Carlos Rodriguez

Effect of ionic surfactants on the phase behavior and structure of sucrose ester/water/oil systems.

The phase behavior and structure of sucrose ester/water/oil systems in the presence of long-chain cosurfactant (monolaurin) and small amounts of ionic surfactants was investigated by phase study and small angle X-ray scattering. In a water/sucrose ester/monolaurin/decane system at 27 degrees C, instead of a three-phase microemulsion, lamellar liquid crystals are formed in the dilute region. Unlike other systems in the presence of alcohol as cosurfactant, the HLB composition does not change with dilution, since monolaurin adsorbs almost completely in the interface. The addition of small amounts of ionic surfactant, regardless of the counterion, increases the solubilization of water in W/O microemulsions. The solubilization on oil in O/W microemulsions is not much affected, but structuring is induced and a viscous isotropic phase is formed. At high ionic surfactant concentrations, the single-phase microemulsion disappears and liquid crystals are favored.

Structure of vesicles in homogeneous short-chain polyoxyethylene cholesterol ether systems

Abstract Mixtures of the homogeneous nonionic surfactant trioxyethylene cholesterol ether, ChEO 3 and water were examined by microscopy, small-angle X-ray scattering, differential scanning calorimetry, electron-spin resonance and fluorescence spectrometry. A lamellar liquid-crystalline phase with peculiar characteristics is found above 75% of surfactant concentration. This phase seems to consist of a rather rigid and ordered bilayer when compared with typical L α -phases although the degree of crystallinity is less than that of L β -phases in nonionic systems with the same EO chain. The peculiarities of this phase are attributed to the rigid and bulky hydrophobic group of surfactant. The dispersion of this lamellar phase in water leads to the formation of very stable vesicles with a wide range of morphologies at rather low surfactant concentrations.

Effect of Novel Alkanolamides on the Phase Behavior and Surface Properties of Aqueous Surfactant Solutions

Abstract The surface tension properties and phase behavior of a new series of alkanolamides, alkanoyl N‐methyl ethanolamides (NMEAs) and their mixtures with sodium dodecyl sulfate (SDS) were investigated. NMEAs alone do not form micelles in aqueous solutions but reduce considerably the surface tension until macroscopic phase separation occurs. According to Gibbs isotherms, the surface layer is less compact for the NMEA with the shortest alkanoyl chain. The critical micelle concentration (CMC) of SDS solutions is greatly reduced upon addition of a small amount of NMEA and the magnitude of this effect increases with the length of the alkanoyl group. The results indicate the presence of attractive interactions between SDS and NMEA molecules inside micelles. The mixing of SDS with NMEA‐16 causes a reduction in the melting temperature of the solid similar to freezing‐point depression in a binary system. On the other hand, the eutectic temperature is higher in SDS‐conventional dodecanoyl mono ethanolamide (DMA) systems in which the mixture is in a solid state at room temperature over a wide range of mixing fractions. Among NMEAs, surface tension decay is faster as the alkanoyl chain length decreases. Only for the dodecanoyl chain could a diffusion‐controlled adsorption be identified at low concentrations. When small amounts of NMEA are added to SDS aqueous solutions, the surface tension decay is retarded; however, and at long times a lower surface tension is reached. For NMEA/SDS and DMA/SDS systems, an adsorption barrier is likely present. The magnitude of this barrier seems to depend on the SDS/alkanolamide ratio.

SOLUBILIZATION OF OIL IN DISCONTINUOUS CUBIC LIQUID CRYSTAL IN POLY(OXYETHYLENE)n OLEYL ETHER SYSTEMS

Abstract The structural change of the discontinuous cubic (I1) phase upon addition of oil (heptane, decane, and hexadecane) is investigated by small-angle x-ray scattering. In polyoxyethylene oleyl ether (C18.1EOn) systems having long polyoxyethylene chain (n =19.2, 30.1, and 50.8), the I 1 phase is formed in a wide concentration range. Only in C18.1EOnEO19.2EOn systems, the structure of the I1 phase changes from body-centered to face centered cubic lattice upon addition of oil. According to the analysis of the change in effective cross-sectional area, the solubilization of hexadecane increases the repulsion between polyoxyethylene chains, while solubilization of heptane makes it decrease. The solubilization of decane keeps the repulsion constant. Since the repulsion hampers the curvature change due to the solubilization, the solubilization capacity is in the order, heptane>decane>hexadecane. The oil penetration and nonpenetration into the palisade layer are also discussed in term of the change in the effective volume of the lipophilic part in the surfactant molecule.

Executable model composition: a multilevel approach

Modularizing concerns is a common strategy to lower application complexity: it results in modules that are easy to maintain, to adapt, and to replace. In some cases, these modules can also be expressed with very expressive concern-specific languages that manage high level concepts. On the other hand, modularization also requires tools and languages to describe the relations and interactions between concerns and to reconstruct the full application semantics. Ideally, these descriptions should be written using languages that work with the same concepts than the concern specific languages. Cumbia is a metamodel-based platform to build applications that support multiple concern specific languages. However, the composition and coordination mechanism between concerns depends on a too low level language called CCL: since it is built around very basic and generic coordination primitives, using the language requires a strong technical knowledge of the platform, and it is difficult to implement tools that offer meaningful validations on compositions. In this paper we propose a composition metamodel to characterize, at metamodel level, the composition and coordination of Cumbia models. By adopting this solution, the mentioned problems are solved, and domain experts can have a more active role in the creation of models for Cumbia-based applications.

Metamodel dependencies for executable models

Cumbia is our platform to develop applications based on multiple, coordinated executable models which can be described using different languages. The coordination of models is achieved by describing how their elements should interact, and mapping those descriptions into low level coordination primitives. Moreover, the description of the coordination is described externally: it does not have an impact either on the metamodels or on the models, and this results in lower coupling and increased flexibility. This approach, which is appropriate when the metamodels are highly independent, has limitations when it comes to describing dependencies that are inherent to the concerns. In those cases, it makes sense to incorporate those dependencies into the metamodels descriptions. The goal of this paper is thus to discuss two alternative ways to establish those dependencies, and illustrate their usage, benefits, and drawbacks in a concrete example.

APLICACIÓN DE LA TEORÍA DE ROBOTS MANIPULADORES A LA BIOMECÁNICA DEL BRAZO HUMANO

Este articulo presenta la aplicacion de un conjunto de tecnicas propias de la teoria de los robots manipuladores al estudio del movimiento del brazo humano. Para ello el brazo humano se modela como un robot manipulador redundante. En particular se aplica el concepto de indices de desempeno para predecir posturas optimas del brazo durante la realizacion de tareas. En el estudio se incluyen tanto posiciones estaticas, como secuencias de posiciones para la formulacion de trayectorias optimas de movimiento.

Effect of mixing lipophilic and hydrophilic silicone surfactant systems

The phase behavior of a hydrophilic A—B-type silicone surfactant, (CH3)3SiO-[(CH3)2SiO]3.8-(CH3) 2SiCH2CH2CH2-O-(CH2CH2O)51.6H, Si5.8C3EO51.6, was investigated by phase study and small-angle X-ray scattering Si5.8C3EO51.6 forms a micellar cubic phase and a hexagonal phase in aqueous mixtures. The structure of the cubic phase seems to be face-centered type. When lipophilic surfactant (Si14C3EO7.8 or Si25C3EO7.8) is added to Si5.8C3EO51.6/water systems, a transition from the hexagonal phase to the lamellar phase takes place, owing to a change in the hydrophile—lipophile balance of the system. The change in the surface area per surfactant molecule is larger as the polydimethylsiloxane chain is longer, even if the EO number remains constant. This fact is attributed to the coiling of the long lipophilic chain in order to reduce the entropy loss.

Configuration Optimization of a Boat Simulation Platform for a Mobile User

Motion simulation platforms are mechanical devices designed to replicate the dynamics of a given vehicle. These devices are very attractive for training individuals as drivers, pilots or passengers. In the case of river boats, the simulator consists of a section of the boat (hull) mounted over a 3 DOF parallel robot with a passive mass compensator (3UPS + PU). If users have mobility in the hull, an uncertainty in the position of the upper platform’s center of mass is produced. This variation may generate excessive loads on the robot that can be prevented by an adequate placement of the hull over the robot. Dynamic calculations, based on measurements of the real boat in motion, are computed by numerical simulations in SimMechanics. Three methodologies are presented for optimizing the configuration of a boat simulation platform. First, a manual procedure is developed in which critical cases are intuitively detected and evaluated. Then, two multi-variable optimization algorithms are used to systematically obtain the best position and orientation (pose) of the boat section: Genetic Algorithms and low discrepancy sequences. The pose is the design variable; the average forces are the objective functions and the maximum difference between the average forces is the fitness function. The article describes the design problem, the proposed optimization methodologies and simulation results for the optimal configuration.Copyright

A new detergent-free dry-cleaning system

The performance of a new detergent‐free dry cleaning machine has been investigated and compared to conventional machines. The new machine includes a highly efficient system for solvent purification, and effectively cleans wool, cotton and synthetic fibers without the need of detergent. Its performance is similar or in some cases better than the conventional machines, which contaminate the clothes with detergent. Since detergent is not needed and solvent is efficiently used in the new machine, environmental impacts and operation costs are reduced, and the negative side effects on the properties of clothes are eliminated.