A study of meniscus formation with application to edge-defined fibre growth process

For the edge-defined fibre growth (EFG) process, the meniscus of liquid bridging the crystal to the melt is critical in determining the properties of the solidified crystal. It is standard practice for existing theoretical models to use equilibrium meniscus shapes with specified contact angle to represent the behaviour of the meniscus. It is shown here that with boundary conditions pertaining to the EFG process, multiple solutions exist to the axisymmetric form of the Laplace-Young equation. Furthermore, these possible meniscus profiles may correspond to minima, maxima or non-extrema points as far as energy is concerned. The implications of this observation on meniscus stability are explored. The interaction of Bond number, pressurisation, aspect ratio and contact angle is shown to result in a variety of meniscus behaviour. The effect of direction of pulling in relation to gravity is also investigated. It is found that directional bias is significant for higher Bond numbers and aspect ratios. From the results it appears that there are cases, particularly for tall menisci, for which commonly adopted equilibrium shapes may be unstable and the consequent dynamic behaviour must be considered. Quasi-equilibrium dynamics of the meniscus is simulated using a simplified hysteresis model for the contact angle at the lop of the meniscus. A variety of behaviour is found to arise, which is not fully captured by relations governing meniscus behaviour used hitherto in simulation of the EFG process.