Changes In Surface Free Energy Research Articles

The oxygenation of hemoglobin as a problem in surface chemistry

The reaction of oxygen with hemoglobin is cooperative, and the free energy change that causes the cooperative effect is believed to result from the conformational change in the hemoglobin molecule upon oxygenation. If hemoglobin is considered a colloid, the changes on the molecular level due to oxygenation can be estimated in terms of surface free energy. Because of the large surface area of such a system, small changes in surface free energy can result in significant changes in the total free energy of the system and, therefore, in the equilibrium. Specifically, changes in the surface free energy could contribute to the cooperative nature of the interaction and the variation of the equilibrium constant with pH and ionic strength. The approach outlined in this paper suggests a relatively simple way of estimating the variation of the equilibrium constant in a complex system where changes in surface free energy are significant.

A wicking method for measuring wetting properties of carbon yarns

A dynamic method for measuring the wettability of carbon yarn has been devised which is based on the rate of wicking of a test liquid by a bundle of the yarn. An equation has been derived which relates the wicking rate data to the change in surface free energy of the yarn caused by wetting. Contact angles are calculated from the free energy values. This method has the advantages of being fast, independent of operator judgment, and only requires a sample size of about 1 g. Since all of the surface area of the sample is involved in the measurement, the average wetting characteristic of about 1 m 2 of carbon yarn surface is determined conveniently in a test.

Relationship between residual microstrain and electrode potential in miller copper powder

X-ray diffraction line-broadening analysis has been used to measure the residual microstrain in ball-milled copper powder. Residual strain energy has been calculated from the microstrains obtained for different degrees of cold working. The stored energy produces changes in the electrode potential; a comparison has been made between the strain energy, obtained from the X-ray data, and the change of surface free energy, derived from the electrode potential measurements. The relationship between the strain energy and the change in the electrode potential, relative to that of the annealed state, is linear. A slow decrease of the electrode potential of the cold worked specimen takes place with time. This is attributed to the exchange current operating at the surface of the electroce.

Reorientation effects in vitreous carbon and pyrolytic graphite

Tubular specimens of vitreous carbon and of pyrolytic graphite, heated in nitrogen or helium for several minutes at 2850 to 3100° K by RF induction, developed a “skin” of crystalline carbon, nodular in appearance and apparently growing into the carbon from the surface. The vitreous carbon was isotropic, with no preferred orientation of “crystallites”; the pyrolytic graphite had a preferred orientation of basal planes at right angles to the axis of the specimen, so that curved surfaces were composed predominantly of edge atoms. X-ray diffraction studies of the skin indicated that it was partially graphitised and strongly orientated with basal planes parallel to the surface. The mechanism of the reorientation process is as yet not clear, but the driving force may be a change in surface free energy.

鉱粒の浮遊現象と濡れとの関連性について

Though it is clear from the preceding report that the floating mineral must satisfy both the supporting force equation (i), and the Young equation (ii), these two do not join mathematically with each other in these states. In this report, the supporting force equation (iii) is substituted for the equation (i), where Tl is the air-water interfacial tension or energy, θ is the contact angle and a is the inclination angle of the mineral plane to the horizontal.f (per unit length) =Tl sin (θ-α)(iii)This f has the positive and the negative sign. +f is the force acting toward the mineral to float and-f is the force acting toward the mineral to sink.On the other hand, instead of the Young equation, the surface free energy change W (the work done by the system per unit area) when the mneal moves at the air-water interface, is given by the following equation. This energy change W is considered a measure of wettability, W=Tl (cos θ-cos α)(viii)expressing all types of wetting of the floating mineral, and when W > 0, the wetting proceeds spontaneously(Ts →Tls) which means “wettable”, or “hydrophilic” and when W<0, the wetting recedes spontaneously (Tls→Ts) which means “nonwettable” or “hydrophobic”, and when W=0, the wetting stops.Combining these two equations (the dynamic and the thermodynamic condition), the following relations are obtained. These relations explain the fundamental principle of flotation that the wettableW=0...f<0 W=0...f>0 W=0...f=0mineral sinks and the nonwettable floats.When the contact angle is 0°<θ<180°, the mineral at the air-water interface has always both the hydrophilic (W > 0) and the hydrophobic surface area (W < 0), and neglecting the gravitational effect, the mineral are moved spontaneously by either the hydrophilic force (-f) on the hydrophobic force (+f) to the area of W=0. This is the reason why the mineral clings to the air-water interface by the hydrophilic and the hydrophobic force, and one can easily understand that the force supporting the mineral at the upper interface of bubble is the hydrophilic force. And the hydrophilic force plays important roles not only in making the mineral to sink into water, but in supporting it at the interface, and cooperates with the hydro phobic force to make up the characteristic of flotation.

THE PORE STRUCTURE AND ADSORPTIVE PROPERTIES OF SOME ACTIVATED CHARCOALS: II. THE APPARENT DENSITY OF CHARCOAL IN LIQUID MEDIA

The apparent density of eight charcoal samples has been determined in a series of liquids at two temperatures, 25° and 55 °C. From the data a correlation between apparent density of the charcoal and surface tension of the measuring fluid is suggested. An attempt is made to explain this approximate regularity in terms of the surface free energy change on immersion.