Novel Device and Preparation Route for Hollow Structures

The proposed project wishes to investigate an encapsulation phenomenon driven by airflow. The processing science and technology is referred to as aerodynamically assisted jets or jetting (AAJ). The apparatus used in this technology has a needle partially fitted in a crystal glass chamber, which can hold a large pressure, which is supplied via a compressor. The central needle axis is in line with the centre of an exit orifice which is on the opposite side to the needle, namely on the base of the glass chamber. As the process utilises airflow for drawing a growing drop of liquid a pendant-like shape is formed from the liquid at the exit of the needle. From the apex of this pendant-shaped droplet a jet evolves which goes onto break down after flowing past the exit orifice of the device. The entire process from the formation of the pendent-like droplet to the generation of droplets will all be recorded in real time with the specialist equipment supplied in-kind by both the project partners namely, Oxford lasers Ltd and Photo-Sonics International Ltd.The first stage is where the construction of a single needle device takes place. Here this device will be constructed and tested with water and ethanol for forming droplets and more importantly monodisperse droplets. Following this study a family of commercially available silicone oils will be employed as their viscosities range from 1-100000mPa s. These liquids will be processed using a single needle device, which will initiate significant modifications to be made on the single needle prototype to accommodate such a large regime of viscosities. There will be several devices constructed for processing a particular range of viscosity respective to that device. Hence the project later introduces a polymer, namely poly(ethylene) oxide (PEO) which when processed in this route will solidify at ambient temperature allowing the characterisation of the collected droplet relics.The next stage employees the know-how in single needle AAJ device design and construction to build a co-axial or concentric needle AAJ device. The idea is to have the inner needle accommodating the flow of a gas stream (could either accommodate a viscous liquid or suspension) with the outer having at the test phase the silicone oils. Subsequently after a robust device is designed and tested for handling both droplet encapsulation and the wide range in viscosities, PEO blends will be processed. PEO blends will be formulated by mixing with water and ethanol making it a liquid medium, which can be made to aerodynamically flow through the exit orifice. At this stage the device will be capable of forming hollow structures and micro-foams from both silicone oils and PEO blends. Note that silicone oils have only been used for testing the devices for the range of viscosities. PEO blends comprising a varying vol. % of PEO will mimic those viscosities of the silicone oils. PEO is employed as it solidifies in ambient temperature hence the hollow droplets or bubbles can be characterised.The final stage will incorporate the addition of commercially available ceramics powders into the PEO blends. The intention here is to heat treat the generated bubbles to obtain a sintered hollow structure. Furthermore the co-axial needle AAJ configuration will be scaled up to accommodate an array of needles for mass scale processing.