Thermodynamics of binary mixtures containing N-alkylamides

Structure of Nanotubes Self-Assembled from a Monoamide Organogelator

Some organic compounds are known to self-assemble into nanotubes in solutions, but the packing of the molecules into the walls of the tubes is known only in a very few cases. Herein, we study two compounds forming nanotubes in alkanes. They bear a secondary alkanamide chain linked to a benzoic acid propyl ester (HUB-3) or to a butyl ester (HUB-4). They gel alkanes for concentrations above 0.2 wt.%. The structures of these gels, studied by freeze fracture electron microscopy, exhibit nanotubes: for HUB-3 their external diameters are polydisperse with a mean value of 33.3 nm; for HUB-4, they are less disperse with a mean value of 25.6 nm. The structure of the gel was investigated by small- and wide-angle X-ray scattering. The evolution of the intensities show that the tubes are metastable and transit slowly toward crystals. The intensities of the tubes of HUB-4 feature up to six oscillations. The shape of the intensities proves the tubular structure of the aggregates, and gives a measurement of 20.6 nm for the outer diameters and 11.0 nm for the inner diameters. It also shows that the electron density in the wall of the tubes is heterogeneous and is well described by a model with three layers.

Thermodynamics of organic mixtures containing amines. IV. Systems with aniline

Binary mixtures of aniline with benzene, toluene, alkane, alkanol, or N,N-dialkylamide have been investigated in the framework of the DISQUAC model. The reported interaction parameters change regularly with the molecular structure of the mixture components. The model consistently describes a set of thermodynamic properties including liquid–liquid equilibria, vapor–liquid equilibria, and molar excess enthalpies. The two latter properties for ternary systems are well-represented by DISQUAC using binary parameters only (i.e., neglecting ternary interactions). A comparison of DISQUAC results and those obtained from the UNIFAC (Dortmund version) and ERAS models is also shown. The experimental molar excess enthalpies for binary and ternary mixtures are better described by DISQUAC than by UNIFAC. ERAS fails when representing molar excess enthalpies of those binary systems including methanol or ethanol. This may be due to the existence of strong dipolar interactions among aniline molecules as well as to effects related to the equation of state term, evaluated comparing molar excess enthalpies, and molar excess internal energies at constant volume. The study of the aniline systems in terms of the concentration–concentration structure factor also underlines the importance of dipolar interactions in solutions with alkanes or alcohols, which may be due to the high polarizability of the aniline molecule.Key words: thermodynamics, mixtures, aniline, dipolar interactions, structural effects.

Identification of dielectric and structural relaxations in glass-forming secondary amides

Dielectric relaxation dynamics of secondary amides is explored in their supercooled state near the glass transition temperature Tg by investigating N-ethylacetamide and its mixtures with N-methylformamide. All the samples are found to exhibit giant dielectric permittivities, reaching over 500 in N-methylformamide-rich mixtures around Tg. For both the neat and binary systems, the predominant relaxation peak is of the Debye-type throughout the viscous regime, which is an unexpected feature for a glass former with intermediate fragility. The present results combined with the earlier reported high-temperature data reveal that the dielectric strength delta epsilon(D) of the Debye relaxation extrapolates to zero at frequencies of 10(10)-10(11) Hz, which is about two orders of magnitude lower than the phonon frequency limit typical of the structural relaxation. This Debye process is remarkably similar to the dielectric behavior of many monohydroxy alcohols, which implies a common nature of purely exponential relaxation dynamics in these liquids. Based on the dielectric properties, we conclude that the Debye relaxation in the secondary amides is not a direct signature of the primary or alpha-relaxation, the latter being obscured at low temperatures due to the relatively low permittivity and close spectral proximity to the Debye peak. As in the case of monohydroxy alcohols, dielectric polarization and structure fluctuate on different time scales in secondary amides. The Kirkwood-Fröhlich correlation factors for Debye-type liquids are also discussed.