A Novel Numerical Analysis on Surface Charge Densities of an Amphoteric O/W-Type Microemulsion in the Presence of CaCl2 and/or AlCl3
The effect of pH on the surface charge density of the O/W-type microemulsion formed in solutions of an amphoteric surfactant, (N alpha , N alpha -dimethyl-N epsilon -lauroyllysine, DMLL)/n -octane/1-pentanol/CaCl2 or AlCl3 , has been investigated. A novel equation for the surface charge densities in the presence of a multivalent cation (Ca2+ and/or Al3+ ) has been derived taking account of the number of DMLL molecules bound to a multivalent cation (q ). By applying a numerical analysis of this equation, it is possible to determine the intrinsic binding constants (K ) of the multivalent cation and the monovalent anion to the hydrophilic groups of DMLL and the adsorption density (N ) of DMLL molecules on the oil/water interface. Furthermore, N has been found to show pH dependence. N has a maximum value around the isoelectric region (in particular, pH 5-7) of DMLL molecules in the presence of CaCl2 , whereas N increases with increasing pH in the presence of AlCl3 . The surfactant (DMLL) numbers per O/W-type microemulsion droplet, i.e., the aggregation numbers, are successfully obtained as a function of pH in the presence of CaCl2 and/or AlCl3 .
Yoshihara
K
Faculty of Science and Technology, Science University of Tokyo, 2641, Yamazaki, Noda, Chiba, 278, Japan
Momozawa
N
Sakai
H
Abe
M