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ABSTRACT: Novel multilayer formation of fluorocarbon compounds at the hexane/water interface was investigated from the view point of intermolecular interaction and miscibility of molecules in the adsorbed film. The two kinds of mixed systems were employed; 1H,1H,2H,2H-perfluorododecanol (FC12OH) - 1H-perflurodecane (HFC10) (System A) and 1-icosanol (C20OH) - HFC10 (System B). The interfacial tension γ between the hexane solution and water was measured as a function of total concentration m and the composition of HFC10 in the mixture X(2) at 298.15K under atmospheric pressure. X-ray reflectivity (XR) measurement was performed at BL37XU in SPring-8 as a function of scattering vector Q(z). In both systems, the γ vs. m curves except for pure HFC10 system have a break at low concentrations, which corresponds to the gaseous - condensed monolayer transition for System A and the expanded - condensed monolayer for System B. Remarkable difference between the two systems was that the curves in a limited bulk composition range (0.45 ≤ X(2) ≤ 0.9) of System A shows another break at high concentrations close to the solubility limit. The total interfacial density above this break point was around 7 ~ 11 μmol m(-2), suggesting the spontaneous molecular piling to form multilayer. The phase diagrams of adsorption in the condensed monolayer indicated that the film composition of HFC10 is negative in the System B but definitely positive above X(2) ≥ 0.45 in the System A. This clearly shows that HFC10 molecules are miscible with FC12OH but immiscible with C20OH in the condensed monolayer. Thus, it is likely that the mixing of HFC10 with FC12OH in the condensed monolayer induces multilayer formation. The X-ray reflectivity normalized by Fresnel reflectivity R⁄R(F) vs. Q(z) plot in the condensed monolayer of system A was fitted by one-slab model with uniform electron density and thickness. The electron density profile was almost same as that of pure FC12OH system. The plot in the multilayer, on the other hand, was fitted well by two-slab model with different electron densities and thicknesses. The electron density profile showed that the multilayer consists of two layers; one of which has slightly higher electron density than bulk hexane phase and piles on the lower layer with almost same electron density as condensed FC12OH monolayer.
The Journal of Physical Chemistry B 10/2012; · 3.70 Impact Factor
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ABSTRACT: We have performed ellipsometry and surface tensiometry at tetradecyltrimethylammonium bromide (TTAB) aqueous solution surface
coexisting with tetradecane lens as a function of the molality of TTAB and the temperature under atmospheric pressure. From
the theoretical analysis of the coefficient of ellipticity, it was clarified that the liquid monolayer comprising the surfactant
and alkane is formed at higher surfactant concentrations by the wetting transition of tetradecane lens on the aqueous solution,
and the solid monolayer is formed by lowering temperature (freezing transition). The results of the surface tension measurement
support the occurrence of wetting transition and the freezing transition. A phase diagram of the wetting film was constructed
by ellipsometry and surface tensiometry, of which the mixed solid monolayer had never been reported before. From the thermodynamic
analysis of the phase diagram, it is also demonstrated that the TTAB surface density decreases accompanied with the freezing
transition, which agrees with surface densities of TTAB calculated from surface tension vs. concentration curves.
KeywordsWetting-Surfactant-Surface freezing-Ellipsometry-Tensiometry
Colloid and Polymer Science 05/2012; 288(12):1333-1339. · 2.33 Impact Factor
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ABSTRACT: The surface tension of aqueous solutions of tetraethyleneglycol octyl ether (C8E4) and octyl-β-d-maltopyranoside (OM) mixture was measured as a function of the total molality of surfactants and the composition of OM under
atmospheric pressure at 298.15K by drop volume technique. The results of surface tension measurements were analyzed by originally
developed thermodynamic equations, then phase diagrams of adsorption and micelle formation were constructed. From the analysis
of the surface tension data, it was found that the C8E4 and OM molecules interact attractively in the adsorbed film and the
excess Gibbs energy of adsorption can be compared with those observed in typical cationic–nonionic surfactant systems; nevertheless,
they are mixed almost ideally in the mixed micelle. Judging from a negative excess surface area calculated by differentiating
the excess Gibbs energy by the surface tension, we concluded that the attraction between C8E4 and OM molecules is a short-range
one originated in the hydrogen bonding between them which favors the planar configuration.
Colloid and Polymer Science 04/2012; 287(9):1077-1082. · 2.33 Impact Factor
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ABSTRACT: The adsorption, micelle formation, and coagel-particle formation of sodium dodecyl sulfate in the presence of calcium chloride
were studied from the viewpoint of mixed adsorption and aggregate formation of inorganic salt and surfactant. Judging from
the phase diagrams of adsorption and aggregate formation, negative azeotropy takes place in the mixed adsorption and aggregate
formation of calcium chloride and sodium dodecyl sulfate due to electrostatic attraction between calcium and dodecyl sulfate
ions. The miscibility of calcium chloride and sodium dodecyl sulfate in the oriented states increases in the order, particle
> adsorbed film > micelle. The difference in the miscibility was ascribed to the difference in geometry between the adsorbed
film and micelle and to the interaction between bilayer surfaces in the particle. The particle-micelle equilibrium was thermodynamically
considered by using the equilibrium composition of aggregates.
KeywordsMixture of calcium chloride and sodium dodecyl sulfate-Miscibility-Adsorption and aggregate formation-Azeotropy-Particle-micelle equilibrium-Surface tension-Thermodynamic treatment of surfactant mixture
Colloid and Polymer Science 04/2012; 288(12):1313-1320. · 2.33 Impact Factor
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01/2011: pages 165 - 182; , ISBN: 9783527631094
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ABSTRACT: The surface tension γ of the aqueous solution of 1H,1H,6H,6H-perfluorohexane-1,6-diol (FC₆diol) and 1H,1H,8H,8H-perfluorooctane-1,8-diol (FC8diol) mixtures was measured as a function of total molality m and composition of FC₈diol in the mixture X₂ at 293.15 K under atmospheric pressure. The γ vs m curves except at X₂ = 0 and 0.05 have a distinct break point due to a phase transition in the adsorbed film. The surface pressure π vs mean area per adsorbed molecule A curves consist of two parts connected by a discontinuous change. The curve was almost vertical just below the phase transition, and the variation of the A value with film composition X(2)(H) was linear corresponding to the fact that FC₆diol and FC₈diol molecules orient parallel to the surface and are densely packed with the same areas of individual condensed films. Above the phase transition, the A value further decreases to around 0.12-0.19 nm² which is much smaller than the cross-sectional area of the fluorocarbon chain, indicating the multilayer formation at the surface. The phase diagram of adsorption (PDA) in the condensed film showed that the m vs film composition X(2)(H) curve is almost linear and the excess Gibbs energy of adsorption g(HE)/RT is at most 0.01, manifesting the ideal mixing of molecules. This is in contrast to a positive deviation (g(HE)/RT ~0.12) observed in the condensed film of the mixture of 1H,1H,2H,2H-perfluorodecanol (FC₁₀OH) and 1H,1H,2H,2H-perfluorododecanol (FC₁₂OH) with perpendicular molecular orientation. The loss of dispersion interaction between different species having different chain lengths is more appreciable in the perpendicular condensed films and thus leads to less miscibility of FC₁₀OH and FC₁₂OH. In the parallel condensed film, on the other hand, FC₆diol and FC₈diol molecules can arrange their position as close as possible to minimize the loss of dispersion interaction. The X(2)(H) value in the multilayer is close to unity, and thus, the multilayer consists of almost FC₈diol molecules which form a multilayer in the single-component system. Furthermore, the condensed monolayer-multilayer phase transition was accompanied by a large increase in surface density of FC₈diol and a small decrease in that of FC₆diol, indicating that FC₈diol molecules pile preferentially to form a multilayer.
The Journal of Physical Chemistry B 01/2011; 115(3):471-7. · 3.70 Impact Factor
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ABSTRACT: Effects of a short-chain phospholipid, dihexanoylphosphatidylcholine (DHPC), on the structure and morphology of membrane assemblies of a long-chain phospholipid, dimyristoylphosphatidylcholine (DMPC), were examined by fluorescence spectroscopy, differential scanning calorimetry (DSC), and cryogenic transmission electron microscopy (cryo-TEM). It was found by fluorescence measurements that DHPC affects on the gel and liquid crystalline state of DMPC vesicle membranes in different ways. Further, the result of DSC suggested that, along the transition process from DMPC vesicle to DMPC-DHPC mixed micelle, there are at least three different concentration regions which are characterized by the individual variation pattern of the transition temperature and enthalpy change. The cryo-TEM micrographs demonstrated the formation of thread-like assemblies in the second region and the coexistence of the assemblies and spherical micelles in the third region. Thus, it was concluded that the structural transition from DMPC vesicle to DMPC-DHPC mixed micelle could occur in a stepwise manner through the formation of the thread-like assembly, which cannot be described by the three-stage model of vesicle to micelle transition.
Colloids and surfaces. B, Biointerfaces 04/2010; 76(2):571-6. · 2.60 Impact Factor
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ABSTRACT: The miscibility and distribution of Br(-) and BF(4)(-) ions of imidazolium ionic liquid mixtures, 1-hexyl-3-methylimidazolium bromide (HMIMBr) + 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIMBF(4)), at the air/water surface were investigated by surface tensiometry and the total-reflection XAFS (TRXAFS) method. Tensiometry showed that the surface density of BF(4)(-) was much larger than that of Br(-), the adsorbed films of the HMIMBr-HMIMBF(4) mixture were greatly enriched in BF(4)(-) at all surface tensions, and the excess Gibbs energy of adsorption was positive. However, TRXAFS revealed that the Br ions were all in the free-Br state solvated by six water molecules in the mixed adsorbed film. Entropy-originated nonideal mixing, where a kind of segregation of the counterion distribution takes place in the interfacial region, was suggested in the mixture.
Langmuir 10/2009; 25(17):9954-9. · 4.19 Impact Factor
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ABSTRACT: The adsorption of 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC10diol) at the hexane solution/water interface was investigated by the measurement of interfacial tension gamma as a function of pressure p and concentration m1 and the thermodynamic data analysis. The results obtained were compared with those of 1H,1H,2H,2H-perfluorodecanol (TFC10OH) in order to clarify the effect of molecular orientation on the structure and property of the adsorbed film from the viewpoint of volume change of adsorption. The interfacial pressure pi versus mean area per adsorbed molecule A curve revealed two types of phase transitions among expanded, parallel condensed, and multilayer states. The A value in the condensed state and the transition pressure between the expanded and condensed states were larger for FC10diol than for TFC10OH, which manifests the different molecular orientation that the dispersion interaction between hydrophobic chains is weaker in the parallel orientation of FC10diol than in the perpendicular orientation of TFC10OH. The partial molar volume of FC10diol in the condensed state nu1H.C is slightly larger than that of TFC10OH, although the partial molar volume in the hexane solution is much smaller for FC10diol than for TFC10OH. This supports the view that the fluorocarbon chains of FC10diol remain in their contact with hexane even in the condensed film because of the parallel molecular orientation. The partial molar volume in the nu1H,M was very close to the molar volume of solid FC10diol nu1S and smaller than that of nu1H.C at the condensed-multilayer phase transition, and increased gradually with molecular piling. This substantiates that FC10diol molecules are densely packed in a first few layers just above the phase transition and a little loosely packed in the upper layers of the multilayer with increasing molecular piling. Furthermore, the volume change associated with adsorption from the solid FC10diol Delta(nu)(S) evaluated from the gamma versus p curve under the existence of solid deposit was positive and showed a minimum against concentration for the multilayer state. This is primarily due to the minimum in interfacial density at the solubility limit Gamma1H,S and thus due to the minimum in nu1H,M.
The Journal of Physical Chemistry B 10/2009; 113(44):14667-73. · 3.70 Impact Factor
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ABSTRACT: The surface tension of the aqueous solution of 1H,1H,8H,8H-perfluorooctane-1,8-diol (FC(8)diol) was measured as a function of temperature and concentration under atmospheric pressure. The interfacial density and the entropy and energy of adsorption were evaluated and compared to those obtained for the adsorption of 1H,1H,10H,10H-perfluorodecane-1,10-diol (FC(10)diol) at the hexane solution/water interface. The surface tension curves show a break point corresponding to a phase transition of the adsorbed FC(8)diol film. The value of mean area per adsorbed molecule A just below the phase transition indicated the formation of a parallel condensed monolayer, and that above the phase transition suggested the spontaneous formation of a multilayer. The multilayer of FC(8)diol is less compressible and shows a smaller increase in layering with pi compared to FC(10)diol. This is probably because the surface force is repulsive for the hexane/FC/water interface, while it is attractive for the air/FC/water interface. The partial molar entropy change of adsorption is positive in the condensed FC(8)diol film, while it is negative in the condensed FC(10)diol film, which is reasonably explained in terms of the difference in entropy change accompanied by desolvation around the hydrophobic chain. From the viewpoints of the energetic stabilization accompanied by adsorption for the FC(8)diol system, the contribution from the replacement of air/water contact with air/fluorocarbon and fluorocarbon/water contacts and that from the molecular ordering in the adsorbed film is almost equal in case of the condensed monolayer, while in the multilayer the latter is comparatively larger than the former due to the hydrogen bonding between hydroxyl groups and the dispersion interaction among the ordered hydrophobic chains.
The Journal of Physical Chemistry B 05/2009; 113(18):6305-10. · 3.70 Impact Factor
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ABSTRACT: The adsorption behavior of 1,1,2,2,-tetrahydroheptadecafluorodecanol (FC10OH), 1-eicosanol (C20OH), and their mixtures at the hexane solution/water interface is summarized briefly and examined from the viewpoints of interfacial tensions in the presence of domains, domain formation, and the correlation between the phase transition and the miscibility of film forming substances in the adsorbed films. The two-dimensional analogue of the Laplace equation showed that the interfacial tension is always higher in the presence of domains than that in the absence of them. The higher tendency of domain formation of FC10OH compared to C20OH is mainly ascribed to the excess Gibbs energy of mixing of fluorocarbon chains and hydrocarbon solvent being positive and to the interaction energy between domains being more stable against cohesion for FC10OH than for C20OH. The thermodynamic equations derived here suggested the heteroazeotropy in the phase diagram of adsorption and the temperature dependence of interfacial tension at the phase transition points, which are in accord with the experimental findings qualitatively.
The Journal of Physical Chemistry B 05/2009; 113(18):6347-52. · 3.70 Impact Factor
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ABSTRACT: The adsorbed film of 1-decyl-3-methylimidazolium bromide (DeMIMB) at the air/water interface was investigated employing the surface tension measurement and the x-ray absorption fine structure method under the total reflection condition (TRXAFS). From the surface tension measurement, the surface excess concentrations of ions were determined. From the XAFS measurement, two solvation states of bromide ion were found in the adsorbed film, which were assigned to be "free-Br" and "bound-Br". The hydration number of the former was estimated to be 6 while that of the latter was estimated to be 4. The results based on the XAFS analysis provided significant information on the formation of domains in the adsorbed film; the most conceivable situation is that the adsorbed molecules are definitely not homogeneously dispersed, but domains (islands or clusters) are dispersed in the adsorbed film. A regular and rather tight stacking of immidazolium rings may be formed in the domains.
Analytical Sciences 11/2008; 24(10):1279-83. · 1.25 Impact Factor
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ABSTRACT: Aggregate formation of a didodecyldimethylammonium bromide (DDAB) and didodecyldimethylammonium chloride (DDAC) mixture in aqueous solution was investigated. The concentration vs composition diagram of aggregate formation was constructed by analyzing the surface tension, turbidity, and electrical conductivity data. The cryogenic transmission electron microscopy was applied to several representative points in the diagram and provided information of the morphology of aggregates. The sequence of monomer (m) - m + small aggregate (A) - m + A + vesicle (V) - m + V was concluded with increasing total concentration of surfactants at all mixing ratios. The compositions of counterions in A and V were estimated on the basis of thermodynamic consideration and examined from the viewpoint of asymmetry of constituents and uneven distribution between outer and inner monolayers of a vesicle bilayer. Vesicle surfaces were suggested to abound in chloride ions compared to bulk solution, which is opposite to spherical micelle surfaces.
The Journal of Physical Chemistry B 10/2008; 112(39):12304-11. · 3.70 Impact Factor
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ABSTRACT: The results of x-ray reflectivity studies of two oil/water (liquid/liquid) interfaces are inconsistent with recent predictions of the presence of a vaporlike depletion region at hydrophobic/aqueous interfaces. One of the oils, perfluorohexane, is a fluorocarbon whose superhydrophobic interface with water provides a stringent test for the presence of a depletion layer. The other oil, heptane, is a hydrocarbon and, therefore, is more relevant to the study of biomolecular hydrophobicity. These results are consistent with the subangstrom proximity of water to soft hydrophobic materials.
Physical Review Letters 09/2008; 101(7):076102. · 7.37 Impact Factor
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ABSTRACT: The total-reflection XAFS measurement possessing bromide ion selectivity at the interfacial region was applied to the adsorbed film of hexadecyltrimethylammonium chloride (HTAC) and dodecyltrimethylammonium bromide (DTAB) mixture. The surface compositions XjH of individual ions j ( j = HTA+, Cl(-), DTA+, and Br (-)) were evaluated by combining the surface excess concentration of Br(-) estimated from the XAFS with the surface composition of the respective surfactants from the surface tension results. It is clearly shown that HTA+ and Br(-) are preferentially adsorbed to DTA+ and Cl(-) at the air/water interface. The preferential adsorption was estimated numerically in terms of activity coefficient fi+/-(H,p) of component i and excess Gibbs energy of adsorption ĝprH,E. Then, the magnitude of ĝprH,E was compared with that of ĝprH,E attributable to intrinsic interaction between ions.
Langmuir 08/2008; 24(13):6693-7. · 4.19 Impact Factor
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ABSTRACT: The results of x-ray reflectivity studies of two oil/water (liquid/liquid) interfaces are inconsistent with recent predictions of the presence of a vapor-like depletion region at hydrophobic/aqueous interfaces. One of the oils, perfluorohexane, is a fluorocarbon whose super-hydrophobic interface with water provides a stringent test for the presence of a depletion layer. The other oil, heptane, is a hydrocarbon and, therefore, is more relevant to the study of biomolecular hydrophobicity. These results are consistent with the sub-angstrom proximity of water to soft hydrophobic materials. Comment: 28 pages, 9 figures, main text plus supplementary, to be published in Physical Review Letters
07/2008;
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ABSTRACT: Miscibility and interaction of decyldimethylphosphine oxide (DePO) with ammonium chloride (AC), hexylammonium chloride (HAC), and dodecylammonium chloride (DAC) in adsorbed films and micelles were studied by surface tension measurements. Phase diagrams were drawn for the mixed adsorption, mixed micelle formation, and equilibrium between adsorbed films and micelles. Nonideal mixing of DAC and DePO was characterized by a negative excess Gibbs free energy and positive excess area of adsorption and negative excess Gibbs free energy of micelle formation. It is concluded that the interaction between DAC and DePO in adsorbed films and micelles is larger than those between the same surfactants alone due to two factors: ion-dipole interactions between the head groups of DAC and DePO and alkyl-chain/alkyl-chain interactions.
Journal of Colloid and Interface Science 07/2008; 322(1):287-93. · 3.07 Impact Factor
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ABSTRACT: The mixed adsorbed film of 1H,1H-perfluorooctanol (DFC8OH) and 1H,1H,2H,2H-perfluorodecanol (TFC10OH) at the hexane/water interface was studied on the basis of interfacial tension measurement and its thermodynamic data analysis. An adsorbed film at any composition of the mixed system as well as those of pure DFC8OH and TFC10OH systems exhibits three states: the gaseous, expanded, and condensed states. Construction of the phase diagram of adsorption clarified that DFC8OH and TFC10OH mix almost ideally in the gaseous and expanded states. On the contrary, the excess Gibbs energy of adsorption gH,E value evaluated in the condensed state was positive. These results are explained by considering the following two factors: (1) The mixing of binary alcohols is accompanied by the loss of dispersion interaction energy due to the difference in extent of fluorination of hydrophobic chains and in their chain length and increases the gH,E value. (2) Since the interchange energy concerning the interaction between dipoles with different dipole moments is negative, the mixing of these alcohols reduces the repulsive force between hydrophilic groups and thus leads to a decrease in the gH,E value. In the gaseous and expanded states, both of above two factors are not effective. On the other hand, the positive gH,E value in the condensed state is attributable to more effective dispersion interaction than the dipole−dipole interaction in short molecular distance, and so factor 1 becomes dominant. Comparison of the gH,E value of the present system with that of the homologous TFC10OH−TFC12OH mixture leads us to a conclusion that the hydrogenation on β-carbons in hydrophobic chains affects appreciably the balance of interactions between hydrophilic and hydrophobic groups which governs the mixing of molecules in adsorbed films.
02/2008;
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ABSTRACT: We measured the line tension of the air/hexadecane/aqueous solution of the dodecyltrimethylammonium bromide (DTAB) system
as a function of the molality of DTAB aqueous solution at 298.15K. The experimental values of the line tension were 10−10 to 10−12N, and they coincided with the theoretical estimates. Furthermore, it was found that the line tension changes in sign from
positive to negative at around 0.750mmol kg−1. This concentration is close to the point of transition from partial to frustrated-complete wetting. Taking into account
the profiles of the free energy of the air/water surface, previously developed by Indekeu to understand the interrelationship
between the wetting transition and line tension, it is suggested that the sign reversal of the line tension can be attributed
to the transition from partial to frustrated-complete wetting.
Colloid and Polymer Science 01/2008; 286(6):647-654. · 2.33 Impact Factor
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ABSTRACT: The adsorption of phase transfer catalysts, 18-crown-6 and dicyclohexano-18-crown-6, at the air/water and the hexane/water interfaces were investigated. Interfacial tension sigma decreased by increasing concentrations of these compounds and therefore both of these crown ethers are accumulated at interfaces. The variation of sigma with concentration for both compounds follows the Szyszkowski equation very well, from which the values of saturated surface densities and interaction parameters have been evaluated. On the basis of occupied surface area of each molecule, the orientation of each of molecules at the air/water and the hexane/water interfaces have been proposed. The present results show that dicyclohexano-18-crown-6 has the higher tendency not only to dissolve into the hexane phase but also to adsorb at the hexane/water interface than 18-crown-6 and that the Starks extraction mechanism was suggested for the present phase transfer catalysis systems.
Journal of Colloid and Interface Science 01/2008; 316(1):25-30. · 3.07 Impact Factor
