Hazard assessment of fluorinated alternatives to long-chain perfluoroalkyl acids (PFAAs) and their precursors: status quo, ongoing challenges and possible solutions.

Hydrodynamic and hydromagnetic stability

In the past twenty five years, microemulsions have been the focus of extensive research worldwide due to their importance in a variety of technological applications. These applications include enhanced oil recovery, combustion, cosmetics, pharmaceuticals, agriculture, metal cutting, lubrication, food, enzymatic catalysis, organic and bio-organic reactions, chemical synthesis of nanoparticles etc. The basic purpose of this review is intended to provide the most important features of microemulsions and their applications. Emphasis is placed on recent works, however, the reference list is by no means complete. In order to limit the size of the review, a more or less arbitary selection has been made with respect to examples chosen from literature. The review is started with a brief introduction and focussed with definition, structure, type, formation characteristics, stability, phase behavior and the effect of additives, pressure, temperature on the phase behavior of microemulsion. In addition, the p...

Microemulsions: an overview

There are at least three fundamental states of matter, depending upon temperature and pressure: gas, liquid, and solid (crystal). These states are separated by first-order phase transitions between them. In both gas and liquid phases a complete translational and rotational symmetry exist, whereas in a solid phase both symmetries are broken. In intermediate phases between liquid and solid, which include liquid crystal and plastic crystal phases, only one of the two symmetries is preserved. Among the fundamental states of matter, the liquid state is the most poorly understood. We argue that it is crucial for a better understanding of liquids to recognize that a liquid generally has the tendency to have a local structural order and its presence is intrinsic and universal to any liquid. Such structural ordering is a consequence of many-body correlations, more specifically, bond angle correlations, which we believe are crucial for the description of the liquid state. We show that this physical picture may naturally explain difficult unsolved problems associated with the liquid state, such as anomalies of water-type liquids (water, Si, Ge, ...), liquid-liquid transition, liquid-glass transition, crystallization and quasicrystal formation, in a unified manner. In other words, we need a new order parameter representing a low local free-energy configuration, which is a bond orientational order parameter in many cases, in addition to a density order parameter for the physical description of these phenomena. Here we review our two-order-parameter model of liquid and consider how transient local structural ordering is linked to all of the above-mentioned phenomena. The relationship between these phenomena is also discussed.

Bond orientational order in liquids: Towards a unified description of water-like anomalies, liquid-liquid transition, glass transition, and crystallization: Bond orientational order in liquids.

We present an overview of recent static and time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state, as well as of crystalline and amorphous ice forms. The structure and dynamics of the complex hydrogen-bond network formed by water molecules in the bulk and interphases are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed, from conventional infrared and Raman spectroscopy to femtosecond pump–probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. Additionally, we discuss novel approaches, such as two-dimensional sum-frequency generation, three-dimensional infrared, and two-dimensional Raman terahertz spectroscopy. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges. Furthermore,...

Vibrational Spectroscopy and Dynamics of Water

Dielectric study: I. Critical phenomena behavior in phase transition of water-in-oil microemulsions

Low temperature study of w/o microemulsions by

By means of thermal analysis (DSC) applied to water-in-oil microemulsions, the experimental evidence is presented that, in the above systems, the water may exist in at least two different configurations, namely: interphasal and free, distinguished by the melting temperatures of respectively 263 K and 273 K. The role of both water and interphase in governing the microemulsion stability and structural changes upon water addition, are analysed. It is also shown that the enthalpic contribution associated with the thermal events ascribed to the dispersed phase (interphasal chorona + water core of the spherical droplet), are not particularly affected by the change of the continuous, hydrocarbon dispersing medium, provided that all the other components of the system as well as their mutual proportions are kept unchanged. The title system is, therefore, presented as a useful tool for studying the properties of water and interphasal water from both a scientific and a practical point of view, with particular regard to the forms of water in biosystems.

http://iopscience.iop.org/article/10.1209/0295-5075/2/6/008/pdf

Experimental Evidence of Interphasal Water in Water-in-Oil Microemulsions

The temperature dependence of the dielectric constant and loss tangent in parallel with differential scanning calorimetry (DSC) were used to study the low-temperature properties of a w/o microemulsion in the concentration interval (C, mass fraction) 0024 ≤ C < 04, within the temperature range (20°C ÷ -150°C) For 0222 < C < 04 the dielectric constant exhibits, with decreasing temperature, a sharp peak centred around - 35 °C It is shown that the latter cannot be justified exclusively in terms of a Maxwell-Wagner interfacial polarization By means of DSC analysis the temperatures of the different thermal transitions occurring in the w/o microemulsion were obtained; a differentiation between samples that possess a « free water » fraction (0222 < C < 04) and those that do not (0024 ≤ C ≤ 0222) was made; the enthalpic change associated with the melting of the dodecane-oil (ΔHd) and the water (ΔHw), contained in the samples was determined against increasing concentration An enthalpic contribution around - 10 °C due to water adsorbed at the interphase region was detected superimposed on that of the dodecane (- 96 °C) Polydispersed samples were identified by means of the analysis of the frequency dependence of the dielectric loss of «liquid» microemulsions at T = 20 °C Samples exhibiting a time dependent behaviour were found in which, upon ageing, the free water Δ Hw tends to zero accompanied by the increase of the dodecane Δ Hd contribution The phenomenon was interpreted in terms of the formation of 4 H2O-molecule hydration structures on the hydrophilic groups of the surface active molecules The hydration process develops at constant surface tension at the expenses of the free water fraction of the dispersed phase The energy balance of the latter process was investigated and the « surface increment » enthalpy associated with the formation of the 4 H2O-molecule hydrated structures was estimated

https://hal.archives-ouvertes.fr/jpa-00209852/document

D. Senatra

Papers

Dielectric study: I. Critical phenomena behavior in phase transition of water-in-oil microemulsions

Low temperature study of w/o microemulsions by

Experimental Evidence of Interphasal Water in Water-in-Oil Microemulsions

Low temperature study of w/o microemulsions by differential scanning calorimetry and dielectric measurements

Perfluorinated surfactants at the perfluoropolyether—water interface