Hristo Solunov - Academia.edu (original) (raw)
Papers by Hristo Solunov
Journal of Polymer Science: Polymer Physics Edition, 1974
ABSTRACT The electrical dipole relaxation in PMMA has been studied by measuring thermostimulated ... more ABSTRACT The electrical dipole relaxation in PMMA has been studied by measuring thermostimulated depolarizing currents. A master curve for the segmental component of the dielectric constant has been constructed. The increment of the dielectric permittivity due to the α-relaxation has been determined. The distribution function of the relaxation times and the average relaxation times in the region from 70°C up to Tg = 105°C have been obtained. A way of describing the electret properties of the polymer is discussed.
The Adam-Gibbs theory of the glass-transition is extended at its molecular level. An expression f... more The Adam-Gibbs theory of the glass-transition is extended at its molecular level. An expression for the number of configurations in the cooperatively rearranging region, which makes the macroscopic and molecular Adam-Gibbs equations compatible, is obtained. The number of configurations in the cooperatively rearranging region depends on the method for estimating the contribution of the vibration entropy to the entropy of the liquid. Two ways of extracting the vibration component from the entropy of the liquid have been used. In the first, the configuration entropy is regarded as the difference between those of the liquid and the crystal, and the second as the difference between the entropies of the liquid and the glass. In both cases the obtained number of configurations is larger than w z =2, as accepted by Adam and Gibbs. The measured number of configurations was found to increase with the size of the cooperatively rearranging regions or the kinetic fragility of the liquids. This i...
Journal of Physics: Condensed Matter, 2002
ABSTRACT The temperature and pressure dependence of the glass-transition process is discussed on ... more ABSTRACT The temperature and pressure dependence of the glass-transition process is discussed on the basis of the molecular Adam–Gibbs equation for the relaxation time. An equation for measuring the temperature and pressure dependence of the Adam–Gibbs size of the cooperative rearranging region is suggested. The apparent activation energy and the apparent relaxation volume by this equation are presented as the product of the activation energy and the activation volume per basic molecular kinetic unit respectively with the size of the cooperative unit to the second power. In this way, for the first time, an equation for measuring the activation volume of a basic molecular kinetic unit involved in the cooperative molecular dynamics is obtained. The isobaric and the isothermal activation volume of a basic molecular species (BMS) measured by this equation correlate with the molar volume of the liquid. From the experimental results it follows that the size of the cooperatively rearranging region at isothermal conditions increases with pressure until at the glass-transition pressures it reaches an apparent limit. On the basis of the activation volume measured per BMS, a method for evaluating their volume in liquids and their number in molecules or in repeated units in polymers is suggested. By this method, for the first time, from a relaxation experiment, the basic kinetic units in several molecular glass-forming liquids are found to be close to the fragments of the monomer segments or molecules known in thermodynamics as Wunderlich's beads.
European Polymer Journal, 1999
The temperature dependence of the average relaxation time in the glass transition region is discu... more The temperature dependence of the average relaxation time in the glass transition region is discussed. The relations for the number of the basic molecular kinetic units and the number of configurations in the cooperative rearranging region are described. The basic molecular kinetic units in the polymers are identified as fragments of the monomeric segments, called beads by Wunderlich. A model
The rearrangements of molecules in the cooperatively rearranging regions of the glass-forming liq... more The rearrangements of molecules in the cooperatively rearranging regions of the glass-forming liquids have been found to be activated hopping and non-activated free-diffusion ones. The total number of configurations in these regions is temperature invariant. At the glass-transition temperature all rearrangements are activated hopping and on rising the temperature they are transformed into the free-diffusion ones. The free diffusion rearrangements are assumed to produce a specific liquid behavior, while the activated-hopping ones a solid-like behavior in the liquid dynamics. The level of the specific liquid dynamics in the fragile liquids at 30-40 K above the glass-transition temperature rises to 50% of the total dynamics, or, the glass-transition represents ``melting'' of the solid-like dynamics. By the identification of the basic molecular units in liquids as thermodynamic ``beads'', it is concluded that molecules do not move like solid spheres as in the Mode Coupling Theory, but through all available intramolecular configurations.
ABSTRACT The rearrangements of molecules in the cooperatively rearranging regions of the glass-fo... more ABSTRACT The rearrangements of molecules in the cooperatively rearranging regions of the glass-forming liquids have been found to be activated hopping and non-activated free-diffusion ones. The total number of configurations in these regions is temperature invariant. At the glass-transition temperature all rearrangements are activated hopping and on rising the temperature they are transformed into the free-diffusion ones. The free diffusion rearrangements are assumed to produce a specific liquid behavior, while the activated-hopping ones a solid-like behavior in the liquid dynamics. The level of the specific liquid dynamics in the fragile liquids at 30-40 K above the glass-transition temperature rises to 50% of the total dynamics, or, the glass-transition represents ``melting'' of the solid-like dynamics. By the identification of the basic molecular units in liquids as thermodynamic ``beads'', it is concluded that molecules do not move like solid spheres as in the Mode Coupling Theory, but through all available intramolecular configurations.
A method for measuring transformation of the activated hopping over potential barriers dynamics i... more A method for measuring transformation of the activated hopping over potential barriers dynamics into free diffusion one in the glass-forming liquid has been found. In the glass-forming liquids the rearrangement of a local molecular structure is a cooperative process and the number of rearranging molecular species during the time of relaxation is defined as the size of the cooperatively rearranging region. At the glass-transition temperature every molecular species in the cooperatively rearranging region overcomes its own potential barrier and the number of the configurations per a basic molecular species is approximately equal to one, so the dynamics is assumed to be entirely activated. The increase of the number of configurations per a basic molecular species with increasing the temperature is applied as a measure for the transformation of the activated dynamics. Strong correlation of the level of transformation and the fragility of the liquid is observed.
Journal of Non-crystalline Solids, 2006
Adam-Gibbs factor at the dynamic phase transition temperature is found out to be 'universal,' as ... more Adam-Gibbs factor at the dynamic phase transition temperature is found out to be 'universal,' as it is at the glass transition temperature. A new scaling has been suggested collecting known 'universalities' related with the relaxation time. The fragility has been discussed in terms of the characteristic length at the glass-transition temperature. The transformation of the activation hopping into free diffusion dynamics in polymers is investigated.
Journal of Polymer Science: Polymer Physics Edition, 1974
ABSTRACT The electrical dipole relaxation in PMMA has been studied by measuring thermostimulated ... more ABSTRACT The electrical dipole relaxation in PMMA has been studied by measuring thermostimulated depolarizing currents. A master curve for the segmental component of the dielectric constant has been constructed. The increment of the dielectric permittivity due to the α-relaxation has been determined. The distribution function of the relaxation times and the average relaxation times in the region from 70°C up to Tg = 105°C have been obtained. A way of describing the electret properties of the polymer is discussed.
The Adam-Gibbs theory of the glass-transition is extended at its molecular level. An expression f... more The Adam-Gibbs theory of the glass-transition is extended at its molecular level. An expression for the number of configurations in the cooperatively rearranging region, which makes the macroscopic and molecular Adam-Gibbs equations compatible, is obtained. The number of configurations in the cooperatively rearranging region depends on the method for estimating the contribution of the vibration entropy to the entropy of the liquid. Two ways of extracting the vibration component from the entropy of the liquid have been used. In the first, the configuration entropy is regarded as the difference between those of the liquid and the crystal, and the second as the difference between the entropies of the liquid and the glass. In both cases the obtained number of configurations is larger than w z =2, as accepted by Adam and Gibbs. The measured number of configurations was found to increase with the size of the cooperatively rearranging regions or the kinetic fragility of the liquids. This i...
Journal of Physics: Condensed Matter, 2002
ABSTRACT The temperature and pressure dependence of the glass-transition process is discussed on ... more ABSTRACT The temperature and pressure dependence of the glass-transition process is discussed on the basis of the molecular Adam–Gibbs equation for the relaxation time. An equation for measuring the temperature and pressure dependence of the Adam–Gibbs size of the cooperative rearranging region is suggested. The apparent activation energy and the apparent relaxation volume by this equation are presented as the product of the activation energy and the activation volume per basic molecular kinetic unit respectively with the size of the cooperative unit to the second power. In this way, for the first time, an equation for measuring the activation volume of a basic molecular kinetic unit involved in the cooperative molecular dynamics is obtained. The isobaric and the isothermal activation volume of a basic molecular species (BMS) measured by this equation correlate with the molar volume of the liquid. From the experimental results it follows that the size of the cooperatively rearranging region at isothermal conditions increases with pressure until at the glass-transition pressures it reaches an apparent limit. On the basis of the activation volume measured per BMS, a method for evaluating their volume in liquids and their number in molecules or in repeated units in polymers is suggested. By this method, for the first time, from a relaxation experiment, the basic kinetic units in several molecular glass-forming liquids are found to be close to the fragments of the monomer segments or molecules known in thermodynamics as Wunderlich's beads.
European Polymer Journal, 1999
The temperature dependence of the average relaxation time in the glass transition region is discu... more The temperature dependence of the average relaxation time in the glass transition region is discussed. The relations for the number of the basic molecular kinetic units and the number of configurations in the cooperative rearranging region are described. The basic molecular kinetic units in the polymers are identified as fragments of the monomeric segments, called beads by Wunderlich. A model
The rearrangements of molecules in the cooperatively rearranging regions of the glass-forming liq... more The rearrangements of molecules in the cooperatively rearranging regions of the glass-forming liquids have been found to be activated hopping and non-activated free-diffusion ones. The total number of configurations in these regions is temperature invariant. At the glass-transition temperature all rearrangements are activated hopping and on rising the temperature they are transformed into the free-diffusion ones. The free diffusion rearrangements are assumed to produce a specific liquid behavior, while the activated-hopping ones a solid-like behavior in the liquid dynamics. The level of the specific liquid dynamics in the fragile liquids at 30-40 K above the glass-transition temperature rises to 50% of the total dynamics, or, the glass-transition represents ``melting'' of the solid-like dynamics. By the identification of the basic molecular units in liquids as thermodynamic ``beads'', it is concluded that molecules do not move like solid spheres as in the Mode Coupling Theory, but through all available intramolecular configurations.
ABSTRACT The rearrangements of molecules in the cooperatively rearranging regions of the glass-fo... more ABSTRACT The rearrangements of molecules in the cooperatively rearranging regions of the glass-forming liquids have been found to be activated hopping and non-activated free-diffusion ones. The total number of configurations in these regions is temperature invariant. At the glass-transition temperature all rearrangements are activated hopping and on rising the temperature they are transformed into the free-diffusion ones. The free diffusion rearrangements are assumed to produce a specific liquid behavior, while the activated-hopping ones a solid-like behavior in the liquid dynamics. The level of the specific liquid dynamics in the fragile liquids at 30-40 K above the glass-transition temperature rises to 50% of the total dynamics, or, the glass-transition represents ``melting'' of the solid-like dynamics. By the identification of the basic molecular units in liquids as thermodynamic ``beads'', it is concluded that molecules do not move like solid spheres as in the Mode Coupling Theory, but through all available intramolecular configurations.
A method for measuring transformation of the activated hopping over potential barriers dynamics i... more A method for measuring transformation of the activated hopping over potential barriers dynamics into free diffusion one in the glass-forming liquid has been found. In the glass-forming liquids the rearrangement of a local molecular structure is a cooperative process and the number of rearranging molecular species during the time of relaxation is defined as the size of the cooperatively rearranging region. At the glass-transition temperature every molecular species in the cooperatively rearranging region overcomes its own potential barrier and the number of the configurations per a basic molecular species is approximately equal to one, so the dynamics is assumed to be entirely activated. The increase of the number of configurations per a basic molecular species with increasing the temperature is applied as a measure for the transformation of the activated dynamics. Strong correlation of the level of transformation and the fragility of the liquid is observed.
Journal of Non-crystalline Solids, 2006
Adam-Gibbs factor at the dynamic phase transition temperature is found out to be 'universal,' as ... more Adam-Gibbs factor at the dynamic phase transition temperature is found out to be 'universal,' as it is at the glass transition temperature. A new scaling has been suggested collecting known 'universalities' related with the relaxation time. The fragility has been discussed in terms of the characteristic length at the glass-transition temperature. The transformation of the activation hopping into free diffusion dynamics in polymers is investigated.