Constant Salt Concentration Research Articles

Solid polymer electrolytes based on alternating copolymers of vinyl ethers with methoxy oligo(ethyleneoxy)ethyl groups and vinylene carbonate

Alternating copolymers (poly(1a-g-alt-VC)) of vinyl ethers with various methoxy oligo(ethyleneoxy)ethyl groups and vinylene carbonate (VC) were prepared, and the thermal and electrochemical properties of their polymer electrolytes with LiTFSI and interfacial stability between the polymer electrolyte and Li metal electrode were investigated. Tg's increased linearly with salt contents, and decreased with an increase in the chain length of methoxy oligo(ethyleneoxy)ethyl groups in the vinyl ethers at constant salt concentration. The slopes of Tg vs. [Li]/[O] were identical, independent of the polymer structure. The ionic conductivities of the polymer electrolytes increased with increasing the side-chain ethyleneoxy (EO) unit length of the vinyl ether unit in the alternating copolymers, and also their temperature dependences became relatively smaller in the polymer electrolytes having longer EO units in the vinyl ethers. The highest ionic conductivity, 1.2×10−4S/cm at 30°C, was obtained in the alternating copolymer with a side-chain EO unit length of 23.5 in the vinyl ether unit. Ion transport coupled with the segmental motion of the polymer is dominant in these polymer electrolytes. Interfacial resistance increased gradually with contact time, indicative of the formation of passivation films on the Li metal electrode. These polymer electrolytes are thermally stable and have large electrochemical windows of use.

Contrasting the Effects of Hydrophobicity and Counterion Size on Anionic Wormlike Micelle Growth

AbstractRheological measurements were performed to understand the effect of benzyltrimethyl ammonium bromide (BTAB) and NaBr on the growth of wormlike micelles formed by sodium oleate (NaOA). Both salts can make the micellar solution viscoelastic, and the rheological responses verify the formation of wormlike micelles. The viscoelastic solution follows the Maxwell model of a single stress relaxation mode in the low‐frequency region. In comparison, the BTAB system exhibits stronger viscoelasticity than the NaBr system at constant salt concentration, but the critical overlapping concentration shows no significant difference; less BTAB can induce the solution to be more viscous than NaBr, but the viscosity maximum of the BTAB system is remarkably lower than that of NaBr at fixed NaOA content. The puzzling result is attributed to the effect of the composition on the packing parameter. In addition, it is shown that the zero‐shear viscosity of the two salt systems decreases upon heating, following the Arrhenius mode well.

Ion concentration polarization near microchannel–nanochannel interfaces: Effect of pH value

This study investigates the effect of the pH value on the ion concentration polarization phenomenon and the nonlinear current-voltage characteristics of a hybrid soda-lime glass micro/nanochannel for a constant KCl salt concentration of about 1 mM. The experimental results show that the electrical conductance of the nanochannel in the Ohmic regime and the critical threshold voltage of the limiting current are both dependent on the pH value of the salt solution when the electrical double layer thickness is considerable in the nanochannel. Specifically, the nanochannel conductance increases and the critical threshold voltage for the limiting current decreases as the pH value is increased. It also suggests that a higher pH value induces a higher surface charge density on the nanochannel walls, and therefore increases both the ionic conductance and the counter-ion flux within the nanochannel.

Energy consumption and constant current operation in membrane capacitive deionization

Membrane capacitive deionization (MCDI) is a water desalination technology based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports the water to be desalinated. In the salt removal step, ions are adsorbed at the carbon–water interface within the micropores inside the porous electrodes. After the electrodes reach a certain adsorption capacity, the cell voltage is reduced or even reversed, which leads to ion release from the electrodes and a concentrated salt solution in the spacer channel, which is flushed out, after which the cycle can start over again. Ion-exchange membranes are positioned in front of each porous electrode, which has the advantage of preventing the co-ions from leaving the electrode region during ion adsorption, while also allowing for ion desorption at reversed voltage. Both effects significantly increase the salt removal capacity of the system per cycle. The classical operational mode of MCDI at a constant cell voltage results in an effluent stream of desalinated water of which the salt concentration varies with time. In this paper, we propose a different operational mode for MCDI, whereby desalination is driven by a constant electrical current, which leads to a constant salt concentration in the desalinated stream over long periods of time. Furthermore, we show how the salt concentration of the desalinated stream can be accurately adjusted to a certain setpoint, by either varying the electrical current level and/or the water flow rate. Finally, we present an extensive dataset for the energy requirements of MCDI, both for operation at constant voltage and at constant current, and in both cases also for the related technology in which membranes are not included (CDI). We find consistently that in MCDI the energy consumption per mole of salt removed is lower than that in CDI. Within the range 10–200 mM ionic strength of the water to be treated, we find for MCDI a constant energy consumption of ∼22 kT per ion removed. Results in this work are an essential tool to evaluate the economic viability of MCDI for the treatment of saltwater.

Wormlike Micelles Formed by Sodium Erucate in the Presence of a Tetraalkylammonium Hydrotrope

Anionic wormlike micelles, particularly those formed by long-chain carboxylate surfactants, are relatively less documented though their cationic or zwitterionic counterparts are frequently reported. In this study, the wormlike micelles of sodium erucate (NaOEr), a C22-tailed anionic surfactant with a monounsaturated tail, in the presence of a tetraalkylammonium hydrotrope were investigated for the first time. The different effects of two hydrotropes, benzyl trimethyl ammonium bromide (BTAB) and tetramethyl ammonium bromide (TMAB), on the phase behavior and rheological behaviors were compared, and the influences of surfactant concentration and temperature on the rheological properties of NaOEr solutions were also examined. Both organic salts can lower the Krafft temperature of NaOEr solutions and thus improve its water solubility, but BTAB can make T(K) drop more sharply. At a fixed NaOEr concentration, less BTAB is demanded to induce the formation of viscoelastic solution and to obtain the maximum viscosity of NaOEr solution; at a constant salt concentration, with increasing NaOEr content, the NaOEr-BTAB system shows a larger zero-shear viscosity (η(0)), relaxation time, and plateau modulus but lower overlapping concentration than those of the NaOEr-TMAB system. The occurrence of maximum η(0) with increasing salt content for the NaOEr-BTAB system results from the formation of vesicles and L(3) phases, which were verified by cryo-TEM observations. η(0) shows an exponential decrease with increasing temperature; nevertheless it still remains above 10(3) mPa·s even at 90 °C.

Optimization of ramified absorber networks doing desalination

An iterated function system is used to generate fractal-like ramified graph networks of absorbers, which are optimized for desalination performance. The diffusion equation is solved for the boundary case of constant pressure difference at the absorbers and a constant ambient salt concentration far from the absorbers, while constraining both the total length of the network and the total area of the absorbers to be constant as functions of generation G. A linearized form of the solution was put in dimensionless form which depends only on a dimensionless membrane resistance, a dimensionless inverse svelteness ratio, and G. For each of the first nine generations G=2,…,10, the optimal graph shapes were obtained. Total water production rate increases parabolically as a function of generation, with a maximum at G=7. Total water production rate is shown to be approximately linearly related to the power consumed, for a fixed generation. Branching ratios which are optimal for desalination asymptote decreasingly to r=0.510 for large G, while branching angles which are optimal for desalination asymptote decreasingly to 1.17 radians. Asymmetric graphs were found to be less efficient for desalination than symmetric graphs. The geometry which is optimal for desalination does not depend strongly on the dimensionless parameters, but the optimal water production does. The optimal generation was found to increase with the inverse svelteness ratio.

Influence of isomerism of the ligand on the enthalpies of formation of copper tetrapyridylporphine

The enthalpy of dissolution of the tetrapyridylporphine isomers in water and in aqueous solutions of magnesium and copper acetates at a constant salt concentration (∼7 mmol/l) were observed for the first time by the calorimetric method with spectrophotometric monitoring. A substantial influence of the electronic effects of the tetrapyridyl fragment with different (para, meta, and ortho) positions of the heteroatom on the enthalpies of coordination of the ligands by the Cu2+ ions was revealed.

Effects of thermal heterogeneity in hydrophobic interaction chromatography

Manipulating temperature and salt concentration can have a powerful effect on the separation effectiveness in hydrophobic interaction chromatography (HIC). However, use of temperature as an operating variable in large-scale applications may involve undesirable consequences such as radial heterogeneity of the column temperature. In this study non-ideal effects of heat transfer in HIC columns were analyzed. The radial temperature gradients were measured by thermocouples immersed in a bed packed into a preparative column. The column wall was either thermostatted by a water jacket or left under ambient conditions. The influence of ineffective column thermostatting and of heat losses on the radial temperature profiles was demonstrated and predicted by a model of heat dispersion in a packed bed. To analyze possible positive or negative effects of thermal heterogeneity on band propagation, non-isothermal chromatographic elution of a model protein (α-chymotrypsinogen A) was recorded under salt gradient conditions as well as at constant salt concentration. To predict temperature and concentration profiles a model of the column dynamics was used. The model accounted for kinetics of mass and heat transfer. A good agreement between experimental and simulated profiles was achieved. It was shown that by proper selection of the process conditions undesirable temperature effects can be avoided or controlled.

Influence of biomass and gold salt concentration on nanoparticle synthesis by the tropical marine yeast Yarrowia lipolytica NCIM 3589

Cell-associated gold nanoparticles and nanoplates were produced when varying number of Yarrowia lipolytica cells were incubated with different concentrations of chloroauric acid (HAuCl 4) at pH 4.5. With 10 9 cells ml −1 and 0.5 or 1.0 mM of the gold salt, the reaction mixtures developed a purple or golden red colour, respectively, and gold nanoparticles were synthesized. Nanoparticles of varying sizes were produced when 10 10 cells ml −1 were incubated with 0.5, 1.0 or 2.0 mM chloroauric acid salt. With 3.0, 4.0 or 5.0 mM HAuCl 4, nanoplates were also observed. With 10 11 cells ml −1 nanoparticles were synthesized with almost all the gold salt concentrations. The cell-associated particles were released outside when nanoparticle-loaded cells were incubated at low temperature (20 °C) for 48 h. With increasing salt concentrations and a fixed number of cells, the size of the nanoparticles progressively increased. On the other hand, with increasing cell numbers and a constant gold salt concentration, the size of nanoparticles decreased. These results indicate that by varying the number of cells and the gold salt concentration, a variety of nanoparticles and nanoplates can be synthesized. Fourier transform infrared (FTIR) spectroscopy revealed the possible involvement of carboxyl, hydroxyl and amide groups on the cell surfaces in nanoparticle synthesis.

Distinct mechanisms of particle aggregation induced by alum and PACl: Floc structure and DLVO evaluation

Interactions of silica microspheres were examined by light scattering in presence of alum and polyaluminum chloride (PACl) with various OH/Al ratios. The coagulation behaviors were investigated using different coagulant dosages at constant pH (6.5) and salt concentration (0.01 mol/L). Based on the measurement of size distribution and zeta potential, charge neutralization was proposed to be the primary coagulation step for all the coagulants while other distinct coagulation steps were also involved depending on in situ formed or preformed hydrolyzing products. Precipitate coverage and sweep flocculation were induced for alum, contrasted to polycation patch and bridge aggregation for PACl. Based on simplified DLVO theory, particle aggregation was explained in terms of interaction forces. It was demonstrated that PACl outperformed alum in particle agglomeration at lower concentration (1–2 μmol/L), owing mainly to the considerable energy barrier reduction and deeper secondary minimum at longer distance induced by high positive polycations. The role of secondary minimum was found to be significant when secondary depth exceeded 12 kT. The interaction energy calculations coincided well with coagulation result for PACl, especially PACl22 with high content Al 13. However, other interaction forces prevailed over the electrical repulsion for alum and PACl containing other aluminum species.

Water, salt, and ethanol diffusion through membranes for water recovery by forward (direct) osmosis processes

Measurements of the diffusive permeances of water, NaCl, and ethanol through several, unoptimized membranes are presented. Such data can facilitate analysis and development of water recovery from highly impaired sources using hybrid processes based on forward (direct) osmosis (FO) with aqueous ethanol solutions as the “osmotic” agent. The membranes we have studied include anion and cation exchange materials and cross-linked poly(vinylalcohol) (PVA) gels, the latter being a membrane chemistry commercially used for ethanol dehydration via pervaporation. The measured transport properties are reported and suitability of these materials for an FO-based water recovery process is discussed in the context of process simulations. A major economic consideration for most FO processes is the cost of the lost “osmotic” agent. Thus, we focus our evaluations around the relative selectivity of the membranes for water versus ethanol, α w/E. We made measurements using initial NaCl concentrations of 3.5–9.5 mass% with constant ethanol mole fraction ( x EtOH = 0.2) in the draw solution. We also varied ethanol mole fraction with a constant initial salt concentration (3.5 mass%). The water/ethanol selectivity of all the membranes showed variability with these changing solution conditions. The average α w/E in PVA, and Selemion AMV and CMV (anion and cation exchange membranes, respectively), over the range of salt concentrations, were ∼7, 11, and 34, respectively. However, all the membranes exhibited a high degree of variability with respect to the changing boundary conditions (interfacial compositions) over the course of these measurements, likely due to differential swelling. We concluded that selectivities reported for pervaporation-based separations do not necessarily translate to dialysis-based ones, and that significantly higher selectivities than we obtained are likely required for commercially viable processes.

Preparation and characterization of PLGA particles for subcutaneous controlled drug release by membrane emulsification

Uniformly sized microparticles of poly( d,l-lactic- co-glycolic) (PLGA) acid, with controllable median diameters within the size range 40–140 μm, were successfully prepared by membrane emulsification of an oil phase injected into an aqueous phase, followed by solvent removal. Initially, simple particles were produced as an oil in water emulsion, where dichloromethane (DCM) and PLGA were the oil phase and water with stabiliser was the continuous phase. The oil was injected into the aqueous phase through an array type microporous membrane, which has very regular pores equally spaced apart, and two different pore sizes were used: 20 and 40 μm in diameter. Shear was provided at the membrane surface, causing the drops to detach, by a simple paddle stirrer rotating above the membrane. Further tests involved the production of a primary water in oil emulsion, using a mechanical homogeniser, which was then subsequently injected into a water phase through the microporous membrane to form a water in oil in water emulsion. These tests used a water-soluble model drug (blue dextran) and encapsulation efficiencies of up to 100% were obtained for concentrations of 15% PLGA dissolved in the DCM and injected through a 40 μm membrane. Solidification of the PLGA particles was followed by removal of the DCM through the surrounding aqueous continuous phase. Different PLGA concentrations, particle size and osmotic pressures were considered in order to find their effect on encapsulation efficiency. Osmotic pressure was varied by changing the salt concentration in the external aqueous phase whilst maintaining a constant internal aqueous phase salt concentration. Osmotic pressure was found to be a significant factor on the resulting particle structure, for the tests conducted at lower PLGA concentrations (10% and 5% PLGA). The PLGA concentration and particle size distribution influence the time to complete the solidification stage and a slow solidification, formed by stirring gently overnight, provided the most monosized particles and highest encapsulation efficiency.

Electrochemical and Mechanical Behavior in Mechanically Robust Solid Polymer Electrolytes for Use in Multifunctional Structural Batteries

Polymer electrolytes were investigated for potential use in multifunctional structural batteries requiring both mechanical and electrochemical properties. Electrolytes were formulated with a broad range of multifunctional behaviors, spanning continuously from highly conductive and structurally weak materials to poorly conductive and highly structural materials. Solvent-free polymer scaffolds were synthesized from monomers containing poly(ethylene glycol) (PEG) oligomers and one to four vinyl ester groups. The electrolytes were formed by dissolving lithium trifluoromethanesulfonate in the monomers prior to thermal cure. Electrochemical, mechanical, and viscoelastic properties were studied with respect to salt concentration, polymer chemistry, and polymer architecture. The addition of salt was found to have minimal impact on compressive stiffness, whereas it increased Tg and significantly influenced ion conductivity, with a maximum conductivity at 9−12% salt w/w PEG. At a constant salt concentration, the homopolymer electrolytes exhibited close to a 1:1 inverse correlation between conductivity and stiffness as monomer composition was changed.

Potable water production from seawater by the reverse osmosis technique in Libya

Tajura seawater desalination plant is the largest operating reverse osmosis plant in Libya with capacity of 10,000 m 3/d. It was commissioned in March 1984 with only 50% of its production capacity. It utilized a double pass of spiral-wound polyamide membranes. The first pass utilized polyamide membranes to desalt seawater and the second pass was used further to desalt the product of the first stage for industrial utilization. The plant used the twostage process of desalination in the period between 1984 and 1999. From 1999 up to date the membranes utilized were directly converting seawater to potable water with conductivity in the range of 500 micro Siemens. The second pass was kept to be utilized in cases when high purity water was needed. This paper summarized the plant design, performance, operation and maintenance experience and non-continuous operation effect on the plant network and membrane modules. It also presents the chemical consumption. During the last twenty years of the plant operation, there were enough operational data that affected the quality of produced water. The data has shown that, at constant seawater feed pressure and salt concentration, the produced water quantity and salt concentration increase with increasing feed water temperature. At constant seawater feed temperature and concentration, the produced water quantity increases with increasing feed pressure. As the operation time elapsed, the seawater feed pressure must be increased in order to maintain the designed water production through the membranes. Noncontinuous plant operation increased differential pressure and salt passage and decreased water production through the membranes. Also, due to the membrane reservation by chemical solutions during the plant shut offs, the membrane salt rejection was decreased. Water stagnation resulted in heavy corrosion and failure in the plant piping network during plant shut offs. This caused maintenance of concentrate pipes, valves and pumps more frequent than that if the plant was in continuous operation. Operating the reverse osmosis desalination plant at only small percent of its design capacity also increases the produced water price several times, the price that would have been if the plant was operated at full design capacity. In spite of the adverse operational conditions of the plant regarding operation and shut offs time, the plant has proven its reliability in terms of meeting membrane life time expectancy, mechanical equipment, instrumentation and control system.

Ion Specificity and Ionic Strength Dependence of the Osmoregulatory ABC Transporter OpuA

The ATPase subunit of the osmoregulatory ATP-binding cassette transporter OpuA from Lactococcus lactis has a C-terminal extension, the tandem cystathionine beta-synthase (CBS) domain, which constitutes the sensor that allows the transporter to sense and respond to osmotic stress (Biemans-Oldehinkel, E., Mahmood, N. A. B. N., and Poolman, B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 10624-10629). C-terminal of the tandem CBS domain is an 18-residue anionic tail (DIPDEDEVEEIEKEEENK). To investigate the ion specificity of the full transporter, we probed the activity of inside-out reconstituted wild-type OpuA and the anionic tail deletion mutant OpuADelta12; these molecules have the tandem CBS domains facing the external medium. At a mole fraction of 40% of anionic lipids in the membrane, the threshold ionic strength for activation of OpuA was approximately 0.15, irrespective of the electrolyte composition of the medium. At equivalent concentrations, bivalent cations (Mg(2+) and Ba(2+)) were more effective in activating OpuA than NH(4)(+), K(+), Na(+), or Li(+), consistent with an ionic strength-based sensing mechanism. Surprisingly, Rb(+) and Cs(+) were potent inhibitors of wild-type OpuA, and 0.1 mM RbCl was sufficient to completely inhibit the transporter even in the presence of 0.2 M KCl. Rb(+) and Cs(+) were no longer inhibitory in OpuADelta12, indicating that the anionic C-terminal tail participates in the formation of a binding site for large alkali metal ions. Compared with OpuADelta12, wild-type OpuA required substantially less potassium ions (the dominant ion under physiological conditions) for activation. Our data lend new support for the contention that the CBS module in OpuA constitutes the ionic strength sensor whose activity is modulated by the C-terminal anionic tail.

A comparative study on the phase behaviour of highly charged colloidal spheres in aconfining wedge geometry

We studied the structures formed in aqueous dispersions ofcharged colloidal spheres under a constant low salt concentration ofc = 6 × 10−6 mol l−1. Particlesof diameter 2a = 1000 nm were confined to a low angle wedge geometry with plate separation0<S<50 µm and observed with video microscopy. Irrespective of the initial particle densityn we reproducibly observe the particles to migrate to the narrow wedge side on thetimescale of a few days. Thereby an interface between a crystalline structure anda near particle free region is formed, which propagates slowly until the diluteregion is exhausted of particles. While the origin of this separation is still unclear,the final extension of the crystalline region is stable on the timescale of months.Within the crystal phase we observe a characteristic sequence of structures withincreasing plate separation similar to that seen in previous experiments on hardsphere-like systems but here with non-touching particles. Moreover, we find thatmechanical equilibrium is a necessary prerequisite for observing the full richness ofdifferent phases. A detailed comparison to recent theoretical calculations for bilayerswas performed and semi-quantitative agreement with the predictions observed.

Effects of Temperature, Salt, and Deuterium Oxide on the Self-Aggregation of Alkylglycosides in Dilute Solution. 2. n-Tetradecyl-β-d-maltoside

The effects of salt, temperature, and deuterium oxide on the self-aggregation of n-tetradecyl-beta-d-maltoside (C(14)G(2)) in dilute solution have been investigated by static light scattering, dynamic light scattering (DLS), small-angle neutron scattering (SANS), tensiometry, and capillary viscometry. SANS data show that the micelles can be described as relatively flexible polymer-like micelles with an elliptical cross section, at least at temperatures between 35 and 50 degrees C. The micelles grow in one dimension with increasing temperature and concentration. DLS and viscometry data suggest that the micelle size reaches a maximum at 60-70 degrees C. Comparison of DLS data in D(2)O and H(2)O shows that the micelles are larger in the former case. The effect of salt on the micelle size was found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreases according to the sequence SO(4)(2)(-) > Cl(-) > NO(3)(-) > I(-) > SCN(-), where I(-) and SCN(-) act as salting-in anions. From tensiometric data, it can be concluded that the temperature effects on micelle morphology do not correlate directly with those on unimer solubility. Rather, the temperature effect on the hydrocarbon chain conformation seems to be decisive for the micelle morphology. At constant temperature, on the other hand, the effect of salt and deuterium isotope is attributable to changes in effective headgroup area, including intermolecular interactions and water of hydration.

The dependence of the interactions in foam films on surfactant concentration

The interaction free energy in foam films is investigated depending on surfactant concentration, to prove the differences between the adsorption density of the stabilizing surfactant at the film surfaces and the surface of the bulk phase of the film forming solution. A change of the adsorption density at the film surface compared to the surface of the bulk phase has been indicated by earlier measurements of the gas permeation through foam films. The film interaction free energy was determined from measurements of the contact angles between free foam films and the surrounding bulk phase meniscus. Also, the disjoining pressure isotherms of foam films were measured and used to estimate the film interaction free energy. The foam films were stabilized with the anionic surfactant sodium dodecyl sulphate (SDS). At the surface of Newton black films, the adsorption density is higher than at a normal surface. The disjoining pressure isotherms measured at constant salt concentration but at different surfactant concentrations, reflect the influence of the surfactant concentration on the total electrolyte concentration. The disjoining pressure is always larger than that predicted from the Derjaguin–Landau–Verwey–Overbeek theory (DLVO theory). The investigation of common black films gives some indication that the adsorption density at the common black film surfaces is smaller than at the normal solution surface. Deviations of the measured interaction free energy from the values expected from the DLVO theory found in our measurements as well as reported in the literature can be explained by this change of adsorption.

Numerical investigation of seawater intrusion at Gooburrum, Bundaberg, Queensland, Australia

Seawater intrusion in coastal agricultural areas due to groundwater abstraction is a major environmental problem along the northeastern coast of Australia. Management options are being explored using numerical modelling, however, questions remain concerning the appropriate level of sophistication in models, choice of seaward boundary conditions, and how to accommodate heterogeneity and data uncertainty. The choice of seaward boundary condition is important since it affects the amount of salt transported into the aquifers and forms the focus of the present study. The impact of this boundary condition is illustrated for the seawater-intrusion problem in the Gooburrum aquifers, which occur within Tertiary sedimentary strata. A two-dimensional variable-density groundwater and solute-transport model was constructed using the computer code 2DFEMFAT (Cheng et al. 1998). The code was tested against an experiment for a steady-state freshwater-saltwater interface and against the Elder (Elder 1967) free-convection problem. Numerical simulations show that the imposition of the commonly-used equivalent hydrostatic freshwater heads, combined with a constant salt concentration at the seaward boundary, results in overestimated seawater intrusion in the lower Gooburrum aquifer. Since the imposition of this boundary condition allows water flow across the boundary, which subsequently takes salt into the aquifer, a careful check is essential to estimate whether too much mass of salt is introduced.

Effects of Temperature, Salt, and Deuterium Oxide on the Self-Aggregation of Alkylglycosides in Dilute Solution. 1. n-Nonyl-β-d-glucoside

The influence of salt, temperature, and deuterium oxide on the self-aggregation of n-nonyl-beta-D-glucoside (beta-C9G1) in dilute solution has been investigated by static and dynamic light scattering, neutron scattering, and tensiometry. Scattering data show that the micelles can be described as relatively stiff, elongated structures with a circular cross section. With a decrease of temperature, the micelles grow in one dimension, which makes it surprising that the critical micelle concentration (cmc) shows a concomitant increase. On the other hand, substitution of D2O for H2O causes a large increase in micelle size at low temperatures, without any appreciable effect on cmc. With increasing temperature, the deuterium effect on the micelle size diminishes. The effects of salt on the micelle size and cmc were found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreased according to the sequence SO4(2-) > Cl- > Br- > NO3- > I- > SCN-, whereas the effect on cmc displays the opposite trend. Here, I- and SCN are salting-in anions. Similarly, the effects of cations decrease with increasing polarizability in the sequence Li+ > Na+ > K+ > Cs+. At high ionic strength, the systems separate into two micellar phases. The results imply that the size of beta-C9G1 micelles is extremely sensitive to changes in the headgroup size. More specifically, temperature and salt effects on effective headgroup size, including intermolecular interactions and water ofhydration, are suggested to be more decisive for the micelle morphology than the corresponding effects on unimer solubility.