J. Peleteiro

Temperature dependence of the volumetric properties of binary mixtures containing oxaalkane + n-heptane

Excess molar volumes of mixtures of n-heptane + 2,5-dioxahexane and n-heptane + 2,5,8-trioxanonane were determined from density measurentents at 5, 15, 25 and 35°C. These results allowed the following mixing quantities to be reported in all range of concentrations: α, (δvE/δT)P and (δhE/δP)T, at 25°C. The obtained values were then compared with the calculated values by using the Flory theory and the Nitta-Chao theory of liquid mixtures. The results are discussed in terms of order or disorder creation.

Polyethyleneglycol–pepsin interaction and its relationship with protein partitioning in aqueous two-phase systems

The interaction between the acidic protein, pepsin, and the non-charged polyethyleneglycol polymer was studied by dynamic light scattering, fluorescence spectroscopy and measurements of the protein thermal stability at neutral pH. Polyethyleneglycol of average molecular mass 1450 showed a higher interaction capacity with the protein than polyethyleneglycol of average molecular mass 8000. Polyethyleneglycol of average molecular mass 1450 showed a molecular mechanism where the interpolymer interaction led to the complex formation. This fact can be explained taking into account that the extended form on this polymer molecule favours the interaction with the protein, which is highly dependent of the polymer total concentration. Polyethyleneglycol of average molecular mass 8000 showed a cooperative interaction between the polymer and protein molecules which was independent of the PEG concentration.

Temperature dependence of the volumetric properties of binary mixtures containing oxaalkane + c-hexane

Excess molar volumes of mixtures of 2,5-dioxahexane + c-hexane, 2,5,8-trioxanonane + c-hexane, 2,5,8,11-tetraoxadodecane + c-hexane, and 2,5,8,11,14-pentaoxapentadecane + c-hexane were determined from density measurements at 283.15, 288.15, 298.15, and 308.15 K. These results allowed the following mixing quantities to be reported in the range of concentration: α, (δVE/δT)P, and (δHE/δP)T, at 298.15 K. The values obtained were then compared with the values calculated by using the Flory theory and the Nitta–Chao theory of liquid mixtures.

Thermal properties of ionic systems near the liquid-liquid critical point

Isobaric heat capacity per unit volume, C(p), and excess molar enthalpy, h(E), were determined in the vicinity of the critical point for a set of binary systems formed by an ionic liquid and a molecular solvent. Moreover, and, since critical composition had to be accurately determined, liquid-liquid equilibrium curves were also obtained using a calorimetric method. The systems were selected with a view on representing, near room temperature, examples from clearly solvophobic to clearly coulombic behavior, which traditionally was related with the electric permittivity of the solvent. The chosen molecular compounds are: ethanol, 1-butanol, 1-hexanol, 1,3-dichloropropane, and diethylcarbonate, whereas ionic liquids are formed by imidazolium-based cations and tetrafluoroborate or bis-(trifluromethylsulfonyl)amide anions. The results reveal that solvophobic critical behavior-systems with molecular solvents of high dielectric permittivity-is very similar to that found for molecular binary systems. However, coulombic systems-those with low permittivity molecular solvents-show strong deviations from the results usually found for these magnitudes near the liquid-liquid phase transition. They present an extremely small critical anomaly in C(p)-several orders of magnitude lower than those typically obtained for binary mixtures-and extremely low h(E)-for one system even negative, fact not observed, up to date, for any liquid-liquid transition in the nearness of an upper critical solution temperature.

Procedure to induce a persistent current in superconducting cylinders or rings

A procedure to induce a persistent current in superconducting cylinders or rings was developed using a coil and a ferromagnetic core. Using the field cooling method, the current is induced from the combined effect of the coil magnetic field and the core magnetization. The proposed method was checked using four Bi-2223 samples. The main usefulness seems to be that a high persistent current can be induced using small both probe currents and coils.

Ability of the Nitta-Chao model for the prediction of pressure and temperature dependence of the volumetric properties of n-alkane + 1-alkanol systems

Volumetric behaviour of n-alkane + 1-alkanol mixtures in a wide range of temperatures and pressures was examined on the basis of the Nitta-Chao model. Literature data of experimental densities in a temperature range from 298.15 to 373.15 K and pressures up to 40 MPa were selected in order to test the model predictions for the following quantities: excess molar volumes υ E and isothermal compressibilities κ T . (δΥ E /δT) p and (δh E /δp) T obtained from density data were compared with those predicted with the Nitta-Chao model.