Aggregation and adsorption behavior of low concentration of aqueous solutions of hexadecyltrimethylammonium ortho, meta and parafluorbenzoate

G. LANDÁZURI; J. ÁLVAREZ; F. CARVAJAL; E. R. MACÍAS; A. GONZÁLEZ-ÁLVAREZ; E. P. SCHULZ; M.A. FRECHERO; J. L. RODRÍGUEZ; R. MINARDI; P.C. SCHULZ; J. F. A. SOLTERO

JOURNAL OF COLLOID AND INTERFACE SCIENCE

ACADEMIC PRESS INC ELSEVIER SCIENCE

Lugar: Chicago; Año: 2012 p. 86 - 93

0021-9797

.The aggregation properties of 2-, 3-, and 4-fluorobenzoic acids (2FBA, 3FBA, and 4FBA, respectively) andtheir salts with hexadecyltrimethylammonium cations (HTA2FB, HTA3FB, and HTA4FB) in water werestudied with a battery of techniques. Their activity at the air/solution interface has been also studied.The position of the fluorine atom in the acid affected the solubility, adsorption, and aggregation in thepure acids solutions. The 4FBA is less water soluble, more hydrophobic, and has the lower critical aggre-gation concentration of the three isomers. The behavior of the HTA2FB compound in aqueous solution isdifferent from that of HTA3FB and HTA4FB. The critical micelle concentration, critical concentration forsphere-to-rod-like micelle transition, and Krafft point of HTA3FB and HTA4FB are lower than those ofthe other surfactant but their surface activities are higher. The differences between the HTA2FB andthe other two surfactants have been explained on the basis of the regular solution theory of mixedmicelles and in light of the analysis of the hydration shell of the acids through molecular dynamic sim-ulations. The results of the present work suggest that the different behaviors are due to a combination ofdifferent dehydration tendencies and the steric possibility of inclusion of the counterions in the micellepalisade layer. The formation of rod-like micelles by HTA2FB, while the tetradecyltrimethylammonium2-fluorobenzoate only forms spherical aggregates, is explained on the basis of the packing parameter.The mentioned factors are complementary to others presented in literature. These conditions may beused in the rational design of micelles by means of molecular dynamics simulations, reducing thetrial-and-error approach used to date.