Modele entropowe w opisie dynamiki molekularnej cieczy poddanych zmianom temperatury i ciśnienia w pobliżu przejścia do fazy szklistej

Podstawę niniejszej pracy doktorskiej stanowią artykuły naukowe A1-A3. Głównym celem przeprowadzonych badań było sformułowanie nowych równań stanowiących rozszerzenie temperaturowo-objętościowe wybranych modeli entropowych, opisujących dynamikę molekularną cieczy przechłodzonych w pobliżu przejścia szklistego oraz sprawdzenie możliwości skalowania termodynamicznego w tych modelach [A2,A3]. Dodatkowo, sformułowanie uniwersalnych reguł określających własności parametru kruchości w różnych warunkach termodynamicznych [A1], pozwoliło na weryfikację wyprowadzonych równań modeli AG(T,V) i MYEGA(T,V)

Thermodynamic consequences of the kinetic nature of the glass transition

In this paper, we consider the glass transition as a kinetic process and establish one universal equation for the pressure coefficient of the glass transition temperature, dTg/dp, which is a thermodynamic characteristic of this process. Our findings challenge the common previous expectations concerning key characteristics of the transformation from the liquid to the glassy state, because it suggests that without employing an additional condition, met in the glass transition, derivation of the two independent equations for dTg/dp is not possible. Hence, the relation among the thermodynamic coefficients, which could be equivalent to the well-known Prigogine-Defay ratio for the process under consideration, cannot be obtained. Besides, by comparing the predictions of our universal equation for dTg/dp and Ehrenfest equations, we find the aforementioned supplementary restriction, which must be met to use the Prigogine-Defay ratio for the glass transition

Adam-Gibbs model in the density scaling regime and its implications for the configurational entropy scaling

To solve a long-standing problem of condensed matter physics with determining a proper description of the thermodynamic evolution of the time scale of molecular dynamics near the glass transition, we have extended the well-known Adam-Gibbs model to describe the temperature-volume dependence of structural relaxation times, τα(T, V). We also employ the thermodynamic scaling idea reflected in the density scaling power law, τα = f(T−1V−γ), recently acknowledged as a valid unifying concept in the glass transition physics, to differentiate between physically relevant and irrelevant attempts at formulating the temperature-volume representations of the Adam-Gibbs model. As a consequence, we determine a straightforward relation between the structural relaxation time τα and the configurational entropy SC, giving evidence that also SC(T, V) = g(T−1V−γ) with the exponent γ that enables to scale τα(T, V). This important findings have meaningful implications for the connection between thermodynamics and molecular dynamics near the glass transition, because it implies that τα can be scaled with SC

Relative Cation-Anion Diffusion in Alkyltriethylammonium-Based Ionic Liquids

19F Nuclear Magnetic Resonance spin-lattice relaxation experiments have been performed for a series of ionic liquids including the same anion, bis(trifluoromethanesulfonyl)imide, and cations with alkyl chains of different lengths: triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, dodecyltriethylammonium, decyltriethylammonium, and hexadecyltriethylammonium. The experiments have been carried out in a frequency range of 10 kHz to 10 MHz versus temperature. A thorough analysis of the relaxation data has led to the determination of the cation–anion as a relative translation diffusion coefficient. The diffusion coefficients have been compared with the corresponding cation–cation and anion–anion diffusion coefficients, revealing a correlation in the relative translation movement of the anion and the triethylhexylammonium, triethyloctylammonium, decyltriethylammonium, and dodecyltriethylammonium cations, whereas the relative translation diffusion between the anion and the cations with the longer alkyl chains, decyltriethylammonium and hexadecyltriethylammonium, remains rather uncorrelated (correlated to a much lesser extent)

Exploring the water mobility in gelatin based soft candies by means of Fast Field Cycling (FFC) Nuclear Magnetic Resonance relaxometry

© 2020 Elsevier Ltd1H spin-lattice relaxation experiments for gelatin-based candies prepared by different amounts of D-allulose have been performed in the frequency range of 4 kHz–40 MHz. In addition, physical properties such as moisture content and hardness were also measured. Analysis of NMR dispersion profiles showed the presence of two fractions of water: confined and free-water. The relaxation data have been associated with parameters characterizing translation diffusion and rotation of the confined-water molecules and dynamics of the free-water fraction. The translation dynamics has turned out to be about three orders of magnitude slower compared to bulk water; the time scale of the rotational dynamics is similar to that of translation diffusion. Moreover, quantitative analysis of the relaxation data has provided a unique parameter, the number of water molecules undergoing translation dynamics within the confined-water fraction per unit volume. On this basis, the influence of D-allulose on the mechanisms of water motion has been discussed