A joint investigation of n-undecane (n-UND) in the bulk and confined states in irregular silica g... more A joint investigation of n-undecane (n-UND) in the bulk and confined states in irregular silica gel (SG) matrices differing in their surface composition via two extrinsic probes using positron annihilation lifetime spectroscopy (PALS) and electron spin resonance (ESR) as well as DSC technique is presented. Ortho-positronium (o-Ps) exhibits a pronounced change in the annihilation behavior as detected by the o-Ps lifetime,τ 3 , as a function of temperature due to the enhanced amorphization of the n-UND after confinement with respect to the bulk solid n-UND. In addition, with an exception of the low-T region it exhibits rather small alterations in the confined state in the unmodified (virgin) SG100Å-SIL compared to modified (silanized) SG100Å-C4. On the other side, the stable free radical of nitroxide type 2,2,6,6-tetramethylpiperidinyl-1-oxy(TEMPO) shows the essential differences in the spectral properties with temperature not only in the confined n-UND with respect to the bulk sample, but especially in the confined state in the modified SG-C4 matrix compared to the unmodified SG100Å-SIL one. These differences are attributed to the presence and absence of the preferential interaction of the polar spin probe TEMPO with the polar surface of the virgin SG matrix or the apolar surface of the silanized SG100Å-C4 one, respectively. The coinciding relationships between the characteristic PALS and ESR temperatures reflecting the changes in annihilation and rotation dynamics of the respective extrinsic probes are related to the dynamic and phase transitions as found by wide-T DSC.
Collection of Czechoslovak Chemical Communications, 1985
The kinetic data of decay of alkyl macroradicals in two temperature regions in isotactic polyprop... more The kinetic data of decay of alkyl macroradicals in two temperature regions in isotactic polypropylene exposed to gamma radiation at 77 K were interpreted in terms of the model of diffusion-limited reactions at the activation energy level. The potential molecular mechanisms of transfer of the radical centres were tested from the point of view of their physical and/or chemical migration. Two mechanisms are suggested for the mutual approach of the centres in macroradical decay regions I and II in the amorphous zones of the matrix. Both of them involve the contribution of segmental conformational motions, the mobility of the terminal segments being of importance in region I whereas in region II the mutual nearing of the reactants proceeds in a relay way via intermolecular H-abstraction in conjunction with crank and crankshaft motions of the end and inner segments of the chain.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry, 1986
In this experiment, the meltingbehaviour of crystalline phase in unirradiated and irradiated samp... more In this experiment, the meltingbehaviour of crystalline phase in unirradiated and irradiated samples of poly(vinylidenefluoride) was investigated by means of DSC tecnique.
A combined study of one of the simplest aromatic hydrocarbons, i.e., methylbenzene (toluene) (TOL... more A combined study of one of the simplest aromatic hydrocarbons, i.e., methylbenzene (toluene) (TOL), via the annihilation of an ortho-positronium (o-Ps) probe via positron annihilation lifetime spectroscopy (PALS) and the rotation dynamics of nitroxide spin probe 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) using electron spin resonance (ESR) over a wide temperature range, 10–300 K, is reported. The o-Ps lifetime, τ3, and the relative o-Ps intensity, I3, as a function of temperature exhibit changes defining several characteristic PALS temperatures in the slowly and rapidly cooled samples. Similarly, the spectral parameter of TEMPO mobility in TOL, 2Azz‘, and its correlation time, τc, reveal several effects at a set of the characteristic ESR temperatures, which were determined and compared with the PALS results. Finally, the physical origins of the changes in free volume expansion and spin probe mobility are revealed. They are reflected in a series of the mutual coincidences between ...
A free-volume theory is developed based on the defect diffusion model ͑DDM͒. In addition, positro... more A free-volume theory is developed based on the defect diffusion model ͑DDM͒. In addition, positronium annihilation lifetime spectroscopy ͑PALS͒ ortho-positronium free-volume and intensity data are presented for poly͑propylene glycol͒ with a molecular weight of 4000 ͑PPG 4000͒ in both the glassy and liquid states and dielectric relaxation and electrical conductivity data are reported for PPG 4000 in the liquid state. The DDM is used to interpret all of the data for PPG 4000 and previously reported PALS and dielectric relaxation data for glycerol. It is shown that while the PPG 4000 data exhibit a preference for the three-halves power law, the data for glycerol favor the first power ͑standard Vogel-Fulcher-Tammann͒ law. Good agreement between the DDM and the experimental results is found for all of the electrical data and the PALS free-volume data. While reasonable agreement is also found for the PALS intensity data for PPG 4000, a discrepancy exists between the experimental PALS intensity data and theory for glycerol. For the electrical conductivity for PPG 4000, a transition is observed at the same temperature ͑about 1.4T g where T g is the glass transition temperature͒ where the PALS free volume changes from steeply rising with temperature to approximately independent of temperature. The same behavior is observed at about 1.5T g for previously reported dielectric relaxation and PALS data for glycerol. Model parameters are presented that show the dominance of mobile single defects above ͑1.4-1.5͒T g and the dominance of immobile clustered single defects below T g. Finally, a coherent picture of glasses and glass-forming liquids is presented based on the theory and results of the experiments.
ABSTRACT Free radical decay in γ-irradiated atactic poly(propylene) (a-PP) and microscopic chain ... more ABSTRACT Free radical decay in γ-irradiated atactic poly(propylene) (a-PP) and microscopic chain dynamics in the same polymer have been studied by electron spin resonance and quasi-elastic neutron scattering simultaneously. It was found that an acceleration of the decay at the first acceleration temperature Tacc,1 = 190 K in the sub-T9 region correlates not only with the literary values of the Vogel temperature T0 for α-segmental dynamics, but also with the onset temperature of the so-called fast motion at Tf. The other acceleration temperature Tacc,2 = 250 K agrees not only with the macroscopic glass transition temperature Tg from DSC measurement, but also with the course of conformational transitions as evidenced by the recent two-dimensional 13C NMR study on the same sample. The relationships between Tacc,1, Tf and T0 both for a-PP as a typical polymer with the simple chemical structure and for the more complex polymers studied previously, where Tacc-T0 correlation is present but Tacc-Tf correlation absent, are discussed.
ABSTRACT A joint external probe ESR and PALS study on n-tridecane (n-TRD) using stable free radic... more ABSTRACT A joint external probe ESR and PALS study on n-tridecane (n-TRD) using stable free radical 2,2,6,6-tetra-methyl-1-piperidinyloxy (TEMPO) or ortho-positronium (o-Ps), respectively, is presented. In contrast to n-hexadecane (n-HXD) [PhysicaB430,99(2013)], five crossovers in the spin probe TEMPO mobility coin- ciding with those in the o-Ps probe annihilation parameters at the characteristic ESR and PALS tem- peratures in the solid phase were revealed: 1) acceleration within the slow regimeat TX1 slow in accordance with the changes in both o-Ps lifetime, τ3, and relative o-Ps intensity, I3, at Tb1cr* in the rigid crystalline solid are related to very local end-methyl group dynamics,2)slow to fast regime transition at T50G<<Tm (DSC) is similarly as for n-HXD ascribed to the spin probe TEMPO dynamics in the expanding inter-lamellar gap due to the molecular probe deformation induced enhanced end-chain mobility close to the rigid to soft crystalline solid transitionat Tb1cr being connected also with the starting dominance of electron detrapping over positron mobility, 3) the first change within the fast regime at TX1fast coinciding with reduction of I3 at Tb2cr** is related to strong electron detrapping due to longitudinal disordering and 4) the next one at TX2 fast* is related to the soft to plastic crystalline solid phase transitionat Tb2cr*=Tss (DSC) = 0.95Tm(DSC). Finally, similarly as for n-HXD the highest T crossover at TX2 fast≅Tm (PALS) is related with the collective chain dynamics of the melting transition Tm (DSC). The underlying structural-dynamic processes behind the observed ESR and PALS crossover coincidencies are discussed in the light of the present thermodynamic DSCandreported dynamic NMR, QENS and IR data.
Free radical decay kinetics and local chain dynamics in semicrystalline trans-1,4-polychloroprene... more Free radical decay kinetics and local chain dynamics in semicrystalline trans-1,4-polychloroprene have been investigated by electron spin resonance (ESR) and quasielastic neutron scattering (QENS), respectively. Three regions of distinct decay of allyl macroradicals characterized by two acceleration temperatures were found. Their comparison with the results of dynamic study revealed that i) the first acceleration in sub-T g region at around 199 K approximately coincides not only with the literary value of the Vogel temperature T 0 = 189 K for a-segmental mobility but also with the onset temperature of the fast motion at about T f = 180 l 10 K and ii) the second change in decay behavior occurs in the vicinity of a global dynamic change at the glass transition temperature T g and coincides with the onset of the slow conformation-segmental motion in amorphous phase of the polymer matrix.
The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric gl... more The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric glass transition temperatures for a series of amorphous polymers reveals empirical correlations of average lifetime of o-Ps ~3g, and of its product with a relative intensity I3g with appropriate T Dsc values. These-g trends in terms of free volume mean that both the average size of free volume hole entity Vhg and the fractional free volume grow with increasing T Dsc The results are-g 9 discussed considering the chemical microstructure as well as possible mechanisms acting in glass transition. A relation is indicated between geometric and flexibility characteristics of chains and the ~hg and fg parameters of free volume microstructure on the one side and potential motional processes responsible for solidification of the amorphous system on the other side.
A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilatio... more A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilation spectroscopy (PALS) and the dynamics from viscosity studies on two typical glassforming compounds within the framework of the two-order parameter (TOP) model is presented. The dynamical data are accounted for by the modified Vogel-Fulcher-Tamman-Hesse (M-VFTH) equation. Subsequently, the quasi-sigmoidal course of the o-Ps lifetime, τ 3 , with or without the high-temperature plateau region as a function of the temperature over a wide temperature range can be described by an effective free volume version of the TOP model. This simultaneous description suggests a close relationship between the PALS response and the dynamics of supercooled liquids and seems to support the liquid-like and solid-like domain physical picture of all the three physical states of the disordered phase of the condensed systems.
A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilatio... more A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilation spectroscopy (PALS) and the dynamics from viscosity studies on two typical glassforming compounds within the framework of the two-order parameter (TOP) model is presented. The dynamical data are accounted for by the modified Vogel-Fulcher-Tamman-Hesse (M-VFTH) equation. Subsequently, the quasi-sigmoidal course of the o-Ps lifetime, τ 3 , with or without the high-temperature plateau region as a function of the temperature over a wide temperature range can be described by an effective free volume version of the TOP model. This simultaneous description suggests a close relationship between the PALS response and the dynamics of supercooled liquids and seems to support the liquid-like and solid-like domain physical picture of all the three physical states of the disordered phase of the condensed systems.
In this work positron annihilation lifetime spectroscopy (PALS) is employed to study the ortho-Po... more In this work positron annihilation lifetime spectroscopy (PALS) is employed to study the ortho-Positronium lifetime parameters τ3>, σ3 and I3 in two structurally simple amorphous polymers 1,2-poly(butadiene) and cis-1,4-poly(isoprene). The ortho-Positronium mean lifetime parameter τ3> is compared with dynamics data from broadband dielectric spectroscopy (BDS) and electron spin resonance (ESR) experiments. Coincidences of characteristic temperatures from PALS with BDS and ESR experiments show close relationships between positron lifetime and dynamics of polymers.
A joint investigation of n-undecane (n-UND) in the bulk and confined states in irregular silica g... more A joint investigation of n-undecane (n-UND) in the bulk and confined states in irregular silica gel (SG) matrices differing in their surface composition via two extrinsic probes using positron annihilation lifetime spectroscopy (PALS) and electron spin resonance (ESR) as well as DSC technique is presented. Ortho-positronium (o-Ps) exhibits a pronounced change in the annihilation behavior as detected by the o-Ps lifetime,τ 3 , as a function of temperature due to the enhanced amorphization of the n-UND after confinement with respect to the bulk solid n-UND. In addition, with an exception of the low-T region it exhibits rather small alterations in the confined state in the unmodified (virgin) SG100Å-SIL compared to modified (silanized) SG100Å-C4. On the other side, the stable free radical of nitroxide type 2,2,6,6-tetramethylpiperidinyl-1-oxy(TEMPO) shows the essential differences in the spectral properties with temperature not only in the confined n-UND with respect to the bulk sample, but especially in the confined state in the modified SG-C4 matrix compared to the unmodified SG100Å-SIL one. These differences are attributed to the presence and absence of the preferential interaction of the polar spin probe TEMPO with the polar surface of the virgin SG matrix or the apolar surface of the silanized SG100Å-C4 one, respectively. The coinciding relationships between the characteristic PALS and ESR temperatures reflecting the changes in annihilation and rotation dynamics of the respective extrinsic probes are related to the dynamic and phase transitions as found by wide-T DSC.
Collection of Czechoslovak Chemical Communications, 1985
The kinetic data of decay of alkyl macroradicals in two temperature regions in isotactic polyprop... more The kinetic data of decay of alkyl macroradicals in two temperature regions in isotactic polypropylene exposed to gamma radiation at 77 K were interpreted in terms of the model of diffusion-limited reactions at the activation energy level. The potential molecular mechanisms of transfer of the radical centres were tested from the point of view of their physical and/or chemical migration. Two mechanisms are suggested for the mutual approach of the centres in macroradical decay regions I and II in the amorphous zones of the matrix. Both of them involve the contribution of segmental conformational motions, the mobility of the terminal segments being of importance in region I whereas in region II the mutual nearing of the reactants proceeds in a relay way via intermolecular H-abstraction in conjunction with crank and crankshaft motions of the end and inner segments of the chain.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry, 1986
In this experiment, the meltingbehaviour of crystalline phase in unirradiated and irradiated samp... more In this experiment, the meltingbehaviour of crystalline phase in unirradiated and irradiated samples of poly(vinylidenefluoride) was investigated by means of DSC tecnique.
A combined study of one of the simplest aromatic hydrocarbons, i.e., methylbenzene (toluene) (TOL... more A combined study of one of the simplest aromatic hydrocarbons, i.e., methylbenzene (toluene) (TOL), via the annihilation of an ortho-positronium (o-Ps) probe via positron annihilation lifetime spectroscopy (PALS) and the rotation dynamics of nitroxide spin probe 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) using electron spin resonance (ESR) over a wide temperature range, 10–300 K, is reported. The o-Ps lifetime, τ3, and the relative o-Ps intensity, I3, as a function of temperature exhibit changes defining several characteristic PALS temperatures in the slowly and rapidly cooled samples. Similarly, the spectral parameter of TEMPO mobility in TOL, 2Azz‘, and its correlation time, τc, reveal several effects at a set of the characteristic ESR temperatures, which were determined and compared with the PALS results. Finally, the physical origins of the changes in free volume expansion and spin probe mobility are revealed. They are reflected in a series of the mutual coincidences between ...
A free-volume theory is developed based on the defect diffusion model ͑DDM͒. In addition, positro... more A free-volume theory is developed based on the defect diffusion model ͑DDM͒. In addition, positronium annihilation lifetime spectroscopy ͑PALS͒ ortho-positronium free-volume and intensity data are presented for poly͑propylene glycol͒ with a molecular weight of 4000 ͑PPG 4000͒ in both the glassy and liquid states and dielectric relaxation and electrical conductivity data are reported for PPG 4000 in the liquid state. The DDM is used to interpret all of the data for PPG 4000 and previously reported PALS and dielectric relaxation data for glycerol. It is shown that while the PPG 4000 data exhibit a preference for the three-halves power law, the data for glycerol favor the first power ͑standard Vogel-Fulcher-Tammann͒ law. Good agreement between the DDM and the experimental results is found for all of the electrical data and the PALS free-volume data. While reasonable agreement is also found for the PALS intensity data for PPG 4000, a discrepancy exists between the experimental PALS intensity data and theory for glycerol. For the electrical conductivity for PPG 4000, a transition is observed at the same temperature ͑about 1.4T g where T g is the glass transition temperature͒ where the PALS free volume changes from steeply rising with temperature to approximately independent of temperature. The same behavior is observed at about 1.5T g for previously reported dielectric relaxation and PALS data for glycerol. Model parameters are presented that show the dominance of mobile single defects above ͑1.4-1.5͒T g and the dominance of immobile clustered single defects below T g. Finally, a coherent picture of glasses and glass-forming liquids is presented based on the theory and results of the experiments.
ABSTRACT Free radical decay in γ-irradiated atactic poly(propylene) (a-PP) and microscopic chain ... more ABSTRACT Free radical decay in γ-irradiated atactic poly(propylene) (a-PP) and microscopic chain dynamics in the same polymer have been studied by electron spin resonance and quasi-elastic neutron scattering simultaneously. It was found that an acceleration of the decay at the first acceleration temperature Tacc,1 = 190 K in the sub-T9 region correlates not only with the literary values of the Vogel temperature T0 for α-segmental dynamics, but also with the onset temperature of the so-called fast motion at Tf. The other acceleration temperature Tacc,2 = 250 K agrees not only with the macroscopic glass transition temperature Tg from DSC measurement, but also with the course of conformational transitions as evidenced by the recent two-dimensional 13C NMR study on the same sample. The relationships between Tacc,1, Tf and T0 both for a-PP as a typical polymer with the simple chemical structure and for the more complex polymers studied previously, where Tacc-T0 correlation is present but Tacc-Tf correlation absent, are discussed.
ABSTRACT A joint external probe ESR and PALS study on n-tridecane (n-TRD) using stable free radic... more ABSTRACT A joint external probe ESR and PALS study on n-tridecane (n-TRD) using stable free radical 2,2,6,6-tetra-methyl-1-piperidinyloxy (TEMPO) or ortho-positronium (o-Ps), respectively, is presented. In contrast to n-hexadecane (n-HXD) [PhysicaB430,99(2013)], five crossovers in the spin probe TEMPO mobility coin- ciding with those in the o-Ps probe annihilation parameters at the characteristic ESR and PALS tem- peratures in the solid phase were revealed: 1) acceleration within the slow regimeat TX1 slow in accordance with the changes in both o-Ps lifetime, τ3, and relative o-Ps intensity, I3, at Tb1cr* in the rigid crystalline solid are related to very local end-methyl group dynamics,2)slow to fast regime transition at T50G<<Tm (DSC) is similarly as for n-HXD ascribed to the spin probe TEMPO dynamics in the expanding inter-lamellar gap due to the molecular probe deformation induced enhanced end-chain mobility close to the rigid to soft crystalline solid transitionat Tb1cr being connected also with the starting dominance of electron detrapping over positron mobility, 3) the first change within the fast regime at TX1fast coinciding with reduction of I3 at Tb2cr** is related to strong electron detrapping due to longitudinal disordering and 4) the next one at TX2 fast* is related to the soft to plastic crystalline solid phase transitionat Tb2cr*=Tss (DSC) = 0.95Tm(DSC). Finally, similarly as for n-HXD the highest T crossover at TX2 fast≅Tm (PALS) is related with the collective chain dynamics of the melting transition Tm (DSC). The underlying structural-dynamic processes behind the observed ESR and PALS crossover coincidencies are discussed in the light of the present thermodynamic DSCandreported dynamic NMR, QENS and IR data.
Free radical decay kinetics and local chain dynamics in semicrystalline trans-1,4-polychloroprene... more Free radical decay kinetics and local chain dynamics in semicrystalline trans-1,4-polychloroprene have been investigated by electron spin resonance (ESR) and quasielastic neutron scattering (QENS), respectively. Three regions of distinct decay of allyl macroradicals characterized by two acceleration temperatures were found. Their comparison with the results of dynamic study revealed that i) the first acceleration in sub-T g region at around 199 K approximately coincides not only with the literary value of the Vogel temperature T 0 = 189 K for a-segmental mobility but also with the onset temperature of the fast motion at about T f = 180 l 10 K and ii) the second change in decay behavior occurs in the vicinity of a global dynamic change at the glass transition temperature T g and coincides with the onset of the slow conformation-segmental motion in amorphous phase of the polymer matrix.
The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric gl... more The analysis of annihilation characteristics of ortho-positronium at conventional calorimetric glass transition temperatures for a series of amorphous polymers reveals empirical correlations of average lifetime of o-Ps ~3g, and of its product with a relative intensity I3g with appropriate T Dsc values. These-g trends in terms of free volume mean that both the average size of free volume hole entity Vhg and the fractional free volume grow with increasing T Dsc The results are-g 9 discussed considering the chemical microstructure as well as possible mechanisms acting in glass transition. A relation is indicated between geometric and flexibility characteristics of chains and the ~hg and fg parameters of free volume microstructure on the one side and potential motional processes responsible for solidification of the amorphous system on the other side.
A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilatio... more A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilation spectroscopy (PALS) and the dynamics from viscosity studies on two typical glassforming compounds within the framework of the two-order parameter (TOP) model is presented. The dynamical data are accounted for by the modified Vogel-Fulcher-Tamman-Hesse (M-VFTH) equation. Subsequently, the quasi-sigmoidal course of the o-Ps lifetime, τ 3 , with or without the high-temperature plateau region as a function of the temperature over a wide temperature range can be described by an effective free volume version of the TOP model. This simultaneous description suggests a close relationship between the PALS response and the dynamics of supercooled liquids and seems to support the liquid-like and solid-like domain physical picture of all the three physical states of the disordered phase of the condensed systems.
A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilatio... more A phenomenological description of the ortho-positronium (o-Ps) response from positron annihilation spectroscopy (PALS) and the dynamics from viscosity studies on two typical glassforming compounds within the framework of the two-order parameter (TOP) model is presented. The dynamical data are accounted for by the modified Vogel-Fulcher-Tamman-Hesse (M-VFTH) equation. Subsequently, the quasi-sigmoidal course of the o-Ps lifetime, τ 3 , with or without the high-temperature plateau region as a function of the temperature over a wide temperature range can be described by an effective free volume version of the TOP model. This simultaneous description suggests a close relationship between the PALS response and the dynamics of supercooled liquids and seems to support the liquid-like and solid-like domain physical picture of all the three physical states of the disordered phase of the condensed systems.
In this work positron annihilation lifetime spectroscopy (PALS) is employed to study the ortho-Po... more In this work positron annihilation lifetime spectroscopy (PALS) is employed to study the ortho-Positronium lifetime parameters τ3>, σ3 and I3 in two structurally simple amorphous polymers 1,2-poly(butadiene) and cis-1,4-poly(isoprene). The ortho-Positronium mean lifetime parameter τ3> is compared with dynamics data from broadband dielectric spectroscopy (BDS) and electron spin resonance (ESR) experiments. Coincidences of characteristic temperatures from PALS with BDS and ESR experiments show close relationships between positron lifetime and dynamics of polymers.
Uploads
Papers by Jozef Bartos