How to study microemulsions

A tutorial on dielectric (relaxation) spectrometry of liquids is given in this article. Some methods of measuring complex (electric) permittivity spectra are briefly described. Results for water are presented and related to characteristic properties of the liquid structure and to models of the molecular dynamics, particularly as resulting from computer simulation studies. Dielectric spectra for aqueous solutions of low weight electrolytes, polyelectrolytes, small molecules, and polymers are discussed to illustrate effects of kinetic depolarization, structure saturation, as well as positive, negative, and hydrophobic hydration. Reference is also made to fluctuations in the hydrogen bond network of mixtures of water with liquids that are completely miscible with this unique solvent.

The dielectric properties of water in its different states of interaction

This review provides a short introduction into the basic principles of dielectric spectroscopy and it covers modern methods in use to measure the dielectric properties of liquid samples over the frequency range from about 10?6 Hz to 1012 Hz. The approaches described include frequency domain and time domain techniques, low frequency, high frequency and microwave measurement systems, as well as broadband and spot-frequency modes of operation. Reflection, transmission and resonant methods are presented, sketches of suitable sensors and block diagrams of measurement set-ups are shown. Accuracy aspects and the merits and limitations of the different techniques of measurement are discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/17/2/R01/pdf

Broadband dielectric spectrometry of liquids and biosystems

This review gives a brief introduction to the principles of microwave measurements of the complex permittivity of materials. The fundamentals of reflection, transmission and resonant methods are summarized and examples of sample cell design and measurement systems are presented for each category. The frequency domain and the fast response time domain methods are discussed in view of their merits and limitations. Accuracy aspects and reference materials for calibration procedures are mentioned briefly. Selected examples of applications indicate the diverse usability spectrum of microwave dielectric measurements in basic research and in the characterization of materials in manufacturing processes as well as monitoring and control routines.

https://iopscience.iop.org/article/10.1088/0026-1394/47/2/S10/pdf

Techniques for measuring the microwave dielectric properties of materials

Fibrous elastin of the biological elastic fiber is a cross-linked condensed state in which there is roughly one-half polypeptide and one-half water. The precursor protein tropoelastin, a chemical fragmentation product α-elastin, and a sequential polypeptide (l·Val1-l·Pro2-Gly3-l·Val4-Gly5)
 n
 , which is a prominent primary structural feature of tropoelastin, are each soluble in all proportions in water at 20°C. On heating to physiological temperatures, each undergoes aggregation and forms a dense viscoelastic phase, which as the fiber itself, is about 60% water. This reversible heat-elicited condensed phase is called the coacervate. Circular dichroism studies show coacervation to be a process of increasing intramolecular order. Electron microscopy (light, scanning, and transmission) shows coacervation to be a process of increasing order intermolecularly. Thus a rise in temperature between 20 and 40°C results in an increase in order of the polypeptide. Coacervation is an inverse temperature transition, and the condensed state is anisotropic at the molecular level. Thermoelasticity studies in water on bovine ligamentum nuchae fibrous elastin and on γ-irradiation cross-linked polypentapeptide coacervates show increases in elastomeric force,f, over the same 20–40°C temperature range in which the inverse temperature transition gives rise to the coacervate, and the constancy off/T with temperature, once the transition is effectively completed, suggests a high-entropy component to the elastomeric force. Thus the data argue for an anisotropic-entropic elastomer. Detailed conformational studies on the polypentapeptide result in the development of a β-spiral conformation in which there are regularly recurring β-turns in loose helical array (a structure that forms on raising the temperature) and in which there are recurring dynamic suspended segments that are the focal point of large, low-energy oscillatory motions called librations. The structure gives rise to a librational entropy mechanism of elasticity wherein the amplitudes of the rocking motions become damped on stretching. This perspective is substantiated by dielectric relaxation studies on the coacervate state and by characterization of synthetic analogs of the polypentapeptide. Dielectric relaxation studies on a concentrated state of about 60% water show the development of a regular structure over the same temperature range as for the development of the coacervate state, and the development of the regular structure with increasing temperature is seen to parallel the development of elastomeric force with increasing temperature. Increasing elastomeric force coincides with increasing regularity of structure! Synthetic analogs of the polypentapeptide, designed to interfere with the librational processes of the suspended segment, impair elastic function, and an analog that makes the β-turn more rigid results in increased elastic modulus. This development of a librational entropy mechanism for protein elasticity is a departure from the kinetic theory of rubber elasticity, the random network perspective that has dominated the traditional view of biological elasticity for the past several decades. The new perspective opens the way to insightful consideration of new elastomeric biomaterials with numerous biomedical applications.

Protein elasticity based on conformations of sequential polypeptides: the biological elastic fiber

A technique is presented to determine the complex permittivity epsilon = epsilon '-j epsilon " by means of a coaxial line set-up for transmission coefficient measurement within the frequency range of 1 to 1000 MHz A highly sensitive broad-band vectorvoltmeter and dielectric sample cells of the cut-off variety enable precise measurements in a comparatively short time and ease of handling The cells are designed for the investigation of weakly as well as highly polar liquid dielectrics The relative error of the real part epsilon ' of the complex permittivity typically amounts to 1-2% and the absolute error of the dielectric loss angle up to 03 degrees 

https://iopscience.iop.org/article/10.1088/0022-3735/17/9/013/pdf

A Dittrich

Papers

A broad-band measuring equipment for determining the complex permittivity of liquid dielectric materials within the frequency range of 1 MHz to 1 GHz