Nuclear spin relaxation in molecular fluids near the critical point

Topol, Richard; Krynicki, K.; Powles, J.G.

doi:10.1080/00268977900101211

Cited by 8 publications

(6 citation statements)

References 4 publications

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“…The retarded effect or memory function involved in the generalized Langevin equation is assumed to be proportional to the density fluctuation correlation function which, near the critical point, is calculated from the classical hydrodynamic central line of S(q, co) [1][2][3]. To be consistent with the previous discussion, the time-independent proportionality function is determined so that, near the critical point, rh/T,~= 1.…”

Section: (H(o)h(t))mentioning

confidence: 99%

“…Temperature dependence of the power spectrum ~.v(to) Now, we focus on the temperature dependence of the power spectrum, with ~ given by equation (34), at some frequencies. We have chosen 10, 20, 40 and 80 MHz so as to use the Larmor frequency range cited in [1][2][3]. If, for different temperatures near the critical point, In q~N(to) versus In ~o is drawn, we note that the intersection between the low and high frequency parts of the ~v(2)(to) g 2cr 1 (L)(co)/eo~ oC co -5 I~.…”

Section: ~-Dependence and [Requency Limits O[ The Normalized Power Spmentioning

confidence: 99%

“…The liquid-gas critical point is described by the spatial-and time-dependence of the density fluctuation correlation function [1][2][3]7], whose characteristics are all contained in the dynamic structure factor S(q, oJ). Near the critical point, the density fluctuations induce a modulation of the interactions (between the spins), which give the relaxation mechanisms : the closer temperature is to the critical point, the larger and the slower the fluctuations.…”

Section: (H(o)h(t))mentioning

confidence: 99%

“…Measurements of the proton spin-lattice relaxation time, Tx, near the critical point have been reported in fluid chloroform, CHC1 a [1,2], hydrogen chloride, HC1 [3], and hydrogen sulphide, H2S [3]. In the theoretical calculations of 7"1, near the critical point, the main problem is to relate the fluctuations of the local magnetic field to the density fluctuations.…”

Section: Introductionmentioning

confidence: 98%

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An approximate theoretical calculation of the spin-lattice relaxation times in fluids near—but above—the critical point

Topol

1980

Molecular Physics

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We present a theory to calculate, first, the correlation function of the physical quantity (angular momentum for spin-rotation interaction, second order spherical harmonics for the dipolar interaction), involved in magnetic spin-lattice relaxation and then the relaxation times. The time behaviour of the physical quantity h(t) is described by a generalized Langevin equation whose memory function, K(t), is assumed to be proportional to the density fluctuation correlation function, N(t). The time-independent proportionality function, ~, is obtained by assuming that the relaxation time Tn (for h(t) to reach local equilibrium) is equal to the correlation time, ~'n, of the density fluctuations. The density fluctuation correlation function is calculated by using the classical hydrodynamics form of the structure factor S(q, to) [1,2]. The definition chosen for N(t) forces us to consider only temperatures above the critical temperature, since we do not know the particle density of the liquid below the critical temperature.The ~-dependence of the memory function, the total effect correlation function and the normalized power spectrum is presented. Once the choice of ~ is made (~ is temperature dependent), the main result of the theory is to give a minimum, above the critical temperature, for the spinlattice relaxation times. The variation law (ATocto 1/*) of the shift, AT, in the temperature of the minimum from the critical temperature with respect to the frequency, found experimentally by Krynicki et al. [2], is verified. But while this result is consistent with experimental T1 measurements for CHC13, it is not with those for HCI (and H2S) : for dipolar and spin-rotation interaction we found a similar temperature dependence.

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Section: (H(o)h(t))mentioning

confidence: 99%

Section: ~-Dependence and [Requency Limits O[ The Normalized Power Spmentioning

confidence: 99%

Section: (H(o)h(t))mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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An approximate theoretical calculation of the spin-lattice relaxation times in fluids near—but above—the critical point

Topol

1980

Molecular Physics

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“…8 In those studies, nuclear spin relaxation rates were used to probe the power spectra of the critical fluctuations in liquids, crystals, and magnetic systems. 9,10,11 However, due to practical limitations, systematic time-resolved NMR studies of the kinetics of morphological changes accompanying phase transitions had not been reported until this work.…”

Section: Introductionmentioning

confidence: 99%

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

Cau

Lacelle

1995

The Journal of Chemical Physics

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NMR study of liquid and supercritical benzene

Asahi¹,

Nakamura²

1997

Ber Bunsenges Phys Chem

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Density, spin-lattice relaxation time and self-diffusion coefficient of benzene have been measured under vaporliquid coexistence from room temperature up to above the critical temperature. Measurements were made for four samples with the density in the supercritical region being respectively 0.302, 0.250, 0.154 and 0.101 g ~m -~. The density has been determined by the NMR one-dimensional projection technique, and the Carr-Purcell-Meiboom-Gill method has been adopted to the measurement of the self-diffusion coefficient. The results obtained have been discussed in terms of hard sphere models and various contributions to the relaxation rates have been separated and the correlation times for each molecular motion have been estimated at 470 K. It has been shown that the spin-rotational relaxation is dominant near and above the critical temperature.

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Nuclear spin relaxation in molecular fluids near the critical point

Cited by 8 publications

References 4 publications

An approximate theoretical calculation of the spin-lattice relaxation times in fluids near—but above—the critical point

An approximate theoretical calculation of the spin-lattice relaxation times in fluids near—but above—the critical point

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

NMR study of liquid and supercritical benzene

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