Self-assembly, hydration, and structures in N-decanoyl-N-methylglucamide aqueous solutions: effect of salt addition and temperature

The influence of NaCl addition and temperature on the self-assembly, hydration, and structures of N-decanoyl-N-methylglucamide (MEGA-10) in dilute solution has been investigated by using several experimental techniques, including tensiometry, steady-state fluorescence, density, viscosity, and static and dynamic light scattering. Tensiometry and fluorescence probe studies, by using pyrene as a probe, were used to obtain the critical micelle concentration (cmc) upon the electrolyte addition. The mean micellar aggregation numbers (N(agg)) as a function of the salt addition were obtained by both static light scattering and static quenching methods. The N(agg) values estimated by both methods were found to be in good agreement. It was found that the increase in the micelle size, produced by the addition of NaCl, is due to the increase in the aggregation number and in the amount of water non-specifically associated to the micelle. On the other hand, we have observed that the aggregation number remains invariant in the temperature range studied, whereas the hydrodynamic radius slightly decreases. The effect of electrolyte addition and temperature on the properties of MEGA-10 micelles is much less pronounced than those observed in the traditionally used POE-based surfactants.     

Thermodynamics of aqueous bile salt solutions: Heat capacity,enthalpy and entropy of dilution

Heat capacity data at various temperatures and enthalpies of dilution at 25°C are reported for aqueous bile salt solutions. The apparent molal heat contents _L have been combined with osmotic and activity coefficients to obtain the excess molal entropies. Measurements of some of these properties have also been carried out with the anionic detergent sodium dodecylsulfate so that the bile salt micellization process may be compared with that of a classical detergent. The observed data have been interpreted in terms of the hydrophobic association properties of bile salts in aqueous solution.     

Measurement of bilirubin partition coefficients in bile salt micelle/aqueous buffer solutions by micellar electrokinetic chromatography

The partition coefficients for the distribution of bilirubin between aqueous phosphateborate buffer and cholic, taurocholic, taurodeoxycholic, and taurochenodeoxycholic micelles have been measured by micellar electrokinetic chromatography at pH 8.5. Determination of the partition coefficients required that the critical micelle concentration and partial specific volumes be determined for each bile salt. Critical micelle concentrations were slightly higher for the trihydroxy bile salts. Partial specific volumes of the bile salt micelles differed very little from each other, and for each bile salt they were constant over the concentration range studied, which was typically from slightly above the critical micelle concentration to 35 mM. Capacity factors were corrected for the effects of applied voltage by extrapolation of the capacity factor to zero applied volts. The free solution mobility of bilirubin, determined in the absence of bile salt, was also corrected for the effects of applied voltage. Plots of extrapolated capacity factor versus phase ratio yield the partition coefficient as the slope of a linear fit to the data. Partition coefficients for bilirubin were significantly higher for dihydroxy bile salts than for trihydroxy bile salts.     

Solubility of sodium soaps in aqueous salt solutions

The solubility of sodium soaps in dilute aqueous salt solutions has been systematically investigated by direct visual phase behavior observations. The added electrolytes, including simple inorganic salts and bulky organic salts, influence the solubility of sodium soaps in water, as represented by the varied soap Krafft point. Two inorganic salts, sodium chloride and sodium perchlorate, demonstrate a "salting-out" property. On the other hand, tetraalkylammonium bromides show an excellent ability to depress the soap Krafft point and enhance the soap solubility in water. With increasing the tetraalkylammonium ionic size, the degree of "salting-in" of soaps in water increases. However, solubility of pure tetraalkylammonium bromide in water decreases as the length of the alkyl chains increases. Furthermore, in the ternary water-tetrapentylammonium bromide (TPeAB)-sodium myristate (NaMy) system, we observed an upper cloud point phenomenon, which greatly shrinks the 1-phase micellar solution region in the phase diagram. This miscibility gap, together with the organic salt solubility limitation, restricts the use of tetraalkylammonium bromides with alkyl chains longer than 4 carbon atoms as effective soap solubility enhancement electrolytes. We also found that for sodium soap with a longer hydrocarbon chain, more tetrabutylammonium salt is required to reduce the soap Krafft point to room temperature.     

Homogeneous nucleation temperatures in aqueous mixed salt solutions

This is the first report on the measurement of homogeneous nucleation temperature, TH, in the presence of aqueous mixed salt systems of varying compositions and ionic strengths. The TH,m (TH value in aqueous mixed salt system) data for these systems have been analyzed in terms of a simple empirical equation. The TH,m values in simple aqueous mixed salts like NaCl-KCl can be approximated by linear summation of the products of ionic strength fraction and the TH values of pure salt solutions at the same ionic strength as that of the mixture. The empirical parameter, q0, indicating ionic interaction is related to the viscosity B-coefficients. The TH,m data, though correlated on the basis of the B-coefficients also depends upon the mixing of two ions of like charges. Further, a linear correlation exists between the q0 parameter and self-diffusion coefficient, D0, of the ionic solute. The q0 parameter is also well correlated with the rotational correlation time, tauch/tauc0 of the ionic species involved in the mixtures. It is possible to compute TH,m for the salt mixtures with no common ions from the knowledge of the TH,m values of the salt mixtures with common ions.     

The solubility of toluene in aqueous salt solutions

The solubility of toluene has been measured in distilled water, and in various inorganic salt solutions. Values of the Setschenow constant, K(S), which quantify toluene solubility versus salt concentration, have been determined for each salt. Values of K(S) are compared to the activity of water for the salt solutions. Data from this study, consistent with earlier data, suggests that the effects of salts upon toluene solubility are non-additive. This contrasts the additive behavior of inorganic salts upon the solubility of nonpolar organic compounds, such as benzene and naphthalene, reported in the literature. Specific interaction between slightly polar toluene and ions in solution is suggested as a possible explanation for the non-additive effect of salts on the solubility of toluene.     

Structural aspects of aqueous tetraalkylammonium salt solutions

Various thermodynamic and spectroscopic investigations on aqueous tetraalkylammonium salt solutions are reviewed from a structural viewpoint. At present, it is not yet clear what kind of water structure is formed around the alkyl groups of the large cations. However, the importance of cosphere overlap and ion-ion interaction (cation-anion, cation-cation, cation-anion-cation, etc.) in determining the solution properties are emerging more clearly. In this regard, model calculations based on the approach of Friedman and his coworkers are expected to be of considerable value.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Self-assembly in mixed aqueous solutions of amphiphilic block copolymers and vesicle-forming surfactant

The self-assembly behavior of mixed solutions consisting of poly(isoprene-b-ethylene oxide) (IEO) copolymer micelles and vesicle-forming didodecyldimethylammonium bromide (DDAB) was investigated. Dynamic light scattering indicated the presence of two populations of nanoassemblies in the solutions. By aid of atomic force microscopy, the larger ones were identified as block copolymer modified surfactant vesicles (BCMSVs) and the smaller ones as surfactant-modified block copolymer micelles (SMBCMs). This identification is based on the amphiphilic character of the low and high molecular weight molecules and the notion that exchange of unimers of both types can take place between the initial nanoassemblies in aqueous solution. Electrophoretic light scattering experiments showed that the nanostructures carry positive charges originating from the surfactant. The sizes of the nanoassemblies depend on the relative concentrations of both components. The behavior of the mixed systems was also found to depend on block copolymer composition and temperature. Nanoassemblies of smaller sizes were formed at higher temperatures. BCMSVs and SMBCMs are thermosensitive, in contrast to the temperature stability of pure block copolymer micelles. On the other hand, BCMSVs showed lesser sensitivity to temperature increase compared to the pure DDAB vesicles. This indicates that incorporation of macromolecules into the DDAB bilayer increases the stability of the vesicles.     

Self-assembly and phase behavior of germanium oxide nanoparticles in basic aqueous solutions

We show that germania nanoparticle self-assembly in basic aqueous solutions occurs at a critical aggregation concentration (CAC) corresponding to a 1:1 GeO2/OH- molar ratio. A combination of pH, conductivity, and small-angle X-ray scattering (SAXS) measurements was used to monitor the effect of incremental additions of germanium (IV) ethoxide to basic solutions of sodium hydroxide or tetraalkylammonium cations. Plots of pH versus total germania concentration at varying alkalinities generated a phase diagram with three distinct regions. The diagram was analyzed with a thermodynamic model based on the chemical equilibria of germania speciation and dissociation. The model, which uses the GeO-H dissociation constant (pK = 7.1) as the single fitting parameter, quantitatively captures trends in the CAC and pH. SAXS patterns reveal that the germania nanoparticles have either a cubic or a spherical geometry of dimension approximately 1 nm that is independent of solution pH and cation. On the basis of these and other literature findings, we propose that the germania nanoparticle structure is that of the cubic octamer (double four-membered ring, Ge8O12(OH)8), which is common among condensed GeO2 materials and building units in [Ge,Si]-zeolites. Comparisons between germania and silica solutions show distinct differences in their phase behavior and nanoparticle structure. The results presented here, in combination with previous studies of siliceous solutions, provide a framework for ongoing studies of combined germania-silica phase behavior, which is part of an overarching effort to understand the influence of heteroatoms in the growth and structure direction of zeolites.     

Ionic liquid salt bridge in dilute aqueous solutions.

A new type of salt bridge composed of a hydrophobic room-temperature ionic liquid, recently proposed (T. Kakiuchi and T. Yoshimatsu, Bull. Chem. Soc. Jpn., 2006, 79, 1017), has been shown to be satisfactorily usable in dilute aqueous solutions of submillimolar range. A stable phase-boundary potential has been demonstrated between an ionic liquid, 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(8)mim+][C(1)C(1)N-), and an aqueous KCl solution of submillimolar level, which is lower than the solubility of [C(8)mim+][C(1)C(1)N-] in water, 1.6 mmol dm(-3) at 25 degrees C. The phase-boundary potential between [C(8)mim+][C(1)C(1)N-] and water is maintained constant over more than four orders of magnitude change in the concentration of an aqueous electrolyte solution. The ionic-liquid salt bridge is a superior alternative to salt bridges based on equitransferent electrolytes in practical applications, particularly, the potentiometry of samples of low ionic strengths, such as potentiometric pH measurements of rainwater.     

Extraction of ethylene glycol from aqueous salt solutions

A method is proposed for extracting ethylene glycol from aqueous salt solutions by dialysis through ion-exchange membranes, based on the Donnan exclusion of the electrolyte. Dialysis is performed in the continuous and batch modes. It is found that the batch mode of dialysis is more effective for extracting ethylene glycol from its aqueous salt solutions. The effect of the ionic form of the membrane on ethylene glycol fluxes is explained through computer simulation.     

The surface structure of concentrated aqueous salt solutions

The surface-normal electron density profile rhos(z) of concentrated aqueous salt solutions of RbBr, CsCl, LiBr, RbCl, and SrCl2 was determined by x-ray reflectivity (XR). For all but RbBr and SrCl2 rhos(z) increases monotonically with depth z from rhos(z)=0 in the vapor (z<0) to rhos(z)=rhob of the bulk (z>0) over a width of a few angstroms. The width is commensurate with the expected interface broadening by thermally excited capillary waves. Anomalous (resonant) XR of RbBr reveals a depletion at the surface of Br- ions to a depth of approximately 10 A. For SrCl2, the observed rhos(z)>rhob may imply a similar surface depletion of Cl- ions to a depth of a few angstorms. However, as the deviations of the XRs of RbBr and SrCl2 from those of the other solutions are small, the evidence for a different ion composition in the surface and the bulk is not strongly conclusive. Overall, these results contrast earlier theoretical and simulational results and nonstructural measurements, where significant surface layering of alternate, oppositely charged, ions is concluded.     

Osmotic and activity coefficients of aqueous bile salt solutions at 25, 37, and 45°C

Osmotic coefficients measured by vapor pressure osmometry are reported for aqueous bile salt solutions at 25, 37, and 45°C. Solute activities decrease rapidly with increasing concentration due to premicellar association and micelle formation. In all cases, activities of the dihydroxy bile salts are lower than those of the trihydroxy bile salts. Osmotic coefficients and activity coefficients increase with increasing temperature. It is suggested that hydrophobic forces contribute substantially to the stability of primary bile salt aggregates and micelles.     

间对二氯苯在盐水溶液中活度系数的研究

本文用紫外可见分光度法测定了25℃下间位和对位二氯苯在NaF,NaCI,KBr,Na~2CO~3,K~2So~4,Et~4NBr水溶液中的活度系数,Logf-c~5关系符合Setschenow 盐效应经验公式,盐效应次序为,Na~2CO~3>K~2So~4>NaF>NaCi>NaBr>Et~4NBr. 通过比较发现:二氯苯的偶极矩对盐效应几乎没有影响,本文选取Debye-Mcaulay( DMT)和Conway-Desnoyers-smith(CDST)静电作用理论,定表标粒子理论(SPT)及改进前后的内压力理论IPT和XIPT),计算出理论值,与实验值进行比较, 证实的内压力理论计算值更接近实际.     

Elastic properties of swollen polyelectrolyte gels in aqueous salt solutions

The elastic relaxation responding to a uniaxially stretched poly(acrylic acid) rodlike gel in the aqueous NaCl solution was investigated. The relaxation elucidated the shear (mu) and bulk (K) moduli and the frictional coefficients (sigma) of the fully ionized gel at pH above 9 as functions of the degree of swelling, which was controlled by the NaCl concentration (C(S)) of the solution. Two gels, cross-linked chains of which consist of 500 (GelA500) and 50 (GelA50) monomeric units, were examined to investigate the effect of the chain length on the elastic behavior. The moduli of GelA500 increased with swelling at C(S) below 100 mM and decreased at C(S) above it. The mu values of both gels can be characterized by the power function of gel diameter, d as mu proportional, variantd(beta). The beta values being -1 at C(S) above 100 mM transitionally changed to 1.2 at C(S) about 100 mM. That is, the dimensionality of space for the chains to distribute, n(dim) [= (beta+5)/(beta+2) according to the conventional theory [Sasaki et al., J. Chem. Phys. 102, 5694 (1995)]], changed from 4 (n(dim) of ideal chain) to 1.9 at C(S) = 100 mM. This indicates that the electrostatic repulsion between gel chains reduces the n(dim) at C(S) below 100 mM but not at C(S) above it. It was found that the K values of GelA500 were well described by the conventional theory but those of GelA50 not. The sigma(zr)/sigma(rr) (sigma(zr) is an off-diagonal element of the friction coefficient tensor and sigma(rr) is a diagonal element of the friction coefficient tensor) was found to be 2.7 x 10(-2), which was the same as the previously reported value for the swollen poly(acrylamide) gel [Sasaki, J. Chem. Phys. 120, 5789 (2004)]. The sigma(rr) of unit volume of the GelA500 is well explained by the free draining model while the sigma(rr) of GelA50 is less than that of the free draining model, suggesting the slip between water and ionized chain.     

萘在盐水溶液中活度系数的研究

本文用紫外可见分光光度法测定了25℃下萘在NaNo3、NaClO3、(NH4)sSO4、Na2SO4、K2SO4、SrCl2、BaCl2和MgSO4八种盐的水溶液中的活度系数, 所作Logf-c, 图均为通过原点的直线, 符合Setschenow盐效应经验公式。计算了Debye-McAulayhe7 Cenway-Dcsnoyers-Smith静电作用理论值, Masterton-Lee定标粒子理论值以及改进前后的MeDevit-Long内压力理论值, 并将它们和实验值进行比较, 证实了改进的内压力理论计算值比其它理论计算值更加符合实际;同时再一次证明了黄子卿提出的Van der Waals力盐效应机构的正确性。     

Polymer gel/organic dye complexes in aqueous salt solutions

The present work is devoted to the study of the complex formation of polymer gel with organic dye and their properties in the aqueous salt solutions. Two systems were studied: 1) polyelectrolyte gel based on poly(diallyldimethylammonium chloride) and water soluble oppositely charged organic dyes (alizarin red S and catechol violet) and 2) organogel based on poly(N-vinylcaprolactam) and dithizone. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depends on the dye concentration. In the case of PVCa gel in organic media the dye absorption takes place. The main attention has been concentrated on the study of the behaviour of gel/dye complex immersed in the salt solution if dye is the chelating ligand for metal ions. It was shown that polyelectrolyte gels generally form stable complexes with oppositely charged dyes. The behaviour of PVCa-dithizone-chloroform system was studied in AgNO₃ aqueous solution. The release of dithizone to the external aqueous solution of AgNO₃ reservoir is completely suppressed. Absorption spectra of gel/dye and gel/dye/metal ion systems were studied. It was shown that metal ions penetrate inside the gel phase and the dye/metal ion complexes form within the gel. The dependence of the optical density for the systems of gel/dye/metal ion on the salt concentration is observed.     

Copolymerization of acrylamide with sodium acrylate in aqueous salt solutions

Kinetic relationships in homogeneous radical copolymerization of acrylamide with sodium acrylate, initiated by potassium peroxosulfate in concentrated aqueous solutions at 60°C, were examined in relation to the ionic strength of the solution and pH of the medium.