Papers by Stella Hensel-Bielówka
Soft Matter, 2015
Scaling exponent as a key parameter to probe self-organization changes in solution with respect t... more Scaling exponent as a key parameter to probe self-organization changes in solution with respect to the IL structure.
Journal of the American Chemical Society, 2015
Ionic systems with enhanced proton conductivity are widely viewed as promising electrolytes in fu... more 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
The Journal of Chemical Physics, 2000
The pressure and temperature dependent dielectric relaxation times are compared with the predicti... more The pressure and temperature dependent dielectric relaxation times are compared with the predictions of the model proposed by Avramov. Remarkable agreement is found in whole P and T plane. It was also pointed out that the tested model predicts no pressure effect on fragility and nonlinear character of pressure dependence of glass transition temperature. Our data provide also an assessment of the generalized Vogel–Fulcher–Tammann (VFT) law. However, it is inferred that the generalized VFT law is not able to accurately reproduce the surface described by experimental relaxation times. Additionally, isothermal data are analyzed by the pressure counterpart of the temperature VFT law. The isothermal data expressed in terms of the reduced relaxation time and reduced pressure form a master curve.
The Journal of Chemical Physics, 1999
This paper presents the effect of pressure on liquid fragility in poly(bisphenol A-co-epichlorohy... more This paper presents the effect of pressure on liquid fragility in poly(bisphenol A-co-epichlorohydrin), glycidyl end capped. On the basis of temperature dependences of dielectric relaxation times measured for several different pressures, the steepness or fragility index mT has been calculated. We proved that liquid fragility is independent of pressure within experimental error. The influence of pressure on glass transition temperature has also been studied. It turned out that pressure dependence of glass transition temperature is well represented by the second-order polynomial.
The Journal of Chemical Physics, 2005
The dielectric spectra of the glass former, m-fluoroaniline (m-FA), at ambient pressure show the ... more The dielectric spectra of the glass former, m-fluoroaniline (m-FA), at ambient pressure show the presence of a secondary relaxation, which was identified in the literature as the universal Johari–Goldstein (JG) β relaxation. However, published elastic neutron scattering and simulation data [D. Morineau, C. Alba-Simionesco, M. C. Bellisent-Funel, and M. F. Lauthie, Europhys. Lett. 43, 195 (1998); D. Morineau and C. Alba-Simionesco, J. Chem. Phys. 109, 8494 (1998)] showed the presence of hydrogen-bond-induced clusters of limited size in m-FA at ambient pressure and temperature of the dielectric measurements. The observed secondary relaxation may originate from the hydrogen-bond-induced clusters. If so, it should not be identified with the JG β relaxation that involves essentially all parts of the molecule and has certain characteristics [K. L. Ngai and M. Paluch, J. Chem. Phys. 120, 857 (2004)], but then arises the question of where is the supposedly universal JG β relaxation in m-FA....
The Journal of Chemical Physics, 2001
The relaxation dynamics of a low molecular supercooled liquid, cresolphthalein-dimethylether (KDE... more The relaxation dynamics of a low molecular supercooled liquid, cresolphthalein-dimethylether (KDE), has been investigated in the vicinity of glass transition temperature by dielectric relaxation measurements. Glass transition is approached and studied by the use of isothermal and isobaric paths. Under isobaric condition, the departure of the correlation function of the α-relaxation from exponential decay with time (nonexponentiality) is even less than the intermediate liquids such as glycerol. However, the Tg-scaled temperature dependence of the α-relaxation time, τ, resembles “fragile” glass-formers like orthoterphenyl (OTP). Thus KDE, like propylene carbonate (PC) that has in common a basic chemical structural unit, is an exception to the correlation between “fragility” and nonexponentiality found to hold for most glass formers. The dielectric relaxation measurements with the application of pressure show that KDE has large pressure coefficient of the glass transition temperature, ...
The Journal of Chemical Physics, 2002
Two relaxation processes, involving dc conductivity and the glass (α) structural relaxation, resp... more Two relaxation processes, involving dc conductivity and the glass (α) structural relaxation, respectively, were measured in the low-molecular-weight glass-forming liquid, bisphenol- A-propoxylate(1 PO/phenol)diglycidylether, by dielectric spectroscopy, as a function of temperature and pressure. We focused on the correlation between dc conductivity and the α-relaxation time, proving that the fractional Debye–Stokes–Einstein relation is valid for both isobaric and isothermal data. The value of the exponent was independent of both temperature and pressure, and related to the ratio of the apparent activation volume of the relaxation processes being considered. The shape of the dielectric loss α peak did not change with either temperature or pressure; i.e., frequency–temperature–pressure superposition was valid in the vicinity of the glass transition.
Current Medicinal Chemistry, 2010
Physical Review B, 2005
The  relaxation is a principal source of information about the dynamics in the glassy state; how... more The  relaxation is a principal source of information about the dynamics in the glassy state; however, the nature of this process remains a controversial issue. In this paper, we show that properties of the  relaxation measured below T g are sensitive to the structure of the glass; that is, the thermodynamic path from the equilibrium liquid strongly affects the  relaxation times, their distribution, and the activation energy quantifying their temperature dependence. These results support the idea that the Johari-Goldstein  process is the precursor to the structural relaxation transpiring at longer times. We discuss the experimental findings in light of the heterogeneous and homogeneous scenarios for the  process.
Physical Review E, 2004
New dielectric spectroscopy results are reported for propylene carbonate (PC), glycerol, and thre... more New dielectric spectroscopy results are reported for propylene carbonate (PC), glycerol, and threitol, measured at very high ͑1.8 GPa͒ pressure. These glass formers all exhibit an excess wing in their dielectric spectrum above T g. We show that the shape of the ␣ peak and excess wing of PC are invariant to pressure and temperature, when compared at a fixed value of the ␣-relaxation time. However, for the hydrogen-bonded liquids, there is a marked breakdown of this temperature-pressure superpositioning, due to a change in chemical structure (i.e., concentration of hydrogen bonds) with change of temperature or pressure. For all these materials, we can conclude that the excess wing is merely a secondary relaxation, masked under ordinary conditions by the intense, overlapping ␣ peak.
Physical Review E, 2000
The effect of pressure variation on dynamics of ␣ relaxation process in poly͓͑phenyl glycidyl eth... more The effect of pressure variation on dynamics of ␣ relaxation process in poly͓͑phenyl glycidyl ether͒-co-formaldehyde͔ has been investigated both under isothermal (Tϭ293 K) and isobaric (Pϭ0.1, 60, 120, 180, and 240 MPa͒ conditions using broad band dielectric spectroscopy (10 Ϫ2 to 10 6 Hz). The ␣ relaxation is analyzed by means of the Havriliak-Negami relaxation function which has two shape parameters ͑␣ and ␥͒ to characterize non-Debye behavior. As a result we found that the shape parameters of the dielectric function collected for different pressures fall on master curves constructed by plotting ␣ and ␣␥ against the logarithm of relaxation time. The scaling of shape parameters for different pressure stems from pressure independence of fragility. This provides strong experimental evidence supporting correlation of non-Debye behavior with non-Arrhenius relaxation under high pressure. From an analysis of the shape parameters of relaxation function, in terms of the Schonhals and Schlosser model, we drew conclusions that the molecular mobility of PPG is controlled in the same way by temperature and pressure. The relaxation times exhibit a clear non-Arrhenius behavior under isothermal and isobaric condition.
Physical Review B, 2005
ABSTRACT The temperature behavior of the secondary relaxation in tri-propylene glycol under isoba... more ABSTRACT The temperature behavior of the secondary relaxation in tri-propylene glycol under isobaric pressure up to 1.7 GPa was studied in detail. We show that dynamics of the secondary process is changed during crossing glass temperature Tg, and secondary relaxation time show minimum in the temperature dependence as recently suggested by Dyre and Olsen Phys. Rev. Lett. 91 1557031 (2003) The effect of pressure on asymmetric double-well potential was determined by analyzing the temperature dependence of the secondary relaxation at elevated pressure by means of the minimal model.
Physical Chemistry Chemical Physics, 2014
During this research, we present a study on the thermal properties, such as the melting, cold cry... more During this research, we present a study on the thermal properties, such as the melting, cold crystallization, and glass transition temperatures as well as heat capacities from 293.15 K to 323.15 K of nine in-house synthesized protic ionic liquids based on the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate ([H-Im-C1OC(n)][Sal]) with n = 3-11. The 3D structures, surface charge distributions and COSMO volumes of all investigated ions are obtained by combining DFT calculations and the COSMO-RS methodology. The heat capacity data sets as a function of temperature of the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate are then predicted using the methodology originally proposed in the case of ionic liquids by Ge et al. 3-(Alkoxymethyl)-1H-imidazol-3-ium salicylate based ionic liquids present specific heat capacities higher in many cases than other ionic liquids that make them suitable as heat storage media and in heat transfer processes. It was found experimentally that the heat capacity increases linearly with increasing alkyl chain length of the alkoxymethyl group of 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate as was expected and predicted using the Ge et al. method with an overall relative absolute deviation close to 3.2% for temperatures up to 323.15 K.
Journal of Non-Crystalline Solids, 2006
We report dielectric relaxation measurements of the mixture 25% w/w cyclohexane in decahydroisoqu... more We report dielectric relaxation measurements of the mixture 25% w/w cyclohexane in decahydroisoquinoline. Cyclohexane is a nonpolar liquid that acts as an external parameter influencing relaxation dynamics of pure decahydroisoquinoline. Two different secondary relaxation processes dominate the relaxation dynamics below the glass transition temperature, as previously observed in the pure decahydroisoquinoline. Based on the coupling model analysis we identified the fastest secondary process as the genuine secondary Johari Goldstein process, reflecting the motion of the whole molecule. On the other hand, the microscopic origin of the slowest secondary process still remains unknown.
The Journal of Physical Chemistry B, 2008
Broad-band isothermal dielectric relaxation measurements of anhydrous sucrose were made at ambien... more Broad-band isothermal dielectric relaxation measurements of anhydrous sucrose were made at ambient pressure in its liquid and glassy states. We found a new secondary relaxation that is slower than the one commonly observed in sugars. Additionally, we carried out the dielectric measurements of the equimolar mixture of D-glucose and D-fructose in wide ranges of temperature and frequency. Comparison of the behavior of these two systems allowed us to make suggestions on the origin of the slower beta-relaxation in sucrose. Computer simulations and coupling model calculations were performed to support our interpretation of the kind of molecular motions responsible for the slower secondary relaxation in the disaccharide considered.
The Journal of Chemical Physics, 2008
Broadband dielectric measurements on leucrose were performed under ambient and high pressure. We ... more Broadband dielectric measurements on leucrose were performed under ambient and high pressure. We showed that in this disaccharide, there are two secondary relaxation modes, a slower one sensitive to pressure and a faster one that is not. This finding clearly indicates that the faster secondary relaxation originates from the intramolecular motion. This conclusion contradicted previous interpretations of this mode observed for trehalose and maltitol, systems very closely related to leucrose. In addition, pressure sensitivity of the slower relaxation confirms our recent interpretation about the character of this process. Furthermore, we discovered that unlike the faster relaxation, the slower secondary relaxation is sensitive to the thermodynamic history of measurements. Finally, monitoring the changes in maximum loss of the slower secondary relaxation measured at the same pressure and temperature conditions for glasses obtained via different thermodynamic routes enabled us to draw a conclusion about the density of the formed glasses. Our observations may be helpful in establishing a new method of suppressing crystallization of amorphous drugs.
NATO Science Series II: Mathematics, Physics and Chemistry, 2007
ABSTRACT Dielectric relaxation measurements have been performed to study effect of the molecular ... more ABSTRACT Dielectric relaxation measurements have been performed to study effect of the molecular structure on the primary and secondary relaxations in two materials with very similar structure: diisooctyl phthalate (DIOP) and diisooctyl maleate (DIOM). The dielectric spectra were measured over ten decades of frequency and a broad range of temperature. The results show that the temperature dependence of the α-relaxation times cannot be described by a single Vogel–Fulcher–Tammann equation and the temperature dependence of the β-relaxation times in the glassy state obey the Arrhenius law with different activation energies, i.e., E A /k = 4231 K and E A /k = 2917 K for DIOP and DIOM, respectively. Moreover, third relaxation process visible as an excess wing of the high frequency part of the α loss peak was identified in dielectric spectra of DIOM.
NATO Science Series II: Mathematics, Physics and Chemistry
... STELLA HENSEL-BIELOWKA, MONIKA SEKULA, SEBASTIAN PAWLUS, TATIANA PSUREK AND MARIAN PALUCH Ins... more ... STELLA HENSEL-BIELOWKA, MONIKA SEKULA, SEBASTIAN PAWLUS, TATIANA PSUREK AND MARIAN PALUCH Institute of Physics, Silesian University ... Meier, G., Gerharz, B., Boese, D. and Fischer, EW (1990) Dynamical processes in organic glassforming van der Waals ...
Colloid and polymer science, 2014
Dielectric and mechanical spectroscopy methods have been employed to describe the temperature dep... more Dielectric and mechanical spectroscopy methods have been employed to describe the temperature dependencies of the segmental and macromolecular relaxation rates in epoxy/hydroxy functionalized polybutadiene. Dielectric studies on the dynamics of segments of the polymer as well as the mobility of small ions trapped in the system have been carried out both as a function of temperature and pressure under isobaric and isothermal conditions, respectively.
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Papers by Stella Hensel-Bielówka