Alejandro González-Álvarez

Phase and rheological behavior of the hexadecyl(trimethyl)azanium; 2-hydroxybenzoate/water system

The phase and rheological behavior of hexadecyl(trimethyl)azanium; 2-hydroxybenzoate (CTAS), and water as a function of surfactant concentration and temperature are investigated here. The critical micellization concentration (cmc(1)) and the concentration at which the structure of aggregates changes (cmc(2)) as well as the Krafft temperature (T(K)) are reported. A large micellar solution region exhibiting high viscosity, as well as hexagonal- and lamellar-phase regions were identified. In the dilute region, below the overlapping entanglement concentration (C*), the micellar solutions exhibit shear thickening. Above C*, wormlike micelles form and the solutions show strong viscoelasticity with Maxwell behavior in the linear regime and shear banding flow in the non-linear regime. The linear viscoelastic regime was analyzed with the Granek-Cates model, showing that the relaxation is controlled by the kinetics of reformation-and-scission of the micelles. The steady response in the non-linear regime is compared with the predictions of the Bautista-Manero-Puig (BMP) and the Giesekus models.

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

The aggregation properties of 2-, 3-, and 4-fluorobenzoic acids (2FBA, 3FBA, and 4FBA, respectively) and their salts with hexadecyltrimethylammonium cations (HTA2FB, HTA3FB, and HTA4FB) in water were studied 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 the pure acids solutions. The 4FBA is less water soluble, more hydrophobic, and has the lower critical aggregation concentration of the three isomers. The behavior of the HTA2FB compound in aqueous solution is different from that of HTA3FB and HTA4FB. The critical micelle concentration, critical concentration for sphere-to-rod-like micelle transition, and Krafft point of HTA3FB and HTA4FB are lower than those of the other surfactant but their surface activities are higher. The differences between the HTA2FB and the other two surfactants have been explained on the basis of the regular solution theory of mixed micelles and in light of the analysis of the hydration shell of the acids through molecular dynamic simulations. The results of the present work suggest that the different behaviors are due to a combination of different dehydration tendencies and the steric possibility of inclusion of the counterions in the micelle palisade layer. The formation of rod-like micelles by HTA2FB, while the tetradecyltrimethylammonium 2-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 be used in the rational design of micelles by means of molecular dynamics simulations, reducing the trial-and-error approach used to date.

THE USE OF POLYSACCHARIDES EXTRACTED FROM SEED OF Persea americana var. Hass ON THE SYNTHESIS OF ACRYLIC HYDROGELS

Vicente Arturo Lara-Valenciaa,b, Haydeé Dávila-Sotoc, Francisco Javier Moscoso-Sanchezd, Edgar Benjamin FigueroaOchoad, Francisco Carvajal-Ramose, Victor Vladimir Amilcar Fernández-Escamillaf, Alejandro González-Álvarezg, J. Félix Armando Soltero-Martínezg, Emma Rebeca Macías-Ballezag,* and Salvador GarcíaEnríquezh Departamento de Ingeniería de Proyectos. Centro Universitario de Ciencias Exactas e Ingenierías. Universidad de Guadalajara, 44430 Guadalajara, Jalisco. México División Ingeniería Ciencias Básicas. Centro de Enseñanza Técnica Industrial, 44638 Guadalajara, Jalisco. México Tecnologías Químicas. Centro de Enseñanza Técnica Industrial, 44638 Guadalajara, Jalisco. México Departamento de Química, Centro Universitario de Ciencias Exactas e Ingenierías. Universidad de Guadalajara, 44430 Guadalajara, Jalisco. México Departamento de Ingenierías. Centro Universitario de Tonalá. Universidad de Guadalajara, 45400 Tonalá, Jalisco. México Departamento de Ciencias Tecnológicas. Centro Universitario de la Ciénega. Universidad de Guadalajara, 47819 Ocotlán, Jalisco. México Departamento de Ingeniería Química. Centro Universitario de Ciencias Exactas e Ingenierías. Universidad de Guadalajara, 44430 Guadalajara, Jalisco. México Departamento de Madera Celulosa y Papel. Centro Universitario de Ciencias Exactas e Ingenierías. Universidad de Guadalajara, 45020 Guadalajara, Jalisco. México