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1.
J Oleo Sci ; 67(6): 763-771, 2018 Jun 01.
Article in English | MEDLINE | ID: mdl-29760327

ABSTRACT

We investigated the hydration behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers containing sodium ß-sitosteryl sulfate (PSO4). PSO4 was found to enhance hydration in the headgroup region of DPPC bilayers. Therefore, with the incorporation of PSO4 into DPPC membranes, the amount of water required to reach the fully hydrated state was enhanced as indicated by the constant values of the main phase transition temperature (Tm) and the bilayer repeat distance (d). For example, with the addition of 20 mol% of PSO4, the saturation point was shifted to ~70 wt% water compared to ~40 wt% for pure DPPC and 47 wt% for DPPC-cholesterol. The effectiveness of PSO4 in fluidizing the membrane and enhancing its hydration state can be useful in the pharmaceutical and cosmetic industries.


Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Sitosterols/chemistry , Water/chemistry , Cholesterol/chemistry , Cosmetics , Drug Industry , Lipid Bilayers/chemistry , Phase Transition , Transition Temperature
2.
J Oleo Sci ; 67(4): 433-443, 2018 Apr 01.
Article in English | MEDLINE | ID: mdl-29526873

ABSTRACT

We have studied the phase behavior of distearoylphosphatidylcholine (DSPC) in the presence of sodium ß-sitosteryl sulfate (PSO4). PSO4 was found to induce sterol-rich and sterol-poor domains in the DSPC membrane. These two domains constitute a fluid, liquid ordered (Lo) phase and a gel (Lß) phase. PSO4 was less miscible in DSPC than in a dipalmitoylphosphatidylcholine (DPPC) membrane, as evidenced by its tendency to separate from the bilayer at a concentration of 50 mol%. This lack of miscibility was attributed to the greater van der Waals forces between the PC hydrocarbon chains. In addition to affecting the phase behavior, PSO4 also enhanced the hydration of the membrane. Despite its weaker interaction with DSPC compared to DPPC, its tendency to fluidize this phospholipid and enhance its hydration can be useful in formulating cosmetics and pharmaceutical products.


Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Phase Transition , Phosphatidylcholines/chemistry , Sitosterols/chemistry , Calorimetry, Differential Scanning , Hydrocarbons, Cyclic/chemistry , Lipid Bilayers , Microscopy, Polarization , Molecular Structure , Scattering, Small Angle , Transition Temperature
3.
Colloids Surf B Biointerfaces ; 161: 59-66, 2018 Jan 01.
Article in English | MEDLINE | ID: mdl-29040835

ABSTRACT

We have studied the phase behavior of dipalmitoylphosphatidylcholine (DPPC) containing sodium ß-sitosteryl sulfate (PSO4). PSO4 was found to lower the phase transition temperature of DPPC to a higher degree than cholesterol or ß-sitosterol. It also gave rise to the formation of a modulated (ripple) phase (Pß) at low to moderate concentrations. At concentrations greater than 25 mol%, it completely changed the membrane into a fluid phase. This shows that PSO4 is capable of disordering the hydrocarbon chains of PC efficiently. The characteristics of PSO4 for fluidizing the membrane can be useful for the pharmaceutical and cosmetics industries.


Subject(s)
1,2-Dipalmitoylphosphatidylcholine/chemistry , Phase Transition , Sitosterols/chemistry , Transition Temperature , Cholesterol/chemistry , Freeze Fracturing/methods , Lipid Bilayers/chemistry , Membrane Fluidity , Microscopy, Electron, Transmission , Scattering, Small Angle , X-Ray Diffraction
4.
J Oleo Sci ; 65(6): 499-506, 2016 Jun 01.
Article in English | MEDLINE | ID: mdl-27181249

ABSTRACT

The interfacial properties of polyoxyethylene alkyl ether-type nonionic surfactants (CnEm) were studied in a hydrophilic room-temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), in the presence of water. These properties were assessed using static surface tension, pyrene fluorescence, and dynamic light scattering measurements. The interfacial properties were strongly dependent on the solution composition. Increased water concentration lowered the critical micelle concentration (cmc). The cmc was also affected by the lengths of both the alkyl and polyoxyethylene chains, but a greater impact was observed for the alkyl chain length. These results indicate that micellization occurs as a result of solvophobic interaction between surfactant molecules in the water/bmimBF4 mixed solutions, similar to aqueous surfactant systems. The cloud point phenomenon was observed for CnEm with a relatively low hydrophilic-lipophilic balance (HLB) value, and the relationship between the cloud point and water/bmimBF4 composition exhibited a convex upward curve. Furthermore, the mixing of bmimBF4 with water increased the surfactant solubility for water-rich compositions, suggesting that bmimBF4 acts as a chaotropic salt.


Subject(s)
Imidazoles/chemistry , Ionic Liquids/chemistry , Polyethylene Glycols/chemistry , Surface-Active Agents/chemistry , Water/chemistry , Adsorption , Hydrophobic and Hydrophilic Interactions , Micelles , Surface Properties
5.
J Oleo Sci ; 65(5): 419-30, 2016.
Article in English | MEDLINE | ID: mdl-27150334

ABSTRACT

Mutual miscibility of soylecithin, tristearin, fatty acids (FAs), and curcumin was assessed by means of surface pressure-area isotherms at the air-solution interface in order to formulate modified solid lipid nanoparticles (SLN). Appearance of minima in the excess area (Aex) and changes in free energy of mixing (∆G(0)ex) were recorded for systems with 20 mole% FAs. Modified SLNs, promising as topical drug delivery systems, were formulated using the lipids in combination with curcumin, stabilized by an aqueous Tween 60 solution. Optimal formulations were assessed by judiciously varying the FA chain length and composition. Physicochemical properties of SLNs were studied such as the size, zeta potential (by dynamic light scattering), morphology (by freeze fracture transmission electron microscopy), and thermal behavior (by differential scanning calorimetry). The size and zeta potential of the formulations were in the range 300-500 nm and -10 to -20 mV, respectively. Absorption and emission spectroscopic analyses supported the dynamic light scattering and differential scanning calorimetry data and confirmed localization of curcumin to the palisade layer of SLNs. These nanoparticles showed a sustained release of incorporated curcumin. Curcumin-loaded SLNs were effective against a gram-positive bacterial species, Bacillus amyloliquefaciens. Our results on the physicochemical properties of curcumin-loaded SLNs, the sustained release, and on antibacterial activity suggest that SLNs are promising delivery agents for topical drugs.


Subject(s)
Anti-Bacterial Agents/pharmacology , Bacillus amyloliquefaciens/drug effects , Curcumin/pharmacology , Fatty Acids/chemistry , Lipids/chemistry , Nanoparticles/chemistry , Polysorbates/chemistry , Anti-Bacterial Agents/chemistry , Calorimetry, Differential Scanning , Curcumin/chemistry , Drug Carriers/chemistry , Microbial Sensitivity Tests , Solutions , Thermodynamics
6.
Adv Colloid Interface Sci ; 231: 36-58, 2016 05.
Article in English | MEDLINE | ID: mdl-27063924

ABSTRACT

The current review covers recent advances on development and investigation of cationic surfactants containing imidazolium headgroup, which are being extensively investigated for their self-aggregation properties and are currently being utilized in various conventional and non-conventional application areas. These surfactants are being used as: soft template for synthesis of mesoporous/microporous materials, drug and gene delivery agent, stabilizing agent for nanoparticles, dispersants for single/multi walled carbon nanotubes, antimicrobial and antifungal agent, viscosity modifiers, preparing nanocomposite materials, stabilizing microemulsions, corrosion inhibitors and catalyst for organic reactions. Recently several structural derivatives of these surfactants have been developed having many interesting physicochemical properties and they have demonstrated enormous potential in the area of nanotechnology, material science and biomedical science.


Subject(s)
Imidazoles , Surface-Active Agents , Nanotechnology
7.
J Oleo Sci ; 65(3): 201-6, 2016.
Article in English | MEDLINE | ID: mdl-26876680

ABSTRACT

Previously, we reported a new preparation method for liposomes and niosomes (nonionic vesicles) using supercritical carbon dioxide (scCO2) as the solvent (scRPE method). In this study, niosomes were prepared from polyglycerol fatty acid ester (PG ester)-type nonionic surfactants. These surfactants are made from naturally derived materials and are neither harmful to the human body nor to the environment. Niosomes were prepared using the scRPE method with ethanol as the co-solvent. Through this method, decaglycerol distearate (DG2S) and decaglycerol diisostearate (DG2IS) formed niosomes. On the other hand, decaglycerol monostearate (DG1S), which has a high hydrophilic-lipophilic balance (HLB) value, yielded a solution of spherical micelles, and decaglycerol tristearate (DG3S), which has a low HLB value, yielded a gel-like solution. Niosomes of DG2IS had higher trapping efficiencies and dispersion stabilities than those of DG2S because the membrane fluidity of the DG2IS niosomes was greater than that of the DG2S niosomes. The niosomes obtained in the present study are candidates for cosmetic and pharmaceutical applications because they are formed from nonionic surfactants derived from natural sources, and prepared using the scRPE method, which avoids the use of harmful organic solvents.


Subject(s)
Carbon Dioxide/chemistry , Chemistry, Pharmaceutical/methods , Esters/chemistry , Fatty Acids/chemistry , Glycerol/chemistry , Liposomes/chemical synthesis , Polymers/chemistry , Surface-Active Agents/chemistry , Chemical Phenomena , Ethanol/chemistry , Glycerides/chemistry , Hydrophobic and Hydrophilic Interactions , Membrane Fluidity , Solutions , Solvents/chemistry , Stearates/chemistry , Volatilization
8.
J Oleo Sci ; 64(6): 663-72, 2015.
Article in English | MEDLINE | ID: mdl-26028328

ABSTRACT

Silica nanotubes are synthesized through a sol-gel reaction of tetraethyl orthosilicate (TEOS) using myelin figures of Pluronic P123 as the structure-directing agent. The simultaneous progression of the formation of molecular assemblies that act as templates and the formation of silica frameworks though a sol-gel reaction of the silica precursor is a characteristic of this reaction system. The synthesized silica nanotubes were characterized using transmission electron microscopy (TEM), nitrogen adsorption/desorption measurements, and Fourier-transform infrared spectroscopy (FT-IR). The silica nanotubes were unilamellar with diameters of approximately 30 nm, membrane thicknesses of approximately 10 nm, and lengths exceeding a few hundred nanometers. The Brunauer-Emmett-Teller (BET) specific surface area was 589.46 m(2)/g. Silica nanotubes can also be obtained using other Pluronic surfactants that can form myelin figures. In this work, we also investigated the formation mechanism of the silica nanotubes. The typical diameter of a myelin figure is a few tens of micrometers. However, myelin figures with diameters of approximately 10 µm can form in systems with TEOS because bifurcation is induced by minute silica nuclei that form during the initial reaction between TEOS and water. Freeze fracture TEM (FF-TEM) observations revealed the existence of myelin figures with diameters of 20 to 30 nm, which are the same size and shape as the synthesized silica nanotubes. These results indicate that bifurcation of the myelin figures is induced by the silica nuclei that form via the initial reaction of TEOS, which result in the formation of bifurcated myelin figures with diameters of ~10 µm. Myelin figures with diameters of 20 to 30 nm form on the surface, and they become templates where the reaction of TEOS progresses to form silica nanotubes with diameters of approximately 30 nm.


Subject(s)
Myelin Sheath/chemistry , Nanotubes , Poloxalene/chemistry , Silanes/chemistry , Silicon Dioxide/chemistry , Silicon Dioxide/chemical synthesis , Freeze Fracturing , Microscopy, Electron, Transmission , Particle Size , Phase Transition , Spectroscopy, Fourier Transform Infrared
9.
Langmuir ; 31(22): 6085-91, 2015 Jun 09.
Article in English | MEDLINE | ID: mdl-25996798

ABSTRACT

Effects of the addition of water on solvation layers of imidazolium-type room temperature ionic liquids (RT-ILs) have been studied through force curve measurements of atomic force microscopy (AFM). Two kinds of RT-ILs were employed in this study; one is a hydrophilic RT-IL (1-butyl-3-methylimidazolium tetrafluoroborate, BmimBF4), and the other is a hydrophobic one (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, EmimTFSI). These RT-ILs form solvation layers on hydrophilic solid substances (i.e., silica and mica) in the absence of added water. The addition of water into BmimBF4 resulted in the disruption of the solvation layers and then the formation of an interfacial water phase on silica. In contrast, the formation of the interfacial water phase was not evidenced on mica because of the absence of hydrogen-bonding sites on the mica surface. Interestingly, the addition of water into EmimTFSI induced the formation of the interfacial water phase on the two solid surfaces. In the EmimTFSI system, importantly, significantly greater adhesion forces were observed on silica than on mica. This reflects the different formation mechanisms of the interfacial water phase on the two solid surfaces. We conclude that the hydrogen bonding is a key factor in determining whether water molecules can be adsorbed on the solid surfaces, but it is also necessary to take into account the hydrophilic/hydrophobic nature of the RT-ILs.

10.
J Phys Chem B ; 119(18): 5904-10, 2015 May 07.
Article in English | MEDLINE | ID: mdl-25874408

ABSTRACT

Photoresponsive micellar systems of 4-butylazobenzene-4'- (oxyethyl)trimethylammonium bromide (AZTMA) were examined with and without ethylbenzene using small-angle neutron scattering (SANS). Analysis of SANS profiles showed that an aqueous solution containing 5, 10, and 50 mM AZTMA forms prolate spheroids with a long radius (Ra) of 38 Å and a short radius (Rb) of 21 Å. In the 5 mM AZTMA solution, the concentration of micelles decreased upon UV light irradiation, while their size and shape remained almost unchanged. Subsequent visible light irradiation reversed the decrease and increased the number of micelles. In contrast, 10 and 50 mM AZTMA solutions showed that the number and long radius of the micelles decreased with UV light irradiation, while subsequent exposure to visible light irradiation restored them. For AZTMA micellar solutions equilibrated with excess ethylbenzene, the solubilized amount of ethylbenzene increased upon UV light irradiation due to enhanced swelling of the micelles with cis-AZTMA. This photoinduced uptake of the solubilizate has potential applicability for the collection and removal of hazardous oily substances.


Subject(s)
Benzene Derivatives/chemistry , Micelles , Photochemical Processes , Surface-Active Agents/chemistry , Bromides/chemistry , Chromatography, High Pressure Liquid , Isomerism , Light , Models, Chemical , Molecular Structure , Neutron Diffraction , Scattering, Small Angle
11.
J Phys Chem B ; 119(11): 4251-62, 2015 Mar 19.
Article in English | MEDLINE | ID: mdl-25715819

ABSTRACT

Ion-pair amphiphiles (IPAs) are neoteric pseudo-double-tailed compounds with potential as a novel substitute of phospholipid. IPA, synthesized by stoichiometric/equimolar mixing of aqueous solution of hexadecyltrimethylammonium bromide (HTMAB) and sodium dodecyl sulfate (SDS), was used as a potential substituent of naturally occurring phospholipid, soylecithin (SLC). Vesicles were prepared using SLC and IPA in different ratios along with cholesterol. The impact of IPA on SLC was examined by way of surface pressure (π)-area (A) measurements. Associated thermodynamic parameters were evaluated; interfacial miscibility between the components was found to depend on SLC/IPA ratio. Solution behavior of the bilayers, in the form of vesicles, was investigated by monitoring the hydrodynamic diameter, zeta potential, and polydispersity index over a period of 100 days. Size and morphology of the vesicles were also investigated by electron microscopic studies. Systems comprising 20 and 40 mol % IPA exhibited anomalous behavior. Thermal behavior of the vesicles, as scrutinized by differential scanning calorimetry, was correlated with the hydrocarbon chain as well as the headgroup packing. Entrapment efficiency (EE) of the vesicles toward the cationic dye methylene blue (MB) was also evaluated. Vesicles were smart enough to entrap the dye, and the efficiency was found to vary with IPA concentration. EE was found to be well above 80% for some stable dispersions. Such formulations thus could be considered to have potential as novel drug delivery systems.


Subject(s)
Biomimetic Materials/chemistry , Hydrophobic and Hydrophilic Interactions , Membranes, Artificial , Air , Buffers , Cholesterol/chemistry , Drug Carriers/chemistry , Hydrodynamics , Hydrogen-Ion Concentration , Lecithins/chemistry , Methylene Blue/chemistry , Models, Molecular , Molecular Conformation , Pressure , Glycine max/chemistry
12.
J Oleo Sci ; 62(6): 363-70, 2013.
Article in English | MEDLINE | ID: mdl-23728327

ABSTRACT

We studied the effect of water addition on interfacial properties and aggregate behavior of nonionic surfactants (polyoxyethylene alkyl ether; CnEm) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate; bmimPF6). When a small amount of water was added to mixtures of CnEm and bmimPF6, two breaking points (cac1, cac2) were observed in the surface tension/CnEm concentration plots, suggesting the formation of two kinds of aggregates. This two-step aggregate formation was also confirmed by the fluorescence probe method using pyrene. The particle size of the aggregates measured by dynamic light scattering (DLS) was around 200 nm at cac1, and decreased to 4 nm above cac2. These results, together with freeze-fracture TEM observations, showed that the aggregate formed at cac1 was water in bmimPF6 emulsions, which then transformed to micelles solubilizing water in the palisade layer above cac2. This concentration-dependent aggregate formation was supported thermodynamically by studying the dependence of cacs on temperature and alkyl and POE chain lengths of the surfactant.


Subject(s)
Hydrophobic and Hydrophilic Interactions , Imidazoles , Ionic Liquids , Polyethylene Glycols/chemistry , Surface-Active Agents/chemistry , Water , Agglutination , Chemical Phenomena , Emulsions , Micelles , Particle Size , Solubility , Surface Tension , Temperature , Thermodynamics
13.
J Oleo Sci ; 61(3): 135-41, 2012.
Article in English | MEDLINE | ID: mdl-22362144

ABSTRACT

The temperature-concentration phase behavior of nonionic surfactants in an aprotic imidazolium-type room-temperature ionic liquid (RT-IL) was evaluated on the basis of a combination of visual appearance, polarized optical microscopy, and small angle X-ray scattering data. Phytosterol ethoxylates (BPS-n, where n denotes oxyethylene chain lengths of 5, 10, 20, and 30) were used as surfactants in the RT-IL, 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6). The two component mixtures yielded various phases such as discontinuous cubic, hexagonal, and lamellar phases. An increased tendency toward formation of lesser-curved molecular assemblies was observed at higher BPS-n concentrations, at lower temperatures, and for shorter oxyethylene chain surfactants. These trends are similar to those observed in aqueous BPS-n systems; however, notable differences in the phase states of the aqueous system versus the BmimPF6 system were evident. Comparison with the water system showed that the BmimPF6 system yielded fewer phases and generally required higher BPS-n concentrations to induce phase transitions. Evaluation of the effects of addition of a third component (e.g., 1-dodecanol and dodecane) to the binary system on the phase behavior showed that at a given composition ratio of BPS-20 to BmimPF6, the addition of 1-dodecanol generally results in the phase transition to lesser-curved assemblies whereas dodecane generated no significant effects. The observed phase change is satisfactorily rationalized by localized solubilization of the third component into the binary surfactant assemblies.


Subject(s)
Imidazoles/chemistry , Ionic Liquids/chemistry , Phase Transition , Phytosterols/chemistry , Temperature , Oils/chemistry
14.
J Oleo Sci ; 60(11): 563-7, 2011.
Article in English | MEDLINE | ID: mdl-22027021

ABSTRACT

The physicochemical properties of nonionic surfactant mixtures in an aprotic, imidazolium-type room-temperature ionic liquid (RT-IL) have been studied using a combination of static surface tensiometry, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM). The surfactants used in this study are phytosterol ethoxylates (BPS-n, where n is an oxyethylene chain length of either 5 or 30) and the selected RT-IL is 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)). The shorter chain oxyethylene surfactant (BPS-5) exhibits greater surface activity in BmimPF(6) than BPS-30; hence, BPS-5 is a major component in driving the interfacial adsorption and molecular aggregation of the mixed system. The surface tension data demonstrate that an increased mole fraction of BPS-5 results in a decreased critical aggregation concentration (cac) and negatively increased Gibbs free energies estimated for molecular aggregation (ΔG(0)(agg)) and interfacial adsorption (ΔG(0)(ads)). Indeed, the compositions of the monolayer adsorbed at the air/solution interface and the molecular aggregate formed in the bulk solution are enriched with BPS-5. The combination of the DLS and cryo-TEM results demonstrates the spontaneous formation of multi-lamellar vesicles resulting from the BPS-5-rich composition of the molecular aggregates.


Subject(s)
Imidazoles/chemistry , Ionic Liquids/chemistry , Surface-Active Agents/chemistry , Adsorption , Ethylene Glycols/chemistry , Microscopy, Electron, Transmission , Phytosterols/chemistry , Scattering, Radiation , Surface Tension , Temperature
15.
J Colloid Interface Sci ; 358(2): 527-33, 2011 Jun 15.
Article in English | MEDLINE | ID: mdl-21481888

ABSTRACT

Surface adsorption and aggregation behavior of polyoxyethylene (POE)-type nonionic surfactants in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)), were investigated by means of surface tension, (1)H NMR, and dynamic light-scattering (DLS) measurements. The maximum surface excess in bmimPF(6) is much lesser than those observed for aqueous solution, reflecting a much weaker solvophobicity exhibited by the surfactant hydrocarbon chain in the ionic liquid compared with the hydrophobicity experienced in water. Compared with another ionic liquid with different anion species, 1-butyl-3-methylimidazolium terafluoroborate (bmimBF(4)), the surfactant solution in bmimPF(6) brings about higher critical micelle concentration (cmc), smaller micellar aggregation number, and weaker dependence of cmc on the surfactant hydrocarbon chain length. This indicates that the solvophobic interaction between surfactant hydrocarbon chains acts more weakly in bmimPF(6) than in bmimBF(4). The weaker solvophobic effect in bmimPF(6) is also appreciable in the thermodynamic parameters for micelle formation derived from temperature dependence of cmc, and would be attributed to weaker attractive interaction between bmim cation and PF(6)(-) ion compared with that between bmim cation and BF(4)(-) ion. Present results give an insight into a better understanding of the importance of anion species for the properties of ionic liquids as a solvent to support a self-assembly of amphiphilic molecules.


Subject(s)
Adsorption , Imidazoles/chemistry , Ionic Liquids/chemistry , Surface-Active Agents/chemistry , Dimerization , Hydrophobic and Hydrophilic Interactions , Temperature
16.
J Colloid Interface Sci ; 338(1): 308-11, 2009 Oct 01.
Article in English | MEDLINE | ID: mdl-19501832

ABSTRACT

The melting behavior of polyethyleneglycol dodecyl ethers (C(12)E(6), C(12)E(7), and C(12)E(8)) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), was investigated by means of differential scanning calorimetry (DSC). The melting temperature as a function of the surfactant concentration, combined with the cmc curve and cloud point curve, provided phase diagrams for the surfactant/bmimBF(4) mixtures in solvent-rich region. The characteristic feature of the mixtures is an existence of the Krafft temperature which is usually not observed with aqueous solutions of nonionic surfactants. The heat of fusion as a function of the surfactant concentration provided the interaction energy between the surfactant and bmimBF(4). The interaction energy shows a linear dependence on the length of polyoxyethylene (POE) chain of the surfactants, which suggests that the solvation takes place around the POE chain.

17.
J Colloid Interface Sci ; 337(1): 247-53, 2009 Sep 01.
Article in English | MEDLINE | ID: mdl-19486995

ABSTRACT

Cloud point temperatures, T(c), of polyoxyethylene (POE)-type nonionic surfactants in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF(6)), were measured and compared with those previously obtained for the surfactant solution in bmimBF(4). The T(c)s for bmimPF(6) solution are higher than those for bmimBF(4) solution by approx. 40 degrees C. This means that the surfactant molecules are more solvophilic in bmimPF(6) compared to bmimBF(4). The analysis of (1)H NMR chemical shift measurements proved that the higher solvophilicity of the surfactants in bmimPF(6) is attributed to weaker hydrogen-bond interaction between bmim cation and PF6- anion than that between bmim cation and BF4- anion. This interpretation is consistent with the interaction energy parameters derived from the thermodynamic analysis of cloud point curve applying the Flory-Huggins model for phase separation in polymer solution. The present work demonstrates that the property of imidazolium-based ionic liquids as a solvent is determined by a balance of interactions among imidazolium cation, counter anion, and solute molecule.

18.
J Colloid Interface Sci ; 326(2): 483-9, 2008 Oct 15.
Article in English | MEDLINE | ID: mdl-18656889

ABSTRACT

The cloud point phenomenon has been investigated for the solutions of polyoxyethylene (POE)-type nonionic surfactants (C(12)E(5), C(12)E(6), C(12)E(7), C(10)E(6), and C(14)E(6)) in 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), a typical room temperature ionic liquid (RTIL). The cloud point, T(c), increases with the elongation of the POE chain, while decreases with the increase in the hydrocarbon chain length. This demonstrates that the solvophilicity/solvophobicity of the surfactants in RTIL comes from POE chain/hydrocarbon chain. When compared with an aqueous system, the chain length dependence of T(c) is larger for the RTIL system regarding both POE and hydrocarbon chains; in particular, hydrocarbon chain length affects T(c) much more strongly in the RTIL system than in equivalent aqueous systems. In a similar fashion to the much-studied aqueous systems, the micellar growth is also observed in this RTIL solvent as the temperature approaches T(c). The cloud point curves have been analyzed using a Flory-Huggins-type model based on phase separation in polymer solutions.

19.
J Colloid Interface Sci ; 314(1): 334-6, 2007 Oct 01.
Article in English | MEDLINE | ID: mdl-17617418

ABSTRACT

In a work published in this journal by J.P.S. Cabral and A.R.W. Smith [J. Colloid Interface Sci. 149 (1992) 27], it is reported that the 1-dodecylguanidinium acetate (dodine) exhibits first CMC at 20-30 microM and second CMC at 110-120 microM in aqueous solution at 22.5 degrees C. Such low CMCs are unusual for ionic surfactants with dodecyl chain, and is quite interesting if this is the case. Thus, we investigated the micelle formation of dodine by electrical conductivity measurements. The specific conductivity, kappa, vs concentration plot showed no evidence for micelle formation up to a few hundreds microM at 25 degrees C. The Krafft temperature of dodine was found to be approx. 52 degrees C. When conductivity measurements were made at 54 degrees C, a clear break point was observed in the kappa vs concentration plot at 9.5 mM, which must correspond to the CMC of dodine. This CMC value is quite normal for cationic surfactant with dodecyl chain.


Subject(s)
Guanidines/analysis , Guanidines/chemistry , Micelles , Solutions , Surface-Active Agents/chemistry , Temperature
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