A STUDY OF THE ELECTROPHORETIC MOBILITY OF A VERY SMALL INERT-GAS BUBBLE SUSPENDED IN AQUEOUS INORGANIC ELECTROLYTE AND CATIONIC SURFACTANT SOLUTIONS

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.