B. M. Abraham

Longitudinal surface waves for the study of dynamic properties of surfactant systems: I. Instrumentation

Abstract An instrument for studying longitudinal surface waves on water is described. The waves were generated by an oscillating barrier in a Langmuir trough and were detected with a capillary wave propagating orthogonal to the longitudinal waves as an oscillating surface tension. Except for the barrier, none of the components of the instrument touched the surface: thus, the disturbances to the wave propagation were minimized. By signal averaging, we were able to detect a surface tension change as small as 1 mdyn/cm without difficulty. The limit to detection of surface tension change by this technique resulted from ripples and other mechanical noise caused by the barrier motion.

X-ray diffraction study of the in-plane structure of an organic multilayer (“langmuir—blodgett”) film

Abstract Using X-ray diffraction at glancing angles, we find that in Langmuir—Blodgett films of lead stearate the lead atoms form plane arrays identical to one set of planes in a bulk crystal, but with little correlation between the planes. The resulting system of two-dimensional layers is similar in its static structure to an ideal smectic-B liquid crystal

Experimental determination of the molar volume and derivation of the expansion coefficient, entropy change on compression, compressibility, and first-sound velocity for liquid3He from 35 to 1200 mK and from the saturation pressure to 24 atm

The molar volume of liquid3He,V(P, T), was determined from measurements of the dielectric constant over the temperature range 35–1200 mK and from the vapor pressure to 24 atm. Analytical expressions were fitted to the molar volumes in order to calculate the isobaric expansion coefficient αP, the isothermal compressibility κKT, and the first-sound velocityc1; the expansion coefficient was integrated numerically to arrive at the entropy change on compression. Values ofV(P, T) and the derived quantities are presented in tabular form at even temperatures and pressures. From this work it was found thatV(0, 0)=36.873±0.015 cm3/mole and thatc1(0, 0)=178.4 m/sec, about 2.5% lower than the presently accepted value of 183.4 m/sec.

Centro‐symmetric technique for measuring shear modulus, viscosity, and surface tension of spread monolayers

We have constructed an apparatus which enables one to measure, simultaneously, the shear modulus, the viscosity, and the surface pressure of a monomolecular film on water under a hydrostatic compression. It is particularly suitable for measurements of the static shear modulus of insoluble monolayers. A capillary wave generator/detector system was also incorporated to determine the surface pressure. The trough is a Teflon cup 12.7 cm (5.4 in.) in inner diameter with sloping interior sides. As the cup is raised, while maintaining the water elevation fixed, the film is uniformly compressed. A rotor suspended at the center from a fine torsion fiber is used to measure the mechanical properties (surface viscosity and/or surface shear modulus). To measure the quasistatic shear properties, the cup is rotated through a small angle and the residual deflection of the rotor determined. Dynamic shear response is probed by studying transient torsional oscillations following a sudden angular displacement of the torsion ...

YH3 and YD3: Heat Capacities and Thermodynamic Functions from 15° to 350°K and Infrared Absorption Spectra

The heat capacities of YH3 and YD3 were determined in an adiabatic calorimeter from 15° to 350°K. The heat capacity, entropy, enthalpy, and Gibbs free‐energy function for YH3 at 298.15°K are 10.363±0.021 cal deg—1 mole—1, 10.019±0.020 cal deg—1 mole—1, 1613.3±3.2 cal mole—1, and —4.608±0.009 cal deg—1 mole—1, respectively. The corresponding quantities for YD3 are 13.727±0.028, 12.028±0.024, 2024.8±4.0, and —5.237±0.010.The infrared absorption spectra of YH3 and YD3 were taken in the range 400 to 4000 cm—1. Maxima in the absorption bands of YH3 were observed at 1295, 920, and 640 cm—1 and in the absorption bands of YD3 at 1295/√2, 920/√2, and 640/√2 cm—1. A reasonable assignment of these frequencies to Y—H and Y—D vibrations satisfactorily accounts for the difference between the heat capacities of YH3 and YD3 in the temperature range 50° to 350°K. The lattice parameters as determined by x‐ray diffraction for the hexagonal close‐packed trihydrides were a0 = 3.672±0.002 A and c0 = 6.625±0.018 A for YH3 and a...

A low-temperature thermal process for the decomposition of water.

The following three reactions, each of which has been shown to proceed at the temperature indicated above the arrow, are suggested as a cycle for the thermal decomposition of water:

Sound propagation, density, and viscosity in liquid3He

We have measured the temperature dependence of the velocity and the attenuation of sound in the range 60–700 mK. The maximum in the sound velocity observed by Abraham and Osborne is confirmed. The viscosity deduced from the attenuation measurements is in good agreement with that of Abel, Anderson, and Wheatley but differs from that of Betts, Keen, and Wilks. The sound velocity as a function of pressure at 150 mK was also measured and from this the low-temperature pressure dependence of the density was determined.

Shear rigidity of spread stearic acid monolayers on water

The effect of Al3+, Fe3+, Ca2+, and Mg2+ ions and of pH on the two‐dimensional shear modulus of stearic acid spread on a water substrate was determined. A large shear modulus was displayed by the films when the subphase contained Al3+ and Fe3+ ions at the self‐buffered pH. With Fe2+ dissolved in the subphase, the film displayed a viscous relaxation when strained but no residual stress was observed. No effect was observed with the Ca2+ or Mg2+. Reducing the pH value in the subphase with the trivalent ions caused the shear modulus to disappear. The observations are interpreted in terms of hydrogen bonding.

Techniques for measuring sound propagation in liquid 4He and 3He-4He solutions☆

Abstract The description of an instrument for the accurate measurement of ultrasonic attenuation and velocity in liquid 4 He and 3 He- 4 He solutions, and the details of the cell in which they were made, are presented. Measurements were made by matching the amplitude of a signal traversing the helium to a reference pulse of equal amplitude but opposite phase (both signals being derived from the same oscillator). By observing the change with temperature in the amplitude and phase of the signal passing through the helium, both the change in the velocity and in the attenuation could be determined. The cell in which the measurements were made employed two matched x-cut quartz crystal transducers, separated by a fused quartz spacer. The crystals, which were clamped only at the rim, were loaded on both sides by liquid helium.

The phases of insoluble monolayers: Comparison between the surface pressure-molecular area (Π-A) diagram and shear modulus measurements

Simultaneous measurements of the surface pressure‐molecular area (Π‐A) diagrams and the shear modulus of a series of long chain aliphatic alcohols C18OH, C20OH, C21OH, and C22OH spread on water indicate that the conventional phase assignments based on the compressibility are not reliable.