Nonparabolic nanoscale shift of phase boundaries in binary systems with restricted solubility

Abstract

Computer simulations were used to study the interplay of the diffusion asymmetry (composition dependence of diffusion coefficient) and the phase-separation tendency (chemical effect) in the kinetics of the interface shift during dissolution in a binary system with restricted solubility. We have found that---on nanoscale, taking into account only the diffusion asymmetry---the shift of the chemically sharp interface is not proportional to the square root of the time as would be expected from Fick's laws but to ${t}^{{k}_{c}},$ where $0.25<{k}_{c}<1$ (deviations from the parabolic law). In ideal systems $0.5<~{k}_{c}<~1,$ but with increasing mixing energy $(V)$ the interface shift returns to the parabolic law ${(k}_{c}\ensuremath{\approx}0.5),$ and at very large V values ${k}_{c}$ can be even less than $0.5.$ This effect is a real ``nanoeffect,'' because after dissolving a certain number of layers (long time or macroscopic limit), the interface shift returns to the parabolic behavior. It is also illustrated that these phenomena can be observed experimentally as well.