Water Solubilization Using Nonionic Surfactants from Renewable Sources in Microemulsion Systems

In this study the effect of temperature, NaCl and oils (hydrocarbons: C8–C16) on the formation and solubilization capacity of the systems of oil/monoacylglycerols (MAG):ethoxylated fatty alcohols (CEO20)/propylene glycol (PG)/water was investigated. The effects of the surfactant mixture on the phase behavior and the concentration of water or oil in the systems were studied at three temperatures (50, 55, 60 °C) and with varied NaCl solutions (0.5; 2; 11%). Electrical conductivity measurement, FTIR spectroscopy and the DSC method were applied to determine the structure and type of the microemulsions formed. The dimension of the microemulsion droplets was characterized by dynamic light scattering. It has been stated that the concentration of CEO20 has a strong influence on the shape and extent of the microemulsion areas. Addition of a nonionic surfactant to the mixture with MAG promotes an increase in the area of microemulsion formation in the phase diagrams, and these areas of isotropic region did not change considerably depending on the temperature, NaCl solution and oil type. It was found that, depending on the concentration of the surfactant mixture, it was possible to obtain U-type microemulsions with dispersed particles size distribution ranging from 25 to 50 nm and consisting of about 30–32% of the water phase in the systems. The conditions under which the microemulsion region was found (electrolyte and temperature—insensitive, comparatively low oil and surfactant concentration) could be highly useful in detergency

Ultrasonic characterization of ultrasound contrast agents

The main constituent of an ultrasound contrast agent (UCA) is gas-filled microbubbles. An average UCA contains billions per ml. These microbubbles are excellent ultrasound scatterers due to their high compressibility. In an ultrasound field they act as resonant systems, resulting in harmonic energy in the backscattered ultrasound signal, such as energy at the subharmonic, ultraharmonic and higher harmonic frequencies. This harmonic energy is exploited for contrast enhanced imaging to discriminate the contrast agent from surrounding tissue. The amount of harmonic energy that the contrast agent bubbles generate depends on the bubble characteristics in combination with the ultrasound field applied. This paper summarizes different strategies to characterize the UCAs. These strategies can be divided into acoustic and optical methods, which focus on the linear or nonlinear responses of the contrast agent bubbles. In addition, the characteristics of individual bubbles can be determined or the bubbles can be examined when they are part of a population. Recently, especially optical methods have proven their value to study individual bubbles. This paper concludes by showing some examples of optically observed typical behavior of contrast bubbles in ultrasound fields

Thermodynamics of superspreading

A simple model for calculation of the spreading coefficient of an aqueous surfactant solution on an apolar solid is proposed. The spreading coefficient is predicted to have two components: i) the van der Waals component, which is similar to the spreading coefficient of the alkane, making up the surfactant tail; and ii) the monolayer frustration component, dependent on the bending moduli and the spontaneous curvature of the surfactant. The frustration term is minimized at a negative spontaneous curvature. In order for a solution to spread, the van der Waals component of the spreading coefficient must be positive and larger than the monolayer frustration term. The spreading is facilitated by surfactants having very short and branched alkyl tails

Diffusion in evaporating solutions

We present an analysis of the colloidal dynamics of particles in a mixture of two solvents subjected to evaporation. For simplicity, only one out of the two solvents is considered to be volatile. The evaporation generates a distribution of the solvent concentration in the system. As the particles selectively interact with the solvents, their migration becomes affected by a "chemotaxis" force, caused by the gradient in the solvation energy along the diffusion path. The net particle flux is the result of the interplay between the migration under the action of the chemotaxis and the bulk convection flow caused by the evaporation. The most unusual features of the particle migration occur when the particles have an affinity to the evaporating solvent. In this case, the particles may diffuse against the concentration gradient and form bands with increased particle concentration, i.e., undergo focusing. The resulting particle concentration patterns are strongly dependent on the geometry of the container in which the evaporation occurs. This model has important practical applications. It provides a framework for understanding and controlling the skin formation at the surface of evaporating colloidal suspensions, an effect that is briefly illustrated experimentally on the example of ink-jet printing. On a thermodynamic level, the model is also applicable to cases, in which the third component is molecularly dispersed, although a smaller magnitude of the effects is predicted