3 research outputs found
Glass transition cooperativity from broad band heat capacity spectroscopy
Molecular dynamics is often studied by broad band dielectric spectroscopy (BDS) because of the wide dynamic range available and the large number of processes resulting in electrical dipole fluctuations and with that in a dielectrically detectable relaxation process. Calorimetry on the other hand is an effective analytical tool to characterize phase and glass transitions by its signatures in heat capacity. In the linear response scheme, heat capacity is considered as entropy compliance. Consequently, only processes significantly contributing to entropy fluctuations appear in calorimetric curves. The glass relaxation is a prominent example for such a process. Here, we present complex heat capacity at the dynamic glass transition (segmental relaxation) of polystyrene (PS) and poly(methyl methacrylate) (PMMA) in a dynamic range of 11 orders of magnitude, which is comparable to BDS. As one of the results, we determined the characteristic length scale of the corresponding fluctuations. The dynamic glass transition measured by calorimetry is finally compared to the cooling rate dependence of fictive temperature and BDS data. For PS, dielectric and calorimetric data are similar but for PMMA with its very strong secondary relaxation process some peculiarities are observed
Liquid Organic Hydrogen Carriers: Thermophysical and Thermochemical Studies of Benzyl- and Dibenzyl-toluene Derivatives
The heat transfer oils dibenzyltoluene
and benzyltoluene are promising
materials as a new class of liquid organic hydrogen carrier compounds
(LOHC). Thermophysical properties (heat capacity, density, viscosity,
and surface tension) of the commercially available thermofluids Marlothem
LH (benzyltoluene) and Marlotherm SH (dibenzyltoluene) and their completely
hydrogenated derivatives were measured. Thermochemical properties
(enthalpies of combustion and enthalpies of vaporization) were derived
from experiments. Gas-phase molar enthalpies of formation were derived
and validated with group-additivity and high-level quantum chemical
calculations. Enthalpies of the hydrogenation/dehydrogenation reactions
of the LOHC pairs under study were derived
Molecular Origin of Enhanced Proton Conductivity in Anhydrous Ionic Systems
Ionic systems with
enhanced proton conductivity are widely viewed
as promising electrolytes in fuel cells and batteries. Nevertheless,
a major challenge toward their commercial applications is determination
of the factors controlling the fast proton hopping in anhydrous conditions.
To address this issue, we have studied novel proton-conducting materials
formed via a chemical reaction of lidocaine base with a series of
acids characterized by a various number of proton-active sites. From
ambient and high pressure experimental data, we have found that there
are fundamental differences in the conducting properties of the examined
salts. On the other hand, DFT calculations revealed that the internal
proton hopping within the cation structure strongly affects the pathways
of mobility of the charge carrier. These findings offer a fresh look
on the Grotthuss-type mechanism in protic ionic glasses as well as
provide new ideas for the design of anhydrous materials with exceptionally
high proton conductivity