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Dielectric study of methanol–ethanol mixtures using TDR method

Study of H1 spin lattice relaxation and dielectric relaxation in Poly(propylene glycol) system

The magnetic proton relaxation behaviour of free radical solutions of diethylether and diethoxyethane has been studied by a nuclear-electron double resonance method. The dielectric relaxation in the solvents has also been determined from a study of the frequency dependance of the complex dielectric constant. The motional properties of the spin-carrying molecules which govern the magnetic interactions between different spin species are described by the model of randomly diffusing hard spheres. The time dependence is assumed to result from a combination of the relative translational diffusion of the spheres and the random rotational motions of complexes of spheres. Expressions and curves are given for the nuclear electron coupling parameter of dynamic nuclear polarisation and its frequency dependence. The comparison with experimental data taken at four different frequencies corresponding to magnetic fields of 15, 175, 1070 and 3230 gauss confirms the absence of scalar interactions and yields limits for the predominating translational diffusion. Correlation times at different temperatures and distances of closest approach of spins are evaluated. The dielectric studies in ether yield a single relaxation time which is attributed to the orientation of the molecule as a whole. Diethoxyethane has a spectrum of dielectric relaxation times. The dielectric relaxation times and also their activation energies are smaller than the correlation times obtained by magnetic measurements. The viscosity is more closely related to the translational diffusion of molecules than to the dielectric relaxation time. The results are discussed in terms of the different mechanisms of motion.

The MW dielectric properties of aqueous potassium trimethylacetate (pivalate) solutions have been measured at six frequencies (10–25 GHz) at 288, 298, and 308 K. The static dielectric constants and dielectric relaxation times and activation parameters have been calculated. Trimethylacetate ion leads to the decrease in the mobility of water molecules and strengthening of their hydrogen bonds. These changes of water are similar to those in solutions of other carboxylates with a large number of nonpolar groups. The hydrophobic hydration of the trimethylacetate ion is maximal in this series.

Cellulose nanofibers (CNFs) are plant-derived nanomaterials with promising potential for sustainable applications. However, their aqueous dispersions are susceptible to microbial contamination, necessitating sterilization for long-term storage and applications in food, cosmetics, and toxicity testing. Although gamma irradiation effectively inactivates microorganisms, it can alter the physical and chemical properties of cellulose, especially at high doses. In this study, we evaluated the effects of low-dose gamma irradiation (1–25 kilo Grays, kGy) on four types of commercially available CNFs. The 2,2,6,6-tetramethylpiperidine-1-oxyl radical-oxidized CNFs (TO-CNFs) subjected to gamma irradiation showed decreased molecular weight, fiber length, hydrodynamic particle size, and glycosidic bond-related infrared (IR) peak intensity, along with increased reducing ends and C=O stretching-related IR peak areas, indicating glycosidic bond cleavage and fiber shortening. Similar changes were observed in phosphorylated CNFs (P-CNFs) and aqueous counter collision CNFs (ACC–CNFs). In contrast, mechanically fibrillated CNFs (MF-CNFs) exhibited minimal changes. The viscosity and dynamic modulus of TO-CNFs and P-CNFs decreased, likely due to degradation, whereas these properties increased in ACC–CNFs and MF-CNFs, possibly due to cross-linking effects. Given the broad distributions of molecular weight and fiber length in native CNFs, the effect of gamma irradiation at a few kGy appeared to be minimal. Our findings offer a valuable reference for determining optimal gamma radiation doses for sterilization while preserving the CNF properties.

Studies on dielectric dispersion, relaxation kinetics and a.c. conductivity of Na2O[sbnd]CuO[sbnd]SiO2 glasses mixed with Bi2O3-Influence of redox behavior of copper ions

Dielectric and enthalpic relaxation behavior of polyesters, polycarbonates and polystyrene and their blends near Tg

Dynamic Heat Capacity and Relaxation Time of Ultraviscous Melt and Glassy Acetaminophen

Using standing-wave techniques, the dielectric constant ( epsilon ') and the dielectric loss ( epsilon ") of dilute solutions of N,N-dimethylformamide (DMF) in benzene, dioxane and carbon tetrachloride have been measured at 9.987 GHz at 25, 35, 45 and 55 degrees C. Following the single-frequency concentration variational method, the dielectric relaxation time ( tau ) and the dipole moment ( mu ) at various temperatures (25, 35, 45 and 55 degrees C) have been evaluated. From these studies the monomer structure of DMF in various solutions (benzene, dioxane and carbon tetrachloride) has been inferred and for a DMF-in-benzene solution a solute-solvent type of molecular association has been found. The energy parameters ( Delta Fepsilon , Delta Hepsilon and Delta Sepsilon ) for the dielectric relaxation of DMF in benzene, dioxane and carbon tetrachloride solutions have been calculated and compared with the corresponding viscosity parameters. A comparison between these two sets of parameters shows that the dielectric relaxation, like the viscous flow, can be considered as a rate process.

Summary. Since about 1981, operators in the northern U.K. Continental Shelf (UKCS) have become increasingly aware that scale deposited in production tubing and equipment can be mildly radioactive. Although not a production tubing and equipment can be mildly radioactive. Although not a major hazard, such scale could present a long-term risk if handled indiscriminately, and safe systems of work are necessary both offshore and onshore. Such systems must both conform with relevant legislation and be practical in typical offshore working conditions. The training of staff at practical in typical offshore working conditions. The training of staff at all levels is an important feature in the successful control of the hazards presented by naturally radioactive scale. presented by naturally radioactive scale. Introduction The phenomenon of scaling in both downhole and topside production equipment is well known in the oil industry where water-drive production equipment is well known in the oil industry where water-drive reservoirs are in production. Sulfate scales, consisting mainly of barium, strontium, and calcium, occur mostly downhole, whereas carbonate scales, mainly calcium and magnesium, occur on topside equipment. Table 1 shows analyses of typical samples from the Thistle field in the northern North Sea; the variation from sulfate to carbonate between downhole and topside can be seen clearly. Traces of radium and thorium may also be present in such scales. This has been reported previously (e.g., see Ref. 1) but is not always common knowledge. These substances can be detected most easily by measurement of the amount of radioactivity per gram of scale (specific activity), information that is also included in Table 1. It will be seen that the specific activity varies roughly in proportion to the barium plus strontium content: the principal effect is proportion to the barium plus strontium content: the principal effect is that radium is coprecipitated with the barium and strontium. Uranium and thorium minerals occur widely in nature, particularly in shales and clays. This is the basis of downhole gamma particularly in shales and clays. This is the basis of downhole gamma logs, which are used to distinguish between shales and sandstones and thus to identify pay zones. The complex decay series for uranium 238 is shown in Table 2, radium 226 being one of the long-lived daughter isotopes. There are similar decay series for uranium 235 and thorium 232, the other main naturally occurring heavy radio-active elements. The complex interaction between the geology and the water chemistry of typical UKCS oil fields is outlined in Ref. 2. In summary, radium is the most soluble of the long-lived, naturally occurring heavy nuclides, more so in chloride-rich than in sulfate-rich water, and is therefore present in the interstitial water in oil-bearing strata. As this formation water is coproduced with oil, reductions in temperature and pressure as it rises to the surface tend to cause precipitation in the form of scaling. Such scaling is more pronounced in mature fields where treated seawater is injected to maintain reservoir pressure, although it has been observed even where injection is not practiced. In the oil industry, many workers are familiar with the use of sealed radiation sources, including the concepts of classified persons, personal dose meters, barriers, and signs. High-activity persons, personal dose meters, barriers, and signs. High-activity unsealed sources are also used, for instance, to check cementing programs or reservoir flows, but direct involvement with these is programs or reservoir flows, but direct involvement with these is limited to a few specialists. Work with low-activity unsealed radioactive substances involves additional concepts and less familiar means of measurement, and there is no single number akin to 0.75 mrem/h [7.5 mu Sv/h] to mark the boundary between "normal" and "specialist" work. The phenomenon of natural radioactive scale was first identified in the northern North Sea in 1981–82. Significant effort was then necessary to develop safe systems of work and to ensure that these systems were understood by all those involved with such scale, not by just a few specialists who were already familiar with work with unsealed radioactive sources. Hazards of Naturally Radioactive Scale The different effects of alpha, beta, and gamma radiation on tissue must be understood clearly. In each case, the hazard is that the energy of the radiation will either kill the cell or cause it to replicate differently, perhaps to form a cancerous growth. Because alpha radiation is stopped very easily, all its energy is lost over extremely short distances. If alpha radiation is external, only the outer (dead) layers of skin can be affected; therefore, no serious consequences develop. In contrast, if alpha radiation is internal, sensitive organs can be affected quite easily. Gamma radiation is more penetrating, thus affecting more cells as it is absorbed, but each to a lesser extent. The effects of gamma radiation are therefore similar, whether the source is internal or external. Beta radiation can penetrate a few millimeters of tissue. Because the majority of sensitive organs in the body are deeper than this, beta radiation is only a minor external hazard but a significant internal hazard. Table 2 gives details of the stages in the radium decay chain at which alpha radiation (helium nuclei) and beta radiation (electrons) are emitted. Gamma radiation is also emitted at each decay stage. The decay chain for thorium 232 similarly involves alpha, beta, and gamma radiation. Radium and thorium form only a very small fraction of the scale, which therefore falls into the category of low-specific-activity radioactive material. Thus, for such scale, there is a low-level external hazard, but a much more serious internal hazard, if the substance enters the body by inhalation, ingestion, or skin absorption. One common misconception should be noted. Low-level radioactivity cannot be induced in one substance by another. Once the scale is removed from the contaminated equipment or surfaces, there is no further hazard. The principal difficulty is to do this without creating dust that would present a significant inhalation hazard. Maximum annual levels of intake (ALI) for various radionuclides are specified by the Intl. Commission for Radiological Protection (ICRP). Levels for the public are one-tenth of those for a radiation worker. The figures for radium 226 are detailed in Table 3, covering both inhalation and ingestion. It can be seen that ingestion is less hazardous than inhalation, basically because the lung is more sensitive to alpha radiation than the stomach. Because accidental ingestion of scale is also much less likely than accidental inhalation, safe working procedures are based on the need to avoid inhalation, and ingestion can be neglected by comparison. Inhalation ALI's for radium 226, expressed in radiation units, can be converted to weights of dust by dividing by the specific activity (amount of radioactivity per unit weight). This is done in Table 3, with typical specific activities for scale and sand, the two common forms of contamination. Similar figures can be derived for scale or sand containing traces of thorium 232, and numbers can be factored for material of higher or lower specific activity. Note, however, that these ALI's cannot be used simply as a basis for safe working, because the overriding principle is that all exposure to ionizing radiation must be kept as low as reasonably achievable. It is also obvious that reasonably accurate analysis of the scale is an important feature of a safe system of work.

The presence of caged dynamics, the Johari-Goldstein (JGβ) relaxation preceding the cooperative α-relaxation, and the fact that their properties are interconnected have been established universally for glass-forming liquids of various kinds [K. L. Ngai, Prog. Mater. Sci. 139, 101130 (2023)]. We apply the universal properties of the three processes in interpreting or reinterpreting the calorimetric and dielectric relaxation data of four amorphous waters: amorphous solid water (ASW), hyperquenched glassy water (HGW), low-density liquid water (LDL), and high-density liquid water (HDL). The presence of the JGβ relaxation and the caged dynamics before the terminal α-relaxation, and the interrelations between their respective properties, are found in the four amorphous waters exactly as in other glass-formers. The existence of the JGβ glass transition temperature, Tgβ, is found indirectly from the response of the caged dynamics in ASW, HGW, and HDL, and its value of ∼113K is consistent with the extrapolation of the dielectric JGβ relaxation times τβ(T) to long times. The calorimetric data of LDL at a heating rate of 10 K/min show Tgα of LDL is 136K, which is the same as that of ASW and HGW incidentally. The calorimetric and dielectric data of HDL at temperatures below 125K, before it transforms to LDL at higher temperatures, are interpreted as originating from the JGβ relaxation and not from the α-relaxation. The value of Tgβ of HDL obtained from calorimetry or deduced from the dielectric JGβ relaxation times τβ(T) is also near 113K. The α-relaxation glass transition temperature Tgα of HDL, obtained by extrapolating the values from calorimetric and volumetric studies at elevated pressure to ambient pressure, are 137 and 128K respectively. The 137K for Tgα is supported by observation of glass transition at the same temperature by DSC in samples of HDL prepared by compressing droplets of HGW. Assuming τα(Tgα) is 100s, the value of the calorimetric Tgα for HDL is close to the calorimetric and dielectric τα(T) of HGW. The τα(T) of HGW and LDL have Arrhenius temperature dependence with a small fragility index m. The Arrhenius temperature dependence of τβ(T) for HGW, HDL, and LDL are similar as well. Applying the relation between τα(T) and τβ(T) from the Coupling Model, the averaged coupling parameter nav ∼ 0.18 is deduced for all four amorphous waters. Such a small value of nav is consistent with the frequency dependence, ∼ν-nav, on the high-frequency flank of the α-loss peak of HGW and LDL Thus, the small nav correlates with the small m, in accord with the correlation found in other glass-formers.

The chain conformation, relaxation dynamics and thermodynamics of poly(acrylamide- co -diallyldimethylammonium chloride) solution: Dielectric analysis coupled with scaling approach

Effects of Gamma and Electron Beam Radiation on Brazil Nuts Artificially Inoculated with Aspergillus flavus

Dielectric relaxation study of dimethylene chloride with ethanol using time domain reflectometry

Dielectric relaxation study of chlorobenzene with formamide at microwave frequency using time domain reflectometry