Aqueous Sodium Salicylate Research Articles

Ternary diffusion in aqueous sodium salicylate + sodium dodecyl sulfate solutions

A Taylor dispersion method has been used to measure ternary mutual diffusion coefficients (D11, D22, D12 and D21) in aqueous sodium salicylate (NaSal) (component 1) + sodium dodecyl sulfate (NaDS) (component 2) solutions at 25.00 °C and concentrations up to 0.050 mol dm−3. In general, the data show that diffusion of NaDS drives co-current flow of NaSal, and that diffusion of NaSal drives also co-current flows of NaDS. The experimental ternary diffusion coefficients are compared with Nernst-Planck coefficients allowing a better interpretation of the electrostatic mechanism for the coupled diffusion of NaSal and SDS. From these equations, at compositions below the critical micelle concentration (cmc) of NaDS, small positive values of D12 and D21 are obtained resulting from fully dissociation of NaDS; however, at compositions above the cmc, the coupled diffusion of NaSal and NaDS becomes significant, as indicated by the experimental and predicted large positive cross-diffusion coefficients, D21. There is a good agreement between our data and those predicted by the Nernst-Planck equations for NaDS concentrations below and above the cmc.

Study to reconnoiter solvation consequences of l-arginine/l-histidine and sodium salicylate in aqueous environment probed by physicochemical approach in the temperature range (293.15–318.15) K

Abstract The densities, ρ, ultrasonic speeds, u and viscosities, η of l-arginine and l-histidine in aqueous-sodium salicylate (1% and 2% sodium salicylate in water, w/w) solvents were measured at temperatures (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K and at atmospheric pressure in seven different concentrations. The experimental density data have been used to calculate the apparent molar volume, Vϕ, limiting apparent molar volume, Vϕ° and transfer volume, Vϕ, tr°. Likewise from the ultrasonic speed data, different thermo-acoustical parameters, such as apparent molar compressibility, Ks,ϕ, limiting apparent molar compressibility, Ks, ϕ° and transfer compressibility, Ks, ϕ, tr° have been evaluated. The viscosity data have been used to determine Falkenhagen Coefficient, A, Jones-Dole coefficient, B, free energy of activation of viscous flow per mole of solvent, Δμ1°# and solute, Δμ2°#, entropies, ΔS°# and enthalpies, ΔH°# of activation of viscous flow. These parameters have been discussed in light of solute-solute and solute-solvent interactions prevailing in these solutions and their variations are revealed to get the basic picture of the molecular interactions occurring in the systems studied. The negative values of dB/dT favour structure making behavior of amino acids in aqueous solutions of sodium salicylate. The free energy parameters indicate the formation of transition state in the presence of amino acids.

Solid State Conductivity of Optimized Polypyrrole Coatings on Iron Obtained from Aqueous Sodium Salicylate Solution Determined by Impedance Spectroscopy

Solid State Conductivity of Optimized Polypyrrole Coatings on Iron Obtained from Aqueous Sodium Salicylate Solution Determined by Impedance Spectroscopy

Thermodynamic and NMR study of aggregation of dodecyltrimethylammonium chloride in aqueous sodium salicylate solution

The complex aggregation processes of dodecyltrimethylammonium chloride (DTAC) have been studied in dilute solutions of sodium salicylate (NaSal) by isothermal titration calorimetry and electrical conductivity at temperatures between 278.15 K and 318.15 K. A structural transformation that was dependent on the concentrations of DTAC and NaSal was observed. The micellization process in dilute solutions of DTAC has been subjected to a detailed thermodynamic analysis and shown to occur at considerably lower critical micelle concentrations than reported for DTAC in water and NaCl solutions. Gibbs free energy, ΔmicGo, and entropy, ΔmicSo, were deduced by taking into account the degree of micelle ionization, β, estimated from conductivity measurements. From the temperature dependence of the enthalpy of micellization, ΔmicHo, the heat capacities of micellization, \( {\Delta_{{{\rm mic} }}}c_p^o \) were determined and discussed in terms of the removal of large areas of non-polar surface from contact with water upon micellization. The process is exothermic at all temperatures, indicating, in addition to the hydrophobic effect, the presence of strong interactions between surfactant and salicylate ions. These were confirmed by 1H NMR spectroscopy and diffusion NMR experiments. Salicylate ions not only interact with the headgroups but also insert further into the micelle core. At cNaSal/cDTAC > 2.5, the structural rearrangements occur even at relatively low concentrations of NaSal.

Aggregation and adsorption behavior of cetylpyridinium chloride in aqueous sodium salicylate and sodium benzoate solutions

The critical micelle concentration (cmc) values of cetylpyridinium chloride (CPC) were determined in the presence of salicylate and benzoate ions in the less explored concentration region where viscosity is Newtonian. The cmc of CPC decreased from 9 × 10 −4 to 7 × 10 −7 and 3 × 10 −6 mol kg −1 by adding about 0.3 mol kg −1 of salicylate and benzoate, respectively. The ortho hydroxyl group in salicylate thus has a remarkable influence on the micellization of CPC and the extent of this favorable effect is found to be about 3.5 kJ mol −1. The Corrin–Harkins equation was modified to explain the variation of cmc with electrolyte concentration in the presence of mixed counterions. The slope of the equation does not provide the value of the total counterion binding constant ( β), but gives us information about the lower limit to the value of β, which is found to be 0.66. Addition of salicylate and benzoate increases the counterion binding to CPC micelles compared to that in the presence of chloride alone. An adsorption isotherm was derived to estimate the surface excess of CPC in the presence of mixed counterions.

Corrosion protection aspects of electrochemically synthesized poly( o-anisidine- co- o-toluidine) coatings on copper

The poly( o-anisidine- co- o-toluidine) coatings were synthesized on copper substrates by electrochemical copolymerization of o-anisidine with o-toluidine using sodium salicylate as supporting electrolyte. These coatings were characterized by cyclic voltammetry, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and scanning electron microscopy (SEM). The formation of the copolymer with the mixture of monomers in the aqueous sodium salicylate solution was ascertained by a critical comparison of the results obtained with the polymerization of the individual monomers, o-anisidine and o-toluidine, respectively. The corrosion protection aspects of poly( o-anisidine- co- o-toluidine) coatings to copper was investigated in aqueous 3% NaCl solution by potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results of the potentiodynamic polarization measurements and EIS studies showed that the poly( o-anisidine- co- o-toluidine) coatings provided the effective corrosion protection to copper than that of respective homopolymers. The corrosion rate is observed to depend on the feed ratio of o-toluidine used for the synthesis of the copolymer coatings.

Rheo-optics of Equilibrium Polymer Solutions: Wormlike Micelles in Elongational Flow in a Microfluidic Cross-Slot

The rheo-optical analysis of polymer solutions and melts is a critical tool in elucidating their molecular response to flow fields. We therefore evaluate the measurement of flow-induced birefringence (orientation) under extension in microfluidic cross-slots, whose flow kinematics was examined by microparticle image velocimetry. The effects of planar extension on the (non)linear viscoelasticity of wormlike micellar surfactant solutions (comprising either cetyltrimethylammonium bromide or cetylpyridinium chloride in aqueous sodium salicylate) were measured. The effect of wall shear was found to be negligible compared to extension. The birefringence is linear (indicating the validity of the stress−optical rule) for very small extensional Weissenberg numbers, as expected. This rule fails, however, when a sharp birefringence band appears at modest Weissenberg number (indicating the alignment of wormlike micelles along the outflow direction). Experiments that measure average birefringence may misidentify the point of failure of the stress−optical rule. These bands also scatter light and appear in transmittance images, yet with distinctive features. At higher flow rates, the birefringent band broadens after the peak retardation saturates, but the transmittance band remains narrow and eventually the flow becomes asymmetric. This asymmetric transition is elasticity-induced, and no shear banding is observed by particle velocimetry: the velocity profiles remain linear, while the flow becomes asymmetric. These phenomena are common to both fluids studied, but the stress−optical coefficient and the Weissenberg numbers at saturated birefringence differ quantitatively, possibly due to differences in micellar length and scission kinetics, as determined from linear viscoelastic measurements.

Shear-induced structure change and flow-instability in start-up Couette flow of aqueous, wormlike micelle solution

The occurrence of shear-induced structures (SIS) of a wormlike micellar solution is investigated using an aqueous solution of cethyltrimetylammonium bromide (CTAB)/aqueous sodium salicylate (NaSal) with composition CTAB (0.03mol∕L)∕NaSal (0.23mol∕L). A concentric cylinder Couette cell made of transparent glass is used to generate stepwise start-up shear flow. The shear stress and the brightness, which is an index of the transparency of the fliud, are measured simultaneously and the fluid motion is observed by adding tracer particles to the fluid. Measurements of flow birefringence and light intensity of a transmitted laser beam passing parallel to the vorticity axis are also carried out to monitor flow-induced microstructural changes. The transient behavior of the macroscopic properties, i.e., the shear stress and the brightness, are consistent with each other and with the optical microstructural measurements, confirming that the occurrence of the transparent-to-opaque change in the wormlike micelle solution is caused by a change in its structure. The transient behavior of SIS with the time is correlated to the shear strain and divided into four regions depending on the shear rate. At the highest shear-rate range, a strong instability occurs immediately following a maximum in the shear stress. Upon cessation of the shear stress, elastic recoil is observed along with a sudden recovery to the original transparent state of the solution.

NMR and neutron scattering studies on spherical and rod-like micelles of dodecyltrimethylammonium bromide in aqueous sodium salicylate solutions

The effect of sodium salicylate (NaSal) additives on micellar structure and dynamics in aqueous solution of dodecyltrimethylammonium bromide (DTAB) has been studied by means of 1H-NMR and quasielastic neutron scattering (QENS) measurements. The molar ratio R (= C NaSal/ C DTAB) dependence on the peak shape of the NMR spectra revealed that a sphere-to-rod-like micellar transition took place around R=0.5. The chemical shift for the 1H atoms of the alkyl group of DTA + ion gave the information for the binding site of Sal − ion in micelles. The R dependence on the chemical shift for the aromatic group of Sal − ion clarified the selective binding feature of Sal − ion in micelles. The dynamic structure factor, S( Q, E), of the micellar molecules exhibited apparent broadening of the elastic scattering peak which was fitted well to a single Lorentzian function. The self-diffusion coefficient D was obtained from the Q-dependence of the HWHM of the Lorentzian function. The slope of D vs. R curve changed around the transition ratio ( R=0.5), reflecting the dynamic slowing down of the local relaxational motion of the micellar molecules in rod-like micelles.

Hydrotropic agents for study of in vitro paclitaxel release from polymeric micelles

A new experimental method for in vitro release studies of poorly soluble drugs from polymeric micelle systems was developed using a hydrotropic agent, sodium salicylate. It is difficult to maintain a good sink condition for poorly water-soluble drugs, such as paclitaxel (PTX), because of their low aqueous solubility. In this study, a good sink condition for PTX was achieved by using aqueous sodium salicylate solution which solubilized more than 10 times the total amount of PTX incorporated in polymeric micelles. Sodium salicylate at 1 M concentration increased the aqueous PTX solubility by 100 times without destroying the micellar structure of poly(ethylene glycol)-block-poly(phenylalanine) (PEG-b-PPhe) copolymer. PTX was continuously released from PEG-b-PPhe micelles in the hydrotropic release medium. The hydrotropic solution presents a simple method for studying in vitro release behavior of poorly soluble drugs from polymeric micelles in aqueous media.

K-1222 マッハツェンダー干渉計を利用した流体の弾性力評価法の検討(S17-6 粘弾性流体の流れ計測)(S17 非ニュートン流体の複雑流路内の流れ)

Elasticity of viscoelastic fluids can be estimated from the anisotropy of refractive index by optical stress law. In the present study, we observed the anisotropy of refractive index in the elongational flow field of a two-dimensional channel, using Mach-Zhender interferometer. The displacement of interference fringe of this interferometer indicates variations of refracrtive index. The anisotropy of refractive index was not seen in the flow field of water. However, it was observed in the flow field of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal). CTAB-NaSal solution is known to have strong elasticity, and therefore it is thought Mach-Zhender interferometer is promising to estimate the elasticity of fluids.

Viscoelasticity of CTAB:NaSal/W detergent micelles. Salt and temperature effects

Dynamic viscoelasticity is measured for threadlike micelles from cetyltrimethyl‐ammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at temperatures T=25, 33, 40, and 50 °C. The CTAB concentration of the solutions is fixed at CD=0.01 M and a ratio of NaSal concentration CS to CD, CS/CD, is varied from 1 to 41. Effects of both CS/CD and T on frequency dependence of storage and loss shear moduli, G’(ω) and G‘(ω), are described in this paper in detail. Characteristic features of this micelle system may be summarized as (1) at 25 and 33 °C, the steady viscosity η and the mechanical relaxation time τM both show a minimum at CS/CD∼4 that is followed by a maximum at CS/CD∼10 as CS/CD increases. (2) The η and τM monotonically decrease with increasing T in the range of CS/CD from 1 to 20, but the maximum itself gradually disappears as T increases. (3) The steady state compliance Je is independent of T and decreases at lower CS/CD. A rapid increase in Je is observed at higher T and CS/CD ends. (4) An additional viscoelastic relaxation process is observed at the high frequency side. This mode appears in the same ω range independent of the salt concentration and exhibits the T dependence such as a type of the local friction factor, ηS/T. The discussion is mainly devoted to the applicability of a couple of models proposed so far.

Dynamic Light Scattering of CTAB/NaSal Threadlike Micelles in a Semidilute Regime. 3. Dynamic Coupling between Concentration Fluctuation and Stress

Dynamic light scattering measurements are made on viscoelastic networks formed by threadlike micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at three temperatures T of 25, 33, and 40 o C. Dynamic shear moduli of the same samples are also measured in the angular frequency range from 1×10 -2 to 1×10 2 rad s -1 at T=25, 33, 40, 50, and 60 o C. The surfactant concentration C D of the samples is fixed at 0.1 M and a ratio of the salt concentration C S to C D is varied from 0.8 to 6. The time correlation function A q (t) of light intensity scattered from the solutions with 0.8≤C S /C D ≤4 exhibits the bimodal distribution of the decay rate Γ. The fast and the slowly decaying components are assigned as the diffusive gel mode and the relaxation mode, respectively, from the scattering vector dependences of the first cumulant Γ i (i=f, s) estimated from respective time profiles of the decay curves at short and long times. The dynamical correlation length ξ H calculated from D c =Γ f /q 2 is found to take a constant value of 10.5±1.5 nm irrespective of C S /C D and T for 1≤C S /C D ≤6. The characteristic relaxation time τ s (≡Γ s -1 ) for the slow mode agrees with the mechanical relaxation time τ M which is obtained by a fit of the dynamic shear modulus data of the same solutions to a Maxwell model with the single relaxation time τ M . The results demonstrate that concentration fluctuation in the micellar network decays by local cooperative diffusion of network strands at the short time as well as by the slow relaxation of elastic stress generated by the network deformation due to the mass flow

Dynamic light scattering of CTAB:NaSal threadlike micelles in the semidilute regime. II. effect of surfactant concentration

Dynamic light scattering measurements are made on networks formed by elongated threadlike micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at 25°C. The surfactant concentrationCD of the samples is varied from 0.006 to 0.3 M and the ratio of the salt concentrationCs toCD is fixed at unity. The time correlation functionAq (t) of light intensity scattered from the solutions exhibits transition from the unimodal to the bimodal distribution of the decay rate Γ at aroundCD=0.05 M. The dependence of the first cumulant Γe on the scattering vectorq for the samples withCD≦0.03 M is described by the dynamic scaling law. The cooperative diffusion coefficientDc is obtained from extrapolation of Γe/q2 for the samples withCD≦0.03 M and of Γf/q2 forCD≧0.05 M where Γf is the first cumulant from the fast mode. TheDc is found in proportion toCD0.45, being in agreement with the theoretical prediction for a rigid rod in the semidilute regime by the scaling law. The decay rate Γs characteristic of the slow mode is independent ofq, and Γs−1 roughly agrees with the mechanical relaxation time τ estimated from a fit of the dynamic viscoelastic data of the same samples by a Maxwell type of model with the single relaxation time τ.

Self diffusion and viscoelasticity of elongated micelles from cetyltrimethyl-ammonium bromide in aqueous sodium salicylate solution. II. Temperature effect

Forced Rayleigh scattering and dynamic viscoelastic experiments are performed to study slow global motions of networks formed by elongated micelles from cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions at six temperatureT from 25° to 60°C. The CTAB concentrationCD of the solutions is fixed atCD=0.01 M and a ratio of salt concentrationCs toCD is varied from 1 to 41. The self-diffusion coefficientD of the dye-labeled cetyldimethylamine incorporated in the micelles shows a complicatedCs/CD dependence with a maximum that is followed by a minimum at lower temperatures, but these two extremes gradually disappear with increasingT. TheCs/CD dependencies of both the steady-state viscosity η and the terminal relaxation time τ are found consistent with the diffusion behaviour. TheD of all solutions tested monotonically increases withT, but shows different functional dependence onT asCs/CD varies. The applicability of the theory of Brownian motion of a rigid rod in the semidilute regime is examined usingD and τ values.

Self diffusion and viscoelasticity of aqueous detergent solutions II. Effect of salt concentration (abstract)

Diffusion of rod‐like micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions were studied by varying CTAB concentration CD and NaSal concentration CS. For solutions with CD=0.01 and 0.1 M, a ratio CS/CD ranged from 1.0 to 41 and from 0.70 to 6.0, respectively. For measurement of the diffusion coefficient D, the forced Rayleigh scattering technique was employed at 25 °C. Plots of D against CS/CD gave very complicated behavior such that D took a maximum and afterward took a minimum with increasing CS/CD. CS/CD values of the maximum and minimum for solutions with CD=0.01 M was very different from that for CD=0.1 M. But the magnitude of D was of the same order of 10−9 cm2 s−1 for both solutions. Diffusion data could be reduced to one master curve by plotting D against the concentration CS* of free salicylate ion Sal− in the low CS* region. The CS* dependence of D at low CS* was found to roughly correspond to that of the relaxation time τ obtained in earlier investigations from a fit of the complex shear modulus data of the same solutions to a Maxwell model with one relaxation time. At high CS*, however, D appeared to increase more rapidly for solutions with CD=0.01 M than those with CD=0.1 M. The diffusion mechanism of rod‐like micelles was interpreted in terms of a theory of Brownian motion of a rod in the semidilute region at low CS* and the breaking and reforming process of network strands at high CS*.

Self Diffusion and Viscoelasticity of Aqueous Detergent Solutions II. Effect of Salt Concentration

Diffusion of rod-like micelles of cetyltrimethylammonium bromide (CTAB) in aqueous sodium salicylate (NaSal) solutions were studied by varying CTAB concentration CD and NaSal concentration CS. For solutions with CD=0.01 M and 0.1M, a ratio CS/CD ranged from 1.0 to 41 and from 0.70 to 6.0, respectively. For measurement of the diffusion coefficient D, the forced Rayleigh scattering technique was employed at 25°C.Plots of D against CS/CD gave very complicated behavior such that D took a maximum and afterward took a minimum with increasing CS/CD. CS/CD values of the maximum and minimum for solutions with CD=0.01 M was very different from that for CD=0.1 M. But the magnitude of D was of the same order of 10-9cm2s-1 for both solutions.Diffusion data could be reduced to one master curve by plotting D against the concentration CS* of free salicylate ion Sal- in the low CS* region. The CS* dependence of D at low CS* was found to roughly correspond to that of the relaxation time τ obtained in earlier investigations from a fit of the complex shear modulus data of the same solutions to a Maxwell model with one relaxation time. At high CS*, however, D appeared to increase more rapidly for solutions with CD=0.01 M than those with CD=0.1 M.The diffusion mechanism of rod-like micelles was interpreted in terms of a theory of Brownian motion of a rod in the semidilute region at low CS* and the breaking and reforming process of network strands at high CS*.

Fluorescence of aqueous sodium salicylate. Solutions under excitation by ionizing radiations

The equations derived in the expanding sphere model1 are applied to the experimental results on the fluorescence from aqueous salicylate solutions under X-irradiation. The results fit the theory well over a wide concentration range and their deviation from the behaviour of the same system under u.-v. irradiation agrees quantitatively with a mechanism involving the non-homogeneous quenching by radiation-induced radicals of solute molecules excited by the same ionizing radiations.

Laboratory studies on solvent extraction of low‐temperature tar oils by aqueous sodium salicylate

AbstractThe use of aqueous saturated sodium salicylate for the extraction of tar acids from a low‐temperature tar fraction is discussed. Solubility and equilibrium data for the system:neutral oil‐tar acids‐aqueous sodium salicylate when plotted on a ternary diagram showed two types of curves: an ordinary bite type and another a loop containing solid and liquid phases. The tie‐line data agree with most of the empirical relationships reported in the literature. The plait point for the system had a tar acid concentration of 47%. The results have been compared with the earlier data for the system: phenol‐α‐methylnaphthalene‐aqueous sodium salicylate.