“…At ambient pressure and temperature, oil and water tend not to mix. These boundaries between two immiscible liquids have been the subject of increasing scrutiny during the past decade due to their roles in solvent extraction, , phase transfer catalysis, , and environmental remediation . Furthermore, liquid/liquid interfaces frequently serve as biomimetic models of cell membranes , and are used to guage anaesthetic efficacy as well as protein binding affinity .…”
Section: Introductionmentioning
confidence: 99%
“…These boundaries between two immiscible liquids have been the subject of increasing scrutiny during the past decade due to their roles in solvent extraction, 1,2 phase transfer catalysis, 1,2 and environmental remediation. 3 Furthermore, liquid/ liquid interfaces frequently serve as biomimetic models of cell membranes 4,5 and are used to guage anaesthetic efficacy 6 as well as protein binding affinity. 4 Numerous experimental and computational techniques have been used to examine how the asymmetry inherent to interfaces affects interfacial structure and long-range order.…”
Molecular ruler surfactants, solvatochromic probes of solvent polarity, have been used to examine changes in solvent polarity across weakly associating liquid/liquid interfaces. The water/alkane interfaces were formed between an aqueous subphase and either cyclic (cyclohexane and methylcyclohexane) or linear (octane and hexadecane) alkanes. Resonance-enhanced second-harmonic generation was used to collect effective excitation spectra of species adsorbed to these interfaces. As surfactants lengthened, the surfactant probe sampled an increasingly nonpolar environment as evidenced by an excitation wavelength that shifted toward the alkane limit. Data suggest that all four water/alkane interfaces are molecularly sharp (<9 Å), but that differences in the solvent molecular structure alter the transition from aqueous to organic solvation across the interface. Polarity across two interfaces (cyclohexane and hexadecane) changes gradually over the distance spanned by ruler surfactants. In contrast, the transitions at the interfaces between water and methylcyclohexane and octane appear much more abrupt. These findings appear to correlate with each organic solvent's ability to pack and associated free volume. More free volume in the organic phase leads to a more abrupt water/alkane interface. Results are interpreted on the basis of recent molecular dynamics simulations examining polarity at different water/monolayer interfaces.
“…At ambient pressure and temperature, oil and water tend not to mix. These boundaries between two immiscible liquids have been the subject of increasing scrutiny during the past decade due to their roles in solvent extraction, , phase transfer catalysis, , and environmental remediation . Furthermore, liquid/liquid interfaces frequently serve as biomimetic models of cell membranes , and are used to guage anaesthetic efficacy as well as protein binding affinity .…”
Section: Introductionmentioning
confidence: 99%
“…These boundaries between two immiscible liquids have been the subject of increasing scrutiny during the past decade due to their roles in solvent extraction, 1,2 phase transfer catalysis, 1,2 and environmental remediation. 3 Furthermore, liquid/ liquid interfaces frequently serve as biomimetic models of cell membranes 4,5 and are used to guage anaesthetic efficacy 6 as well as protein binding affinity. 4 Numerous experimental and computational techniques have been used to examine how the asymmetry inherent to interfaces affects interfacial structure and long-range order.…”
Molecular ruler surfactants, solvatochromic probes of solvent polarity, have been used to examine changes in solvent polarity across weakly associating liquid/liquid interfaces. The water/alkane interfaces were formed between an aqueous subphase and either cyclic (cyclohexane and methylcyclohexane) or linear (octane and hexadecane) alkanes. Resonance-enhanced second-harmonic generation was used to collect effective excitation spectra of species adsorbed to these interfaces. As surfactants lengthened, the surfactant probe sampled an increasingly nonpolar environment as evidenced by an excitation wavelength that shifted toward the alkane limit. Data suggest that all four water/alkane interfaces are molecularly sharp (<9 Å), but that differences in the solvent molecular structure alter the transition from aqueous to organic solvation across the interface. Polarity across two interfaces (cyclohexane and hexadecane) changes gradually over the distance spanned by ruler surfactants. In contrast, the transitions at the interfaces between water and methylcyclohexane and octane appear much more abrupt. These findings appear to correlate with each organic solvent's ability to pack and associated free volume. More free volume in the organic phase leads to a more abrupt water/alkane interface. Results are interpreted on the basis of recent molecular dynamics simulations examining polarity at different water/monolayer interfaces.
“…Microemulsions are being used for nanoparticle , formation as well as in chemical synthesis, − and increasingly also for polymer formation. − However, in applications, often systematic investigations of the phase behavior are lacking, although the underlying microstructure in connection with the total area and elastic properties of the internal interface might be important parameters for the polymerization process. This insight led us to examine the phase behavior (and microstructure) of microemulsions first, before applying the systems to polymerization.…”
The phase behavior of ternary water−alkyl methacrylate−alkyl polyglycol ether (C
i
E
j
) systems has been
examined. Specifically, using seven different alkyl methacrylates ranging from methyl to hexadecyl
methacrylate and C10E6 as surfactant, vertical sections through the phase prism were determined, from
which the phase inversion temperature, the upper and lower critical temperature of the three-phase body,
and the efficiency of the surfactant and its monomeric solubility in the oil were obtained. Keeping hexyl
methacrylate as oil-fixed, 18 different surfactants were applied including short- and long-chain surfactants
such as C4E3 and C14E8. The microemulsion systems examined here show the same general patterns as
the well-known nonionic microemulsions with alkanes as oil. Notably, the phase inversion temperature
is highly dependent on the alkyl chain length of the oil, a fact that is often left out of consideration when
choosing a surfactant in emulsion polymerization. For a given oil the phase inversion temperature can
be adjusted by appropriate choice of the number of ethylene glycol units of the surfactant. The efficiency
of the surfactant systematically depends on the alkyl chain length of both the surfactant and the oil.
Interestingly, there is a striking parallel between efficiency of a surfactant and its monomeric solubility
in the oil. Finally, in preparation for applying these systems to the synthesis of nanoscaled latexes in
microemulsion polymerization the water-rich part of the phase prism was examined. Both the expected
shape of the emulsification failure phase boundary and the near-critical phase boundary with its
nonmonotonic decay characteristic of branched network structures are delineated. The results of some
preliminary polymerizations are briefly discussed.
“…Water-in-oil (w/o) microemulsions are optically transparent nanometer-scale droplets of water in a bulk apolar organic solvent formed by surfactant and cosurfactant molecules organized at the organic−water interface (Figure ). , A plethora of biomolecules including proteins, enzymes, and nucleic acids have been solubilized in the reversed micellar water pools without the loss of their biological activities, − and w/o microemulsions are being used in a variety of commercial products and synthetic applications. − However, the supramolecular structural and compositional details of w/o microemulsions are still incompletely understood. Ion distributions in the interior of w/o microemulsions have been studied by solubility, conductivity, potentiometry, NMR, UV/visible, fluroscence spectroscopy, and reaction kinetics. , The experimental methods for determining the size of the water-in-oil microemulsion droplets include ultracentrifugation, , static 22 and dynamic light scattering, − small-angle neutron scattering (SANS), − small-angle X-ray scattering, − and time-resolved fluorescence quenching. − 1 Schematic representation of cationic water-in-oil microemulsion.…”
The first simultaneous experimental estimates of the water pool core size (R
w) and the interfacial thickness
(d) of a cationic water-in-oil microemulsion, CTAB/isooctane/n-hexanol/water, was achieved by the combined
use of chemical trapping and the time-resolved fluorescence quenching. Our estimated values of R
w = 29.1
± 1.5 Å compares reasonably well with the reported size of the water pool core (32 Å) of a structurally and
compositionally similar CTAB/dodecane/n-hexanol/water cationic water-in-oil microemulsion (Atik, S. S.;
Thomas, J. K. J. Am. Chem. Soc.
1981, 103, 4367), and our estimated interfacial thickness (6.3 Å ± 0.3)
is consistent with the recently estimated thickness for the hydration layer (10 Å) of the cationic CTAB/n-hexane/n-pentanol/water water-in-oil microemulsions (Giustini, M. et al. J. Phys. Chem.
1996, 100,
3190). To our knowledge, this is the first simultaneous experimental estimate of the size of the water pool
core and interfacial thickness of a cationic water-in-oil microemulsion using a chemical reaction.
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