A series of measurements of dielectric properties for food materials were made in the temperature range —20 to +60°C using the cavity perturbation technique described in the first paper of this series Variables studied besides temperature were preparation technique, pretreatment and composition of the food materials Results obtained were consistent, reproducible and in fair agreement with literature data availableFor moist foods a very sharp rise in dielectric properties is seen during thawing, followed by a gradual decrease with further temperature increase, except for salted foods where a continued increase with temperature in loss factor was found A clear positive correlation between water content and e′r was found but not for e"rDielectric properties decreased with increasing fat content, and loss factor increased with salt content In general, freezing, short time frozen storage, thawing and rate of heating had little influence on the data determined, with the exception of thickened grav

Dielectric Properties of Foods at 3 GHz as Determined by a Cavity Perturbation Technique.

With the ongoing proliferation of terahertz time-domain instrumentation from semiconductor physics into applied spectroscopy over the past decade, measurements at terahertz frequencies (1 THz ≡ 10(12) Hz ≡ 33 cm(-1)) have attracted a sustained growing interest, in particular the investigation of hydrogen-bonding interactions in organic materials. More recently, the availability of Raman spectrometers that are readily able to measure in the equivalent spectral region very close to the elastic scattering background has also grown significantly. This development has led to renewed efforts in performing spectroscopy at the interface between dielectric relaxation phenomena and vibrational spectroscopy. In this review, we briefly outline the underlying technology, the physical phenomena governing the light-matter interaction at terahertz frequencies, recent examples of spectroscopic studies, and the current state of the art in assigning spectral features to vibrational modes based on computational techniques.

https://journals.sagepub.com/doi/pdf/10.1366/14-07707

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

https://www.repository.cam.ac.uk/bitstream/1810/253142/1/Sibik%20%26%20Zeitler%202016%20Advanced%20Drug%20Delivery%20Reviews.pdf

Direct measurement of molecular mobility and crystallisation of amorphous pharmaceuticals using terahertz spectroscopy.

The local structure of liquid water as a function of temperature is a source of intense research. This structure is intimately linked to the dynamics of water molecules, which can be measured using Raman and infrared spectroscopies. The assignment of spectral peaks depends on whether they are collective modes or single-molecule motions. Vibrational modes in liquids are usually considered to be associated to the motions of single molecules or small clusters. Using molecular dynamics simulations, here we find dispersive optical phonon-like modes in the librational and OH-stretching bands. We argue that on subpicosecond time scales these modes propagate through water's hydrogen-bond network over distances of up to 2 nm. In the long wavelength limit these optical modes exhibit longitudinal-transverse splitting, indicating the presence of coherent long-range dipole-dipole interactions, as in ice. Our results indicate the dynamics of liquid water have more similarities to ice than previously thought.

/pdf/the-hydrogen-bond-network-of-water-supports-propagating-8a109o7md0.pdf

The hydrogen-bond network of water supports propagating optical phonon-like modes

After defining the boundaries for the dielectric constant of a heterogeneous mixture, the behaviour of such a mixture is studied as a function of the frequency, when one of its components is polar. Deviations from a semicircle are to be expected for the functione″
 m
 =f(e′
 m
 ) even when the dielectric properties of the polar constituent can be described with a semicircular Cole-Cole-arc. The relaxation time of the mixture is shorter than that of the polar constituent.

Dielectric properties of heterogeneous mixtures with a polar constituent

The chief purpose of the present investigation is the measurement and analysis of the microwave dispersion of some polar liquids. An outline of the problem and a historical survey of experimental work on the dielectric behaviour of polar liquids are given in Chapter I. A number of theoretical expressions for the dielectric constant in the static case and their extension to alternating fields are reviewed in Chapter II. A formula for the dielectric dispersion in liquids composed of ellipsoidal molecules is derived and its consequences are investigated. Chapter III deals with the experimental details of the investigation. A new microwave measuring technique is described, accurate in most cases to about 1% for both the real and imaginary part of є. In order to make the theories applicable, the investigation has been restricted mainly to polar liquids of simple structure, in particular to the mono-substituted benzenes. The results refer to wavelengths down to 0.8 cm. The analysis of our measurements in Chapter IV reveals discrepancies between the dielectric constant e∞, extrapolated from the side of cm-waves, and n2, the square of the refractive index, extrapolated from measurements in the visible and infrared. This leads to assuming an additional region of dipolar absorption in the neighbourhood of 1 mm. The mechanism to which such an absorption may be due is sought in the strong local fields exerted on a molecule by its immediate neighbours.

/pdf/microwave-dispersion-of-some-polar-liquids-1wqp2jfbto.pdf

J.P. Poley

Papers

Microwave dispersion of some polar liquids