A unified simulation framework for water phase transition based on particles

This paper presents the results of a study of the temperature dependences of the magnetic susceptibility of water-based magnetic fluids (magnetic colloids) with magnetite particles stabilized by their electrostatic interaction. The average size of dispersed particles was 8 nm, and the volume concentration of particles in the selected samples under study was 1.4% and 1.6%. The investigations were carried out over a wide temperature range. The temperature dependence of the susceptibility, for the first time, was obtained in the region of the colloidal phase transition under supercooling of the dispersion medium (water). Significant differences were found between the temperature dependences of the magnetic susceptibility of such magnetic fluids, where as similar dependences have been found for the susceptibility of magnetic hydrocarbon-based fluids. The observed behavior of such dependences near the water phase transition temperature is determined by the changes in the water phase state, heat release and structuring of the colloid as a result of water crystallization. Moreover, it is suggested that a certain impact on the dependence behavior in the region of the colloidal solidification temperature can also come from the process of blocking the Brownian degrees of freedom of a small fraction of large dispersed particles. It is concluded that the observed maxima in the investigated susceptibility temperature dependences in the lower temperature region are due to magnetic transformations in the colloidal zones formed at the solidification front of the disperse medium with a dense packing of single-domain colloidal particles.

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Dynamic Mechanical Freezing Points of Cosmetic O/W Emulsions and Their Stability at Low Temperatures

Applied Rheology ◽

10.1515/arh-2000-0007 ◽

2000 ◽

Vol 10 (3) ◽

pp. 114-118 ◽

Cited By ~ 7

Author(s):

Frank Hetzel ◽

Jens Nielsen ◽

Stefan Wiesner ◽

Rüdiger Brummer

Keyword(s):

Phase Transition ◽

Cold Storage ◽

Low Temperatures ◽

Storage Temperature ◽

Test Methods ◽

Test Method ◽

Water Phase ◽

Scanning Calorimetry ◽

The Stability ◽

Cosmetic Emulsions

Abstract To develop cosmetic products quickly and effectively, developers need reliable test methods for evaluating product stability. Phenomena that determine the stability of cosmetic emulsions include phase transitions taking place in the relevant application and storage temperature range. The tendency of ingredients to crystallize influences the stability of emulsions especially at low temperatures. In this article a Differential Scanning Calorimetry (DSC) was used to determine the temperature of the water/ice phase transition of the continuous water phase for oil in water emulsions. A rheological, oscillating test method was developed to measure the phase transition temperature and the results were compared with those of the DSC and standard cold storage tests. There was a correlation of the crystallization temperature of the external water phase with the storage stability at –10°C. The accompanying increase in viscosity with cold storage due to structural alteration of the emulsions could be confirmed by TEM micrographs.

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