Search

Chemical gardens are self-assembled structures with intricate plant-like morphologies and consist of mineralized membranes, which form spontaneously at interfaces between compartments with dissimilar chemical composition, most typically acidic metal salt and alkaline sodium silicate solutions. While this phenomenon is thought to occur in a number of practical settings, it has also proven to be valuable for investigating transport characteristics in distinct applied systems. For example, coupled diffusion and precipitation processes were monitored in silica gardens based on calcium and iron salts, considered to be models for cement hydration and steel corrosion, respectively. Here we extend these studies to the case of aluminum-based silica gardens, one of the so far less frequently investigated examples of silica gardens. To this end, single macroscopic tubes were prepared in a reproducible way by the controlled addition of sodium silicate solution to a pellet of pressed aluminum nitrate. Continued sampling of the volumes enclosed by and surrounding the formed membraneous structure allowed the time-dependent development of ion concentration gradients to be tracked over extended periods of time, while both the pH and electrochemical potential differences across the membrane were recorded online by immersed probes. The dynamic behavior revealed in this way was finally complemented by ex-situ analyses of the composition of the formed tubes. The collected data shows that the as-prepared tubular structures consist of sodium aluminosilicate phases with certain similarities to zeolites and geopolymers. The emerging tube wall was further found to be permeable to all ionic species present in the system, allowing significant electrochemical potential to be sustained over tens of hours until diffusion had eventually diminished the initially generated gradients. The findings of this work may have important implications for the geochemical fate of natural aluminosilicate sources, the use of such geopolymers in construction applications, and the synthesis and properties of zeolites.

Vapor pressure measurements were applied to the systems guanidinium hydrochloride (methanamidine hydrochloride) + sodium l-glutamate (S-aminopenthanedioic acid sodium salt) + water at varying conce...

This study presents the fabrication of novel lignin/chitin films from a solvent system composed of the ionic liquid 1-butyl-3-methylimidazolium acetate and γ-valerolactone as a biosourced cosolvent. Scanning electron microscopy and attentuated total reflectance Fourier transform infrared spectroscopy confirmed the successful preparation of the lignin/chitin films. The application of lignin/chitin film as an adsorbent for Fe(III) and Cu(II) cation uptake from aqueous solutions is discussed. It was observed that the maximum adsorption capacity for Fe(III) was 84 wt % and for Cu(II) was 22 wt % within 48 h. The lignin/chitin films could be regenerated by desorption of the Fe(III) and Cu(II) ions. Up to 12 and 46 wt %, respectively, could be released within 48 h by directly soaking the metal ion loaded film within water at room temperature. The lignin/chitin film can be considered as a stable and recyclable bioadsorbent material with a high adsorption metal ion capacity for water purification.

Vapor pressure osmometry was applied to the system aminomethanamidine hydrochloride (guanidinium hydrochloride, GndmCl) + (S)-aminobutanedioic acid hemimagnesium salt (magnesium l-aspartate, Mg-(l-Asp)2) + water for varying molalities of GndmCl and Mg-(l-Asp)2 (mMg-(Asp)2 = 0.1, 0.2, and 0.3 mol/kg and mGndmCl = 0.1–1.2 mol/kg) at T = 298.15 and 310.15 K. From vapor pressure osmometry, activities of water, activity coefficients of water, and the corresponding osmotic coefficients of the mixtures Mg-(l-Asp)2 + water and Mg-(l-Asp)2 + GndmCl + water have been calculated, both being directly related to the chemical potentials of the different species and therefore to their Gibbs energy. Electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) accounting for Coulomb and short-range (hard chain, dispersion, association) interactions was used to model the own experimental data of binary Mg-(l-Asp)2 + water and ternary GndmCl + Mg-(l-Asp)2 + water solutions. ePC-SAFT was further applied to mod...

Osmotic coefficients are inferred from vapor pressure osmometry measurements that were performed at T = 298.15 K for ternary amino acid–electrolyte–water systems with variation in the concentrations of amino acid (aminoethanoic acid, glycine) and electrolyte (NaCl) up to high concentrations of aminoethanoic (3 mol·kg–1) and NaCl (3 mol·kg–1). From the consideration of the Gibbs–Duhem equation at mutual data treatment, interparticle interactions in ternary aminoethanoic acid–NaCl–water systems have been deduced in a wide concentration range. A two-parameter fit (third order terms in the power series) according to Bower and Robinson is used for calculation of component activity coefficients.

Mineralization of alkaline-earth carbonates in silica-rich media at high pH leads to fascinating crystal morphologies that strongly resemble products from biomineralization, despite the absence of any organic matter. Recent work has demonstrated that elaborate CaCO3 structures can be grown in such systems even at high supersaturation, as nanoparticles of amorphous calcium carbonate (ACC) were spontaneously coated by skins of silica and thus served as temporary storage depots continuously supplying growth units for the formation of crystalline calcite. In the present study, we have precipitated barium carbonate under similar conditions and found surprisingly different behavior. At low silica concentrations, there was no evidence for an amorphous carbonate precursor phase and crystallization occurred immediately, resulting in elongated crystals that showed progressive self-similar branching due to the poisoning influence of silicate oligomers on the growth process. Above a certain threshold in the silica co...

In this study, we show a strategy of formulating highly and fully water dilutable sustainable microemulsions with dibasic esters as oil pseudophase. First, dimethyl or diethyl DBEs with different numbers of carbon atoms between the ester functions (succinate C2, glutarate C3, and adipate C4) or DBE blends and a surfactant–cosurfactant melt consisting of sodium dodecylsulfate and 1-pentanol with a constant weight ratio of 1:2 are used. We investigated the extent of the realms of existence of homogeneous single phases and represent them with pseudoternary phase diagrams. It was possible to formulate fully water dilutable oil-rich single-phase solutions with all dimethyl dibasic esters but not with the diethyl ones. By mixing the most hydrophilic dibasic ester with the most hydrophobic one with a mass ratio of 3:2, a fully water dilutable oil-rich single phase could also be obtained. The presence of water-in-oil, bicontinuous, and oil-in-water microemulsions was checked with conductivity and dynamic light sc...

Osmotic coefficients of ternary systems amino acid–electrolyte–water; aminoethanoic acid (glycine) + NaCl + H2O; aminoethanoic acid + KCl + H2O; aminoethanoic acid + NaNO3 + H2O; aminoethanoic acid + NaSCN + H2O; aminoethanoic acid + NaCOOCH3 + H2O; (S)-2-aminopentanedioic acid sodium salt (sodium l-glutamate) + NaCl + H2O; (S)-2-aminobutanedioic acid sodium salt (sodium l-aspartate) + NaCl + H2O; (S)-2-aminopentanedioic acid sodium salt + KCl + H2O; (S)-2-aminobutanedioic acid sodium salt + KCl + H2O, are inferred from vapor pressure osmometry measurements performed at T = 310.15 K.

Crystal architectures delimited by sinuous boundaries and exhibiting complex hierarchical structures are a common product of natural biomineralization. However, related forms can also be generated in purely inorganic environments, as exemplified by the existence of so-called “silica-carbonate biomorphs”. These peculiar objects form upon coprecipitation of barium carbonate with silica and self-assemble into aggregates of highly oriented, uniform nanocrystals, displaying intricate noncrystallographic morphologies such as flat sheets and helicoidal filaments. While the driving force steering ordered mineralization on the nanoscale has recently been identified, the factors governing the development of curved forms on global scales are still inadequately understood. In the present work, we have investigated the circumstances that lead to the expression of smooth curvature in these systems and propose a scenario that may explain the observed morphologies. Detailed studies of the growth behavior show that morpho...

Recently, a new family of ionic liquids based on oligoether carboxylates was introduced. 2,5,8,11-Tetraoxatridecan-13-oate (TOTO) was shown to form room-temperature ionic liquids (RTILs) even with small alkali ions such as lithium and sodium. However, the alkali TOTO salts suffer from their extremely high viscosities and relatively low conductivities. Therefore, we replaced the alkali cations by tetraalkylammonium (TAA) ions and studied the TOTO salts of tetraethyl- (TEA), tetrapropyl- (TPA), and tetrabutylammonium (TBA). In addition, the environmentally benign quaternary ammonium ion choline (Ch) was included in the series. All salts were found to be ionic liquids at ambient temperatures with a glass transition typically at around -60 °C. Viscosities, conductivities, solvent polarities, and Kamlet-Taft parameters were determined as a function of temperature. When using quaternary ammonium ions, the viscosities of the resulting TOTO ionic liquids are600 times lower, whereas conductivities increase by a factor of up to 1000 compared with their alkali counterparts. Solvent polarities further reveal that choline and TAA cations yield TOTO ionic liquids that are more polar than those obtained with the, per se, highly polar sodium ion. Results are discussed in terms of ion-pairing and structure-breaking concepts with regard to a possible complexation ability of the TOTO anion.

We report on the effects of electrolytes spanning a range of anions (NaOc, NaSCN, NaNO(3), NaBr, NaCl, NaBu, NaOAc, Na(2)SO(4), Na(2)HPO(4), and Na(2)CO(3)) and cations (LiCl, NaCl, KCl, CsCl, and choline chloride) on the aqueous solubility of an extended surfactant. The surfactant is anionic with a long hydrophobic tail as well as a significant fraction of propylene oxide groups and ethylene oxide groups (C(12-14)-PO(16)-EO(2)-SO(4)Na, X-AES). In the absence of electrolytes, X-AES exhibits a cloud-point temperature that decreases with increasing surfactant concentration. After the addition of salts to the surfactant solutions, various shifts in the solubility curves are observed. These shifts follow precisely the same Hofmeister series that is found for salting-in and salting-out effects in protein solutions. In the presence of different concentrations of sodium xylene sulfonate (SXS), the solubility of the surfactant increases. In this context, SXS can be considered to be a salting-in salt. However, when the electrolytes are added to an aqueous solution of X-AES and SXS the Hofmeister series reverses for divalent anions such as Na(2)SO(4), Na(2)HPO(4), and Na(2)CO(3). Studies on the phase behavior and micelle structures using polarization microscopy, freeze-etch TEM, and NMR measurements indicate a dramatic change in the coexisting phases on the addition of SXS.

The formation of microemulsions with triglycerides at ambient conditions can be improved by increasing the surfactant-water and surfactant-oil interactions. Therefore, extended surfactants were developed, which contain hydrophilic/lipophilic linkers. They have the ability to stretch further into the oil and water phase and enhance the solubility of oil in water. In this work, the phase behavior of a chosen extended surfactant (C(12-14)-PO(16)-EO(2)-SO(4)Na, X-AES) in H(2)O/D(2)O at high surfactant concentrations (30-100 wt %) and at temperatures between 0 and 90 °C is studied for the first time. The lyotropic liquid crystals formed were determined by optical microscopy, small-angle X-ray scattering (SAXS), and (2)H and (23)Na NMR, and a detailed phase diagram of the concentrated area is given. The obtained mesophases are a hexagonal phase (H(1)), at low temperatures and small concentrations, a lamellar phase (L(α)) at high temperatures or concentrations, a bicontinuous cubic phase (V(2)) as well as a reverse hexagonal phase (H(2)). To our knowledge, this is the first surfactant that forms both H(1) and H(2) phases without the addition of a third compound. From the (2)H NMR quadrupole splittings of D(2)O, we have examined water binding in the L(α) and the H(2) phases. There is no marked difference in the bound water between the two phases. Where sufficient water is present, the number of bound water molecules per X-AES is estimated to be ca. 18 with only small changes at different temperatures. Similar results were obtained from the (23)Na NMR data, which again showed little difference in the ion binding between the L(α) and the H(2) phases. The X-ray diffraction data show that X-AES has a much smaller average length in the L(α) phase compared to the all-trans length than in the case for conventional surfactants. At very high surfactant concentrations an inverse isotropic solution (L(2)), containing a small fraction of solid particles, is formed. This isotropic solution is clearly identified and the size of the reversed micelles was determined using (1)H NMR measurements. Furthermore, the solid particles within the L(2) phase and the neat surfactant were analyzed. The observed results were compared to common conventional surfactants (e.g., sodium dodecyl sulfate, sodium lauryl ether sulfate, and sodium dodecyl-p-benzene sulfonate), and the influence of the hydrophilic/lipophilic linkers on the phase behavior was discussed.

The effect of the anion, namely dicyanamide, hexafluorophosphate, trifluoroacetate, or trifluoromethanesulfonate, on the conductivity (κ) of 1-N-butyl-3-N-methylimidazolium-based room-temperature ionic liquids (RTILs) was studied over the temperature range (248 to 468) K. The uncertainty in κ was estimated to be less than 0.5 %. The conductivity values obtained are well-described by the Vogel−Fulcher−Tammann equation. Additionally, densities (ρ) and the corresponding molar conductivities (Λ) are reported for the temperature range (278 to 338) K. The data for Λ and the associated viscosities (η) were found to fit fractional forms of the Walden relationship.

The formation of microemulsions with triglycerides under ambient conditions has been a challenge for scientists for many decades. For this reason, so-called extended surfactants were developed that contained hydrophilic/lipophilic linkers to stretch further into the oil and water phase, and enhance the solubility of triglycerides in water. Currently, only limited information about the properties of these surfactants and its behavior in water is available. Therefore, in this work, mixtures of a chosen extended surfactant (C(12-14)-PO(16)-EO(2)-SO(4)Na, X-AES) with H(2)O/D(2)O over the whole concentration range were studied by optical microscopy. A schematic phase diagram has been obtained, which shows two isotropic liquid phases at the lowest and highest surfactant concentrations. Furthermore, between the isotropic solutions, four liquid-crystalline phases occur: a hexagonal phase (H(1)), a lamellar phase (L(alpha)) with a change in birefringence, a bicontinuous cubic phase (V(2)), and a reverse hexagonal phase (H(2)). The structure of the micellar solution (L(1)) was determined by cryo-TEM, dynamic light scattering, and (1)H NMR, which gave information about the size, the aggregation number, and the area per molecule of the micelles. Liquid-crystal formation occurs from the micellar solution in two different ways. The first route appeared by increasing the temperature, going from an L(1) to an L(alpha) phase. By increasing the surfactant concentration (at low temperatures), a second route showed a transition from L(1) to H(1). In addition, the effect of sodium chloride on the cloud point of the extended surfactant was examined, indicating that small amounts of NaCl have no influence on the phase behavior. The monolayer behavior of the extended surfactant at the air-water interface was also determined. Despite its water solubility, an isotherm on the water subphase was found, showing slow kinetics of the molecules to go into the bulk. Thus, the determination of the cmc of the extended surfactant using conventional methods was found to be impossible.

Data for the conductivity (κ) of the ionic liquids [emim][BF4], [bmim][BF4], [hmim][BF4], and [omim][BF4] from (−35 to 195) °C are reported. The data can be well-fit with the Vogel−Fulcher−Tammann ...

Hollow silica microspheres were produced by coating yeast cells with amorphous SiO2. In the precipitation reaction, yeast cells of Saccharomyces cerevisiae were used as a biological template. The silica shell was synthesized by the hydrolysis of tetraethylorthosilicate (TEOS) in water−alcohol mixtures as solvent using ammonia as a catalyst according to the Stoeber process. The hollow microspheres were characterized by means of scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Both smooth and textured coatings were prepared. The biological template can be removed by calcining, after which the particle morphology persists. Additionally, density and light scattering coefficients of the pigment were measured.

31P NMR difference spectra of sodium caseinate sols with and without silicate ions provide direct evidence of interactions between silicate ions and casein serine phosphate groups. The addition of Ca2+ to sodium caseinate solution without silicate ions and, subsequently, the diffusion of atmospheric CO2 to the resulting mixture do not lead to CaCO3 mineralization, whereas comparable experiments in the presence of silicate ions induce the precipitation of hemispherical three-component microstructures composed of silica, casein, and calcium carbonate. Apparently, the silicate−protein interaction plays a role as promoter for calcium carbonate mineralization in aqueous sols. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses reveal that vaterite is the crystalline phase of the composites. The observed materials are flat on one side and curved outward on the other side. In time, the flat surface cracks to display a star-like shape. Occasionally, in the center of the crack, layer-by-layer sp...

Catanionic microemulsions formed by dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfate (SDS), n-hexanol, dodecane, and citrate buffer have been characterized by using dynamic light scattering (DLS) and spectroscopic studies. While the DLS measurements provide information about the hydrodynamic diameters of the microemulsion droplets formed upon variation of the constituents, steady-state and time-resolved fluorescence emission experiments probe the polarity and the dynamics of the trapped solvent pool inside of the microemulsion droplets of nanometer dimension. In addition, time-resolved fluorescence anisotropy shows the rigidity of the confined solvent pool as well as the coupling between the motion of a solute and those of the solvent molecules. The results obtained from the DLS and those from the steady-state and time-resolved fluorescence emission studies have been found to correlate well with the superactivity of horseradish peroxidase enzyme in the catanionic microemulsions. Subsequently, the time-zero estimate for the dynamic Stokes shift in these microemulsions reveals that approximately 50% of the total solvent dynamical response is missed due to the limited time resolution employed in our experiments. The amplitude of the missing portion is similar to what has been observed recently for nanoscopic water by Fayer and co-workers (Piletic, I. R.; Tan, H.-S.; Fayer, M. D. J. Phys. Chem. B 2005, 109, 21273).

We consider within a modified Poisson-Boltzmann theory an electrolyte, with different mixtures of NaCl and NaI, near uncharged and charged solid hydrophobic surfaces. The parametrized potentials of mean force acting on Na+, Cl-, and I- near an uncharged self-assembled monolayer were deduced from molecular simulations with polarizable force fields. We study what happens when the surface presents negative charges. At moderately charged surfaces, we observe strong co-ion adsorption and clear specific ion effects at biological concentrations. At high surface charge densities, the co-ions are pushed away from the interface. We predict that Cl- ions can also be excluded from the surface by increasing the concentration of NaI. This ion competition effect (I- versus Cl-) may be relevant for ion-specific partitioning in multiphase systems where polarizable ions accumulate in phases with large surface areas.

Ion binding to a lipid membrane is studied by application of a rapid solution exchange on a solid supported membrane. The resulting charge displacement is analyzed in terms of the affinity of the applied ions to the lipid surface. We find that chaotropic anions and kosmotropic cations are attracted to the membrane independent of the membrane composition. In particular, the same behavior is found for lipid headgroups bearing no charge, like monoolein. This general trend is modulated by electrostatic interaction of the ions with the lipid headgroup charge. These results cannot be explained with the current models of specific ion interactions.

The properties of a series of aliphatic and aromatic carboxylates and phenolate-mimicking functional groups of humic acid are discussed with regard to their behavior in aqueous solutions close to the surface. Both surface tension measurements and MD simulations confirm that sodium formate behaves in accord with the classical theory of surfaces of electrolytes, whereas sodium acetate and, much more pronounced, sodium benzoate and sodium phenolate show a more hydrotropic behavior with surface active anions. Further to the surface tension data, the MD results suggest that these hydrotropes are highly oriented at the solution−vapor interface.

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured as functions of concentration (0.0145 ≤ m/mol·kg-1 ≤ 6.545) and temperature 273.15 ≤ T/K ≤ 323.15. The results are in reasonable agreement with literature data where comparisons are possible. The viscosity and electrical conductivity data are consistent with greater ion association in Mg(OAc)2 solutions.

Ionic hydration and association are included in the MSA-NRTL model for a description of the thermodynamic properties of aqueous ionic solutions. Hydration effects are introduced using the classic model of Robinson and Stokes, in which hydration numbers are independent of salt concentration. Association is accounted for through a mass action law. New compact conversion formulas are given expressing the individual ionic, and mean salt, activity coefficients at the Lewis−Randall level. The model is applied to the representation of strong and associating aqueous electrolytes at 25 °C. In the case of solutions of associating acids, its ability to also describe the speciation of the acid is examined.

The distribution of sodium, choline, sulfate, and chloride ions around two proteins, horseradish peroxidase (HRP) and bovine pancreatic trypsin inhibitor (BPTI), is investigated by means of molecular dynamics simulations with the aim to elucidate ion adsorption at the protein surface. Although the two proteins under investigation are very different from each other, the ion distributions around them are remarkably similar. Sulfate is always strongly attached to the proteins, choline shows a significant, but unspecific, propensity for the protein surfaces, and sodium ions have a weak surface affinity, while chloride has virtually no preference for the protein surface. In mixtures of all four ion species in protein solutions, the resulting distributions are almost a superposition of the distributions of sodium sulfate and choline chloride, except that sodium partially replaces choline close to the proteins. The present simulations support a picture of ions interacting with individual ionic and polar amino acid groups rather than with an averaged protein surface. The results thus show how subtle the so-called Hofmeister and electroselectivity effects are in salt solution of proteins, making all simplified interaction models questionable.

A dielectric relaxation study of binary mixtures of nonionic surfactant C12E5 + water has been made as a function of temperature in the isotropic micellar, lamellar, and hexagonal regions of the phase diagram. Two dielectric dispersion steps were found and could be assigned to the intermolecular cooperative dynamics of water at the micellar interface and in the bulk water domains. A quantitative analysis is given. The relaxation amplitudes were used to determine effective hydration numbers. The activation energies of water relaxation were calculated from the relaxation times. The data indicate weaker surfactant-water and water-water interactions near the micellar interface compared to those of bulk liquid water. Further analysis revealed the presence of water clusters large enough to show a cooperative relaxation mode even at high surfactant concentrations. However, the relaxation time of this mode is larger compared to that of pure water. This points out the importance of confinement effects on water dynamics.

The ultrasonic velocities, densities, viscosities, and electrical conductivities of aqueous solutions of magnesium nitrate and magnesium acetate have been measured from dilute to saturation concentrations at 0 < or = t/degrees C < or = 50. The temperature derivative of the isentropic compressibility, kappa(s), became zero at 2.28 and 2.90 mol kg(-1) for Mg(OAc)2 and Mg(NO3)2 solutions, respectively, at 25 degrees C. The total hydration numbers of the dissolved ions were estimated to be, respectively, 24.3 and 19.2 at these concentrations. Differences in kappa(s) for various M2+ salts, using the present and literature data, correlated with reported M2+-OH2 bond lengths and to a lesser extent with cationic charge densities (ionic radii). The influence of anions on kappa(s) appears to follow the Hofmeister series and also correlates approximately with the anionic charge density. Substantial differences between Mg(OAc)2(aq) and Mg(NO3)2(aq) occur with respect to their structural relaxation times (derived from compressibility and viscosity data) and their electrical conductivities. These differences were attributed to a much greater ion association in Mg(OAc)2 solutions. Raman spectra recorded at 28 degrees C confirmed the presence of various types of contact ion pairs including mono- and bidentate complexes in Mg(OAc)2(aq). In Mg(NO3)2(aq), only noncontact ion pairs appear to be formed even at high concentrations. The experimental results are supported by molecular dynamics simulations, which also reveal the much stronger tendency of OAc- compared to NO3- to associate with Mg2+ in aqueous solutions. The simulations also allow an evaluation of the ion-ion and ion-water radial distribution functions and cumulative sums and provide a molecular picture of ion hydration in Mg(OAc)2(aq) and Mg(NO3)2(aq) at varying concentrations.

A precise static method is used to measure vapor pressures of 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol from 298.15 up to the boiling points of these alcohols. The vapor pressure data are correlated with the Antoine and Wagner equations. From the measured vapor pressures, the enthalpies of vaporization are calculated. The results are compared with literature values.

A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBr, NaI, NaNO(3), NaClO(4), and NaSCN has been made over a wide range of frequencies (0.2or = nu/GHzor = 89) and solute concentrations (0.05or = c/Mor = 1.5) at 25 degrees C. The spectra could be adequately described by a single Cole-Cole (CC) process, symmetrically broadened relative to that of pure water. However, similar quality fits were also obtained with a three-Debye-process (3D) model consisting of a small ion-pair contribution at lower frequencies and two solvent relaxations at higher frequencies. Assuming the ions to be solvent separated, the 3D model provided estimates of their association constants and their rate constants for formation and dissociation. The bulk water relaxation times obtained from both models showed almost no dependence on the nature of the anion. Nevertheless, there were subtle differences in the concentration dependences of the relaxation times which correlated with some, but not all, of the anion properties that are believed to be relevant for explaining the anionic Hofmeister series.

Precise vapor-pressure data for solutions of lithium hydroxide in water from temperatures of 298.15−363.15 K have been measured by a procedure and equipment known to yield data of high precision. The investigated range of LiOH solution molality was from 0.07 to 4.77 mol·kg-1. The values of the osmotic coefficient have been calculated, taking into account the second virial coefficient in the equation for the water vapor pressure. Adjustable parameters of Pitzer's model with Archer's extension and of the mean spherical approximation of a nonrandom two-liquid model were evaluated. The new experimental data are compared to literature values, which exhibit a surprising scattering.

The surface tension of electrolyte solutions shows marked specific ion effects. We here show an important role for both ionic solvation energies and ionic dispersion potentials in determining this ion specific surface tension of salt solutions. The ion self-free energy changes when an ion moves from bulk solution into the interfacial region, with its decreasing water density profile. We will show that the solvation energies of different ions correlate very well with the surface tension of salt solutions. Inclusion of this distance-dependent self-free energy contribution brings qualitative agreement with experiments and the right Hofmeister series. This is so not only for surface tension changes but also for measured surface potentials. The inclusion of ionic dispersion interaction potentials further improves the agreement with experiments. We discuss how further progress in the theory of the surface tension of salts can be achieved.

Small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques have been used to study the structural properties of nonionic surfactant dodecyl-poly(ethylene oxide-23) ether (C12E23, commercial name Brij 35) in water and in various alcohols from ethanol to 1-decanol. All measurements were performed at 25 °C. SAXS experimental data were put on absolute scale using water as a secondary standard and evaluated using the generalized indirect Fourier transformation method (GIFT), which is based on the simultaneous determination of the intra- and interparticle scattering contributions. In this way, the size and shape of interacting scattering particles in real space could be deduced. In the Brij 35/water binary system (surfactant concentrations from 0.5 to 25 mass %) globular micelles with maximum dimensions ranging from 9 to 10.5 nm and radii of the hydrophobic core around 1.7 nm were found. At low surfactant concentrations the micelles were more or less spherical, whereas slight elongation o...

Precise complex permittivity spectra over the frequency range 0.15 GHz

An apparatus for the measurement of vapor pressures of pure solvents and solutions at different temperatures is described. The apparatus is tested for the temperature range (298.15 to 363.15) K using pure water and aqueous NaCl solutions. The vapor pressures are presented for methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol, ranging from temperatures 298.15 K up to the boiling points of these alcohols. The vapor-pressure data of pure alcohols are correlated with the Antoine equation. The results are compared with literature values.

Ternary systems of dodecyltrimethylammonium bromide (C12TAB)/1-hexanol/water are examd. for series with const. surfactant/alc. molar ratios of 8:2, 8:4, 8:6, and 8:8 at surfactant concns. of 6.167-61.67 g/L (0.02-0.20 mol/L). The methods used are cond. measurements, differential refractometry, static and dynamic light scattering, small-angle neutron scattering, and X-ray scattering. Crit. micelle concns. and the degree of dissocn. of the micelles are detd. by cond. measurements. The refractive index increment is given for each series as well as static and dynamic light-scattering intensities plotted as a function of the surfactant concn. From small-angle neutron-scattering expts. a detailed picture of the size and the geometry of the micelles could be obtained, whereas small-angle X-ray scattering allowed information about the thickness of the interfacial film to be inferred. A hypernetted chain calcn. with solvent plus ion-averaged screened Coulombic potentials combined with an ellipsoidal core/shell model permitted a simultaneous and coherent description of all scattering results.

A comparison is given between the osmotic coefficients inferred from direct vapor pressure lowering and from indirect vapor pressure osmometry, for three aqueous surfactant solutions at 25 °C. The results show that vapor pressure osmometry is a rapid but very reliable technique even at room temperature, in contrast to the indications of the manufacturer. Furthermore, the comparison of both techniques reveals that dissolved gas has no noticeable influence on the osmotic coefficients.

The mean spherical approximation is used to describe the vapor pressure over aqueous solutions containing an electrolyte and carbon dioxide. Three electrolytes have been studied: NaOH, NaCl, and acetic acid. A good representation is obtained with a reduced number of parameters as compared to previous models. These parameters account for the concentration and temperature dependence of the solute sizes and the relative permittivity of solution. The numerical values of these physically interpretable parameters are in a reasonable range.

A simple encapsulation technique is presented to produce highly phosphorescent, inert nanospheres that are suitable luminescent markers. It is based on the coprecipitation of phosphorescent ruthenium(II)-tris(polypyridyl) complexes and polyacrylonitrile (PAN) derivatives from a solution in N,N-dimethylformamide. The beads precipitate in the form of very small aggregates of spherical shape and a typical particle diameter of less than 50 nm. This process allows the encapsulation of phosphorescent and fluorescent dyes in an individual nanosphere provided that they are sufficiently lipophilic. Quenching by oxygen is negligible due to the use of PAN. The nanospheres were characterized with respect to their spectral properties (quantum yields of the luminophores, brightness, luminescence decay time), stability in aqueous buffered suspensions, and in terms of size, shape, and surface charge of the particles, as well as storage stability, quenching by oxygen, and dye leaching.

The complex dielectric permittivity spectra of octyl-, dodecyl-, and hexadecyltrimethylammonium bromide and of dodecyltrimethylammonium chloride reveal two low-frequency relaxation processes centered around 80 and 250 MHz. These are assigned to the diffusional relaxation of free and bound counterions, respectively, around the charged micelles. It is found that at low concencentrations the model of Grosse is able to rationalize simultaneously the amplitudes and relaxation times of both relaxation processes. The similar model of Pauly and Schwan, which is restricted to the relaxation of the bound counterions, fits the parameters of the 250 MHz process over the entire concentration range. Both models were used to determine the radius and surface conductivity of the micelles. Volume fractions determined from these radii are in good agreement with literature data and with values obtained from the analysis of the water relaxation processes. This shows that the complex permittivity spectra of theses solutions, d...

The ability of silica to influence the mineralization of alkaline-earth carbonates is an outstanding example for the formation of biomimetic structures in the absence of any organic matter. Under suitable conditions, silica-stabilized carbonate nanocrystals can spontaneously self-assemble into hierarchical materials with complex morphologies, commonly referred to as “silica biomorphs”. However, growth of these crystal aggregates has largely been restricted to the higher homologues in the alkaline-earth series, i.e., SrCO3 and BaCO3, while corresponding architectures of the much more relevant calcium carbonate are quite difficult to realize. To systematically address this problem, we have crystallized metal carbonates in the presence of silica at high pH, using barium and strontium chloride solutions that contained increasing molar fractions of Ca2+. The resulting materials were analyzed with respect to their composition, structure, and crystallography. The obtained data demonstrate that the growth process is already strongly affected by small amounts of calcium. Indeed, morphologies typically observed for SrCO3 and BaCO3 remained absent above certain thresholds of added Ca2+. Instead, globular and hemispherical structures were generated, owing to fractal branching of carbonate crystals as a consequence of poisoning by silica. These alterations in the growth behavior are ascribed to relatively strong interactions of hard calcium ions with silicate species in solution, shifting their speciation toward higher oligomers and even inducing partial coagulation. This notion is confirmed by additional experiments at increased ionic strength. Our results further demonstrate that the observed hemispherical particles exhibit distinct polymorphism, with orthorhombic solid solutions (aragonite-type (Sr,Ca)CO3 and (Ba,Ca)CO3) being formed at lower Ca2+ contents, whereas Sr2+/Ba2+-substituted calcite prevails at higher Ca2+ fractions. In the case of Ba2+/Ca2+ mixtures, there is moreover an intermediate range where virtually identical morphologies were confirmed to be Ba2+-doped vaterite. These findings extend the variety of structures and compositions accessible in these simple systems, and may explain difficulties previously encountered in attempts to prepare CaCO3 biomorphs at standard conditions.

We have used a static method to measure vapor pressures of propylene carbonate (C4H6O3) and N,N-dimethylacetamide (C4H9NO). Measurements for propylene carbonate were made over the temperature range from (298.15 to 473.15) K; pressures ranged from (0.003 to 37.76) kPa. Measurements for N,N-dimethylacetamide were made over the temperature range (298.15 to 423.15) K; pressures ranged from (0.29 to 64.8) kPa. The vapor pressure data are correlated with the Antoine and Wagner equations. From the measured vapor pressures, the enthalpies of vaporization are calculated. The results are compared with literature values.

The authors discuss the theory of electrolytic conductance in weak electrolytes using the concept of ionic assocn. for non-ideal electrolytes within the mean spherical approxn. (MSA). The chem. model approach is tested for solns. of MgSO4 in water and LiBr in acetonitrile.

Cryptates present a quasi-spherical symmetry and a practically const. size for a charge varying from 0 (unchanged empty cryptand) to 1 or 2 (cryptand contg. a monovalent or divalent cation). They are therefore sensible models of heavy and large particles undergoing Brownian motion (brownons). Their transport properties in aq. solns., electrophoretic mobilities, and self-diffusion coeffs. are in good agreement with this Brownian dynamical model.

The elec. conductance of ionic solns. is studied within the context of Fuoss-Onsager theory using equil. pair correlation functions from the hypernetted chain equation and the mean spherical approxn. Simple anal. expressions are obtained using the mean spherical approxn. for the equil. pair correlation function. The agreement with exptl. data of NaCl, KBr, BaCl2, and LaCl3 is found to be very good, considering that there are no adjustable parameters.

Values of osmotic and activity coeffs. are given for n-tetrapentylammonium bromide solns. in 2-propanol at 25 °C. These values were inferred from vapor pressure measurements. Small-angle neutron scattering expts. were also carried out for the same systems. The agreement between the osmotic coeffs. and the coherent solute scattering intensities at scattering angle zero is found to be satisfactory within the exptl. error. All these data are simultaneously described by means of HNC calcns. using empirical solvent-averaged potentials.

NMR measurements of the spin-lattice relaxation rates of the 'H, 13C, and 14N nuclei and spin-echo self-diffusion coefficients are reported for tetrapentylammonium bromide in acetonitrile solutions Over a wide range of temperatures and concentrations. The results are discussed in terms of overall and segmental motions of the aliphatic chains of the organic ions. Order parameters characterizing the geometrical constraints upon local segmental motions are given also. Cationic self-diffusion coefficients are found to differ from those obtained with quasi-elastic neutron scattering techniques (QENS). The difference may be explained in terms of fast and slow modes contributing to the diffusion processes and their selective detection with QENS and NMR techniques.