Abstract
On the basis of the experimental technique proposed by one of present authors, this work is devoted to the measurement of the electromobility of a very small nitrogen bubble suspended in a few aqueous electrolyte solutions. It was confirmed that the isoelectric point (i.e.p.) of a bubble in water exists in a pH range between 2 and 3 irrespective of bubble size in light of the experimental results previously reported.
When the mono- and divalent inorganic salts NaCl and MgSO4 were added to water, the negative mobility at a pH of 5.6 was monotonically depressed with increasing concentration of each salt.
As for the trivalent salts AlCl3 and Al2(SO4)3, a charge reversal was observed at a certain concentration of each salt which agreed with previous data reported by other workers.
Four n-alkyltrimethylammonium bromides of different n-alkyl chain length were also examined and it was observed that the i.e.p. of a surfactant with a smaller total number of carbon atoms in the n-alkyl chain of a n-alkyltrimethylammonium bromide tends to shift to a higher concentration. When the concentration giving the i.e.p. is plotted against the number of carbon atoms, a good linear correlation on a semilogarithmic scale was obtained. Incorporating the Stern-Graham double-layer model and the above linear correlation, the transfer energy required by the n-alkyltrimethylammonium ion when it is brought from the water phase to the nitrogen-water interface was estimated and the result was found to be reasonable.
