J.C.F. Michielsen

The non-linear dielectric effect in liquid xenon

Abstract The non-linear dielectric effect (NLDE), that is the increase in the dielectric constant divided by the square of the applied field, is measured for a number of non-polar molecular liquids and for liquid xenon. The values of the NLDE are compared with results in the literature and with values predicted by theory. The agreement with other experiments is quite good, but with theory is very poor, the only exception being Liquid xenon, where agreement is good. A possible explanation is given. The prediction that the NLDE should increase strongly near the critical point due to the divergence of the isothermal compressibility could not be established by experiment. The conclusion is drawn that this failure is due to the reduction by the theory of second-order effects to first-order thermodynamic and molecular properties.

Small-angle X-ray scattering by PVP-water mixtures

Small-angle X-ray scattering experiments reveal the formation of large-scale structures when a 60 wt% poly(vinylpyrrolidone) (PVP)–water mixture is cooled to 260 K. The formation of these structures leads to an enhancement of continuous small-angle scattering with decreasing temperature. This is accompanied by the appearance of sharp Bragg peaks that have a very short lifetime. The scattering angles of these peaks are in accordance with a hexagonal columnar structure. It appears that such structures occasionally live long enough to undergo rotational Brownian motion.

The density dependence of the depolarized light scattering at high frequencies in rare gas fluids

Measurements of the depolarized light scattering spectra of venon at densities between 0.3 and 2.65 times the critical density are presented. The second moments are compared with the second moments of the scattering functions S(k, ω) of argon at corresponding densities. A conclusion is drawn about the wavevector of the modes that contribute to the high-frequency part of the spectra that are observed at high, liquid densities.

The freezing of supercooled water

Abstract The onset of crystallization of supercooled water upon lowering the temperature is highly unpredictable, depending strongly on the specific sample and its treatment. The mechanism causing this is to be investigated and may be found in terms of the dependence of the transition temperature on the shear acting in the convecting liquid. This effect of shear on the fluctuation spectrum is considered qualitatively.

The non-linear dielectric effect in xenon. The density dependence

Abstract The density dependence of the non-linear dielectric effect in xenon is measured. Experiments were performed along an isotherm with a reduced temperature T * = 1.01 in a reduced density range 0.1 to 1.8. There is a large disagreement with theory, which in first order leads to electrostriction. Arguments are given why experimental conditions and the construction of the measuring cell in our case exclude electrostriction. The results are explained in terms of first- and second-order effects. Use is made of the close relation with the theory of light scattering in first and second order. It is possible to write the non-linear dielectric effect as a sum of two terms, one linear in the density and the other increasing with σ* 3 . Quantitative estimates for the value of the coefficient of σ* 3 cannot be given because of lack of knowledge of four-point correlation functions.

Anomalous density dependence in depolarized light scattering by simple fluids

Abstract An abrupt and possibly discontinuous change in the depolarized light scattering spectrum of fluid xenon with increasing density is reported. An approximate location of this anomaly in the phase diagram is given. The significance of the experimental observation in connection with equilibrium properties of the fluid is discussed.

On the interpretation of the measurement of the non-linear dielectric effect

Abstract The consequences of the publication by Hellemans and De Maeyer of the irrefutable proof that the cell which they used to measure the non-linear dielectric effect (NLDE) deforms under the influence of the high electric field are considered. We conclude that it cannot be excluded that a similar deformation of our own cells used for NLDE measurements contributes to the average values that we have published. However, such an effect would fall within the error bounds that we maintained. The most convincing evidence for the genuineness of the measured NLDE effects is constituted by our measurements of the density dependence of the effect in xenon.