Dielectric experimental approaches

Several comprehensive reviews on the BDS measurement technique and its application have been published recently [3,4,95,98], and the details of experimental tools, sample holders for solids, powders, thin films, and liquids were described there. Note that in the frequency range 10 6-3 x 1010 Hz the complex dielectric permittivity e (co) can be also evaluated from time-domain measurements of the dielectric relaxation function (t) which is related to ( ) by (14). In the frequency range 10-6-105 Hz the experimental approach is simple and less time-consuming than measurement in the frequency domain [3,99-102], However, the evaluation of complex dielectric permittivity in the frequency domain requires the Fourier transform. The details of this technique and different approaches including electrical modulus M oo) = 1/ ( ) measurements in the low-frequency range were presented recently in a very detailed review [3]. Here we will concentrate more on the time-domain measurements in the high-frequency range 105—3 x 1010, usually called time-domain reflectometry (TDR) methods. These will still be called TDS methods. 

In order to model the experimental approach which demonstrates the optimal NP radius, we introduce a NP configuration that comprises a metal core surroimded by an outer shell of dielectric material. This thin outer shell provides a buffer layer which prevents fluorophores from residing directly on the NP surface... 

Adachi, Watanabe, and their collaborators have ingeniously used type-A block copolymers to study aspects of subchain motion. The experimental approach is of enormous potential significance, because it offers one of the few possibilities as of this writing for measuring motional correlations between two identifiable, large parts of a polymer coil. The general approach is to examine dielectric relaxation of... 

The experimental approaches and interpretation strategies for investigators working in the traditional impedance and dielectric analysis areas have drifted apart significantly over the years, often leading to misconceptions about assignments of frequency relaxation ranges and broader data interpretation. A combination of these two techniques in a universal broadband EIS... 

Knowledge of the fundamental aspects that drive hydrothermal/solvothermal processes has increased in recent years, and a solid understanding of changes in solvent parameters (e.g. structure at critical, supercritical and subcritical conditions, dielectric constant, pH, viscosity, density, etc.) under hydrothermal conditions, as well as on changing pressure and temperature, is considered a key aspect for programming experimental approaches, as they influence the solubility and transport behavior of the precursors involved in liquid-solid NP synthesis. 

To go from experimental observations of solvent effects to an understanding of them requires a conceptual basis that, in one approach, is provided by physical models such as theories of molecular structure or of the liquid state. As a very simple example consider the electrostatic potential energy of a system consisting of two ions of charges Za and Zb in a medium of dielectric constant e. 

The most important model parameter in PBFE and MM/PBSA is the dielectric constant used for the solutes. Most studies have taken an empirical approach, viewing the dielectric constant as an adjustable parameter. While this seems plausible, it is prudent to analyze the physical problem in more detail, because, in some cases, the experimental data can be fit by models that are distinctly unphysical, despite some plausible features. We therefore come back to the simplest possible PBFE calculation the important problem of proton binding, or pKa shifts. We discuss a nonem-pirical model that attempts to avoid parameter fitting and that gives insights into the limitations of simplified continuum electrostatic free energy methods. 

A larger protein dielectric constant of four was used by Eberini et al. [124] to fit the experimental pKa, in a case where the protein structural relaxation upon protonation was especially large. The need for a larger protein dielectric suggests a breakdown of the linear response assumption for this system. It may be preferable in such a case to simulate an additional point along the reaction pathway, such as the midpoint, rather than shifting to what is effectively a parameter-fitting approach. 

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