Numerical simulation of spin coating processes involving functionalised Carbon nanotube suspensions

This paper reports the numerical simulation of spin coating for functionalised Carbon Nanotube (CNT) suspensions. Spin coating is a process commonly used to deposit uniform thin films onto flat substrates by means of high rotation velocity and centrifugal force. The functionalised CNTs modelled in this study were chemically treated in a way such that aggregation was prevented through electrostatic repulsion between CNTs. The functionalised CNTs in the semi-dilute suspensions can be modelled as rigid fibres with their orientation dictated by the flow of the solvent. The evolution of CNT orientations was simulated using a pre-averaged kinetic theory with an appropriate rotary diffusion coefficient accounting for randomising events. A Natural Element strategy with an updated Lagrangian framework was implemented to solve the free-surface problem involving large domain deformation and to avoid numerical problems associated with Finite Element modelling. The model reported herein couples micro-scale CNT orientation with the macroscopic suspension kinematics and it offers important insights in relation to the final properties of spin-coated CNT films as well as the processing behaviour of CNT suspensions.