0000000000328590
AUTHOR
B. Geil
Translational and rotational molecular motion in supercooled liquids studied by NMR and forced Rayleigh scattering
It has been shown that translational diffusion coefficients, Dt, in the supercooled van der Waals liquids, orthoterphenyl, phenolphthaleindimethylether, and salol, have a weaker temperature dependence than the shear viscosity, η, at T ≲ 1.2Tg and can be described by Dt ∼ η−χ with χ < 1 whereas Dr ∼ η−1 applies for the mean rotational diffusion coefficients, Dr, down to the glass transition temperature, Tg. This apparent decoupling of translational and rotational motion has been discussed in relation with possible anomalous short time diffusion, spatial heterogeneity, and cooperative molecular motions close to Tg.
Influence of data treatment on the shape of 2H NMR T1 curves
A new interpretation of 2H T1 data of glass-forming systems in the range of the range of the caloric glass transition temperature has been proposed. It is shown that with the traditional treatment of the data the timescale of structural relaxation has an influence on the observed spin-lattice relaxation times. Avoiding this problem with a different treatment of the experimental data, it is possible to compare the 2H T1 data directly with corresponding 1H data.
Translational and rotational diffusion in supercooled orthoterphenyl close to the glass transition
Self diffusion coefficients in supercooled orthoterphenyl (OTP) have been determined down toD t =3·10−14 m2s−1 using a1H-NMR technique applying static field gradients up to 53T m−1 In a range of more than two decades theD t values agree with those of photochromic tracer molecules of the same size determined by forced Rayleigh scattering down to the glass transition temperatureT g . A change of mechanism is found for translational diffusion atT c ≈1.2T g whereD t is proportional to the inverse shear viscosityη −1 atT>T c butD t ∼η ξ with ξ=0.75 atT<T c . Rotational correlation times determined by2H-NMR stimulated echo techniques in deuterated OTP remain proportinal toη −1 down toT g . Our re…