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Thomas Zemb - One of the best experts on this subject based on the ideXlab platform.
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Molecular factors governing the viscosity peak of giant micelles in the presence of salt and fragrances.
Journal of Colloid and Interface Science, 2018Co-Authors: Maximilian Pleines, Daniel Benczédi, Thomas Zemb, Werner Kunz, Wolfgang FieberAbstract:Abstract Hypothesis The formation of transient networks of giant micelles leads to a viscosity peak when salt is added to aqueous solutions of charged surfactants. It is the consequence of an increase of the Packing Parameter due to charge screening of the surfactant headgroups, leading to a continuous transformation of the aggregates from spherical to wormlike micelles, and finally to branched networks. It should therefore be possible to predict the macroscopic viscosity of entangled giant micelles by modelling the Packing Parameter at nanoscale. Experiments A thermodynamic model is presented with a minimum of adjustable Parameters, where branched networks are considered to be built from three coexisting microphases: cylinders, endcaps, and junctions. We use spontaneous Packing Parameters, in which the whole molecular length instead of the commonly used hydrocarbon chain length is considered. Standard reference chemical potentials and subsequently the occurrence of each microphase can be explicitly derived at specific electrolyte concentrations. Effective micellar length of giant micelles can be obtained from the microphase composition and is subsequently used to calculate the viscosity. Findings The model successfully predicts position and intensity of the viscosity maximum observed in experimental salt curves of sodium laureth sulfate (SLES). The robustness of the model was further investigated for various types of added salts or fragrance oils that affect differently spontaneous Packing Parameters or interfacial bending energy. An excellent agreement of the simulated salt curves with experimental data was achieved.
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The role of curvature effects in liquid-liquid extraction: assessing organic phase mesoscopic properties from MD simulations.
Soft Matter, 2017Co-Authors: Magali Duvail, Thomas Zemb, Steven Van Damme, Philippe Guilbaud, Yushu Chen, Jean-françois DufrêcheAbstract:The bending rigidity of small reverse aggregates involved in liquid–liquid extraction processes has been investigated by molecular dynamics simulations. Simulations of a common extractant (DMDOHEMA) with four hydrophobic chains in explicit solvent (n-heptane) and in vacuum have been performed to determine the effect of solvent penetration on film stiffness. Elastic film bending energy that is needed for mesoscopic modelling of transfer of species between complex fluids is harmonic in terms of curvature (Helfrich formalism) and the Packing Parameter only if the solvent is explicitly taken into account. In terms of the Packing Parameter of the real molecular film constituting the reverse water in oil aggregates and taking into account molecular volume, area and film thickness (that is in agreement with Tanford's model), the bending rigidity is calculated to be about 16 kBT per extractant molecule (about 40 kJ mol−1), which is smaller than the free energy of transfer from an isolated “monomer” molecule to a weak aggregate, but of the order of magnitude of the free energy of transfer used in liquid–liquid extraction processes.
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correspondence between curvature Packing Parameter and hydrophilic lipophilic deviation scales around the phase inversion temperature
Langmuir, 2009Co-Authors: Werner Kunz, Fabienne Testard, Thomas ZembAbstract:We show in this paper that three ways of characterizing “spontaneous” lateral Packing of amphiphiles are equivalent: the spontaneous curvature, the molecular Packing Parameter, and the refined hydrophilic−lipophilic balance known as HLD (hydrophilic−lipophilic deviation). Recognition of this equivalence, with its underlying hypothesis of incompressible fluid with lowest surface energy, reinforces the single Parameter bending energy expression implicit in the classical papers by Ninham and Israelachvili, as well as all the predictive models of solubilization developed as yet.
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Solubilization and interfacial curvature in microemulsions. I. Interfacial expansion and co-extraction of oil
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008Co-Authors: VERA TCHAKALOVA, Kwan-Yee Kenneth Wong, Daniel Benczédi, Alan Parker, Fabienne Testard, Thomas ZembAbstract:We show that solubilization in microemulsion droplets is best described as a combination of interfacial adsorption and internal absorption. We progressively add solute to a Winsor type I system, and simultaneously measure the amount of solute at the oil-water interface and its effect on the interfacial curvature. We determine the relationship between the effective Packing Parameter and the amount of solute adsorbed at the oil-water interface. For four solutes, a significant amount of oil is co-extracted with solute into the interfacial film. Moreover, we show that solubilization in microemulsions can be characterized by two physical quantities with precise meaning: (1) the increase in interfacial area per molecule of adsorbed solute and (2) the number of oil molecules co-extracted with each solute molecule into the interfacial film. To quantify these effects, we introduce the constant interfacial thickness (CIT) model. It provides a general relationship between curvature, Packing and interfacial composition in oil/water/surfactant/solute mixtures. Finally, we show that these results can be used to calculate the free energy of transfer of solute and oil from the droplet core to the interface. © 2008 Elsevier B.V. All rights reserved.
Vadim V. Guliants - One of the best experts on this subject based on the ideXlab platform.
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phase transformations in mesostructured vanadium phosphorus oxides
Catalysis Today, 2003Co-Authors: Moises A. Carreon, Vadim V. GuliantsAbstract:Abstract Mesostructured lamellar, hexagonal and cubic vanadium–phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios ∼1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N2 have been observed for the first time. These transformations were explained by the changes in the surfactant Packing Parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO4 and (VO)2P2O7.
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Phase transformations in mesostructured vanadium–phosphorus-oxides
Catalysis Today, 2003Co-Authors: Moises A. Carreon, Vadim V. GuliantsAbstract:Abstract Mesostructured lamellar, hexagonal and cubic vanadium–phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios ∼1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N2 have been observed for the first time. These transformations were explained by the changes in the surfactant Packing Parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO4 and (VO)2P2O7.
Moises A. Carreon - One of the best experts on this subject based on the ideXlab platform.
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phase transformations in mesostructured vanadium phosphorus oxides
Catalysis Today, 2003Co-Authors: Moises A. Carreon, Vadim V. GuliantsAbstract:Abstract Mesostructured lamellar, hexagonal and cubic vanadium–phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios ∼1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N2 have been observed for the first time. These transformations were explained by the changes in the surfactant Packing Parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO4 and (VO)2P2O7.
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Phase transformations in mesostructured vanadium–phosphorus-oxides
Catalysis Today, 2003Co-Authors: Moises A. Carreon, Vadim V. GuliantsAbstract:Abstract Mesostructured lamellar, hexagonal and cubic vanadium–phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios ∼1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N2 have been observed for the first time. These transformations were explained by the changes in the surfactant Packing Parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO4 and (VO)2P2O7.
G B Dutt - One of the best experts on this subject based on the ideXlab platform.
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can critical Packing Parameter depict probe rotation in block copolymer reverse micelles
Journal of Physical Chemistry B, 2013Co-Authors: Sugoshr Prabhu, G B DuttAbstract:Rotational diffusion of two ionic probes, cationic rhodamine 110 (R110) and anionic fluorescein (FL), has been examined in reverse micelles formed with the triblock copolymer (EO)13–(PO)30–(EO)13 (L64), where EO and PO represent ethylene oxide and propylene oxide units, respectively, with small amounts of water in p-xylene. This study has essentially been undertaken to explore the influence of mole ratio of water to copolymer (W) as well as copolymer concentration on probe rotation. On the basis of fluorescence lifetimes and reorientation times, it has been established that both R110 and FL are located in the interfacial region of L64/water/p-xylene reverse micellar system. The average reorientation time decreases by 10–35% with an increase in W for both the probes at a given copolymer concentration. However, for a particular W, the average reorientation time increases by 10–30% as the concentration of the copolymer is enhanced. From the micellar structural Parameters available in the literature, critical...
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can critical Packing Parameter depict probe rotation in block copolymer reverse micelles b
The Journal of Physical Chemistry, 2013Co-Authors: Sugoshr Prabhu, G B DuttAbstract:Rotational diffusion of two ionic probes, cationic rhodamine 110 (R110) and anionic fluorescein (FL), has been examined in reverse micelles formed with the triblock copolymer (EO)₁₃–(PO)₃₀–(EO)₁₃ (L64), where EO and PO represent ethylene oxide and propylene oxide units, respectively, with small amounts of water in p-xylene. This study has essentially been undertaken to explore the influence of mole ratio of water to copolymer (W) as well as copolymer concentration on probe rotation. On the basis of fluorescence lifetimes and reorientation times, it has been established that both R110 and FL are located in the interfacial region of L64/water/p-xylene reverse micellar system. The average reorientation time decreases by 10–35% with an increase in W for both the probes at a given copolymer concentration. However, for a particular W, the average reorientation time increases by 10–30% as the concentration of the copolymer is enhanced. From the micellar structural Parameters available in the literature, critical Packing Parameters have been calculated for the L64/water/p-xylene reverse micellar system, and it has been noticed that the average reorientation times of both the probes scale linearly with the critical Packing Parameter. In essence, the results of this study indicate that the probe mobility in the interfacial region of block copolymer reverse micelles is governed by the micellar Packing.
Aniket Bhattacharya - One of the best experts on this subject based on the ideXlab platform.
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effect of Packing Parameter on phase diagram of amphiphiles an off lattice gibbs ensemble approach
Journal of Chemical Physics, 2007Co-Authors: Geuorgui K Bourov, Aniket BhattacharyaAbstract:We determine the phase diagram of several amphiphilic molecules as a function of the amphiphilic Parameter α defined as the ratio of the volume of hydrophilic to hydrophobic segments using the Gibbs ensemble Monte Carlo method supplemented by configurational bias scheme. Specifically, we study amphiphilic molecules h1t7, h2t6, and h3t5, for which α=0.14, 0.33, and 0.60 respectively, and demonstrate that the former two exhibit phase separation while h3t5 forms micelles, supporting the contention that α=0.5 is the border line for phase separation and micellization, as observed in previous lattice Monte Carlo studies [Panagiotopoulos et al., Langmuir 18, 2940 (2002)]. Further, we study the phase separation in amphiphilic molecules as a function of the Packing Parameter by varying the size of the hydrophilic head for each molecule. We find that a larger hydrophilic head lowers the critical temperature Tc, and raises the critical density ρc.
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effect of Packing Parameter on amphiphilic self assembly a brownian dynamics study
2004Co-Authors: Aniket Bhattacharya, Geuorgui K BourovAbstract:We investigate the role of Packing Parameter in dictating the shape and size of micelles in amphiphilic self-assembly by varying the size of the hydrophilic head for a fixed tail size using a stochastic molecular dynamics simulation.
