TITLE

Nuclear magnetic resonance studies of domain growth in the late stage of phase separation of a binary liquid mixture

AUTHOR(S)
Cau, Franco; Lacelle, Serge
PUB. DATE
August 1995
SOURCE
Journal of Chemical Physics;8/15/1995, Vol. 103 Issue 7, p2670
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The domain growth processes occurring during the gravity-dominated regime of the phase separation of a cyclohexane/aniline critical mixture, following a temperature quench in the unstable region below the temperature-composition coexistence curve, were investigated with high-resolution 1H NMR. Diffusive exchange of cyclohexane molecules between a small volume fraction of immiscible droplets and the surrounding fluid with a different cyclohexane concentration leads to a domain-size dependent 1H NMR cyclohexane chemical shift in the continuous phase. In this case, the equations of motion for the transverse magnetization density reduce to a first-order exchange between two immiscible phases with rate coefficients depending on the droplet size and the transport process across the liquid–liquid interface. Application of this model to the data yields a power law for the growing droplets, R(t)=At[lowercase_phi_synonym], where R is a typical domain size, with the growth exponent [lowercase_phi_synonym]=0.30±0.01 and the amplitude A[bar_over_tilde:_approx._equal_to]0.9×10-6 ms-[lowercase_phi_synonym]. These values are in close agreement with previous visualization studies on the same binary mixture [F. Cau and S. Lacelle, Phys. Rev. E 47, 1429 (1993)]. The results also confirm the presence of a new domain growth regime involving Brownian coagulation and sedimentation in the very late stage of the phase separation processes of binary liquid mixtures. A strong linear composition dependence of the 1H NMR cyclohexane chemical shift in one-phase cyclohexane/aniline mixtures was interpreted on the basis of solvent shift effects induced by intermolecular interactions and susceptibility effects. In each phase of the two-phase equilibrium mixture, inhomogeneous line broadening, arising from the magnetic susceptibility discontinuity at the interface between phases, is also investigated. © 1995 American Institute of...
ACCESSION #
7628118

 

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