Crystal growth in a three-phase system: Diffusion and liquid-liquid phase separation in lysozyme crystal growth
M. C. R. Heijna, W. J. P. van Enckevort, and E. Vlieg

Abstract:
In the phase diagram of the protein hen egg-white lysozyme, a region is present in which the lysozyme
solution demixes and forms two liquid phases. In situ observations by optical microscopy show that the dense
liquid droplets dissolve when crystals grow in this system. During this process the demixed liquid region
retracts from the crystal surface. The spatial distribution of the dense phase droplets present special boundary
conditions for Fick’s second law for diffusion. In combination with the cylindrical symmetry provided by the
kinetically roughened crystals, this system allows for a full numerical analysis. Using experimental data for
setting the boundary conditions, a quasi-steady-state solution for the time-dependent concentration profile was
shown to be valid. Comparison of kinetically rough growth in a phase separated system and in a nonseparated
system shows that the growth kinetics for a three-phase system differs from a two-phase system, in that crystals
grow more slowly but the duration of growth is prolonged.