Theory of a Dielectric Loss in Long Chain Polar Compounds

1955 ◽  
Vol 68 (12) ◽  
pp. 1184-1190 ◽  
Author(s):  
P G Harper ◽  
J J O'Dwyer
Keyword(s):  
Dielectric Loss ◽  
Polar Compounds ◽  
Long Chain

scholarly journals On the mechanism of boundary lubrication. II. Wear prevention by addition agents

1940 ◽  
Vol 177 (968) ◽  
pp. 103-118 ◽  
Keyword(s):  
High Pressures ◽  
Preceding Paper ◽  
Accurate Method ◽  
Polar Compounds ◽  
Experimental Conditions ◽  
Group V ◽  
Highly Sensitive ◽  
Local Pressures ◽  
Steel Balls ◽  
Long Chain

If two metal surfaces slide over each other in the presence of a lubricant and under high load, high pressures and temperatures prevail a t those isolated spots which actually carry the load, leading to wear and possibly to breakdown. The action of wear preventing agents under these conditions has been studied in detail and it has been found that such agents are effective through their chemical polishing action, by which the load becomes distributed over a larger surface and local pressures and temperatures are decreased. Especially effective are compounds containing phosphorus or other elements of group V of the periodic system. These have been found to form a metal phosphide or homolog on the surface which is able to alloy with the metal surface, lowering its melting point markedly, and by this action aiding greatly in maintaining a polish. The wear experiments were carried out with a highly sensitive and accurate method which uses metal-plated steel balls as its sliding elements. Under the experimental conditions additions of 1.5% triphenyl phosphine or triphenyl arsine in white oil gave wear prevention factors of 7.2 and 12.2 respectively (relative to pure white oil). A further addition of 1% of a long chain polar compound is able to double the wear prevention factor obtained with the polishing agents and wear prevention factors as high as 17.6 have been observed. The specifically physical action of the long-chain polar compounds is discussed in the preceding paper.

scholarly journals The heat of adsorption of long-chain compounds and their effect on boundary lubrication

1944 ◽  
Vol 182 (990) ◽  
pp. 270-285 ◽  
Keyword(s):  
Transition Temperature ◽  
Surface Concentration ◽  
Temperature Characteristic ◽  
Polar Compounds ◽  
Heat Of Adsorption ◽  
Particular Solution ◽  
Steel Surfaces ◽  
Frictional Behaviour ◽  
Long Chain ◽  
Good Agreement

The frictional behaviour between mild steel surfaces lubricated with solutions in white oil of long-chain halides, acids, a -substituted acids, esters, cyanide, thiocyanate and a nitro derivative has been investigated under high loads at low speeds. In all cases a transition from smooth sliding to stick-slips occurs at a temperature characteristic of the particular solution employed. For each substance the transition temperature increases 'with the concentration. Each solution builds up, and is in equilibrium with, an adsorbed and oriented film of the polar compound on the surface. Assuming that the transition occurs when the surface concentration of this film decreases to a certain value which, for any one material is independent of temperature, an equation has been deduced relating the concentration, and transition temperature with the heat of adsorption U . All the experimental results are in good agreement with this equation. The values of U show that these long-chain polar compounds are adsorbed by the interaction of their dipoles with the atom s in the metal surface, and not by any chemical reaction. The results also suggest that the esters are similarly oriented at metal and at aqueous surfaces.

The Dielectric Properties of Symmetrical Long-Chain Secondary Alcohols in the Solid State

1951 ◽  
Vol 4 (2) ◽  
pp. 213 ◽  
Author(s):  
RL Meakins ◽  
RA Sack
Keyword(s):  
Hydrogen Bonding ◽  
Solid State ◽  
Dielectric Loss ◽  
Low Temperatures ◽  
Room Temperature ◽  
Molecular Chain ◽  
Hydroxyl Groups ◽  
Crystal Formation ◽  
Secondary Alcohols ◽  
Long Chain

Symmetrical long-chain secondary alcohols in the solid state show very high dielectric loss at audio and radio frequencies. This can be explained by the presence of chains of hydroxyl groups linked by hydrogen bonding and capable of reversing their direction. Further evidence of hydrogen bonding is provided by a study of the melting points of the secondary alcohols and related compounds. The amount of dielectric loss depends markedly on the manner of formation of the solid, being smallest for samples formed by recrystallization from solvents at low temperatures and largest for specimens obtained by slow cooling from the melt. The alcohols of molecular chain-lengths of 13, 15,17, and 19 carbon atoms show a considerable decrease of absorption on storing at room temperature. For alcohols of between 23 and 43 carbon atoms the loss is rather smaller with a peak at higher frequencies, but remains more constant in time. These results are interpreted in terms of competing influences of van der Waals forces and hydrogen bonds during crystal formation ; the former, which lead to a structure unsuitable for the formation of hydrogen-bond chains, are predominant at low temperatures, but become more rapidly neutralized by thermal motion, especially for the shorter molecules. The high temperature modification of the lower homologues is unstable at room temperature, and a molecular diffusion process causes the bond chains to break. Dilute systems of secondary alcohols with hydrocarbons or paraffin wax of similar molecular chain-length show very small dielectric loss suggesting a solid solution in which bond chains cannot be formed ; if the paraffin molecules are appreciably longer, the absorption is large and decreases on storing, presumably owing to the presence of a pure alcohol phase. I.

scholarly journals n-alkanes from Paepalanthus Mart. species (Eriocaulaceae)

2005 ◽  
Vol 19 (4) ◽  
pp. 727-732 ◽  
Author(s):  
Lourdes Campaner dos Santos ◽  
Anne L. Dokkedal ◽  
Miriam Sannomiya ◽  
Maria Carla Piza Soares ◽  
Wagner Vilegas
Keyword(s):  
High Frequency ◽  
Carbon Number ◽  
Polar Compounds ◽  
Aliphatic Hydrocarbons ◽  
Flavonoid Glycosides ◽  
Taxonomic Character ◽  
Carbon Chains ◽  
Nonpolar Compounds ◽  
Long Chain

This work presents the study of nonpolar compounds from plants belonging to the genus Paepalanthus Mart. (Eriocaulaceae). Long-chain linear aliphatic hydrocarbons were identified by GC-FID and GC-MS. The results indicate that Paepalanthus subg. Platycaulon species present a very homogenous profile, with carbon chains of n-alkanes ranging from C25 to C31, most samples presenting higher frequencies of C27 and C29 homologues. Paepalanthus subg. Paepalocephalus species may be distinguished from one another by the distribution of main n-alkanes. P. macrocephalus, subsect. Aphorocaulon species, presents alkanes with odd-carbon numbers and P. denudatus and P. polyanthus, Actinocephalus species, present alkanes with quite distinctive profiles, with many shorter chains and a high frequency of even-carbon number, especially P. polyanthus. The results obtained indicate that the distribution of alkanes can be a useful taxonomic character, as do polar compounds like flavonoid glycosides.

Main Dielectric Dispersion Region of Mixtures of some Long-Chain Alcohols with Non-Polar Solvents

1972 ◽  
Vol 27 (8-9) ◽  
pp. 1363-1367 ◽  
Author(s):  
F. F. Hanna ◽  
I. K. Hakim
Keyword(s):  
Dielectric Constant ◽  
Dielectric Loss ◽  
Dipole Moments ◽  
Relaxation Times ◽  
Dielectric Dispersion ◽  
Concentrated Solutions ◽  
Polar Solvents ◽  
Dispersion Region ◽  
Long Chain

Abstract The dielectric constant ε' and dielectric loss ε" are measured for concentrated solutions of n-dodecanol and n-octanol with five non-polar solvents at five frequencies between 2 and 400 MHz at three temperatures between 20 and 60 °C. The effective dipole moments have been calculated and found to decrease with increasing dilution. The relaxation times of the concentrated solutions are lower than that of the pure alcohols, decrease with dilution and are dependent on the nature of the non-polar solvents.

The Dielectric Properties of Binary Systems of Ketones and Hydrocarbons

1949 ◽  
Vol 2 (3) ◽  
pp. 405
Author(s):  
RL Meakins
Keyword(s):  
Relaxation Time ◽  
Dielectric Properties ◽  
Chain Length ◽  
Binary Systems ◽  
Dipole Interaction ◽  
Polar Compounds ◽  
Electrical Measurements ◽  
Cooperative Effects ◽  
Dielectric Absorption ◽  
Long Chain

Experimental work on the dielectric properties of solid systems of long-chain polar and non-polar compounds has been performed by Jackson(l), Sillars(2), and Pelmore(3) with dilute solutions of esters in paraffin wax. In subsequent theoretical studies in this field Fr�hlich(4) adopted, as a model, a crystalline long-chain paraffin in which a small proportion of the molecules were assumed to be replaced by long-chain polar molecules. Taking Debye's theory of dielectric absorption in polar solids as a basis, this led to the derivation of a relationship between the relaxation time and the number of links in the polar molecule. In order to obtain experimental results more closely related to the theory, electrical measurements have now been made with symmetrical long-chain ketones in pure crystalline hydrocarbon solvents. The variation of dielectric constant and loss angle with frequency for these systems is found to be approximately in agreement with the Debye theory of dielectric absorption. For ketones of chain-length shorter than that of the hydrocarbon solvent the relationship between relaxation time and chain-length is of the type expected from Fr�hlich's theory, but displaced towards lower frequencies. The results show that, in applying the theoretical relationship to systems of long-chain polar and non-polar compounds, it would be necessary to determine new constants for each different type of polar compound and for each different solvent. The results of electrical measurements of ketone-hydrocarbon systems with ketones of varying chain-length (both less and greater than that of the solvent) are in accordance with conclusions from previous X-ray studies of long-chain hydrocarbons. The effects of dipole interaction on the dielectric absorption of systems of laurone and n-hexacosane, are discussed in relation to the solid-liquid phase diagram. The results of dielectric measurements with pure crystalline compounds suggest that dipole interaction and electrical cooperative effects are larger in ketones than in esters of similar chain-length.

The Dielectric Properties of a Series of dl-n-Eicosanols

1951 ◽  
Vol 4 (3) ◽  
pp. 359
Author(s):  
RJ Meakins ◽  
HK Welsh
Keyword(s):  
Dielectric Properties ◽  
Low Frequency ◽  
Polar Compounds ◽  
Carbon Chain ◽  
Hydroxyl Groups ◽  
Secondary Alcohols ◽  
Polar Group ◽  
Dielectric Absorption ◽  
Ready Availability ◽  
Long Chain

Initial investigations of the dielectric properties of normal long-chain secondary alcohols were made with the symmetrical compounds because of their ready availability. The properties of long-chain polar compounds are known to vary considerably, however, with the position of the polar group in the carbon chain and it therefore seemed desirable to make dielectric measurements with some unsymmetrical alcohols. The present paper describes such an investigation of a series of dl-n-eicosanols having the hydroxyl groups in the 2-, 4-, 6-, 8-, and 10-positions, respectively. The results for the melted forms show that slight asymmetry, as in the 10-compound, has little effect on the dielectric properties, but with the more unsymmetrical 4-, 6-, and 8-compounds a considerable enhancement of the dielectric absorption is observed. This is accompanied by increased dispersion of the dielectric constant which, for the 8-compound, reaches a low frequency value of 15. Both ε" and ε' decrease during storage at room temperature. Anomalous results are obtained with dl-n-eicosan-2-ol, probably due to the molecules in the crystal lattice being alternately reversed, end-to-end. As with the symmetrical secondary alcohols, the recrystallized forms give comparatively little dielectric absorption.

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