Georges Pétré

Study of the heat of reversible adsorption at the air-solution interface. II. Experimental determination of the heat of reversible adsorption of some alcohols

Abstract The surface tension of aqueous solutions of higher alcohols is measured as function of temperature at constant pressure and mole fraction. For all the studied alcohols a minimum in the σ (T) curves is obtained for sufficiently high concentrations, which minimum seems not to be explained by a solubility increase. The heat of reversible adsorption (or extension) is calculated for different temperatures following the procedure outlined in part I. The heat of reversible extension of the surface area vanishes at this minimum.

Influence of a surface tension minimum as a function of temperature on the marangoni convection

Abstract Aqueous long chain alcohol solutions have a surface tension which presents a minimum as a function of the temperature. At this particular temperature, the dimensionless Marangoni number is vanishing. It is thus expected that around the temperature of the minimum, Marangoni Convection would be slowered with a convective pattern deeply modified. An experiment to be performed in microgravity during the Texus 8 flight is described.

Experimental evidence for the minimum of surface tension with temperature at aqueous alcohol solution/air interfaces

Abstract The equilibrium surface tension of an aqueous solution of fatty alcohol/air goes through a minimum when the temperature is raised. As a consequence, the surface tension gradient originated by a given temperature difference between two regions of a free surface has to be reversed when the temperature increases. Simple devices are built-up to visualize this effect. A defined local region of the free surface is heated by a metallic plate near the interface. Talc particles on the surface show surface motion using a profile projector. The expected inversion of the direction of the talc particles with increasing temperature is often observed.

Study of the heat of reversible adsorption at the air-solution interface. I. Thermodynamical calculation of the heat of reversible adsorption of nonionic surfactants

Abstract From variation of surface tension with temperature of aqueous solutions of surfactants, the heat of reversible adsorption at constant temperature and surfactant mole fraction in the bulk can be calculated on a thermodynamic basis. Therefore, the Gibbs adsorption equation is rearranged in a suitable form, where the coefficient of dT does not depend on the choice of the standard entropy.

Correcting surface tension data obtained by the oscillating jet method

Abstract In the first waves of an oscillating jet the velocity of the surface is less than that of the center. Application of Bohrs formula to these first waves gives values of the surface tension which are too high. Hansen and collaborators have proposed an empirical method of correction permitting calculation of the correct surface tension even in this part of the jet. This method, valid for pure liquids, is in the case of solutions subject to errors concerning the true surface age, due to the strong extension in area of each element of surface in the first waves. The authors tested the method used by Hommelen which consists in selecting capillaries which reduce the number of waves to which Bohrs formula is not applicable.

Measurement of the variation of interfacial tension with temperature between immiscible liquids of equal density

Abstract For the measurement of interfacial tensions between liquids of equal densities, methods like drop weight, Wilhelmy plate etc. fail. A method is developed using a liquid bridge between a glass tip and a freely hanging piece of density higher than that of the fluids. The volume of liquid bridge that can sustain a piece of given weight cannot exceed some maximal value. This maximal volume is determined experimentally. A computer program makes it possible to tabulate the maximal volumes of the liquid bridge as a function of the interfacial tension for a given tip and metal piece. The program uses iteratively the circle segment approximation for the calculation of the meridian curve given by Kelvin. Results are given for the system aqueous ethanol/paraffin oil of equal densities.

The influence of a surface tension minimum on the convective motion of a fluid in microgravity: D1 mission results

Abstract The experiment STEM (Surface Tension Minimum) was performed in an experimental cell integrated in the FMP (Fluid Physics Module) during the D1 mission of Spacelab. The observation volume (1×2×3) cm3 was constituted by a stainless steel frame and by two optical Pyrex windows. It was fixed on the front disk of the FPM. The cell was filled under microgravity conditions by an aqueous solution of n-heptanol 6,04 10−3 molal. At equilibrium this system presents a minimum of surface tension as a function of temperature around 40°C. The fluid was heated from the front disk side of the cell. A temperature difference of 35°C was maintained between two opposite sides of the cell, by using the large heat capacity of a water reservoir in thermal contact with the cold side of the cell. The thermal gradient was parallel to the liquid/gas interface. The motions of the fluid were recorded on video-tapes and the velocities were determined by following latex particles used as tracers. The convective pattern is analysed and compared with ground experiments. In this case the tracer trajectories allow to determine the convective patterns and the velocities are determined by laser doppler anemometry.

Study of the Marangoni convection around a surface tension minimum under microgravity conditions

Abstract At equilibrium, aqueous fatty alcohol solutions presents a surface tension minimum versus temperature. The influence of such an extremum on the Marangoni convection is studied. Two experiments have been performed under microgravity conditions (Texus 8 (1983) and Texus 9 (1984) flights). The velocity fields are determined by following the paths of tracer particles and furthermore, in the Texus 9 experiment, differential interferograms have been recorded.

Shape of a liquid bridge and interfacial tension

Abstract A method is briefly described making it possible to measure the interfacial tension between two liquids of same density. An axisymmetric liquid bridge is formed between an upper fixed circular horizontal disc and a freely hanging solid pieceof appropriate shape, and of density greater than that of the liquids. The maximal volume of the liquid figure satisfying the mechanical equilibrium condition is computed for desired values of the interfacial tension. The maximal volume of the bridge is measured experimentally. The method is applied to two silicon oil/water systems. The variation of interfacial tension with temperature is obtained between 20°C and 50°C. For one of the systems the results can be compared with those obtained by the drop weight method. The two methods gives interfacial tensions increasing with temperatures.

Konstruktion und Erprobung einer neuartigen Apparatur zur Messung von Grenzflächenspannungen zwischen Fluiden

ZusammenfassungIn der vorliegenden Arbeit wird eine neuartige Meßapparatur beschrieben, welche es erlaubt, die Grenzflächenspannung zwischen Fluiden ungleicher Dichte nach der Methode von Harkins sowie gleicher Dichte nach der relativ neuen Methode von Pétré und Wozniak zu messen. Erste Meßergebnisse werden vorgestellt und diskutiert.