Search results for "Concentration"
showing 10 items of 1906 documents
H and 19F NMR Investigation on Mixed Hydrocarbon−Fluorocarbon Micelles
2003
1H and 1 9 F NMR measurements on aqueous solutions of sodium perfluorooctanoate (SPFO) and sodium dodecanoate (SD) mixtures are reported. The surfactant concentration ranged from ∼0.3 to 10 times the critical micelle concentration (cmc ≅ 0.03 mol L - 1 ). The cmc of the SD/SPFO/water mixed system obtained from NMR data was in good agreement with that previously obtained by conductivity measurements. Below the cmc, the experimental chemical shift (δ) was independent of the total concentration for both surfactants. Above the cmc, however, the 6 values for 1 9 F varied linearly with concentration, whereas the values for the hydrogenated surfactant deviated from linearity. These observations in…
Partitioning of macrocyclic compounds in a cationic and an anionic micellar solution: a small-angle neutron scattering study.
2004
Following a previous investigation on partitioning of some macrocycle compounds in sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) aqueous solutions and their effect on the micellar structure, a small-angle neutron scattering (SANS) study has been performed at fixed surfactant content (0.20 mol/L) and varying macrocycle concentrations from 0.20 up to 1.0 mol/L. Conductivity measurements have been also performed in order to evaluate the effect of the presence of macrocycles on the critical micellar concentration (cmc) of the two surfactants. SANS experimental data were fitted successfully by means of a core-plus-shell monodisperse prolate ellipsoid model. It has been…
Calculation of the pH and the titratable acidity in clinically used infusion solutions.
2006
Clinically used infusion solutions are complex aqueous mixtures composed of a variety of different salts, acids, and non-electrolytes, and are characterized by composition, initial pH, and titratable acidity (TA). By rigorous treatment as a multi-composed acid-base system, pH and TA were calculated from proton dissociation equilibria, mass balance equations and electroneutrality condition. Nine were arbitrarily chosen as model solutions in which pH and TA were experimentally determined. From composition, and based on a set of apparent acidity constants (pK values) at 37 degrees C and total ionic strength 0.155 mol/l, pH was calculated by iteration. In the model solutions, measured pH was in…
Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N-isopropylacrylamide)
2003
The interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (M w = 1 600 kg/mol) poly(N-isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, T cp decreases steadily with rising polymer concentration up to 10 wt.-%. The application of shear supports phase separation and reduces T cp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected wit…
Adsorption of the anionic surfactant sodium dodecyl sulfate on a C18column under micellar and high submicellar conditions in reversed-phase liquid ch…
2015
Micellar liquid chromatography makes use of aqueous solutions or aqueous-organic solutions containing a surfactant, at a concentration above its critical micelle concentration. In the mobile phase, the surfactant monomers aggregate to form micelles, whereas on the surface of the nonpolar alkyl-bonded stationary phases they are significantly adsorbed. If the mobile phase contains a high concentration of organic solvent, micelles break down, and the amount of surfactant adsorbed on the stationary phase is reduced, giving rise to another chromatographic mode named high submicellar liquid chromatography. The presence of a thinner coating of surfactant enhances the selectivity and peak shape, es…
ZnO nanorod arrays fabrication via chemical bath deposition: Ligand concentration effect study
2010
A new ligand, N, N, N', N'-tetramethylethylenediamine, has been used to grow ZnO nanorods on silicon substrates via a two steps approach. A preliminary seeding on silicon substrates has been combined with chemical bath deposition using a Zinc acetate - N, N, N', N'-tetramethylethylenediamine aqueous solution. The used diamino ligand has been selected as Zn(2+) complexing agent and the related hydrolysis generates the reacting ions (Zn(2-) and OH(-)) responsible for the ZnO growth. The seed layer has been annealed at low temperature (<200 degrees C) and the ZnO nanorods have been grown on this ZnO amorphous layer. There is experimental evidence that the ligand concentration (ranging from 5 t…
A modelistic approach showing the importance of the stagnant aqueous layers in in vitro diffusion studies, and in vitro-in vivo correlations
1991
Abstract The present study deals with the role of the aqueous diffusion layers on the in vitro penetration of xenobiotics across artificial lipoidal membranes, and their ability to reproduce biophysical absorption models when in vivo results are to be simulated from the in vitro tests. The aqueous boundary layers which are invariably formed on artificial lipoidal membranes can be optionally preserved or disrupted, according to the type of absorption site which should be simulated, a condition which could reasonably lead to a better correspondence between in vitro and in vivo results; in practice, disruption of water layers can be easily achieved by a synthetic surfactant solution at its cri…
Calorimetric study of the solubilization of ethylenediamine, N,N-dimethylaminoethylamine and N,N,N?,N?-tetramethylethylenediamine by reversed AOT mic…
1993
Distribution constants and standard enthalpies of transfer of ethylenediamine (en), N,N-dimethylaminoethylamine (dmen) and N,N,N′,N′-tetramethylethylenediamine (tmen) partitioned between n-heptane and water containing reversed sodium bis(2-ethylhexyl) sulfosuccinate (AOT) micelles as a function of the molar concentration ratio R (R=[water]/[AOT]) were evaluated by a calorimetric method. The results show that en, dmen and tmen molecules, solubilized in the reversed micelles, are distributed between the micellar aqueous core and the micellar palisade layer. An analysis of the thermodynamic parameters of the partition process demonstrates the peculiar solvent properties of the water containing…
Static and dynamic light scattering by aqueous polyelectrolyte solutions: effect of molecular weight, charge density and added salt
1990
Abstract Aqueous solutions of quaternized poly(2-vinylpyridine) were investigated by static (SLS) and dynamic (DLS) light scattering over a wide range of polyelectrolyte, c pe , and salt concentrations, c s (10 −3 ≤ c pe ≤ 10 2 gl −1 , 10 −5.5 ≤ c s ≤ 10 −1 moll −1 ). Using DLS the cooperative diffusion coefficient D was measured as a function of c pe and c s . D exhibits a characteristic behaviour in each of three different concentration regimes. In the ‘dilute lattice’ regime, where λ = c pe c s ⪡ 1 , one diffusion coefficient is observed. In the transition regime, where λ ≈ 1, D increases with increasing polyelectrolyte concentration and a slow diffusive mode gradually appears. For λ ⪢ 1…
Thermodynamic properties of water-β-cyclodextrin-dodecylsurfactant ternary systems
1995
Densities, heat capacities and conductivities of water-surfactant-β-cyclodextrin (β-CD) ternary systems were determined at 25°C. The surfactants studied were sodium dodecylsulfate (NaDS) and dodecyltrimethylammonium bromide (DTAB). From conductivity data, apparent critical micelle concentrations (cmc*) and degree of ionization of micelles were obtained at a fixed β-CD concentration (mCD). From the cmc* value and that in water (cmc) the stoichiometry of the surfactant-β-CD complex was calculated. At a given mCD, the apparent molar volume Vϕ,CD and heat capacity Cϕ,CD of β-CD in the two surfactants were calculated as functions of surfactant concentration mS. For both NaDS and DTAB, Vϕ,CD incr…