Mihai Todica - Academia.edu (original) (raw)
Papers by Mihai Todica
Indian Journal of Pure & Applied Physics, 2015
Electrical conductivity and structural properties of PAA-graphite membranes after gamma irradiati... more Electrical conductivity and structural properties of PAA-graphite membranes after gamma irradiation at D =1.7 KGy, have been studied. The electrical conductivity of pure PAA membranes is very low, but the introduction of small quantity of graphite increases this property significantly due to the connections established between the graphite trapped in the polymeric holes. The electrical conductivity of the doped membranes increases after irradiation. This behaviour is correlated with the modification of the local ordered structure of the polymeric matrix and the apparition of supplementary unpaired electrons from the graphite. These microscopic modifications have been investigated by XRD and ESR methods.
Ce travail contribue a l'exploration et a la comprehension de la dynamique moleculaire dans l... more Ce travail contribue a l'exploration et a la comprehension de la dynamique moleculaire dans les polymeres fondus ou en solutions concentrees. Nos sujets d'interet sont la diffusion des molecules de solvant dans les solutions polymeres, la dynamique segmentaire dans la chaine polymere et l'effet d'elasticite temporaire des chaines polymeres. La diffusion des petites molecules de solvant, etudiee par la methode des impulsions de gradient de champ magnetique, est decrite dans le cadre des modeles s'appuyant sur le concept de volume libre. Ces modeles permettent de calculer les parametres de volume libre du solvant et du polymere et la taille de l'unite diffusante du polymere. L'effet d'elasticite temporaire est etudie en liaison avec le comportement de type solide des fonctions de relaxation de l'aimantation transversale. Le temps de relaxation de l'aimantation transversale est une fonction de la concentration en polymere, de la temperature et du...
New biodegradable materials, with applications in packaging, can be obtained by plasticization of... more New biodegradable materials, with applications in packaging, can be obtained by plasticization of starch with glycerin and water. The physical properties of new materials are different from those of the initial components, and some properties of the initial components are subject to modifications during the synthesis process. Such modifications were investigated by XRD and IR spectroscopy. For this aim some new types of packaging materials with different starch, glycerin and water (mass %) ratios were prepared and investigated after extrusion process. XRD measurements indicate a progressive degradation of the ordered phase of the starch in function of glycerin and water content of samples. It can be observed that increasing of water concentration leads to a progressive degradation of the ordered structure of pure starch, (samples P1 and P2), until a completely amorphous phase that appears at highest water concentration (sample P3 having starch/glycerin/ water 68/17/15 mass % ratio)....
AIP Conference Proceedings, 2007
In Romania, in the Central Transylvania region, around the Campia Turzii Metallurgical Complex, t... more In Romania, in the Central Transylvania region, around the Campia Turzii Metallurgical Complex, the soil is loaded with Cr, Cu and Pb at levels exceeding in some places, 16 times, the maximum allowable limits ICP spectrometry and NAA measured the concentration of heavy metals.
Open Physics, 2013
The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were inves... more The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were investigated by ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signal appears only for irradiated samples and it is associated with the breaking of the polymeric chain, followed by local reorganization of the polymeric segments and the apparition of the unpaired electrons and free radicals. The intensity of the signal decreases with the concentration of TiO2, indicating a shielding effect of the dopand. That the modification of local order of the polymeric chains has been modified after irradiation is confirmed by XRD method.
Talanta, 2000
A method for preliminary evaluation of the correlation time of local dynamics of the polymeric ch... more A method for preliminary evaluation of the correlation time of local dynamics of the polymeric chains, using the experimental nuclear magnetic resonance spin-lattice relaxation data, is proposed. The algorithm is based on the model of the passage of a particle over a potential energy barrier. This method was utilized for some molten polymers and concentrated polymeric solutions.
International Journal of Molecular Sciences, 2008
The concentration of five soil heavy metals (Pb, Co, Cr, Cu, Hg) was measured in forty sampling s... more The concentration of five soil heavy metals (Pb, Co, Cr, Cu, Hg) was measured in forty sampling sites in central Transylvania, Romania, regions known as centres of pollution due to the chemical and metallurgical activities. The soil samples were collected from locations where the ground is not sliding and the probability of alluvial deposits is small. The concentration of heavy metals was measured by using the Inductively Coupled Plasma Spectrometry method. Data were verified by using the Neutron Activation Analysis method. In some locations, the concentration for the investigated heavy metals exceeds the concentration admitted by the Romanian guideline. The highest concentration of lead (1521.8 ppm) and copper (1197.6 ppm) was found in Zlatna. The highest concentration of chromium was found in Târnăveni (1080 ppm). The maximum admitted concentrations in the sensitive areas revealed to be exceed from five to forty times.
Studia Universitatis Babeș-Bolyai Physica
Materials Today: Proceedings
Materials Today: Proceedings
Studia Universitatis Babeș-Bolyai Chemia
Thermal degradation of commercial polystyrene was investigated by XRD and FT-IR metods. The sampl... more Thermal degradation of commercial polystyrene was investigated by XRD and FT-IR metods. The samples were heated 30 minutes at temperatures 140ºC, 200ºC, 250ºC, 300ºC and 350ºC and then brought back to room temperature. XRD investigation denotes structural modification for samples heated above 200ºC. This modification is confirmed by FT-IR measurments. Some vibration bands are affected by thermal degradation at temperatures higher than 200ºC. Both FT-IR and XRD methods reveal modification of microscopic structure of the polystyrene submitted to thermal degradation.
International Journal of Modern Physics B
The modification of local structure of some commercial polyethylene terephthalate (PET) samples, ... more The modification of local structure of some commercial polyethylene terephthalate (PET) samples, gamma irradiated at different doses, was investigated by X-ray diffraction method before and after thermal treatment. Before the thermal treatment, the samples exposed to different doses of gamma radiations, does not show noticeable structural changes. However, the gamma exposure affects the thermal behavior of samples submitted to melting–cooling process. These modifications have been highlighted by X-ray diffraction, and confirmed also by thermal analysis and electron spin resonance spectroscopy.
Studia Universitatis Babeș-Bolyai Physica
Studia Universitatis Babeș-Bolyai Physica
Studia Universitatis Babeș-Bolyai. Chemia
ABSTRACT
Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. Agriculture, 2016
The recent interest in the field of bioplastics is to obtain packaging material from pure starch ... more The recent interest in the field of bioplastics is to obtain packaging material from pure starch without synthetic polymers. The rheological behaviour represents one of the most important feature of such materials. Samples with different ratio of starch, glycerol and water were prepared and investigate regarding their rheological behaviour. After the samples reaches their limit of swelling and were completely decomposed viscosity was measured with a Brookfield DV-III Ultra rheometer at different temperatures and share rates. The data were analyzed with Kaleidagraph software. For a given sample our measurements show that the viscosity is dependent on share rate and switches from a non-Newtonian to a Newtonian behaviour in function of temperature and sample composition. We used the power law model to describe this dependence and for a given set of data there is only one output for the fit parameters. We consider the best fit of the experimental data when the curve traced by the computer passes almost through all experimental points. In the present research work we establish a particular algorithm of mathematical analysis of experimental data which allows a separation of the contribution of each variable to the viscosity.
The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated ... more The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated were investigated by XRD, UV-VIS and Raman spectroscopies. The increase of UV absorbance is observed after irradiation. This behavior is correlated with the scission effect and local ordering of the polymeric chain induced by irradiation. These effects were probed by XRD and Raman spectroscopy.
Indian Journal of Pure & Applied Physics, 2015
Electrical conductivity and structural properties of PAA-graphite membranes after gamma irradiati... more Electrical conductivity and structural properties of PAA-graphite membranes after gamma irradiation at D =1.7 KGy, have been studied. The electrical conductivity of pure PAA membranes is very low, but the introduction of small quantity of graphite increases this property significantly due to the connections established between the graphite trapped in the polymeric holes. The electrical conductivity of the doped membranes increases after irradiation. This behaviour is correlated with the modification of the local ordered structure of the polymeric matrix and the apparition of supplementary unpaired electrons from the graphite. These microscopic modifications have been investigated by XRD and ESR methods.
Ce travail contribue a l'exploration et a la comprehension de la dynamique moleculaire dans l... more Ce travail contribue a l'exploration et a la comprehension de la dynamique moleculaire dans les polymeres fondus ou en solutions concentrees. Nos sujets d'interet sont la diffusion des molecules de solvant dans les solutions polymeres, la dynamique segmentaire dans la chaine polymere et l'effet d'elasticite temporaire des chaines polymeres. La diffusion des petites molecules de solvant, etudiee par la methode des impulsions de gradient de champ magnetique, est decrite dans le cadre des modeles s'appuyant sur le concept de volume libre. Ces modeles permettent de calculer les parametres de volume libre du solvant et du polymere et la taille de l'unite diffusante du polymere. L'effet d'elasticite temporaire est etudie en liaison avec le comportement de type solide des fonctions de relaxation de l'aimantation transversale. Le temps de relaxation de l'aimantation transversale est une fonction de la concentration en polymere, de la temperature et du...
New biodegradable materials, with applications in packaging, can be obtained by plasticization of... more New biodegradable materials, with applications in packaging, can be obtained by plasticization of starch with glycerin and water. The physical properties of new materials are different from those of the initial components, and some properties of the initial components are subject to modifications during the synthesis process. Such modifications were investigated by XRD and IR spectroscopy. For this aim some new types of packaging materials with different starch, glycerin and water (mass %) ratios were prepared and investigated after extrusion process. XRD measurements indicate a progressive degradation of the ordered phase of the starch in function of glycerin and water content of samples. It can be observed that increasing of water concentration leads to a progressive degradation of the ordered structure of pure starch, (samples P1 and P2), until a completely amorphous phase that appears at highest water concentration (sample P3 having starch/glycerin/ water 68/17/15 mass % ratio)....
AIP Conference Proceedings, 2007
In Romania, in the Central Transylvania region, around the Campia Turzii Metallurgical Complex, t... more In Romania, in the Central Transylvania region, around the Campia Turzii Metallurgical Complex, the soil is loaded with Cr, Cu and Pb at levels exceeding in some places, 16 times, the maximum allowable limits ICP spectrometry and NAA measured the concentration of heavy metals.
Open Physics, 2013
The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were inves... more The effects of gamma radiation on the local structure of PVA membranes containing TiO2 were investigated by ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signal appears only for irradiated samples and it is associated with the breaking of the polymeric chain, followed by local reorganization of the polymeric segments and the apparition of the unpaired electrons and free radicals. The intensity of the signal decreases with the concentration of TiO2, indicating a shielding effect of the dopand. That the modification of local order of the polymeric chains has been modified after irradiation is confirmed by XRD method.
Talanta, 2000
A method for preliminary evaluation of the correlation time of local dynamics of the polymeric ch... more A method for preliminary evaluation of the correlation time of local dynamics of the polymeric chains, using the experimental nuclear magnetic resonance spin-lattice relaxation data, is proposed. The algorithm is based on the model of the passage of a particle over a potential energy barrier. This method was utilized for some molten polymers and concentrated polymeric solutions.
International Journal of Molecular Sciences, 2008
The concentration of five soil heavy metals (Pb, Co, Cr, Cu, Hg) was measured in forty sampling s... more The concentration of five soil heavy metals (Pb, Co, Cr, Cu, Hg) was measured in forty sampling sites in central Transylvania, Romania, regions known as centres of pollution due to the chemical and metallurgical activities. The soil samples were collected from locations where the ground is not sliding and the probability of alluvial deposits is small. The concentration of heavy metals was measured by using the Inductively Coupled Plasma Spectrometry method. Data were verified by using the Neutron Activation Analysis method. In some locations, the concentration for the investigated heavy metals exceeds the concentration admitted by the Romanian guideline. The highest concentration of lead (1521.8 ppm) and copper (1197.6 ppm) was found in Zlatna. The highest concentration of chromium was found in Târnăveni (1080 ppm). The maximum admitted concentrations in the sensitive areas revealed to be exceed from five to forty times.
Studia Universitatis Babeș-Bolyai Physica
Materials Today: Proceedings
Materials Today: Proceedings
Studia Universitatis Babeș-Bolyai Chemia
Thermal degradation of commercial polystyrene was investigated by XRD and FT-IR metods. The sampl... more Thermal degradation of commercial polystyrene was investigated by XRD and FT-IR metods. The samples were heated 30 minutes at temperatures 140ºC, 200ºC, 250ºC, 300ºC and 350ºC and then brought back to room temperature. XRD investigation denotes structural modification for samples heated above 200ºC. This modification is confirmed by FT-IR measurments. Some vibration bands are affected by thermal degradation at temperatures higher than 200ºC. Both FT-IR and XRD methods reveal modification of microscopic structure of the polystyrene submitted to thermal degradation.
International Journal of Modern Physics B
The modification of local structure of some commercial polyethylene terephthalate (PET) samples, ... more The modification of local structure of some commercial polyethylene terephthalate (PET) samples, gamma irradiated at different doses, was investigated by X-ray diffraction method before and after thermal treatment. Before the thermal treatment, the samples exposed to different doses of gamma radiations, does not show noticeable structural changes. However, the gamma exposure affects the thermal behavior of samples submitted to melting–cooling process. These modifications have been highlighted by X-ray diffraction, and confirmed also by thermal analysis and electron spin resonance spectroscopy.
Studia Universitatis Babeș-Bolyai Physica
Studia Universitatis Babeș-Bolyai Physica
Studia Universitatis Babeș-Bolyai. Chemia
ABSTRACT
Bulletin of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca. Agriculture, 2016
The recent interest in the field of bioplastics is to obtain packaging material from pure starch ... more The recent interest in the field of bioplastics is to obtain packaging material from pure starch without synthetic polymers. The rheological behaviour represents one of the most important feature of such materials. Samples with different ratio of starch, glycerol and water were prepared and investigate regarding their rheological behaviour. After the samples reaches their limit of swelling and were completely decomposed viscosity was measured with a Brookfield DV-III Ultra rheometer at different temperatures and share rates. The data were analyzed with Kaleidagraph software. For a given sample our measurements show that the viscosity is dependent on share rate and switches from a non-Newtonian to a Newtonian behaviour in function of temperature and sample composition. We used the power law model to describe this dependence and for a given set of data there is only one output for the fit parameters. We consider the best fit of the experimental data when the curve traced by the computer passes almost through all experimental points. In the present research work we establish a particular algorithm of mathematical analysis of experimental data which allows a separation of the contribution of each variable to the viscosity.
The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated ... more The UV-VIS absorption property and the structural modification of PVA membranes gamma irradiated were investigated by XRD, UV-VIS and Raman spectroscopies. The increase of UV absorbance is observed after irradiation. This behavior is correlated with the scission effect and local ordering of the polymeric chain induced by irradiation. These effects were probed by XRD and Raman spectroscopy.