Interfacial tension and the behavior of microemulsions and macroemulsions of water and carbon dioxide with a branched hydrocarbon nonionic surfactant (original) (raw)
Related papers
2005
During the last two decades colloid and interface science in the field of supercritical fluid technology has brought enormous potentials in the utilization of supercritical carbon dioxide as an environmentally benign solvent. Liquid or supercritical CO2 exhibits solvent properties that are tunable with pressure, and is essentially nontoxic and nonflammable. Emulsions and microemulsions of water and CO2, whether in the form of water-in-CO 2 (w/c) or CO2-in-water (c/w), offer new possibilities for separations on the basis of polarity, and as media for reactions between polar and nonpolar molecules. For the first time, formation of thermodynamically stable c/w microemulsions was characterized by dynamic light scattering (DLS) technique. High-pressure carbon dioxide swells potassium carboxylate perfluoropolyether (PFPE-K) cylindrical micelles in water, elongating the micelles significantly from 20 up to 80 nm. As the micelles swell to form microemulsions, the solubility of pyrene increa...
Langmuir, 2002
Formation and stability of water-in-carbon dioxide microemulsions are described with eight related fluorinated analogues of the anionic surfactant Aerosol-OT. The aim was to identify a structure-performance relationship in CO2 with surfactants of high surface chemical purity that can also be synthesized from readily available reagents. The most effective CO2-philes from this group were sodium bis(1H,1Hperfluoropentyl)-2-sulfosuccinate (di-CF4), sodium bis(1H,1H,2H,2H-perfluorohexyl)-2-sulfosuccinate (di-CF4H), and sodium bis(1H,1H-perfluoroheptyl)-2-sulfosuccinate (di-CF6). All three of these compounds stabilized microemulsions at CO2 bottle pressure (57 bar) at 15°C, with a w value ([water]/[surf]) of 10. A close correlation is demonstrated between limiting aqueous phase surface tension of a given surfactant at its critical micelle concentration, γcmc, and its performance in water-CO2 microemulsions, as measured by the phase transition pressure Ptrans. This finding has important implications for the rational design of CO2-philic surfactants.
The relationship between the tail architecture and performance of hybrid AOT analogue surfactants hasbeen investigated. Three hybrid surfactants were synthesised using hydrocarbon CO2-philic tails with dif-ferent levels of chain branching. The performance of each surfactant was investigated via high-pressurephase behaviour, UV-visible spectroscopy, and air–water (a/w) surface tension measurements. Notably,the incorporation of hydrocarbon CO2-philic tails with a high degree of branching has been found tosignificantly boost CO2-philicity, allowing the surfactant to stabilise water-in-CO2(w/c) microemul-sions at low cloud pressures, Ptrans. The newly synthesised hybrid CF2/SIS1 (sodium (4H, 4H, 5H, 5H,5H-pentafluoropenyl-5,7,7-trimethyl-2-(1,3,3-trimethyl-buthyl)-octyl)-2-sulfosuccinate) is a CO2-philicsurfactant that contains the lowest amount of fluorine (15.01 wt%) and exhibits the highest efficiencyof any di-chain surfactant to date. High-pressure phase behaviour studies provided a maximum water-to-surfactant molar ratio (wmax) of wmax= 39, which is usually only observed from surfactants with longfluorocarbon chains. The present results are beneficial for expanding the pool of economical, effective,and efficient surfactants available for CO2-based technology.
Super-Efficient Surfactant for Stabilizing Water-in-Carbon Dioxide Microemulsions
Langmuir, 2011
The fluorinated double-tailed glutarate anionic surfactant, sodium 1,5-bis[(1H,1H,2H,2H-perfluorodecyl)oxy]-1,5-dioxopentane-2-sulfonate (8FG(EO)2), was found to stabilize water-in-supercritical CO2 microemulsions with high water-to-surfactant molar ratios (W0). Studies were carried out here to obtain detailed information on the phase stability and nanostructure of the microemulsions by using a high-pressure UV−vis dye probe and small-angle neutron scattering (SANS) measurements. The UV−vis spectra, with methyl orange as a reporter dye, indicated a maximum attainable W0 of 60 at 45 and 75 °C, and SANS profiles indicated regular droplet swelling with a linear relationship between the water core nanodroplet radius and W0. This represents the highest water solubilization reported to date for any water-in-CO2 microemulsion. Further analysis of the SANS data indicated critical packing parameters for 8FG(EO)2 at the microemulsion interface >1.34, representing approximately 1.1 times the value for common aerosol-OT in water-in-heptane microemulsions under equivalent conditions.
Soft fluctuating surfactant membranes in supercritical CO2-microemulsions
Physical Chemistry Chemical Physics, 2011
The bending rigidity of surfactant membranes in novel bicontinuous CO 2-microemulsions of the type H 2 O/NaCl-scCO 2-Zonyl FSH/Zonyl FSN 100 was determined using both high pressure small angle neutron scattering and neutron-spin echo spectroscopy. As an important result it was found, that the stiffness of the membrane increases solely by an increase of the pressure. The waste of chemical solvents from chemical processing and related industries represent a huge environmental concern. During the last decades supercritical fluids have attracted much attention as potential replacements for these conventional organic solvents. Supercritical CO 2 (T c = 31.1 1C, p c = 72.8 bar) is seen as the most promising candidate because it is cheap, abundant, incombustible, non-toxic, bio-and foodcompatible. Unfortunately scCO 2 is generally a very poor solvent, in particular for polar and/or high molecular weight solutes. Thus, in applications where both polar and nonpolar components needed to be dissolved, emulsions and microemulsions were used to overcome this severe limitation. 1 Furthermore, scCO 2 microemulsions are also of great interest from a theoretical point of view because, contrary to classical ''state of the art'' microemulsions, the properties of scCO 2 microemulsions can be strongly influenced just by varying the pressure, i.e. the solvent properties of CO 2. So far studies on these novel microemulsion systems concentrate on the phase behavior and the microstructure of CO 2-rich microemulsions. 1-3 Recently, we were able to formulate balanced supercritical CO 2-microemulsions containing equal volumes of water and CO 2 using technical grade n-alkyl-polyglycolether-and perfluoroalkyl-polyglycolether-surfactants. 4,5 The phase behavior of such a microemulsion system H 2 O/NaCl-scCO 2-Zonyl FSH/Zonyl FSN 100 is shown in Fig. 1 for pressures of p = 160 (top), 220 (middle) and 300 bar (bottom) as a function of the overall surfactant mass fraction g and the temperature T. 5 Thereby the mass fraction a of CO 2 in the mixture of water and CO 2 was adjusted to a = 0.40 and the surfactant mixture consists of equal amounts of Zonyl FSH and Zonyl FSN 100 (d = 0.50). NaCl (1 wt% in the mixture of water and NaCl; e = 0.01) was added to screen possible electrostatic interactions induced by ionic impurities.
Microemulsions with CO2 as a solvent
Supercritical CO2 is considered as a promising alternative for volatile organic solvents currently used in certain industrial processes and products, however, the poor solubilizing power of CO2 towards polar substances remains a significant barrier to applications. Employing effective surfactants which generate stable dispersions and water/CO2 microemulsions is accepted as one way to improve the physico-chemical properties of CO2. This article reviews recent studies on microemulsions in liquid CO2, as well as the development of CO2-philic surfactants.
Journal of Colloid and Interface Science, 2010
Whereas microemulsions and emulsions of water and carbon dioxide have been reported for various surfactants with fluorocarbon surfactants, relatively few studies have been successful in forming these emulsions with hydrocarbon surfactants. Stable CO 2 /water and water/CO 2 emulsions with droplets smaller than 1 lm were formed at high shear with the nonionic surfactant polysorbate 80 (Tween 80). In order to understand the emulsion phase behavior at high shear, low shear phase behavior experiments were performed at the same temperature and pressure. For pressures up to 250 bar and temperatures of 25-60°C, C/W emulsions were formed for water concentrations as low as 10%, as the surfactant is highly hydrophilic with limited CO 2 -philicity. However, with added NaCl, the surfactant partitioned away from water toward CO 2 , and W/C emulsions were formed with droplet sizes from a few 100 nm to a few lm in diameter, which were stable for at least 24 h. In addition C/W/C double emulsions are reported for the first time, as well as W/C/W/C triple emulsions. The ability to form emulsions with environmentally benign solvents, CO 2 and water, and biocompatible surfactants is desirable for green reaction and separation processes, as well as production of materials including pharmaceutical particles and composites.
Surfactant-free CO2-based microemulsion-like systems
Chemical Communications, 2014
The presence of water-rich and water-lean nanodomains in a transparent, pressurized ''water-acetone-CO 2 '' mixture was revealed by Raman spectroscopy. This nano-structured liquid can be classified as a surfactant-free microemulsion-like system and has the capacity to dissolve hydrophobic compounds, such as ibuprofen, in the presence of large amounts of water. This finding opens new opportunities in the fields of confined reactions and material templating.
Formation and growth of water-in-CO2 miniemulsions
Langmuir, 2003
We report nonflocculated dilute water-in-CO 2 (W/C) miniemulsions stable for 24 h in contrast with flocculated unstable macroemulsions reported previously. The surfactants, poly(1,1-dihydroperfluorooctyl methacrylate)-b-poly(ethylene oxide) (PFOMA-b-PEO), were synthesized by atom transfer ...