Micron-scale liquid engineering for porous polymer patterning
Porous polymer structures have a rich history of applications from insulation and impact absorption to superhydrophobic coatings, controlled drug release materials, biological scaffolds and photonic materials. Different approaches such as lithography, etching and direct templating were developed to produce porous polymers. There is still a huge development potential in the preparation techniques. In 1994 a self-organisation technique was reported to trap and self-organise condensed water droplets at a solution surface and then imprint their shape directly into a polymer film. This single-step direct templating method operates at ambient conditions and can be processed and controlled to form a wide range of porous structures and surface functionalities. However, there are significant manufacturing challenges that have prevented this technique from reaching the market. This research tackles this problem by combining top-down techniques for precise liquid deposition utilising inkjet printing technique with the same bottom-up self-assembly processes at micron-scale by ordering drops and encapsulating materials in drops to load functional materials into the porous structure directly. This research aims firstly at controlling and simplifying the system to understand the force balances and interfacial phenomena by observing the impact behaviour of droplets generated by inkjet printing onto organic solvent and polymer, with the aid of high-speed imaging systems. Secondly to deliver a new, simple and scalable engineering solution to translate this technique to the manufacturing of materials with controlled surface properties. Inkjet technique enables precise deposition of droplets onto substrates, with controlled volume, speed, and compatible with a wide range of materials by altering the type and dimensions of the printheads also the driving waveforms. Manipulating polymer viscosity is a new approach of regulating pore ordering and geometry. This research made a breakthrough in the porous polymer production, showing highly ordered structures, easy porosity design, biocompatible processing methods, and digitally controllable and programmable production. In addition, it is the first time obtaining highly ordered porous polydimethylsiloxane (PDMS) using droplets as templates. These porous PDMS have a huge potential in the applications of drug delivery device, biosensor, high-throughput screening, and flexible electronics.
porous polymer, inkjet printing, PDMS patterning
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