On the Negative Surface Tension of Solutions and on Spontaneous Emulsification

Abstract

The condition of negative surface tension of a binary regular solution is discussed in this paper using the recently reconfirmed Butler equation (Langmuir 2015, 31, 5796-5804). It is shown that the surface tension becomes negative only for solutions with strong repulsion between the components. This repulsion for negative surface tension should be so strong that this phenomenon appears only within a miscibility gap, that is, in a two-phase region of macroscopic liquid solutions. Thus, for a macroscopic solution, the negative surface tension is possible only in a nonequilibrium state. However, for a nano-solution, negative surface tension is also possible in equilibrium state. It is also shown that nano- and microemulsions can be thermodynamically stable against both coalescence and phase separation. Further, the thermodynamic theory of emulsion stability is developed for a three-component (A-B-C) system with A-rich droplets dispersed in a C-rich matrix, separated by the segregated B-rich layer (the solubility of B is limited in both A and C while the mutual solubility of A and C is neglected). It is shown that when a critical droplet size is achieved by forced emulsification, it is replaced by spontaneous emulsification and the droplet size is reduced further to its equilibrium value. The existence of maximum temperature of emulsion stability is shown. Using low-energy emulsification below this maximum temperature, spontaneous emulsification can appear, which is enhanced with further decrease of temperature. This finding can be applied to interpret the experimental observations on spontaneous emulsification or for the design of stable micro- and nanoemulsions.

Thermodynamic Stability of Nano-grained Alloys Against Grain Coarsening and Precipitation of Macroscopic Phases

“…Compared to the above value of X gb ffi 37:6 kJ/mol it follows that X cr <X gb (see also Figure 3(b)). It can be generally proven that this inequality is obeyed at any reasonable values of x B Á r B , x and T. [116] It means that when the A-B system is in equilibrium as a 1-phase macroscopic solid solution, then r>0, which is a usual boundary condition for any interfacial energy. On the other hand, r<0 takes place only, when the A-B system is in equilibrium as a mixture of two macroscopic solutions of different compositions; however, in this case the Butler equation is not valid as applied above, thus r<0 is not a real result for macroscopic equilibrium systems.…”

Una visión actualizada sobre la síntesis, escalado y aplicaciones de las nanoemulsiones dobles

“…Aproximaciones más modernas incluyen el modelado in silico de microemulsiones basado en la teoría termodinámica y minimización de la energía libre de Gibbs [23] y la simulación mediante dinámica molecular combinada con diversos algoritmos permiten calcular parámetros como potenciales químicos, coeficientes de actividad, densidad de carga de la superficie y coeficientes de partición de los componentes de la microemulsión y la fase continua [24]. El trasfondo termodinámico para la formación de microemulsiones puede ser analizado en [25], [26], [27], [28]- [29].…”

Spontaneous emulsification induced by nanoparticle surfactants

“…scitation.org/journal/jcp capable of stabilizing bicontinuous liquid interfaces, 16,17 particleinduced spontaneous emulsification has only been demonstrated for specific oils, [18][19][20][21] and theoretical efforts have mainly focused on the thermodynamics of molecular microemulsifiers [22][23][24][25][26][27][28][29][30] that lack the functionality of nanoparticles. The aim of this work is to determine the conditions under which nano-scale particles induce spontaneous emulsification.…”