Design, fabrication and process modelling of a near field electrospinning test bench

Abstract

This thesis presents a full test bench design, process modelling and some experimental work on near-field electrospinning. With the original objective of precisely controlling fiber placement with the electrospinning technique, a full analysis of existing techniques was done. Findings revealed design parameters, guidelines and choice technology for a proposed test bench. The main focus being optimization and parametrisation of a near-field electrospinning (NFES) experimentation. The final test bench design implements high precision components. Linear bearings, preloaded ball screws and associated pillow blocks were provided by NSK. Intermediate mounting structures and motors were sized accordingly to machine requirements. High precision drives were coupled to stepper motors to create a 3 stage (x-y-z axis) programmable deposition surface. A computer numerical control (CNC) g-code oriented interface was fully created in the LabVIEW environment. Coupled to this is a novel high voltage NFES design that has a needle to needle setup to focalise the electric field. Full process was modeled by separating and evaluating each physical phenomenon. The overall process, when the fluid shape is in steady state, is simplified to an equivalent solid model. Only linear behaviors such as Newtonian fluid characteristics and constant electric properties were taken into account. A 4% PVA solution was used throughout. A high relative permittivity, in the present case is the majority of the acting forces are at the air-fluid interface. Main forces include: surface tension and electrostatic pull with viscous forces and gravity playing a secondary role. A novel approach was used to estimate viscous forces by using computational fluid dynamics (CFD). Using a moving boundary with a constant tangential speed applied to the transition zone of the Taylor cone all along the formed jet, emulating an electrostatic pull. By varying CFD conditions, a simple linear function was obtained with viscosity and surface speed as variables to estimate overall viscous forces for a specific case. Overall, the viscous forces were so low (under 2%), that they are negligible for similar fluids and setups. A unique evaporation model was developed to estimate solidification distance based on the Langmuir model, which predicts a value of around 1mm of jet length. Finally, a finite element analysis (FEA) with a simplified electrostatic solver reduces the Maxwell equations to Gauss’s and Faraday’s law. A relationship between a resulting pulling force and an electric field for the unique high voltage geometry was determined. Combining all forces by a sum, machine controllable parameters were extracted. These parameters are: flow rate, collector distance, speed and voltage. Although fibers did not produce the desired patterns, within a few tries their production occurred. The observations, numerical simulations and the apparatus made (developed) in this work contribute to a better understanding of the complexity of the electrospinning processes.

Date	15 Jan 2020
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Nicole R. Demarquette (Supervisor) & Ricardo J. Zednik (Co-supervisor)