Caracterización de cristales líquidos por microscopía óptica en sistemas surfactante polietoxilado-alcano-agua

The phase behavior of an alcohol polyethoxylated surfactant with decane and dodecane oil phase varying the water proportion from 5 to 90% to determine compositions in which the formation of liquid crystals and microemulsions ocurred was investigated. Pseudoternary phase diagrams were built to represent the regions of liquid crystals, biphases and microemulsions. Polarized light optical microscopy was used for the analysis and characterization of the separate phases. The micrographs obtained showed characteristics of hexagonal and lamellar phases of liquid crystal, isotropic phases, microemulsions and vesicles. This study is important to propose hypothesis regarding the factors determining the formation and stability of phases composed by surfactant/oil/water systems

Aporte de un sistema predictivo de contraloría médica en la gestión de licencias médicas electrónicas

Introduction: The delay in the processing of sick leaves (SLs) is a public health problema in Chile, considering that this affects the payment of the subsidy to the individuals destined to perform the prescribed medical rest while unable to work. The aim of this study was to explore the differences in the processing time of electronic SLs (ESLs) evaluated by medical audit (MA) and the SLs evaluated by a predictive medical audit system (PMAS) based on artificial neural networks. Materials and methods: The processing time of the ESLs that were processed by PMAS was compared with the processing time of those that were examined only by MA, using Kaplan Meier curves, log-rank test, and multivariate Cox models. Results: The processing rate for PMAS was 1.7-fold to 5.5-fold faster than MA, after adjusting for potential confounding variables. Discussion: The implementation of the PMAS reduced the processing time of ESLs, which benefits the workers affiliated to the public insurance system in Chile.Introducción: El retraso del procesamiento de las licencias médicas (LMs) representa un problema de salud pública en Chile, considerando que esto afecta el pago del subsidio a las personas destinado a realizar el reposo médico prescrito mientras no se pueda trabajar. El objetivo de este estudio fue explorar las diferencias en el tiempo de procesamiento de las licencias médicas electrónicas (LMEs) evaluadas por contraloría médica (CM) y las evaluadas por un sistema predictivo de contraloría médica (SPCM) basado en redes neuronales artificiales. Materiales y métodos: El tiempo de procesamiento de LMEs procesadas con SPCM fue comparado con el tiempo de procesamiento de LMEs examinadas solo con CM, usando curvas de Kaplan Meier, prueba de log-rank y modelos multivariados de Cox. Resultados: La tasa de procesamiento del SPCM fue entre 1,7 a 5,5 veces más rápida que la tasa de procesamiento de la CM, ajustando por potenciales confusores. Discusión: La implementación del SPCM permitió disminuir el tiempo de procesamiento de las LMEs, beneficiando a los trabajadores afiliados al seguro público

Influence of the formulation variables on the viscosity of anionic surfactant-oil-water emulsions.

Phase transition and viscosity behavior of emulsified systems were studied after modifying their physicochemical formulation. Effects of concentration and nature of salts and n-alcohols, and water/oil relation on the rheological properties of emulsions were also studied. Pre-equilibrated systems were emulsified according to an agitation procedure, and the viscosity (cP) was measured at different shear rates ranging from 1 to 300 s-1. The phase behavior, as well as the emulsion type based on electrolytic conductivity, was observed. Several interpretations of the flow and viscosity curves of emulsions were made through the estimation of rheological parameters such as consistency index "k" and behavior index "n"

Síntesis asistida por microondas de derivados acilados de lignina de diferentes masas molares con posible actividad superficial.

Lignins of different molar masses were esterified using microwave radiation and the surface activity of the derivatives obtained were evaluated.The lignin was fractionated by ultrafiltration using ceramic membranes of 15 and 8 kDa. Succinic anhydride and glutaric anhydride were used to modify the lignin. The surface activity of the derivatives was evaluated by measuring the surface tension. FTIR spectra showed the incorporation of carboxylic acid-ester groups in lignin. Esterified products decreased the surface tension between 10-20% with respect to the original lignin, and this effect was greater for glutaric anhydride esterified products at high concentrations. The incorporation of new acid-ester groups in the lignin structure provides a higher amphiphilic character to lignin, due to the presence of new polar functional groups that allow the adsorption on the surface minimizing the attraction forces within the liquid.Se esterificaron ligninas de diferentes masas molares empleando radiación microondas y se evaluó la actividad superficial de los derivados obtenidos. La lignina se fraccionó por ultrafiltración utilizando membranas cerámicas de 15 y 8 KDa. Se emplearon anhídrido succínico y anhídrido glutárico para modificar la lignina. La actividad superficial de los derivados se evaluó midiendo la tensión superficial. Los espectros FTIR mostraron la incorporación de los grupos éster-ácido carboxílico en la lignina. Los productos esterificados disminuyeron la tensión superficial entre un 10-20% con respecto a la lignina original, siendo este efecto mayor para los productos esterificados con anhídrido glutárico a altas concentraciones. La incorporación de los nuevos grupos éster-ácido en la estructura lígnica le proporciona un mayor carácter anfifílico, debido a la presencia de nuevos grupos funcionales polares que permiten la adsorción en la superficie minimizando las fuerzas de atracción en el seno del líquido

Estudio del coeficiente de reparto de ácidos carboxílicos grasos en sistemas modificados heptano/agua

The use of fatty acids (FAs) as amphiphiles is very important because they have a behaving similar to surfactants. The formulation for the preferential partition of these species was studied by varying the amount of salt at constant acid concentration. As the salt concentration increases, a Winsor I→III→II transition is observed for all the systems studied. Furthermore, the electrolyte concentration required to obtain the optimum formulation varies inversely with the chain length of the acid. The partition coefficient of the surfactant allows one to obtain thermodynamic information on the acid transfer process between the phases of the system