THE DIELECTRIC BEHAVIOR OF VAPORS ADSORBED ON SILICA GEL

1953 ◽  
Vol 31 (1) ◽  
pp. 72-83 ◽  
Author(s):  
J. A. Snelgrove ◽  
H. Greenspan ◽  
R. Mcintosh
Keyword(s):  
Temperature Coefficient ◽  
Silica Gel ◽  
Liquid State ◽  
Saturation Pressure ◽  
Adsorbed Water ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Oscillatory Motion ◽  
Molar Polarization

Experiments to determine the dielectric constants of adsorbed butane, ethyl chloride, and water on an activated silica at frequencies up to 3.7 Mc. per sec. are reported. No Debye-type dispersion was observed for the polar adsorbates down to −30 °C, the lowest temperature employed. Mixtures of ethyl chloride and water, and of butane and water, were also studied. The assumption that adsorption of ethyl chloride and water occurs with both adsorbates sharing two types of sites sufficed to explain the findings for this system. No explanation was apparent to account for the behavior of the butane–water system.Formulae due to Kurbatov and to Snelgrove and McIntosh have been used to interpret the results obtained with polar adsorbates. On the assumption that the adsorbates have densities equivalent to those for the liquid state at the same temperature, it is concluded that adsorbed water undergoes oscillatory motion. The first quantities of ethyl chloride adsorbed behave as though the molecules may rotate freely within an angle of 98°. The ethyl chloride adsorbed nearer the saturation pressure shows oscillatory motion, as a negligible temperature coefficient of the molar polarization is observed.

PRELIMINARY OBSERVATIONS OF THE DIELECTRIC CONSTANTS OF VAPORS ADSORBED ON ACTIVATED SILICA

1947 ◽  
Vol 25b (6) ◽  
pp. 566-574 ◽  
Author(s):  
R. McIntosh ◽  
L. McLeod ◽  
H. S. Johnson ◽  
N. Hollies
Keyword(s):  
Dielectric Constant ◽  
Ethylene Oxide ◽  
Silica Gel ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Bulk Liquid ◽  
Temperature Coefficients ◽  
Capacity Change

A measure of the dielectric constants of several substances adsorbed on silica gel has been obtained by measuring the change in the capacity of an electrical condenser when measured amounts of the substances were adsorbed on silica gel situated between the plates of the condenser. The substances examined were ethyl chloride, n-butane, and ethylene oxide. The plot of capacity change vs. amount adsorbed was found, in all cases, to consist of two or more quite distinct sections, each approximating to linearity. The temperature coefficients of dielectric constant were evaluated. The dielectric constant calculated for adsorbed n-butane was close to that calculated for the bulk liquid, whereas the value calculated for adsorbed ethyl chloride was significantly lower than the value calculated for the liquid.

NOTE ON THE DIELECTRIC CONSTANTS OF ETHYL CHLORIDE AND n-BUTANE ADSORBED ON NONPOROUS TiO2

1953 ◽  
Vol 31 (11) ◽  
pp. 998-1003 ◽  
Author(s):  
M. H. Waldman ◽  
J. A. Snelgrove ◽  
R. Mcintosh
Keyword(s):  
Temperature Dependence ◽  
Silica Gel ◽  
Porous Silica ◽  
Adsorbed Molecule ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Capacity Change ◽  
Adsorbed Phase ◽  
Porous Silica Gel ◽  
Linear Sections

The dielectric constants of ethyl chloride and n-butane adsorbed on nonporous TiO2 were measured. The plot of capacity change versus volume adsorbed was found to reveal two linear sections in the case of ethyl chloride with an abrupt change in the slope of the plot occurring at the Vm value calculated using the B.E.T. or Hüttig adsorption equations. With n-butane the plot was linear beyond Vm. For ethyl chloride on rutile a slight temperature dependence in the polarization was observed for the volume of gas adsorbed above Vm, while a negligible temperature dependence was noted for the portion below Vm. It is postulated that the observations with the polar gas on the nonporous rutile can be explained by a change from oscillatory to rotational motion of the adsorbed molecule after the monolayer is complete. It was noted that gases adsorbed on nonporous TiO2 behaved differently from gases adsorbed on porous silica gel. This appears to lead to the necessity of postulating changes of density for the adsorbed phase on silica gel.

Dielectric behavior of low boiling chlorides in the liquid, solid, and adsorbed states

1968 ◽  
Vol 46 (18) ◽  
pp. 2945-2957 ◽  
Author(s):  
T. McMullen ◽  
E. D. Crozier ◽  
R. McIntosh
Keyword(s):  
Sodium Chloride ◽  
Hydrogen Chloride ◽  
Surface Coverage ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Adsorbed Hydrogen ◽  
Adsorption Studies ◽  
Very High ◽  
Monolayer Coverage

The complex dielectric constants of hydrogen, methyl, and ethyl chlorides have been measured, for the purpose of comparison with the present and future adsorption studies. The hydrogen chloride results agree with those of Cole and Swensen (22). Studies of hydrogen and ethyl chlorides adsorbed on finely divided sodium chloride show two particularly interesting phenomena. Adsorbed hydrogen chloride shows an unusually high polarizability at monolayer surface coverage, which then decreases again with increasing adsorption. Adsorbed ethyl chloride also shows a very high polarizability at a particular surface coverage, but this maximum occurs at about one-fourth of monolayer coverage, and is accompanied by loss, in contrast to the former case.

The dielectric behaviour of vapours adsorbed on activated silica gel

1951 ◽  
Vol 208 (1094) ◽  
pp. 292-310 ◽  
Keyword(s):  
Liquid State ◽  
Adsorbed Molecule ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Three Dimensions ◽  
Adsorbed State ◽  
Dielectric Data ◽  
Density Values ◽  
The Difference ◽  
Activated Silica Gel

The increase in capacity of a test cell containing a porous activated silica on the admission of adsorbates such as water, ethyl chloride and butane has been measured. The data confirm the existence of a discontinuity in the slope of the capacity against volume adsorbed plots. The electrical evidence suggests that two types of film are established for the adsorbates butane and ethyl chloride. The first type of film in each case has a density close to that of liquid state, while the second is a much more dilute film. The position of the discontinuity, which is independent of temperature within the experimental precision, indicates that the occurrence of the discontinuity may be related to the number of adsorption centres rather than to the area occupied by the adsorbed molecule. From further evidence it appears that water and butane are adsorbed on the same centres, while ethyl chloride and water are not. In the case of water it is possible that the difference in apparent polarization along the two sections of the dielectric data might be accounted for by assuming molecules free to rotate in the plane of the adsorbing surface for the first section, and molecules free to rotate in three dimensions along the second. Certain other differences in the behaviour of polar molecules along the two sections are suggested by the data, but explanations of these differences are not yet clear. The computation of dielectric constants of adsorbed matter in such systems is discussed, and a method based on considerations put forward by Böttcher for powdered dielectrics is developed. It is emphasized that a knowledge of the density of the adsorbed matter is required for such systems, and a method is devised for determining these density values from the dielectric data which is applicable in the case of non-polar adsorbates. The difficulty of interpretation of the data for such systems shows that dielectric measure­ments are less helpful in examining the adsorbed state than had been anticipated from earlier investigations.

Dielectric properties of aerogels

1993 ◽  
Vol 8 (7) ◽  
pp. 1736-1741 ◽  
Author(s):  
L.W. Hrubesh ◽  
L.E. Keene ◽  
V.R. Latorre
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Bulk Material ◽  
Solid Material ◽  
Adsorbed Water ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
High Porosity ◽  
Microwave Frequencies ◽  
Low Dielectric

We have measured the real (dielectric constant) and imaginary (loss factor) components of the complex relative permittivity at 298 K using microwave frequencies (2, 10, and 18–40 GHz) for bulk SiO2-aerogels and for two types of organic aerogels, resorcinol-formaldehyde (RF) and melamine-formaldehyde (MF). Measured dielectric constants are found to vary linearly between values of 1.0 and 2.0 for aerogel densities from 10 to 500 kg/m3. For the same range of densities, the measured loss tangents vary linearly between values of 2 × 10−4 and 7 × 10−2. The observed linearity of the dielectric properties with density in aerogels at microwave frequencies shows that their dielectric behavior is more gas-like than solid-like. The dielectric properties of aerogels are shown to be significantly affected by the adsorbed water internal to the bulk material. For example, water accounts for 70% of the dielectric constant and 70% of the loss at microwave frequencies for silica aerogels. Because of their very high porosity, even with the water content, the aerogels are among the few materials exhibiting such low dielectric properties. Our measurements show that aerogels with greater than 99% porosity have dielectric constants less than 1.03; these are the lowest values ever reported for a bulk solid material.

THE DIELECTRIC BEHAVIOR AT LOW TEMPERATURES OF SEVERAL GASES ADSORBED UPON POROUS VYCOR GLASS

1962 ◽  
Vol 40 (1) ◽  
pp. 92-103 ◽  
Author(s):  
I. D. Chapman ◽  
R. McIntosh
Keyword(s):  
Low Temperatures ◽  
Molecular Layer ◽  
Dielectric Behavior ◽  
Dielectric Constants ◽  
Ethyl Chloride ◽  
Threshold Temperature ◽  
Hydroxyl Groups ◽  
Vycor Glass ◽  
Oh Groups ◽  
Adsorbed Phase

The complex dielectric constants of several systems comprising a gas adsorbed on Vycor glass have been measured at temperatures between 0 °C and −180 °C and frequencies between 3 kc/sec and 4 Mc/sec. The real and imaginary parts of the dielectric constant of the adsorbed phase have been computed. Loss maxima occurring at low temperatures are observed for some of the matter in the monolayer and are assumed to be due to complexes formed between the gas first admitted and hydroxyl groups which are covalently attached to the surface of the glass. The complexes may be considered either as dipoles having two equilibrium positions, or as highly damped oscillators. Ethyl chloride adsorbed in the first molecular layer and not bonded to OH behaves as an oscillatory system for which no loss is observed in the frequency and temperature ranges studied. Ethyl chloride adsorbed in the multilayers behaves similarly but shows a slightly greater temperature coefficient of ε′. Both these types of adsorbed ethyl chloride interact with the complexes and reduce the threshold temperature at which loss is observed in the complex. Methyl chloride interacts with OH groups in a similar fashion, but n-butane does not.

Tuning the Electric Field Response of MOFs by Rotatable Dipolar Linkers

2019 ◽  
Author(s):  
Johannes P. Dürholt ◽  
Babak Farhadi Jahromi ◽  
Rochus Schmid
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Structural Changes ◽  
Dielectric Behavior ◽  
Two Dimensions ◽  
Dielectric Constants ◽  
Electric Response ◽  
Dipole Strength ◽  
Metal Organic ◽  
Dynamics Simulations

Recently the possibility of using electric fields as a further stimulus to trigger structural changes in metal-organic frameworks (MOFs) has been investigated. In general, rotatable groups or other types of mechanical motion can be driven by electric fields. In this study we demonstrate how the electric response of MOFs can be tuned by adding rotatable dipolar linkers, generating a material that exhibits paralectric behavior in two dimensions and dielectric behavior in one dimension. The suitability of four different methods to compute the relative permittivity κ by means of molecular dynamics simulations was validated. The dependency of the permittivity on temperature T and dipole strength μ was determined. It was found that the herein investigated systems exhibit a high degree of tunability and substantially larger dielectric constants as expected for MOFs in general. The temperature dependency of κ obeys the Curie-Weiss law. In addition, the influence of dipolar linkers on the electric field induced breathing behavior was investigated. With increasing dipole moment, lower field strength are required to trigger the contraction. These investigations set the stage for an application of such systems as dielectric sensors, order-disorder ferroelectrics or any scenario where movable dipolar fragments respond to external electric fields.

Crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 tungsten–bronze glass–ceramics

2001 ◽  
Vol 16 (7) ◽  
pp. 2057-2063 ◽  
Author(s):  
Jiin-Jyh Shyu ◽  
Hsin-Wei Peng
Keyword(s):  
Heat Treatment ◽  
Dielectric Properties ◽  
Tungsten Bronze ◽  
Glass Ceramics ◽  
Dielectric Behavior ◽  
Dendritic Morphology ◽  
Dielectric Constants ◽  
Two Stage ◽  
Tetragonal Tungsten Bronze ◽  
Stage Heat Treatment

The crystallization and dielectric properties of SrO–BaO–Nb2O5–GeO2 glass–ceramics were investigated. One- and two-stage heat-treatment methods were used to convert the parent glass to glass–ceramics. Strontium barium niobate (SBN) with a tetragonal tungsten-bronze structure formed as the major crystalline phase. When the crystallizing temperature/time was increased, the secondary crystalline BaGe2O5 phase coexisted with SBN. BaGe2O5 formed as a surface layer grown from the surface into the interior of the sample. The dendritic morphology of SBN crystals was examined. The glass–ceramics crystallized by two-stage heat treatment have higher dielectric constants than those crystallized by one-stage heat treatment. The highest dielectric constant that was obtained in the present glass–ceramics was 320. The glass–ceramics showed relaxor-type dielectric behavior.

Static dielectric constants of the N,N-dimethylformamide/2-methoxyethanol solvent system at various temperatures

1992 ◽  
Vol 70 (12) ◽  
pp. 2895-2899 ◽  
Author(s):  
Fulvio Corradini ◽  
Luigi Marcheselli ◽  
Lorenzo Tassi ◽  
Giuseppe Tosi
Keyword(s):  
Liquid State ◽  
Specific Interaction ◽  
Solvent System ◽  
Liquid Mixtures ◽  
Dielectric Constants ◽  
Empirical Equations ◽  
Binary Liquid ◽  
Fraction Mixture ◽  
Static Dielectric Constants ◽  
Formation Of Complexes

Measurements of static dielectric constants (ε) have been made for binary liquid mixtures of N,N-dimethylformamide (DMF)/2-methoxyethanol (ME) at 19 temperatures ranging from −10 to +80 °C. Some empirical equations of the type ε = ε(T), ε = ε(X1), and ε = ε(T,X1) have been applied to check their validity. The εE values, which refer to the deviation of the dielectric constants of the binaries from the values arising from mole fraction mixture law, have been calculated. Deviations from ideal behaviour have been found to be positive at all temperatures. The positive εE values are attributed to a specific interaction between unlike molecules, which leads to the formation of complexes between DMF and ME in the liquid state. These nDMF•mME complex moieties were found to have the stoichiometric ratios 2:1, 1:1, and 1:2 in the temperature range of −10 to +80 °C.

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