- University of Patras
Department of Physics
GR-26504, Patras, Greece
Evangelos Vitoratos
University of Patras, Physics, Faculty Member
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The study of students' mental representations of Natural Sciences concepts and phenomena constitutes a central part of Science Education research, as they play a decisive role in teaching. In the study presented here,... more
The study of students' mental representations of Natural Sciences concepts and phenomena constitutes a central part of Science Education research, as they play a decisive role in teaching. In the study presented here, we investigate 157 ninth grade students' mental representations of the magnetic field, after they were taught about it in school. The empirical data was gathered through an interview using 4 tasks which involved the evaluation of actual or hypothetical situations. The research data included mental representations that ...
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The intercalation of conductive polyaniline (PANI) and polypyrrole (PPy) chains in zeolite galleries (Fig. 1) a few nanometers wide, allows obtaining composite materials with significantly improved mechanical, thermal and chemical... more
The intercalation of conductive polyaniline (PANI) and polypyrrole (PPy) chains in zeolite galleries (Fig. 1) a few nanometers wide, allows obtaining composite materials with significantly improved mechanical, thermal and chemical properties [1]. These nanocomposites can find application in hydrogen storage, solid electrolyte cells, chemical gas or pH sensors, membranes, fabrication of molecular wires, etc. Moreover, PANI and PPy combined with ZnO nanoparticles can make composite polymer/insulating materials suitable for solar cells [1-3]. In PANi there is a strong, short 2.45 Å hydrogen bond between neighbouring chains, making PANI semicrystalline, with ordered crystalline regions (grains) characterized by high electrical conductivity embedded in an amorphous insulating matrix. On the contrary, in PPy weak van der Waals forces hold together the aromatic groups at a distance of 3.42 Å making the polymer amorphous [4]. SEM images and XRD patterns of PANI/ZnO composites reveal tha...
Physics (Science) dismisses all the “subjective” aspects under which nature can be regarded and it is confined to only the “objective” ones, which can be measured. However, subjective and objective aspects are always interrelated and... more
Physics (Science) dismisses all the “subjective” aspects under which nature can be regarded and it is confined to only the “objective” ones, which can be measured. However, subjective and objective aspects are always interrelated and supplement each other, so the question arises, if the physical picture of reality given by science is complete or not.
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This study confirms the significant role of oxygen and moisture on the electrical conductivity, as a comparison is made between measurements under inert He and ambient air. Under He the factors increasing conductivity prevail and... more
This study confirms the significant role of oxygen and moisture on the electrical conductivity, as a comparison is made between measurements under inert He and ambient air. Under He the factors increasing conductivity prevail and morphology stabilizes with heating. On the contrary, under ambient air, influences increasing the conductivity compete with others having the opposite result. The destructive role of oxygen and moisture becomes evident from isothermal heating, as well as cooling and heating cycles.
Stakeholders Tune European Physics Studies Two (STEPSTWO) project has been supported by the European Commission through the Life Long Learning (LLL) Programme-Erasmus programme- Academic Networks projects of its Directorate-General for... more
Stakeholders Tune European Physics Studies Two (STEPSTWO) project has been supported by the European Commission through the Life Long Learning (LLL) Programme-Erasmus programme- Academic Networks projects of its Directorate-General for Education and Culture.
Research Interests: Materials Engineering, Condensed Matter Physics, Materials Science, Conducting Polymer, DIELECTRIC, and 13 moreActivation Energy, Polypyrrole, Composite Material, Dielectric Properties, Dielectric Relaxation, Temperature Dependence, Constant Time Delay, Dielectric Loss, Room Temperature, Thermal annealing, Liquid Nitrogen, Electric Conductivity, and Thermal Degradation
ABSTRACT A new type of solid state chemiresistors sensitive to pH-changes is described. The chemical-sensitive layer consists of polypyrrole incorporated into a polyvinyl alcohol polymer matrix by polymerization under vacuum. Preliminary... more
ABSTRACT A new type of solid state chemiresistors sensitive to pH-changes is described. The chemical-sensitive layer consists of polypyrrole incorporated into a polyvinyl alcohol polymer matrix by polymerization under vacuum. Preliminary testing has shown these sensors to be stable in aqueous solutions at temperatures up to 50°C with response times in seconds. At 25°C the sensor sensitivity was 47Ω/pH. Interferences appear to be acceptably small.
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ABSTRACT The charge trapping centers in fresh and thermally aged conductive polyaniline–polypyrrole copolymers (starting from pure polyaniline and ending in pure polypyrrole by steps of 10 wt%) were studied by thermally stimulated... more
ABSTRACT The charge trapping centers in fresh and thermally aged conductive polyaniline–polypyrrole copolymers (starting from pure polyaniline and ending in pure polypyrrole by steps of 10 wt%) were studied by thermally stimulated depolarization current (TSDC) spectroscopy and dc conductivity measurements. One low temperature (115–135 K) relaxation mechanism appears in polyaniline-rich copolymers and disappears after thermal anneal. It is attributed to polaron trapping in the vicinity of chlorine anion dopants. Another relaxation mechanism operates close to room temperature and is related to conformational relaxation, which corresponds to the influence of the annihilation of the conformons on the conduction mechanism. The relaxation is sensitive to thermal aging as a result of the thermal annealing on the conductivity. The temperature derivative of the dc conductivity supports the latter assertion. The activation energy values were obtained as a function of composition for both fresh and heated samples. The TSDC spectroscopy is a sensitive tool which is an alternative to the standard conductivity studies for the characterization of polypyrrole–polyaniline conductive copolymers and the study of the thermal degradation.
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ABSTRACT The dielectric properties of polypyrrole-zeolite composites up to 50% w / w zeolite are studied in the frequency range from 10-2 to 2×106 Hz from room temperature to liquid nitrogen temperature. The complex permittivity formalism... more
ABSTRACT The dielectric properties of polypyrrole-zeolite composites up to 50% w / w zeolite are studied in the frequency range from 10-2 to 2×106 Hz from room temperature to liquid nitrogen temperature. The complex permittivity formalism reveals a temperature dependent relaxation in all samples except for the 25% w / w zeolite composite. The frequency f max where a maximum of a loss peak is located varies with temperature by the Williams-Lander-Ferry law. The values of the activation energy of the relaxation process (which are of the order of polaronic dc conductivity) have the tendency to reach a minimum in the 25% w / w composition, which is a loss-free composite. The 50% w / w zeolite behaves as a dielectric where ionic relaxation dominates. The temperature variation of the strength of the dielectric mechanism follows a Curie law, apart from 50% w / w zeolite where the dielectric strength is practically constant. The frequencies, where loss peaks are maximum, as well as dc conductivity follow qualitatively the same temperature law, but the parameters are quite different. Moreover, the locations of the relaxation peaks diverge from the predictions of Barton-Nakajima-Namikawa model. Long-range electric charge transport (dc conductivity) and the relaxation that corresponds to short-range localized motion probably involve different processes.
Research Interests: Engineering, Materials Science, Applied Physics, Low Frequency, Mathematical Sciences, and 15 moreDIELECTRIC, Physical sciences, Activation Energy, Polypyrrole, Long Range, Composite Material, Dielectric Properties, Dielectric Relaxation, Conductivity, Dielectric Loss, Room Temperature, Charge Transport, Liquid Nitrogen, Complex permittivity, and Permittivity
An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range from 80–360 K on nanocrystalline ZnO:Al films (Al3+ 2%) of thickness 500 nm prepared on glass microscope slides by... more
An experimental study of the temperature dependence of the d.c. conductivity σ as a function of temperature T in the range from 80–360 K on nanocrystalline ZnO:Al films (Al3+ 2%) of thickness 500 nm prepared on glass microscope slides by a dip — coating method is presented. The electrical conductivity σ, which at room temperature varied between 0.1 to 2.7
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Abstract: Children's mental representations about physical concepts and phenomena play a vital role in the learning process. This is confirmed by the data derived from relevant researches which demonstrate that the students formulate... more
Abstract: Children's mental representations about physical concepts and phenomena play a vital role in the learning process. This is confirmed by the data derived from relevant researches which demonstrate that the students formulate incompatible ideas compared with the ...
As the conducted researches have put to the foreground the main problems of Science Teaching in Primary Schools can be grouped in the following categories: 1. Problems related with the social status and economics of Primary School Science... more
As the conducted researches have put to the foreground the main problems of Science Teaching in Primary Schools can be grouped in the following categories: 1. Problems related with the social status and economics of Primary School Science Teachers (PSST). 2. Problems of infrastructure such as poor facilities for experiments. 3. Problems occurring from the “insufficient” education of PSST. 4. Problems related with Cognitive Science and Biology. 5. Lack of motivation and profound interest to teaching Physics. Concerning points (1) and (2), government and local authorities seem to have the main responsibility, but, with respect to (3), (4) and (5), it is the "in service training" that plays a crucial role. Indeed, successful "in service training" leads to continuing professional development and support, enhancing teachers' motivation as well as strengthening their self confidence in teaching Science. Such an example of good practice could be considered the Insti...
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Towards applied semiotics: An analysis of
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This paper describes a study case of the Science and Technology Museum (STM) of Patras University, Greece. It highlights its role in the development of the University’s cultural landscape and in its extension. STM succeeded to influence... more
This paper describes a study case of the Science and Technology Museum (STM) of Patras University, Greece. It highlights its role in the development of the University’s cultural landscape and in its extension. STM succeeded to influence it by offering high quality non-formal education services to society. It was socially endorsed by the university and society. The key lies in sustainability which STM achieved to easily manage change and has endorsed strong and cost effective rules for functioning. New channels for distribution of scientific culture were developed. They have changed how people consume scientific and technological culture and created strong university-community partnerships. UNIVERSITY MUSEUMS AND COLLECTIONS JOURNAL 52 — VOLUME 9 2017
ABSTRACT Samples of conducting nanocomposites of polyaniline (PANI) and polypyrrole (PPy) with zeolite concentrations from 0 to 50% w/w and ZnO from 0 to 40% w/w were synthesized through oxidative polymerization. Their d.c. conductivity... more
ABSTRACT Samples of conducting nanocomposites of polyaniline (PANI) and polypyrrole (PPy) with zeolite concentrations from 0 to 50% w/w and ZnO from 0 to 40% w/w were synthesized through oxidative polymerization. Their d.c. conductivity was measured under He atmosphere from 80 to 350 K and their thermal stability was studied by heating them at 70 °C for times from 0 to 600 h under environmental conditions. The experimental results are consistent with a granular metal structure in which conductive grains are embedded in an insulating matrix and thermal degradation is due to the corrosion–like shrinking of them with thermal treatment. In the PANI/zeolite composites the conductivity and the thermal stability remain practically unchanged with increasing zeolite content. On the contrary, in PPy/zeolite composites these properties improve with increasing zeolite concentration. Moreover, SEM images and XRD patterns of PANI/ZnO composites reveal that a number of the ZnO particles are expelled from the matrix, although in PPy/ZnO composites ZnO is completely encapsulated into the polymer. These differences can be attributed to the stronger bond between PANI chains which justify the formation of crystalline conductive grains in it, in contrast to the much weaker packing of polymer chains in the amorphous PPy.
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This project addressed the difficulties of measuring students’ workload for four major courses, of the Department of Physics, University of Patras. The motivation for this research was the high average of years for graduation that the... more
This project addressed the difficulties of measuring students’ workload for four major courses, of the Department of Physics, University of Patras. The motivation for this research was the high average of years for graduation that the students of the aforementioned department usually have. In the context of seeking the responsible factors it seems reasonable to assume that student’s workload is related with the examination results. Consequently, for the estimation of this parameter, we take into account, professors’ estimation (PE) and students’ estimation (SE). In order to collect the related data, questionnaires, personal interviews and surveys were used. Results indicate that students’ estimations (SE) does not always keep pace to professors’ ones (PE) in order for the students to achieve the minimum passing grade. Both parts agree that daily study is the key in order to pass the final exam. As regard the students’ estimation, seems that personal study predominates in their prefe...
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Abstract In this article we discuss the concept of “materiality” within a framework created by two apparently divergent fields, which, however, converge with regard to their pedagogical and communicative content. Theatre semiotics... more
Abstract In this article we discuss the concept of “materiality” within a framework created by two apparently divergent fields, which, however, converge with regard to their pedagogical and communicative content. Theatre semiotics proposes forms and structures that shed light on such material aspects of learning environments related to physics as the instantiation of “narrative spaces.” Our perspective focuses first on the modalities by means of which various sign-vehicles (ie, verbal, visual, kinesic-corporeal or sound-related signs), being agents of ...
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The way by which ancient Greek philosophers came to the concept of atom is presented. The concept of atom, a great creation of the human mind, gave a direct, modern-like explanation of the world, at times in which the huge amount of... more
The way by which ancient Greek philosophers came to the concept of atom is presented. The concept of atom, a great creation of the human mind, gave a direct, modern-like explanation of the world, at times in which the huge amount of experimental and theoretical information of today was not available. This lack proved not an impossible obstacle for ancient
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The thermal aging of conducting polypyrrole/polyaniline (PPy/PA) blends heated at 70°C for up to about 600 hours was studied by d.c. conductivity measurements and by thermally stimulated depolarization current (TSDC) spectroscopy in the... more
The thermal aging of conducting polypyrrole/polyaniline (PPy/PA) blends heated at 70°C for up to about 600 hours was studied by d.c. conductivity measurements and by thermally stimulated depolarization current (TSDC) spectroscopy in the temperature range from 80 to 300 K. The composition of the samples varied from pure polypyrrole to pure polyaniline with the PA content increasing in steps of 10%. Although the s = s(T) curves seem smooth, the corresponding ?s/?T = f(T) curves exhibit systematically ascattering of points in the temperature ranges from 100 to 140 K and from 225 to 320 K approximately for all the samples before and after the heat treatment. TSDC measurements with the MISIM (metal-insulator-sample-insulator-metal) configuration, show a low temperature peak at 100–120 K and a high temperature peak at 280–300 K. The first disappears when the polypyrrole content exceeds 70% and for all the samples after heat treatment, although the high-temperature peak persists. The expla...
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ABSTRACT The DC conductivity and thermopower of polyaniline derivatives were measured for temperatures ranging from 80 to 345 K. The samples were oxidized to different degrees, fully protonated and further doped with -SO3H, -COOH and... more
ABSTRACT The DC conductivity and thermopower of polyaniline derivatives were measured for temperatures ranging from 80 to 345 K. The samples were oxidized to different degrees, fully protonated and further doped with -SO3H, -COOH and phosphorylated polystyrene additives to concentrations varying from 0 to 100 mol.% of functional group per mole of aniline. The DC conductivity sigma (300 K) ranges from 0.01 to 16 S cm-1, depending on the degree of oxidation and dopant concentration, while sigma (T)= sigma 0 exp(-(T0/T)0.5), where T0 is mainly determined by the degree of oxidation. The thermopower, which is of the order of -15 mu V K-1 at 300 K, changes sign from n to p with increasing temperature at Tr, which varies between 290 and 325 K. This change in sign, which is reversed during cooling, is attributed to the existence of a half-filled polaronic band situated deep in the energy gap of polyaniline.
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An energy-band model is presented for pyrrhotite, based on the energy levels calculated for an octahedral FeS 10− 6 cluster, the X-ray spectroscopical data, the magnetic, electrical and optical properties of this compound and the... more
An energy-band model is presented for pyrrhotite, based on the energy levels calculated for an octahedral FeS 10− 6 cluster, the X-ray spectroscopical data, the magnetic, electrical and optical properties of this compound and the energy-band calculations for NiS. The model ...
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ABSTRACT The dc electrical conductivity (σ) of HCl-protonated polyaniline, polypyrrole, and their blends was measured from 80 to 300 K for thermal aging times between approximately 0 and 600 h. The thermal aging took place at 70°C under... more
ABSTRACT The dc electrical conductivity (σ) of HCl-protonated polyaniline, polypyrrole, and their blends was measured from 80 to 300 K for thermal aging times between approximately 0 and 600 h. The thermal aging took place at 70°C under room atmosphere. The change of σ with the temperature (T) and the decrease of σ with the thermal aging time (t) are consistent with a granular metal type structure, in which conductive grains are randomly distributed into an insulating matrix. Aging makes the grains shrink in a corrosion-like process. From σ = σ(T) measurements the ratio s/d, where s is the average separation between the grains and d their diameter, as well as the rate d(s/d)/dt of their decrease with t were calculated. These revealed that the conductive grains consist of a shell, in which aging proceeds at a decreasing rate, and a central core, which is consumed at a much slower rate. Our measurements not only permitted the estimation of the shell thickness, which lies between 0 and 5 Å, but also gave quantitative information about the quality of the shells and the cores from their aging rates. The shells are consumed with an average rate of d(s/d)/dt = 6.6 × 10−4 (h−1), which is about 5 times greater than the more durable cores. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 117–122, 2005
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ABSTRACT Isotherms of the imaginary part of the permittivity from 10−2 to 2×106 Hz from liquid nitrogen to room temperature for fresh and thermally aged specimens of conducting polypyrrole reveal a dielectric loss peak, which is affected... more
ABSTRACT Isotherms of the imaginary part of the permittivity from 10−2 to 2×106 Hz from liquid nitrogen to room temperature for fresh and thermally aged specimens of conducting polypyrrole reveal a dielectric loss peak, which is affected by the reduction of conducting grains with aging. Charge trapping at the interfaces separating the conductive islands seems invalid. Thermal aging indicates that macroscopic conductivity and short range one have different aging evolution. The first (dc conductivity) is dominated by the tunneling of the carriers between neighboring grains through the intermediate insulating barriers, though the second (ac conductivity) is due to a backward-forward movement of the carriers and is controlled by the intrachain transport of them and their hopping between the chains.
Research Interests: Engineering, Physics, Condensed Matter Physics, Materials Science, DIELECTRIC, and 15 morePhysical sciences, Thermal conduction in Nanomaterials, Polypyrrole, Dielectric Relaxation, Conductivity, Dielectric Loss, Room Temperature, Quantum Tunnelling, Charge Transport, Trapping, Liquid Nitrogen, Organic Compound, Solid Solution, Thermal Degradation, and Permittivity
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The study of students' mental representations of Natural Sciences concepts and phenomena constitutes a central part of Science Education research, as they play a decisive role in teaching. In the study presented here, we investigate... more
The study of students' mental representations of Natural Sciences concepts and phenomena constitutes a central part of Science Education research, as they play a decisive role in teaching. In the study presented here, we investigate 157 ninth grade students' mental representations of the magnetic field, after they were taught about it in school. The empirical data was gathered through an interview using 4 tasks which involved the evaluation of actual or hypothetical situations. The research data included mental representations that ...