size distribution of the final micro/nano patterned surface fabricated through capillary fluid techniques are expected to be functions of an array of variables, such as environmental conditions (temperature, humidity, etc.), interfacial properties of the substrate material and template fluid, and external force field applied during the process. Understanding physical interactions of these variables with the ultimate goal to design well-controlled micro/nano patterned surfaces with specific functionalities is the main focus of this project. Furthermore, in this project the designed and fabricated patterned surfaces will be characterised to evaluate their quality and functionality, especially in terms of pattern uniformity, wettability and adhesion.