Nov., 1959
WETTINGOF LOW-ENERGY SOLIDSBY AQUEOUSHIGHLYFLUORINATED ACIDS
tion of the existence of a “crossed” resonance in the chelate rings and consequently of the presence of Ir-bondings from the central nickel atom. This hypothesis was already brought forth on the basis of spectrophotometric measurements in the case of some nickel(I1) complexes containing chelate rings of the same species.l‘ The present results, therefore, seem to corroborate such a view. The chelate ring in bis-(N-methylsalicylaldimine)-nickel(II), unlike that in the oxime complex, is not planar. The N1-Ce axis bisects the chelate ring into two parts which are not co-planar. This distortion allows the Cx atom to move away from the 0 atom. This effect is facilitated by the fact that the Cs-N-Ni angle is larger than the C r N-Cs one. It should be noted that the three bonds from the N atom lie practically on the same plane, while the three bonds from t$e C6 atom are not eo-planar because the C&7 bond makes a n angle of 13’ with the plane of the other two. (11) L. Sacconi, P. Paoletti and F. Maggio, J . A m . Chem. SOC.,79, 4007 (1957).
1911
The C8-0 distance of 2.68 8. is much shorter than a normal van der Waals distance and this may be due to the existence of a hydrogen bond between the two atoms. This hydrogen bond could arise from a S+ charge induced on the methyl carbon by the nitrogen atom carrying a positive charge. It may be noted that the Cs atom lies between two 0 a t o p s of two neighboring molecules a t 3.21 and 3.79 A,, respectively. The direction O-CH3-0 is approximately parallel t o the axis b of the cell. A very interesting datum is the distance between two neighboring nickel atoms. Actually the diamagnetism of this complex in the solid state could be explained on the assumption of spin-pairing between two nickel atoms, but the structure of the complex shows clearly that this is not the case. I n fagt the shortest Ni-Ni distance is found to be 5.32 A. Acknowledgment.-The authors are indebted to the Italian I‘ Consiglio Nasionale delle Richerche” for the support of this work.
WETTING OF LOW-ENERGY SOLIDS BY AQUEOUS SOLUTIONS OF HIGHLY FLUORINATED ACIDS AND SALTS’ BY MARIANNE K. BERNETT AND W. A. ZISMAN Contribution from the U.S. Naval Research Laboratory, Washington 25, D. C. Received Mall 21, 1969
Wettability studies of aqueous solutions of several series of pure, highly fluorinated, aliphatic acids and salts were carried out on two low-energy organic solids, polyethylene and Teflon. As anticipated, the fluorinated compounds were able to depress the surface t,ension of water below the critical surface tension (yc) of Teflon, and were therefore capable of completely wetting it. I n contrast, conventional hydrocarbon wetting agents do not depress the surface tension of water to this extent. Whenever possible, wettability curves were obtained for each solid surface by plotting the cosine of the contact angle versus the surface tension of the solution. The value of yo, 19 dyneslcm., t,hus obtained for Teflon is in reasonable agreement with the value of 18 dynes/cm. established from previous studies. With polyethylene a value of yc of 20 dynes/cm. was obtained, which is much lower than the established value of 31 dynes/cm. This led to experiments demonstrating that the phenomenon resulted from adsorption of the fluorinated compounds on the polyethylene surface, thereby altering its wetting characteristics to those of a fluorinated surface. As expected from the difference in their surface energies, greater and more tenacious adsorption was observed on polyethylene than on Teflon.
Introduction I n a recent study2 on the wettability of lowenergy solids by aqueous solutions of conventional surface-active agents, it was shown that the equilibrium contact angle (e) and the ability of the i solution to sDread on the surfaces of Dolvethvlene and polytethluoroethylene are raihhe; s
