Lucia Costantino

Diffusion properties of cyclodextrins in aqueous solution at 25°C

Diffusion, density, and viscosity data are collected for the systems α-cyclodextrin and β-cyclodextrin in water. Frictional coefficients were computed with the help of literature activity data and a qualitative discussion of their concentration dependence was attempted.

Transport and thermodynamic properties of the systems (D,L)norleucine-water and (L)phenylalanine-water, at 25°C

Abstract Diffusion coefficients, densities, and viscosities were measured on the systems (D,L)Norleucine-water and (L)Phenylalanine-water, at 25°C as a function of the amino-acid concentration. For the system (L)Phenylalanine-water enthalpies of dilution were also measured. The experimental results are discussed and compared with some literature data available for the amino-acid series.

Diffusion coefficients of the system α-cyclodextrin-n-butylurea-water at 25°C

Diffusion coefficients were measured for the ternary system α-cyclodextrin(I)-n-butylurea(2)-water at three average concentrations. The cross coefficient D12 was found to be almost zero and D21 large and negative. These results are in agreement with the presence of an inclusion complex whose mobility is close to that of the host cyclodextrin molecules. The values of the four experimental diffusion coefficients are used to compute a value of the inclusion constant which is in reasonably good agreement with the calorimetric value.

Dynamic properties of aqueous solutions of ethylene glycol oligomers as measured by the pulsed gradient spin-echo NMR technique at 25[deg ]C

Self-diffusion coefficients for binary systems containing water and an oligomer of ethylene glycol [HO–(CH2CH2–O)nH, n=1–5], have been measured at 25°C in the whole concentration range by the pulsed gradient spin-echo NMR technique. Upon adding oligomer to pure water, both the oligomer and water self-diffusion coefficients decrease until a certain composition is reached, after which they remain approximately constant. This evidence is interpreted in terms of molecular interactions, especially hydrogen-bond formation. A relation between mutual and self-diffusion coefficients for these systems is found and commented upon.

Transport properties of urea and alkylureas aqueous solutions. A velocity correlation study.

Abstract Intradiffusion coefficients were measured at 25°C by the PGSE-NMR technique for the binary systems: water-urea, water-(N-methylurea), water-(N,N′-dimethylurea). The collected data have been combined with osmotic and mutual diffusion coefficients present in the literature to calculate the velocity correlation coefficients (VCC). The results have been interpreted in terms of molecular interactions, showing that alkylureas have a structuring effect on the aqueous medium. The hydration number of the solutes were estimated.

A self-diffusion study of poly(ethylene-oxide) alkyl alcohols

The self-diffusion coefficients of HDO and some surfactants in aqueous mixtures at different concentrations, below the critical micelle concentration, have been determined by means of the NMR, spin-echo pulsed field gradient method. The surfactant solutes chosen were ethylene glycol-pentyl alcohol (diethylene glycolpentylalcohol, ethylene glycol-hexyalcohol, diethylene glycol-hexyl alcohol, triethylene glycol-hexyl alcohol, tetraethylene glycol-hexyl alcohol, pentaethylene glycol-hexyl alcohol). The interactions in solution are studied by analyzing the solute self-diffusion coefficients extrapolated to infinite dilution. These values are compared with those of 1-alkanols. The slope of the self diffusion coefficientsvs. the solute concentration are correlated with the microscopic friction coefficients. A model for interpreting the experimental data is suggested.

Density and viscosity studies of poly(ethylene-oxide) alkyl alcohols

AbstractDensity and viscosity of binary systems water-nonionic surfactants poly(ethylen-oxide) alkyl alcohols type, [CnH2n+1(OCH2CH2)mOH, CnEm], have been studied. The partial molar volumes in the dilute solution range and the viscosity B-coefficients were calculated. The nonionic surfactants partial molar volumes were compared with those of ethylene glycol and poly(ethylenglycol) (PEG). The comparison shows that the ethoxy unit volume,

Isothermal diffusion in a peculiar ternary system: the microemulsion AOT–water–heptane

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