Coarsening and solidification via solvent-annealing in thin liquid films
We examine solidification in thin liquid films produced by annealing amorphous Alq[subscript 3] (tris-(8-hydroxyquinoline) aluminium) in methanol vapour. Micrographs acquired during annealing capture the evolution of the film: the initially-uniform film breaks up into drops that coarsen, and single...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
Cambridge University Press
2014
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| Online Access: | http://hdl.handle.net/1721.1/87630 https://orcid.org/0000-0002-0960-2580 |
| Summary: | We examine solidification in thin liquid films produced by annealing amorphous Alq[subscript 3] (tris-(8-hydroxyquinoline) aluminium) in methanol vapour. Micrographs acquired during annealing capture the evolution of the film: the initially-uniform film breaks up into drops that coarsen, and single crystals of Alq[subscript 3] nucleate randomly on the substrate and grow as slender ‘needles’. The growth of these needles appears to follow power-law behaviour, where the growth exponent, γ, depends on the thickness of the deposited Alq[subscript 3] film. The evolution of the thin film is modelled by a lubrication equation, and an advection–diffusion equation captures the transport of Alq[subscript 3] and methanol within the film. We define a dimensionless transport parameter, α, which is analogous to an inverse Sherwood number and quantifies the relative effects of diffusion- and coarsening-driven advection. For large α-values, the model recovers the theory of one-dimensional, diffusion-driven solidification, such that γ→1/2. For low α-values, the collapse of drops, i.e. coarsening, drives flow and regulates the growth of needles. Within this regime, we identify two relevant limits: needles that are small compared to the typical drop size, and those that are large. Both scaling analysis and simulations of the full model reveal that γ→2/5 for small needles and γ→0.29 for large needles. |
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