Journal of Colloid And Interface Science (v.312, #1)
Reprint of “Fluorescence emission from PAMAM and PPI dendrimers [J. Colloid Interface Sci. 306 (2007) 222–227]
by Dongjun Wang; Toyoko Imae; Masao Miki (pp. 8-13).
A strong fluorescence emission from poly(amido amine) (PAMAM) dendrimers with different terminal groups or a poly(propylene imine) (PPI) dendrimer was studied under different conditions by varying experimental parameters such as pH value, aging time, temperature, and concentration. The increase of fluorescence intensity was fast at low pH or high temperature but linear with respect to dendrimer concentration. It was reasonable that the formation of a fluorescence-emitting moiety had a close relation to protonated tertiary amine groups in PAMAM or PPI dendrimers. Furthermore, oxidation of the tertiary amines was confirmed to play an important role, which was evidently caused by oxygen in air. The results of fluorescence decay indicated that the deactivation of luminescence was raised with increasing temperature. Dendrimers emitted blue photoluminescence along fiber chain templates on a fluorescent microscope.Strong fluorescent emission from poly(amido amine) dendrimers with different terminals or a poly(propylene imine) dendrimer was studied under different conditions. The formation of a fluorescence-emitting moiety has a close relation to the protonated tertiary amine groups in dendrimers. Oxidation of the tertiary amines was believed to play a critical role. The deactivation of luminescence was raised with increasing temperature. The blue photoluminescence on the dendrimer-treated fibers was observed on a fluorescence microscope.
Keywords: Fluorescence; Emission; Photoluminescence; Poly(amido amine) dendrimer; Poly(propylene imine) dendrimer; Dendrimer; Oxidation; Fluorescence lifetime; Fluorescence microscope
Formation and destruction of hydrogen bonds in gels and in aqueous solutions of N-isopropylacrylamide and sodium acrylate observed by ATR-FTIR spectroscopy
by Yumiko Hirashima; Atsushi Suzuki (pp. 14-20).
In this paper, the formation and destruction of hydrogen bonds in gels and in aqueous solutions of N-isopropylacrylamide (NIPA) and sodium acrylate (SA) were studied using Fourier transform infrared (FTIR) spectroscopy with attenuated total reflection (ATR). Aqueous solutions of NIPA and SA monomers with different pHs were prepared, and the ATR-FTIR spectra were obtained immediately after preparing the solution and after having been stored at room temperature for 6 months. It was found that the IR spectra evidently changed after 6 months due to polymerization, and the viscosity of a solution in the lowest pH system increased with time and finally the solution became a gel. The detailed analysis of the IR spectra indicated that the network of the gel was formed by the formation of hydrogen bonds (without crosslinker). Moreover, this physical gel exhibited the re-swelling transition by increasing the pH of solvent. The transition was caused by the destruction of hydrogen bonds due to the dissociation of carboxyl groups, which was also confirmed by the IR spectroscopy.The 3D network was formed by the formation of hydrogen bonds (without crosslinker) and the re-swelling transition by their destructions were observed in aqueous solutions of N-isopropylacrylamide and sodium acrylate.
Keywords: N; -isopropylacrylamide; Sodium acrylate; Hydrogen bonds; ATR-FTIR spectroscopy; Gelation; Re-swelling transition
Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
by Luis A. Bastardo; Joseph Iruthayaraj; Maria Lundin; Andra Dedinaite; Aušvydas Vareikis; Ričardas Makuška; Albert van der Wal; István Furó; Vasil M. Garamus; Per M. Claesson (pp. 21-33).
A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO45MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 Å. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO45MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR.
Keywords: Comb polymer; Comb polyelectrolyte; Polymer–surfactant association; Polyelectrolyte–surfactant aggregate; Small-angle neutron scattering; Light scattering; NMR; Surface tension; Polyelectrolyte; Surfactant; SDS
DC13PC bilayers from anomalous swelling to main transition: An X-ray scattering investigation
by P. Brocca; L. Cantù; M. Corti; E. Del Favero; S. Motta; M.C. Nodari (pp. 34-41).
We have performed small-angle (SAXS) and wide-angle X-ray scattering (WAXS) measurements on the lamellar phase and on large unilamellar vesicles (LUVs) of DC13PC in the temperature range corresponding to the anomalous swelling regime of multibilayer systems, adjacent to the chain melting transition, and across the transition. Our SAXS measurements indicate that on cooling from theLα phase, a uniform progressive swelling of the lamellar system to anomalous distances, starting∼2°C above the main transition, is followed by a region of coexistence, covering the width of the transition (∼0.6°C). Across the transition region, a progressively increasing volume fraction of gel phase with a constantPβ′ interlamellar distance coexists with a decreasing amount of nongel phase that keeps on swelling to longer distances. Along both the swelling and the transition regions, anomalies in the specific heat are observed revealing a two-step process. Simultaneous WAXS experiments show a progressive “density” increase along the swelling region, constituting a direct spectroscopic evidence of an “evolving membrane” approaching the transition in a bulk real system. Calorimetric and densitometric measurements on LUVs are also presented, together with WAXS results, that show the existence of a double step main transition in a single component nanosized closed bilayer.SAXS and WAXS picture of the DC13PC multilamellar system from fluid to gel, along the anomalous swelling region and across the chain melting transition.
Keywords: Phospholipid bilayers; Main transition; SAXS; WAXS; Density; Calorimetry; Density fluctuations; LUVs
Synthesis of highly-ordered mesoporous silica particles using mixed cationic and anionic surfactants as templates
by Takahiro Ohkubo; Taku Ogura; Hideki Sakai; Masahiko Abe (pp. 42-46).
We applied a molecular assembly formed in an aqueous surfactant mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium octylsulfate (SOS) as templates of mesoporous silica materials. The hexagonal pore size can be controlled between 3.22 and 3.66 nm with the mixed surfactant system. In addition, we could observe the lamellar structure of the mixed surfactants with precursor molecules, which strongly shows the possibility of precise control of both the pore size and the structure of pores by changing the mixing ratio of surfactants. Moreover, use of the cationic surfactant having longer hydrophobic chain like stearyltrimethylammonium bromide (STAB) caused the increase ind100 space and shifted the point of phase transition from hexagonal phase to lamellar phase to lower concentration of SOS.
Keywords: Mesoporous silica; Mixed surfactant system; Templating method; X-ray diffraction
Electrostatic effects in films stabilised by non-ionic surfactants
by César Márquez-Beltrán; Dominique Langevin (pp. 47-51).
The disjoining pressure Π of films of aqueous octyl- β-glucoside ( β-C8G1) solutions with and without salt was measured as a function of the film thickness by means of a thin film pressure balance. The analysis of the experiments confirms the presence of an electrostatic double layer which dominates the long-range interactions as found in previous experiments with other non-ionic surfactants in the presence of added salt. In the absence of salt, we find a local ion concentration much higher than that of the residual ionic impurities present in the bulk solution.
Keywords: Thin liquid films; Disjoining pressure; Non-ionic surfactants
Reprint of “Self-diffusion study of micelles in poly(oxyethylene)–polydimethylsiloxane diblock copolymer and poly(oxyethylene) alkyl ether systems” [J. Colloid Interface Sci. 300 (2006) 354–360]
by Kenji Aramaki; Ulf Olsson (pp. 52-58).
Self-diffusion constants of amphiphilic molecules in D2O solutions of mixed poly(oxyethylene)–polydimethylsiloxane diblock copolymer (POE–PDMS,SimC3EOn) and poly(oxyethylene) dodecyl ether (C12EOn) were measured by pulsed-field-gradient NMR method. In the D2O/Si25C3EO51.6/C12EO8 or D2O/Si52C3EO51.6/C12EO8 systems, small and large micelles coexist in a wide range ofSimC3EO51.6 fraction in total amphiphiles, whereas such a coexisting phenomenon does not take place in the D2O/Si5.8C3EO51.6/C12EO8 system. The coexisting phenomenon also takes place in the D2O/Si25C3EO51.6/C12EO5 system although the range of mixing fraction is limited. By obtaining each contribution of surfactant and copolymer molecules to the attenuation decay of the echo signal from the proton of the poly(oxyethylene) chain, we could evaluate the composition of the mixed micelles in the D2O/Si25C3EO51.6/C12EO8 system. The copolymer content in the mixed micelle increases proportionally to the copolymer mole fraction in the aqueous solution. From the series of self-diffusion measurements, we can conclude that the miscibility ofSimC3EOn andC12EOn in aqueous micelles becomes poor and the coexisting phenomenon takes place when the PDMS chain becomes much longer than the dodecyl chain ofC12EOn or the POE chain ofC12EOn becomes long. Furthermore it is also revealed that very few silicone copolymer molecules can be incorporated in small surfactant micelles.
Keywords: Micelle; Self-diffusion study; POE–PDMS block copolymer; Poly(oxyethylene) alkyl ether; Coexisting micelles; Micelle composition
An attempt to detect bicontinuity from SANS data
by Norbert Freiberger; Christian Moitzi; Liliana de Campo; Otto Glatter (pp. 59-67).
SANS is a powerful tool to characterise microemulsions, which can have a discontinuous droplet-like structure (oil in water (O/W), water in oil (W/O)) or a bicontinuous one. In the present study, we try to distinguish O/W, W/O and bicontinuous microemulsions by SANS measurements under practical conditions and by a certain evaluation technique. For this reason we chose the well characterised ternary system water–non-ionic surfactant (C12E5)–oil ( n-octane), at a fixed surfactant concentration and performed SANS measurements throughout its one-phase channel where droplet-like phases as well as bicontinuous phases are well established. We evaluated the scattering data via the ‘Generalised Indirect Fourier Transformation’ method (GIFT) which is based on a particulate picture. It should therefore give good results in the droplet domains while a poor fit could be expected for the bicontinuous regime. For comparison we also applied the model of Teubner and Strey (TS) which was developed especially for bicontinuous phases, here a bad fit can be expected for the particulate regime. The data evaluation via GIFT leads to relatively good fits throughout the one-phase channel. The results are physically meaningful and are comparable to those of the TS model. We show that the scattering pattern of a bicontinuous microemulsion can be represented by that of a polydisperse particulate system. This is in clear contradiction to the expectation that the particle picture used in the GIFT method must fail when the bicontinuous regime is reached.Scattering experiments (SANS) cannot differentiate between particulate and bicontinuous microemulsions using GIFT evaluation technique.
Keywords: Microemulsion; Bicontinuous; One-phase channel; SANS; GIFT
Generation of metal oxide nanoparticles in optimised microemulsions
by Ali Bumajdad; Julian Eastoe; Mohamed I. Zaki; Richard K. Heenan; Lata Pasupulety (pp. 68-75).
The phase behavior and structure of aqueous-in- n-heptane microemulsions, stabilized by surfactant mixtures of di- n-didodecyldimethylammonium bromide, DDAB, and Brij®35 were studied by small angle (neutron or X-ray) scattering techniques. The aqueous nanodroplets contain either a precursor reactive salt or a precipitating agent, so that simple mixing induces nanoparticle formation. These formulated microemulsions display good phase stability against added polar additives such as monovalent, divalent, trivalent metal ions, ammonia solution, tetrabutylammonium hydroxide, and their mixtures. Nanoparticle formation was demonstrated via precipitation of metal oxides inside the water nanodroplets, affording control over the resulting particle size. Nanoparticle characteristic size (XRD- and HR-TEM derived sizes) and specific surface areas (SBET(m2g−1)) for iron oxide and CeO2 prepared in these mixed microemulsions, are compared with those stabilized by single surfactants DDAB and Pure AOT.Both, small-angle neutron and X-ray scattering (SANS and SAXS) show that the proposed microemulsion system is not perturbed by different salt additives and the outcome of such microemulsion systems are nanoparticles as small as 5 nm.
Keywords: Surfactant mixtures; Nanoparticles; Water-in-oil microemulsions; DDAB; Brij; Metal oxide; SANS; SAXS
Coexisting lamellar phases in water–oil–surfactant systems induced by the addition of an amphiphilic block copolymer
by Christian Frank; Reinhard Strey; Claudia Schmidt; Cosima Stubenrauch (pp. 76-86).
We report here a pioneering study using quadrupolar splitting NMR to detect new phases and phase compositions in the quasi-ternary microemulsion system water–decane–C10E4/PEP5-PEO5. The striking observation is that at certain compositions the polymer is apparently no longer incorporated into the membranes of the lamellar phase due to space restrictions. The polymer therefore induces a phase separation into two different lamellar phasesLα1 andLα2 such that it fits intoLα1 while the excess surfactant forms a polymer-freeLα2 phase.
Keywords: Lamellar phases; Amphiphilic block copolymers; Lyotropic liquid crystals; 2; H NMR
DNA encapsulation by biocompatible catanionic vesicles
by Mónica Rosa; M.G. Maria da Graça Miguel; Björn Lindman (pp. 87-97).
The encapsulation of DNA by catanionic vesicles has been investigated; the vesicles are composed of one cationic surfactant, in excess, and one anionic. Since cationic systems are often toxic, we introduced a novel divalent cationic amino-acid-based amphiphile, which may enhance transfection and appears to be nontoxic, in our catanionic vesicle mixtures. The cationic amphiphile is arginine– N-lauroyl amide dihydrochloride (ALA), while the anionic one is sodium cetylsulfate (SCS). Vesicles formed spontaneously in aqueous mixtures of the two surfactants and were characterized with respect to internal structure and size by cryogenic transmission electron microscopy (cryo-TEM); the vesicles are markedly polydisperse. The results are compared with a study of an analogous system based on a short-chained anionic surfactant, sodium octylsulfate (SOS). Addition of DNA to catanionic vesicles resulted in associative phase separation at very low DNA concentrations; there is a separation into a precipitate and a supernatant solution; the latter is first bluish but becomes clearer as more DNA is added. From studies using cryo-TEM and small angle X-ray scattering (SAXS) it is demonstrated that there is a lamellar structure with DNA arranged between the amphiphile bilayers. Comparing the SOS containing DNA–vesicle complexes with the SCS ones, an increase in the repeat distance is perceived for SCS. Regarding the phase-separating DNA–amphiphile particles, cryo-TEM demonstrates a large and nonmonotonic variation of particle size as the DNA–amphiphile ratio is varied, with the largest particles obtained in the vicinity of overall charge neutrality. No major differences in phase behavior were noticed for the systems here presented as compared with those based on classical cationic surfactants. However, the prospect of using these systems in real biological applications offers a great advantage.
Keywords: Catanionic vesicles; DNA
The EACN scale for oil classification revisited thanks to fish diagrams
by S. Queste; J.L. Salager; R. Strey; J.M. Aubry (pp. 98-107).
The phase behavior of C10E4–oil–water systems at constant o/w ratio and variable temperature (fish diagram) has been investigated for several homologous oil families. The temperatureT∗ and surfactant concentrationC∗ at the critical point were determined for 10 n-alkanes varying from C6 to C28 as well as for a series of alkylcyclohexanes and alkylbenzenes. On the basis ofT∗, equivalent alkane carbon numbers (EACN) were assigned to nonlinear alkanes, alkylbenzenes, and alkylcyclohexanes. The consistency of the method was shown by corroborating that the EACN values of oils previously investigated with other C iE j (dibutyl ether, squalane, isopropyl myristate, and dodecylbenzene) are the same when determined with C10E4. The fact that two oils of different nature but with the same EACN (i.e., the sameT∗) do not exhibit the sameC∗ is discussed in terms of monomeric solubility of the surfactant in the oil (CMCoil).The assignment of EACN values to oils requires the determination of their X-point temperature whose evolution is linear with increasing alkyl chain length.
Keywords: Oil; Surfactant; Classification; Fish diagram; Microemulsion; EACN
Unusual formation of small aggregates by mixing giant multilamellar vesicles
by Carlos Rodríguez-Abreu; Lok Kumar Shrestha; Manuel Arturo López Quintela (pp. 108-113).
The phase behavior and structure of aggregates in a hydrophobic block copolymer (L121)/double-tailed surfactant (AOT)/water system have been studied by phase study, fluorescence spectrometry, dynamic light scattering, transmission electron microscopy, small angle X-ray scattering (SAXS) and conductivity measurements. An isotropic, one-phase region is found between two biphasic regions containing large vesicles, namely, transparent samples are formed by mixing two turbid solutions. Depending on the AOT/L121 ratio, the isotropic region can be quite stable against temperature. The phase transition between the two regions can be detected by the used techniques, and structural transitions in the aggregates are inferred. The experimental evidence indicates that mixed aggregates are formed at very low concentrations, much lower than the critical micellar concentration of AOT. These micelle-like aggregates contain a mixed hydrophobic core, are small (2–4 nm), and seem to be quasi-spherical, which is an unexpected result since the packing parameters of the single amphiphiles do not favor such small quasi-spherical shapes. This behavior might have interesting implications in the release of substances from vesicles when their structure is disrupted.
Keywords: Phase behavior; Vesicles; Micelles; SAXS; Fluorescence spectroscopy; Dynamic light scattering
Triacylglycerol microemulsions stabilized by alkyl ethoxylate surfactants—A basic study
by S. Engelskirchen; N. Elsner; T. Sottmann; R. Strey (pp. 114-121).
As triacylglycerols are the main components of natural fats and oils their solubilization in the form of emulsions or microemulsions was of great interest within the last years. However, systematic studies of their properties along the classical lines of complex fluids science are still missing. In the present paper we focus on the phase behavior, the interfacial tension and the microstructure of systems of type H2O/NaCl–triacylglycerol–alkylpolyglycolether (C iE j). The interfacial tension between water and oilσab is high in a microemulsion system containing triolein. Thus, one needs high surfactant mass fractions to formulate a single-phase microemulsion. We show that this is not only true for triolein, but also for saturated long-chained triacylglycerols. The determination of the amphiphilicity factorfa and the calculation of the bending rigidities of the amphiphilic film confirm that despite the fact that high surfactant mass fractions and high temperatures are needed to solubilize triolein in a system of type H2O/NaCl–triacylglycerol–alkylpolyglycolether (C iE j), this is still a microemulsion in the narrower sense.The solubilization of triacylglycerols either in emulsions or in microemulsions was in the focus of many research groups within the last years. However, a systematic study of the properties of triacylglycerol microemulsions is still missing. In the present paper we focus on the phase behavior, the interfacial tension and the microstructure of systems of type H2O/NaCl–triacylglycerol–alkylpolyglycolether (C iE j). We show that despite the fact that high surfactant mass fractions and high temperatures are needed to solubilize long-chained triacylglycerols, these systems are still microemulsions by definition.
Keywords: Triacylglycerol; Microemulsion; Efficiency; Phase behavior; Interfacial tension; Microstructure
Micelle structures in aqueous solutions of glucose-based surfactants having an isoprenoid-type hydrophobic chain
by Taiki Kato; Youhei Kawabata; Masatoshi Fujii; Tadashi Kato; Masakatsu Hato; Hiroyuki Minamikawa (pp. 122-129).
Surfactant self-diffusion coefficients have been measured on a binary system of 1- O- β-3,7-dimethyloctyl-d-maltopyranoside ( β-Mal2(Ger))/water and a mixed surfactant system of β-Mal2(Ger)/1- O- β-3,7-dimethyloctyl-d-glucopyranoside ( β-Glc(Ger))/water at 25 °C. For comparison, measurements have also been made on 1- O- β-decyl-d-maltopyranoside ( β-Mal2C10)/water and β-Mal2C10/1- O- β-decyl-d-glucopyranoside ( β-GlcC10)/water. The hydrodynamic radius of β-Mal2(Ger) micelles obtained from the micellar diffusion coefficient is around 3 nm and nearly equal to that of β-GlcC10 micelles within experimental error. In the mixed surfactant systems, the hydrodynamic radii for both systems increase with increasingXG (the mole fraction of β-Glc(Ger) or β-GlcC10 in the total mixed solute) aboveXG≅0.4 when the total surfactant concentration is kept constant at 2 wt%. TheRH of β-Glc(Ger)/Mal2(Ger) micelles increases more rapidly than β-GlcC10/ β-Mal2C10 micelles, and then phase separation occurs atXG≅0.65. On the other hand, theRH of β-GlcC10/ β-Mal2C10 micelles continues to increase until the phase separation occurs atXG≅0.92. Measurements have also been performed as a function of total surfactant concentration at constantXG (=0.6). The CMC of the β-Glc(Ger)/Mal2(Ger) system is larger than that of the β-GlcC10/ β-Mal2C10 system as expected from the results of the pure surfactant systems published previously. TheRH increases with increasing total surfactant concentration for both systems. At higher concentrations, theRH of β-Glc(Ger)/Mal2(Ger) micelles increases more rapidly than β-GlcC10/ β-Mal2C10 micelles. These results can be explained by the fact that the geranyl and decyl chains have the same volume but different chain lengths.
Keywords: Sugar-based surfactant; Glucose-based surfactant; Self-diffusion; Micelles; Hydrodynamic radius
Phase and rheological behavior of the polymerizable surfactant CTAVB and water
by J.F.A. Soltero; J.G. Alvarez-Ramírez; V.V.A. Fernández; N. Tepale; F. Bautista; E.R. Macías; J.H. Pérez-López; P.C. Schulz; O. Manero; C. Solans; J.E. Puig (pp. 130-138).
The phase and rheological behaviors of the polymerizable surfactant, cetyltrimethylammonium benzoate (CTAVB), and water as a function of surfactant concentration and temperature are investigated here. The critical micelle concentration (cmc) and the (cmc2), as well as the Krafft temperature (TK), are reported. A large highly viscous micellar solution region and hexagonal- and lamellar-phase regions were identified. The micellar solutions exhibit shear thickening in the dilute regime, below the overlapping or entanglement concentration. At higher concentrations, wormlike micelles form and the solutions show strong viscoelasticity and Maxwell behavior in the linear regime and shear banding flow in the nonlinear regime. The linear viscoelastic regime is analyzed with the Granek–Cates model, showing that the relaxation is controlled by the kinetics of reformation and scission of the micelles. The steady and unsteady responses in the nonlinear regime are compared with the predictions of the Bautista–Manero–Puig (BMP) model. Model predictions follow the experimental data closely.The CTAVB/water system exhibits a large highly viscous micellar region and hexagonal- and lamellar-phase regions. The micellar solutions exhibit shear thickening at low concentrations and strong viscoelasticty and shear banding at higher concentrations.
Keywords: Phase behavior; Linear viscoelasticity; Nonlinear viscoelasticity; Shear-banding flow; Polymerizable surfactant
Phase behavior of mixed solution of a glycerin-modified cationic surfactant and an anionic surfactant
by Koji Tsuchiya; Jun Ishikake; Tae Seong Kim; Takahiro Ohkubo; Hideki Sakai; Masahiko Abe (pp. 139-145).
The phase behavior of mixed solution of newly synthesized monoglycerylcetyldimethylammonium chloride (MGCA) and sodium octyl sulfate (SOS) in water was investigated by cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), differential scanning calorimetry (DSC), and fluorescence polarizing for evaluation of the microviscosity of bilayers. No precipitate was observed in the mixed solution except at concentrations below 20 mM over all mixing ratios, and stable vesicles were formed in a considerably wide range of mixing ratio, even at the equimolar ratio. Vesicles formed in aqueous 1/1 MGCA/SOS mixture were found to exhibit no phase transition, and fluorescence polarizing measurements showed that the vesicle bilayers have a high fluidity. This flexibility allows the bilayers to have a spontaneous curvature, and thus vesicles rather than flat lamellae can be stabilized in the mixture even at the equimolar ratio. In addition, because the glycerin group of MGCA interacts strongly with water, the hydration repulsion contributes to prevent the bilayers consisting of MGCA and SOS from adhering and flocculating even though the charge neutralization between MGCA and SOS occurs at the equimolar ratio.
Keywords: Catanionic surfactant; Glycerin-modified surfactant; Thermodynamically stable vesicles
Novel viscoelastic systems from cationic surfactants and hydrophobic counter-ions: Influence of surfactant chain length
by R. Abdel-Rahem; H. Hoffmann (pp. 146-155).
In continuation of our previous investigations on the aqueous phase behavior of cetyltrimethylammonium 2-hydroxy-1-carboxy-naphthoate (CTA-2,1-HCN) (see J. Colloid Interface Sci. 288 (2005) 570), we have studied the phase behavior and the properties of the phases of the two shorter homologues, C14TA-2,1-HCN and C12TA-2,1-HCN. The phases were prepared from the alkyltrimethylammonium hydroxides RTAOH and the naphtholcarboxylic acid. By preparing the systems in this way the surfactant solutions contain no excess salt. With increasing counter-ion–surfactant ratio r we observed the same sequence of phases as for the previously studied C16-system, namely a L1-phase and a L α-phase with multilamellar vesicles (MLV). The single phases are separated by a two-phase L1/L α region. The phases were characterized with FF-TEM, rheological and SANS measurements. For both systems the viscosity of the L1-phases passes with increasing counter-ion/surfactant ratio over a maximum. The height of the maximum decreases strongly with decreasing chain length while the complex viscosity of the MLV-phase depends little on the chain length. For 100 mM solution both MLV phases behave like a weak gel and have a yield stress value. It is thus shown that it is possible to prepare viscoelastic surfactant solutions with a yield stress value from single chain surfactants with a dodecyl chain.
Keywords: Surfactant; Vesicles; FF-TEM; Liquid crystalline; Viscosity
Super water-repellent poly(alkylpyrrole) films having environmental stability
by Kazutomo Kurogi; Hu Yan; Hiroyuki Mayama; Kaoru Tsujii (pp. 156-163).
We present electrochemical synthesis of super water-repellent poly(alkylpyrrole) films which exhibit excellent environmental stability in terms of contact angle (>150°) for water. The poly(alkylpyrrole) films synthesized under an optimized electrochemical condition consisted of thousands of micro-scaled ‘needles’ which densely aligned by shoulder to shoulder. The surface of the aligned ‘needles’ was analyzed by a box-counting method, to be a fractal structure with a dimension of 2.18.An electrochemical synthesis of super water-repellent poly(alkylpyrrole) films which exhibit excellent environmental stability in terms of contact angle (>150°) to water was reported. The poly(alkylpyrrole) films consisted of thousands of micro-scaled ‘needles’ which densely aligned by shoulder to shoulder. The surface of the aligned ‘needles’ was analyzed by a box-counting method, to be a fractal structure with a dimension of 2.18.
Keywords: Super water-repellency; Fractal structure; Electrochemical polymerization; Conductive polymer
The leading edge of evaporating droplets
by G. Guéna; C. Poulard; A.M. Cazabat (pp. 164-171).
New experiments on drops evaporating in normal atmosphere from smooth substrates in the situation of complete wetting are reported and compared with the available theoretical model. They are the continuation of previous work with alkane or water sessile drops, which is first briefly summarized. The model accounts very well for the dynamics of the drop radius, but the predictions are only qualitative for the contact angle, especially for small angles. Experiments with hanging drops allow us first to discard any influence of convection in the gas phase on the drops dynamics. Then the main part of the paper concerns new experiments with polydimethylsiloxane oligomers. These silicone oils are similar to alkanes as far as evaporation rate is concerned, but have lower surface tensions, and therefore smaller dynamic contact angles. The purity of the oils appears to be critical for the experiments, and requires a preliminary investigation. Then a systematic study of the drops dynamics is presented, as a basis for forthcoming theoretical work.Typical picture of an evaporating droplet. The thickness profile can be reconstructed from the equal thickness interference fringes. A slight change of curvature is visible at the contact line, suggesting the presence of a thin film ahead.
Keywords: Moving contact line; Surface tension gradients; Contact angle; Evaporating drops
Formation of intermediate micellar phase between hexagonal and discontinuous cubic liquid crystals in brine/ N-acylamino acid surfactant/ N-acylamino acid oil system
by Yuji Yamashita; Hironobu Kunieda; Eiko Oshimura; Kazutami Sakamoto (pp. 172-178).
The phase behavior in the brine/sodium N-dodecanoyl sarcosinate (Sar)/isopropyl N-dodecanoyl sarcosinate (SLIP) system has been investigated by means of phase study, static light scattering, and small-angle X-ray scattering. The liquid crystal phases, hexagonal (H1) and discontinuous cubic (I1), melt upon the addition of NaCl, which shows the similar effect to the increasing of temperature. The addition of SLIP to the brine/Sar solution at high Sar concentration induces the phase transition from H1 to I1 via the isotropic micellar solution (Wm2). The micellar structure in the Wm2 phase also changes from the wormlike to the globular micelle with SLIP concentration. Adding NaCl reduces the repulsive force between the Sar head groups and simultaneously the space of the solubilized SLIP in the palisade layer, leading SLIP to shift their location further into the micelle core. As a consequence, the hexagonal symmetry breaks into the micelle solution and the liquid crystal order is destabilized entropically.SLIP an amphiphilic oil turns micelle 1st to H1 then to I1, while additive of NaCl melts H1 to micelle (Wm2) before I1 as temperature does.
Keywords: Amino acid derived oil; Acylsarcocinate; Phase behavior; Electrolyte; Micelle structure; Hexagonal phase; Cubic phase; SAXS; Static light scattering