Barium Stearate Research Articles

Photoelectron mean free paths in barium stearate layers

Barium stearate monolayers were deposited on polished clean germanium and copper substrates using the Blodget technique. Film thicknesses were determined by ellipsometry by assuming the films were optically isotropic with a refractive index of 1.5 and an absorption coefficient of zero. X-ray photoelectron spectroscopy intensity ratios, obtained at 223 K to minimize vaporization, were used to determine electron inelastic mean free paths (IMFP) in the barium stearate layers. The substrate photoelectron lines cover a binding energy range of 1200 eV. IMFP values range from approximately 27 ± 5 Å at about 230 eV to 65 ± 12 Å at about 1480 eV kinetic energy. The approximately linear shape of this function, together with the throughput function of the instrument, suggests that over the binding energy range of 0–600 eV, the photoelectron mean free paths and throughput effects in the Hewlett-Packard instrument approximately cancel.

Electrical Properties of Langmuir Films of Fatty Acid Salts and Carotenoic Acid

Abstract Electric conductivities have been studied for Langmuir molecular layers of barium salt of fatty acids and for the layers of barium arachidate mixed with all-trans-β-apo-8′-carotenoic acid. These results have been interpreted based on an electron tunneling model taking account of the mirror image force. The conduction levels of the layers have thereby been estimated to be 1.00 eV for barium stearate, 1.31 eV for barium arachidate and 1.45 eV for barium behenate below vacuum level. The conduction level of the carotenoic acid has been derived to be 1.9 eV from these results. The structure of these layers has been discussed from the above mentioned experimental results, together with those on surface pressure, absorption spectrum and electric capacitance.

Electrical and Spectroscopic Investigations of Molecular Layers of Fatty Acids Including Carotene

Abstract Spectroscopic and electrical studies have been made for the mono- and multi-molecular layers of barium stearate mixed with carotene. The results of the electronic spectra have indicated that the carotene molecules lie parallel to the monolayer plane and are aggregated. The capacitances measured are expressed well as those of parallel plate capacitors. From these results, the structure of the layers containing carotene has been deduced.

Ellipsometry as a tool to study protein films at liquid-solid interfaces

A description is given of an ellipsometer, automated by means of computer-steered stepping motors. Conversion of analyzer and polarizer readings into thickness and refractive index is done by a graphic procedure on (Δ, ψ)→( n, d) conversion plots. The method is tested by means of Langmuir-Blodgett monolayers of barium stearate. Adsorption of fibrinogen and albumin onto hydrophilic and hydrophobic chromium surfaces, the interaction of fibrinogen with anti-fibrinogen, and the interaction of albumin with anti-albumin are shown as illustrations of the technique.

Thickness dependence of internal voltage in metal-insulator-metal structure with dissimilar electrodes

A study of the thickness dependence of internal voltage in a metal-insulator-metal structure with barium stearate as the dielectric film has been carried out with aluminum and tin electrodes and the internal voltage has been found to decrease linearly with thickness of the dielectric film. The internal voltage is directly related to the difference of the work function of the two metals when the dielectric film has no net dipole moment. For the case when the insulator has a net dipole moment, the internal voltage is found to increase when aluminum is the bottom and tin the top electrodes. The measured internal voltage is found to be consistent with that derived from the study of tunneling currents.

Thin film thickness step gauge

The Blodgett-Langmuir technique is used to deposit multilayer films of barium stearate on EDF glass. The thickness of the film varies in steps of 10 monolayers, and the thickness of each monolayer is about 25 A. When viewed in white light at near normal incidence vivid interference colours are seen in reflection, with good contrast between adjacent steps. The reliability of the step gauge is tested for dielectric films of MgF2.

Diode Characteristics of a Metal-Insulator-Metal Structure

The large intrinsic field that can exist inside a thin insulator film which is sandwiched between dissimilar electrodes, is utilized to make the MIM (Metal-Insulator-Metal) structure operate as a diode. Dielectric monomolecular films of barium stearate are sandwiched between an aluminium and a tin electrode. The maximum value of forward bias current is of the order of a few nanoamperes. It is suggested that the value of current may be increased by utilizing a suitably doped dielectric.

Thickness influence on dielectric loss

Dielectric loss is essentially a macroscopic property valid for sufficiently thick samples. However, if the sample has a defect structure which varies with thickness and takes part in a particular relaxation process, the dielectric loss is expected to become thickness dependent. The present work reports the thickness influence on dielectric loss of barium stearate films. The results are explainable qualitatively in terms of the void structure of the film.

Critical surface tension of poly(vinyl butyral) and poly(vinyl benzal) multilayers and its relation to their surface orientation. I. Effect of surface pressures during deposition

AbstractCritical surface tensions γc of poly(vinyl butyral) and poly(vinyl benzal) multilayers built up by the Langmuir‐Blodgett method were measured with polyhydric alcohols and n‐alkanes. The γc values of both polymer multilayers increased with increasing pressures of the piston oils used to control pressures of polymers on the water surface during deposition. The γc value of poly(vinyl butyral) multilayers built up to lower pressure of the piston oil was approximately consistent with a crystalline hydrocarbon surface, while the γc value of the multilayer built up to higher pressure of the piston oil was approximately consistent with a—CH3 rather than a CH2 CH2 surface. All results for γc values of poly(vinyl benzal) multilayers were very close to the γc value of benzene ringrich surface. The γc value of the multilayer built up to lower pressure of the piston oil almost coincided with the γc value for amorphous polystyrene, while the γc value for the multilayer built up to higher pressure of the piston oil was in fair agreement with γc for an aromatic ring edge in the crystalline state. Values of γsd, the dispersion force contribution to the surface free energy of multilayers calculated by Fowkes' relation, were in fair agreement with the corresponding observed γc values, respectively. It is concluded from these measurements that orientations and surface structures in both polymer multilayers are affected by pressure change of piston oils. The properties on monolayers of two polymers at a air‐water interface and on barium stearate multilayers are also presented.

Stabilization of poly(vinyl chloride). I. Change in color of poly(vinyl chloride) compounded with some metal soaps

AbstractPoly(vinyl chloride) (PVC) with one or more metal salts added was colored by the action of heat to investigate the stabilization mechanism. The coloration and the color difference of heated PVC compound films varied according to the metal salt added. The decoloration of the colored compound films was advanced markedly in THF, DMF, acetone, and ammonia. On the other hand, the heated achromatic PVC film containing Cd/Ba soaps underwent an opposite change, from colorless to yellow orange, in the above materials. This means that the coloration of heated compound films may result from the formation of some complex (for example, π complex of the polyene with the metal chloride). Furthermore, the colored film with cadmium stearate was decolored by roll mixing with the colored film containing barium stearate. These results indicate that the stabilization with metal soaps may be founded on a physical phenomenon such aa an effect of complementary color.

Instability of Langmuir-Blodgett layers of barium stearate, cadmium arachidate and tripalmitin, studied by means of electron microscopy and infrared spectroscopy.

Results of an investigation of the stability of n-layers of barium stearate, cadmium arachidate and tripalmitin by means of electron microscopy and attenuated total reflection infrared spectroscopy are reported. Odd and even numbered barium starate n-layers with n - 1,2,3,4,5 are found to rearrange spontaneously from a regular film into ultrastructures of irregular, flat islands of varying thickness. The kinetics of the phase transformation of the first layer depends on the substrate, that of n-layers appears to be dependent on n, the temperature, and the surrounding medium. The kinetic behaviour of odd and even numbered layers is distinctly different. Similar studies on cadmium arachidate layers reveal much slower kinetics of the rearrangement process. In the case of tripalmitin n-layers it is shown that electron microscopy and infrared spectroscopy yield valuable complementary information about ultrastructure and molecular structure of the layers in correlation with the rearrangement process, which also occurs with this system. Consequences of the results of this paper for work published in various fields are briefly discussed.

Destructive D.C. breakdown in “built-up” barium stearate films : V. K. Agarwal and V. K. Srivastava. Electrocompnt. Sci. and Technol.1, 87 (1974)

Destructive D.C. breakdown in “built-up” barium stearate films : V. K. Agarwal and V. K. Srivastava. Electrocompnt. Sci. and Technol.1, 87 (1974)

Validity of Schopper's formulas for anisotropic films

The present work reports a detailed experimental investigation of Schopper's formula for investigating the case of a uniaxial nonabsorbing film of barium stearate on a transparent substrate. The required theoretical conditions for the experimental study of Schopper's formulas are well fulfilled for the film studied. The experimentally measured values of the reflectances and transmittances for Ba stearate films are found to be in agreement with the corresponding values calculated from the corrected Schopper's formulas. The experimental values, in general, are found to be in considerable disagreement with the corresponding values calculated by assuming the films to be isotropic. The studies have thus tested the validity of Schopper's formulas and have, indeed, confirmed the films to be anisotropic. Thus, assuming the validity of Schopper's formulas, the refractive indices of several other Blodgett-Langmuir films have been determined.

Destructive D.C. Breakdown in “Built-Up” Barium Stearate Films

The thickness dependence of maximum breakdown voltage (d.c.) leading to the destruction of the film has been reported for “built-up” barium stearate films in the thickness range (400 Å–1000 Å). These films were chosen because of their promising applications for making dielectric devices, and because their thickness is accurately known and controllable (within 25 Å). The breakdown voltage is found to be almost independent of thickness and microscopic observations in transmission did not show the occurrence of “single-hole” and “propagating” breakdowns, as observed by Kleinet al. in evaporated film systems. The I–V characteristics in the “non-destructive” phase have also been studied and the observed maximum breakdown voltage has been distinguished from the “maximum voltage breakdown” observed by Kleinet al.

Ac breakdown studies of built-up barium stearate films

The potential importance of built-up films of barium stearate for making dielectric devices has led to the necessity of the study of their ac breakdown characteristics. In the present work, the thickness and frequency dependence of the ac breakdown field has been reported in the thickness range 100–1500 Å and in the frequency region 10–200 kHz. The breakdown field is found to vary with thickness as d–a (α=0.68) and the breakdown voltage is found to increase with increasing thickness and frequency in the specified ranges. Although the experimental results could not be interpreted at present, the results obtained may prove useful in ac device applications of the films.

Temperature dependence of the breakdown field in barium stearate multilayer films

Since “built-up” barium-stearate films seem to be promising for making dielectric devices, it has become essential to study their breakdown characteristics also. The present paper reports a systematic study of the temperature dependence of d.c. breakdown in “built-up” multilayer films of barium stearate in the temperature range -40° to 40°C. These films are well suited for such studies because of their high dielectric strength, good reproducibility and highly uniform thicknesses which are controllable (to 25 Å) and accurately known. The breakdown field is found to decrease slightly with increasing temperatures. This result cannot be interpreted in terms of the theories of Fröhlich and Callen. Detailed current-voltage characteristics of the films have also been studied in the present work. The data reported on the films may prove useful in their device applications.

Temperature dependence of d.c. destructive breakdown field in ‘built-up’ barium stearate films

Since the ‘built-up’ molecular films of barium stearate have been shown to be promising for making thin film dielectric devices, a study of their breakdown characteristics is essential. Particularly, in device applications, the range of operating voltage is very important and therefore a study of the maximum dielectric strength of the films is highly desirable. Since the devices may be required to operate at various temperatures, it is all the more necessary to investigate the temperature dependence of the maximum dielectric strength. Such a temperature dependent study of the dielectric strength of barium stearate films has been reported in the present work in the range (−40–40°C). The dielectric strength is found to decrease with increasing temperature. Typical current-voltage characteristics with and without a series resistor and a representative transmission micrograph have also been given. The photomicrograph shows destruction of the film over large areas. As the modern theories do not describe the actual mechanism of destruction adequately, no attempt has been made to interpret the results theoretically. However, the results may prove useful in device applications of barium stearate films, involving self heating, nonshorting capacitor systems.

Studies of built-up films by means of the polarized infrared ATR spectrum. II. Mixed films of stearic acid and barium stearate

Polarized infrared attenuated total reflection studies have been made of mixed multilayers of stearic acid and barium stearate built up on a germanium plate by the Blodgett technique. Infrared transmission spectra of the built-up films have also been recorded by using polarized radiation. It is concluded that the films are made of an assembly of crystallites of the triclinic system, where all the trans-zigzag planes of the hydrocarbon chains are parallel to one another. The orientation of the hydrocarbon chains in the germanium-sample interface is found to be independent of the dipping direction of the plate during the process of monolayer transfer, while largely dependent upon the polishing direction of the plate in its cleaning procedure. The angle between the plane of the hydrocarbon chains and the polishing direction is estimated to be ca. 40° with the aid of reflectivities of the polarized radiations at 2920 and 2850 cm −1 and the dichroic ratio in the polarized transmission spectra. Furthermore, from the penetration depth of the totally reflected radiation and changes in reflectivity with the number of layers, the film thickness per layer is found to be ca. 24.3 A, being in good agreement with the half of the long spacing, 49.06 A, of the mixed films determined by X-ray diffraction studies.

The Kapitza resistance and thin surface films

Experimentally observed values for the Kapitza resistance across a solid-liquid He II boundary show that for specimens of gold, copper, and sapphire an enhanced heat flow is achieved between the two media if a surface film of barium stearate is deposited on the solid. The magnitude of the improved heat flow is less than that predicted from a simple model for phonon transmission across a solid-film-liquid arrangement, but is greater than that expected from the Khalatnikov theory.

Study of the effect of stabilizer on the degradation of poly(vinyl chloride) by pyrolysis–gas chromatography

AbstractThe effect of stabilizer on the thermal degradation of poly(vinyl chloride) was studied by means of pyrolysis–gas chromatography. The stabilizers used in this study were dibutyltin dilaurate, dibutyltin bis(n‐dodecyl mercaptide), barium stearate, and zinc stearate. PVC containing these stabilizers was degraded in a stream of nitrogen at temperatures ranging from 350 to 570°C. It was found that observed drastic reduction of benzene yield from the PVC containing zinc stearate had a close correlation with the formation of crosslinking structures.