Biomedical subjects

Stig E Friberg

Publications and source records attributed to Stig E Friberg.

6 recordsLinked to original sources

PubMed2006

Evaporation from an ionic liquid emulsion.

The conditions during evaporation in a liquid crystal-in-ionic liquid microemulsion (LC/microEm) were estimated using the phase diagram of the system. The equations for selected tie lines were established and the coordinates calculated for the sites, at which the evaporation lines crossed the tie lines. These values combined with the coordinates for the phases connecting the tie lines were used to calculate the amounts and the composition of the fractions of the two phases present in the emulsion during the evaporation. One of the emulsion phases was a lamellar liquid crystal and high energy emulsification would lead to the liquid crystal being disrupted to form vesicles. Such a system tenders a unique opportunity to study the interaction between vesicles and normal micelles, which gradually change to inverse micelles over bi-continuous structures. The amount of vesicles in the liquid phase versus the fraction liquid crystal was calculated for two extreme cases of vesicle core size and shell thickness. The limit of evaporation while retaining the vesicle structure was calculated for emulsions of different original compositions assuming the minimum continuous liquid phase to be 50% of the emulsion.

Journal Article↗

PubMed2006

Some non-equilibrium phenomena in the malic acid/water/Polysorbate 81 system.

Topical formulations undergo radical structural changes after application and the action on the skin is not directly related to the original structure of the formulation. This fact has been well established in the scientific literature. However, and more essential, is the fact that these changes in the formulation structure are not equilibrium ones. Especially so, with the hydroxy acids, which are widely used in cosmetic and dermatological treatment of skin. The article reports the first investigation into the non-equilibrium conditions in a hydroxy acid system. Different phases in the title system, which were not in mutual equilibrium, were brought in contact while avoiding convection. The transfer of substance between them was estimated from the changes in volume of each phase. The results showed, unexpectedly, that the systems were far from equilibrium even after prolonged times in contact. The kinetics of the changes varied to significant degree, from extremely slow, when solid phases were involved to fast for liquid phases. In one case was observed a separated layer, which was not found in the phase diagram under equilibrium conditions.

Chemistry, Pharmaceutical↗

PubMed2006

Some pertinent factors in skin care emulsion.

Emulsion structures are reviewed with special consideration given to the conditions in emulsions for topical applications with more phases than the traditional two liquids. The fundamentals of emulsions containing liquid crystals and vesicles are described, focussing on the dependence of the volume ratios of liquid crystals and vesicles on the surfactant content.

Computer Simulation↗

PubMed2006

Phase behavior of beta hydroxy-acids with laureth 4.

The colloidal structures of beta carboxylic acid topical vesicle formulations were determined and the changes during evaporation after applications were estimated from phase diagrams. The results showed significant difference during evaporation between salicylic acid on one hand and three water soluble acids; malic, tartaric, and citric acid, on the other. The water soluble acids showed an increase in the acid concentration in the aqueous solution to levels that must be considered harmful, while salicylic acid showed no increase in concentration in the individual phases even after 99% evaporation of water.

Carboxylic Acids↗

PubMed2005

Analytical expressions to calculate relative amounts of phases in a three-component phase diagram.

The relative amounts of different phases in multiphase regions in the common three-component phase diagrams are usually estimated graphically using geometrical features of the diagram. The present contribution introduces algebraic expressions for the lines in the diagram, which allow these numbers to be calculated directly from the experimental results. The method is an extension of the classical methods, which were translated into convenient computer programs [Laughlin, R. G. The Aqueous Phase Behavior of Surfactants; Academic Press: New York, 1994] to calculate the amount of different phases for individual compositions. The introduction of analytical geometry allows simplified expressions to be used for the calculations and the amounts to be presented as continuous functions of the total composition.

Journal Article↗

PubMedDate not supplied

Phase behavior of the alpha-hydroxyoctanoic acid/Laureth 4/white oil/water system and preliminary evaluation of the phase changes during evaporation of its emulsion.

The phase diagram was determined for the alpha-hydroxyoctanoic acid/Laureth 4/white oil/water system using visual observation with an optical microscope. Typical emulsions were evaporated to determine the structural changes. These were compared to those predicted from the phase diagram. Small-angle x-ray diffraction was used to determine the location of the alpha-hydroxyoctanoic acid in the lamellar liquid crystal. The most important result is the fact that irrespective of initial composition, the final result was a suspension of solid acid particles with dissolved oil and surfactant in a surfactant/oil liquid with only minute amounts of solubilized acid.

Caprylates↗