Vibrating jets

Two dynamic methods have been developed for measurement of the surface tensions, the method of ripples first employed by Rayleigh and the vibrating jet method developed by Bohr. 

More closely approaching the conditions desirable for determining the true dynamic surface tension is the vibrating jet method. 

The experimental data on the subject of the surface tensions of such solutions is scanty. The early work of Valson (G.R. LXXIV. 103, 1872) and of Morgan (cf. J.A.G.S. xxxv. 1753, 1913) cannot be considered as reliable. More accurate appear to be the data of Stocker (vibrating jet) Zeit Phys. Ghem. xciv, 149, 1920), who compared his values with those of Grabowski and Pann (Diss. Kdnigsberg, 1904) (capillary rise) and Sentis (hanging drops) Thhe, Paris, 1897). 

That adsorption occurs with great ease on mercury surfaces is demonstrated by the wide variations observed in the literature for the surface tension of this substance in contact with various gases. Thus Meyer obtained by the vibrating jet method the following values ... 

Addison, C.C. (1943) The properties of freshly formed surfaces. Part I. The application of the vibrating-jet technique to surface-tension measurements of mobile liquids. J. Chem. Soc. 535-541. 

A difficulty encountered in the measurement of the surface tension of solutions is that it is often different when measured by so-called dynamic methods (vibrating jets, etc.), in which the value for a freshly-formed surface is measured rapidly, and when measured by so-called static methods (capillary rise, etc.), which determine the value for a surface which has been in existence for some time. The difference is due to the fact that the composition of the surface is different from that in the bulk of the solution, and in a fresh surface a change of concentration occurs, which, as it involyes diffusion, usually occurs slowly, so that rapid measurements give results different from those which deal with a surface which has come into equilibrium. In capillary active solutions, the surface is enriched in solute, whilst in capillary inactive it is usually richer in solvent. In the case of electrolyte solutions, the surface layer is considered to consist of a unimolecular layer of solvent molecules. The thermodynamic theory was established by Gibbs, and indicates that when the solute... 

FIGURE 6.1 Techniques to produce microcapsules at high production rates (a) vibrating jet, (b) jet cutting, and (c) spinning disk. 

Vibrating jet techniques also have the disadvantage that the produced bead size is related to the nozzle diameter, which can therefore be problematic when large particle or cell clusters have to be encapsulated. However concentric air-flow enables to encapsulate those large particles as the particle size can be more smaller than the nozzle size. " ... 

Fig.3. Photographs showing (a) rapid drop formation from a vibrating jet, and (b) the resultant oxide gel spheres after dehydration. [Courtesy of Harwell Laboratory]...

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