Cavitation, Tensile Strength, and the Surface Films of Gas Nuclei 



NUMBER OF CARBON ATOMS 

 INCREASING MOLECULAR WEIGHT 



Fig. 13 - Effects of the length of linear 

 hydrocarbons on film formation 



Double Surface Films 



In order to prevent appreciable dissolving of nuclei, an effective diffusion 

 coefficient must be obtained for a surface film that is much lower than any 

 realized for a monomolecular film. That such a coefficient must exist is indi- 

 cated by the behavior of tap water in which algae were growing. This water had 

 negligible tensile strength gain due to dissolving when cavitated. 



How can a lower diffusion coefficient be obtained? The monomolecular films 

 applied to nuclei were the thickest and most compact monomolecular films pos- 

 sible. Therefore, to obtain a better film, one is forced to conclude that additional 

 material must be made to collect about a monomolecular film to increase its 

 thickness or perhaps "plug" leaks that may exist. This would improve the ef- 

 fectiveness of the film as a barrier to gas diffusion, and possibly reinforce the 

 film so that it is stronger and more capable of structurally opposing the surface 

 tension acting to cause dissolving. A likely way to do this would be surround 

 the nucleus and its monomolecular surface film with polar materials capable of 

 bonding to the polar groups that face the water in the film. 



To test this supposition, various nonsurfactant polar materials were added 

 to water containing either lauric acid or egg albumin. The polar materials used 

 were gelatins or gelling agents that had previously shown no surface film ac- 

 tivity (Table 8). They therefore should be unable to interfere with the formation 

 of a monomolecular film by attempting to form a competing film. However, 

 once the monomolecular film is in place, the polar groups in the film should 

 provide a stationary surface to which the nonsurfactant polar material can 

 adhere and start to build a structure. 



The combination of a saturated egg albumin solution plus a 0.01% Jaguar 

 solution worked well, resulting in zero tensile 30 minutes after cavitation. The 

 combination of a saturated cetyl alcohol solution plus a 0.1% gelatin (Fisher 

 G-8) solution was not as good, but improved a cetyl alcohol film from 21.9 psi 

 tensile strength to 6.5 psi. 



103 



