Molecular Dynamics and Entropy Effects in Hydrogen-Bonded Supramolecular PolymerN,N′-Di(2-methyl-2-pentylheptyl)urea Dissolved in Nonpolar Medium

Abstract

On the basis of the static dielectric permittivity temperature behavior of the supramolecular polymer formed by N,N'-di(2-methyl-2-pentylheptyl)urea (MPHU) in carbon tetrachloride diluted solution (10% in mole fraction) and that of neat acetonitrile, it was found that two liquids of the same macroscopic polarity (expressed by the same value of the dielectric permittivity approximately 35) exhibit an essential difference in the field-induced orientational entropy change. A much higher entropy effect is observed for the liquid composed of not too numerous but highly polar molecular entities (MPHU + CCl(4)) than for the liquid composed of numerous but less polar entities (neat acetonitrile). The analysis of the dielectric relaxation spectra of MPHU + CCl(4) solutions was performed with the Davidson-Cole (DC) model. It was found that the DC exponent beta changes its value in a quite important range of 0.4-0.8, depending on MPHU concentration and temperature. This reflects an important deviation of the relaxation mechanism occurring in the supramolecular system investigated from that corresponding to the normal Brownian rotational diffusion (beta = 1).

Fractional Stokes–Einstein–Debye relation and orientational entropy effects in strongly hydrogen-bonded liquid amides

“…As it was shown recently, 10,[35][36][37] temperature dependence of the static permittivity of a given liquid allows one to deduce some important information on the intermolecular interactions and the molecular self-aggregation abilities of the liquid. The molecular interpretation of the e s (T) dependence, as a matter of fact-its temperature derivative, leads through the analysis of the entropic effects induced in the liquid by the probing electric field.…”

“…7À9 In the static electric field the entities orient themselves as a whole and, as a consequence, one detects the orientational entropy effect highly exceeding that corresponding to the non-hydrogenbonded molecules of similar polarity. 10 Liquid amides exhibit a relatively high electric conductivity what is expected for such polar compounds where an ionic dissociation process of inevitable electrolytic impurities meets the thermodynamic favorite conditions. Besides, the dc conductivity in hydrogen-bonded liquids may also result from the proton translocation along the hydrogen bonds for which the breaking of a hydrogen bond and the diffusion of a molecule are necessary before the hydrogen bond is reforming with other neighbors.…”

Does water belong to the homologous series of hydroxyl compounds H(CH2)nOH?

“…But whatever the experimental circumstances, the anomalously large difference between n D 2 and e N of water seems to be real and we will get back to that problem later. As shown in numerous papers, [41][42][43][44][45] an alternative method which reveals the state of dipolar aggregation of molecular dipoles in liquids is also related to the liquid permittivity, but only with its static part, e S . Namely, it was shown first by Fröhlich in 1958 33 and next by Becker, 46 Landau, Lifshitz and Pitaevskii 47 and Scaife, 48 that the probing electric field, applied to the dipolar liquid, induces an increment of the thermodynamic quantities (internal energy, entropy and Helmholtz free energy), which are quite simply related to the static permittivity of a liquid, e S , its temperature derivative, de S /dT, and the square of the electric field strength E. For the purposes of this work, we are interested in the change of entropy, which is dependent exclusively on the permittivity temperature derivative:…”

Hierarchical Structure of Supramolecular Polymers Formed by N,N′-Di(2-ethylhexyl)urea in Solutions

“…(a) Dependence of the static permittivity of EHU + heptane solutions on mole fraction of the urea at different temperatures (the temperature difference between the neighboring curves is equal to 10 °C). (b) Comparison of the experimental ε s ( x ) dependences for EHU and (less self-associated) MPHU in nonpolar solvents at 25 °C …”