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Dr Constantin-Paul Ganea

CS III

Laboratory of

paul_ganea[AT]yahoo[DOT]com

Expertize

  • Broadband Dielectric Spectroscopy study on soft matter: the dielectric properties and phase transition of the liquid crystals (0.01Hz – 20MHz); dynamics of molecules and confinement effects in composite systems containing liquid crystals; other type of composites.
  • Study of ceramic, ferroelectric materials, ferroelectric composites by broadband Dielectric Spectroscopy: the temperature influence on of dielectric permittivity; paraelectric-ferroelectic phase transition; composition dependence of Curie Temperature.
  • Characterization of materials by Thermal Analysis and FTIR measurements.

Selected publications

 

1. Involvement of cyan and ester groups in surface interactions of aerosil –Cyanophenyl alkylbenzoate systems with high silica density. FTIR and TG-DTA Investigations, L. Frunza, S. Frunza, I. Zgura, T. Beica, N. Gheorghe, P. Ganea, D. Stoenescu, A. Dinescu, A.Schonhals, Spectrochimica Acta Part A: Molecularand Biomolecular Spectroscopy, 75, 1228-1235, 2010;

2. Dielectric Ba(Ti1-xSnx)O3(x=0,13) Ceramics, sintered by spark plasma and conventional methods, Ghe. Aldica, M. Cernea, P. Ganea, J. Mat. Sci. 45, 26062610, 2010;

3. Electrical investigations of holmium-doped BaTiO3 derived from sol-gel Combustion, M. Cernea, C. Galassi, B. Vasile,P. Ganea, R. Radu, G. Ghita, J. Mater. Res. 25, 1057-1063, 2010;

4. Dielectric and Ferroelectric Characterization of Ba0,95Tm0,05TiO3 Ceramics Derived from Sol to Gel, M. Cernea, B. S Vasile, P. Ganea, R. Radu, V.Mihalache, A. Husanu, J. Amer. Ceram. Soc, 94, 736-741, 2011;

5. Molecular Relaxation Processes in a MOF-5 Structure Revealed by Broadband Dielectric Spectroscopy: Signature of Phenylene Ring Fluctuations, S. Frunza, A. Schonhals, L. Frunza, P. Ganea, H. Kosslick, J. Harloff, A. Schulz, J. Phys.Chem. B, 114, 12840-12846, 2010;

6. Dynamics of cyanophenyl alkylbenzoate molecules in the bulk and in a surface Layer adsorbed onto aerosil. Variation of the lengths of the alkyl chain, S. Frunza, A. Schönhals, L. Frunza, T. Beica, I. Zgura, P. Ganea, D. Stoenescu, Chem.Phys. 372, 51 60, 2010;

7. Nanostructured SiOx layers as substrates for liquid crystal local ordering. I. Functionalization to bind Bovine Serum Albumin, I. Zgura, T. Beica, S. Frunza, L.Frunza, P. Ganea, C. Negrila, F. Ungureanu, A. Nuta, A. Sorescu, I. Bunea, C.N.Zaharia, J. Optoelectron. Adv. Mat. 5, 318–323, 2011;

8. Spectroscopic analysis of the interstitial anions in some layered double Hydroxide materials, L. Frunza, N. Gheorghe, F. Iova, P. Ganea, F. Neatu, V.I. Parvulescu, Rev. Chimie (Bucuresti), 62/8, 766-772, 2011;

9. Investigation of electrical and electro-optical properties of liquid crystal/copolymer clay nanostructured systems, D. Manaila-Maximean, C. Rosu, L. Frunza, P. Ganea, D. Donescu, M. Ghiurea, Mol. Cryst. Liq. Cryst. 546/1, 143155, 2011;

10. Liquid crystal/copolymer-caly nanostructured systems: contribution to the conductivity of the electrode polarization, C.P. Ganea, D. Manaila-Maximean/Politehn. Univ. Bucharest. Sci. Bull. Ser. A Appl. Math. Phys. 73, 209-216, 2011;

11. New approach of the AC electrode polarization during the measurement of impedance spectra, C.P.Ganea, Rom. J. Phys. Vol. 57/3–4 (2012) 664–675;

12. Dielectric relaxation of pure TGS crystals, C. Mîndru, C.P. Ganea, H.V. Alexandru, J. Optoelectron. Adv. Mater. 14/1-2 (2012) 157-162;

13. Pentylcyanobifenyl as test molecule for the acid sites of powered Tinanium(IV) Oxides: sensitivity of core levels to the local structure, F. Ungureanu, A. S. Manea, L. Frunza, S. Frunza, C.P. Ganea, F. Cotorobai, L.Diamandescu, A. Schönhals, Molec. Cryst. Liq. Cryst. 562 (2012) 200-217;

14. Electrode polarization and interface effects in liquid crystal systems with mobile ions: development of a model of bipolar diffusion, C.P. Ganea, Cent. Eur.J. Phys. 11(4) 497-511, 2013;

15. Synthetic Fabrics Coated with Zinc Oxide Nanoparticles by Electroless deposition:Structural Characterization and Wetting Properties, L. Frunza, E.Matei, S. Frunza, C.P. Ganea, A. M. Vlaicu, L. Diamandescu, A. Dorogan, J.Polymer Sci.Part B: Polymer Phys. 51/9 (2013) 1427-1437;

16. Conductivity in ferroelectric transition, R. Bacsei, C. Mindru, C.P. Ganea, H.V. Alexandru, J. Optoelectron. Adv. Mater. 15/11 – 12 (2013) 1369 – 1374;

17. Polyester fabrics coated with SiOx nanoparticles by vacuum deposition at small angle. Structural characterization and wetting properties, L. Frunza, I.Zgura, M. Enculescu, C.P. Ganea, et al. J. Optoelectron. Adv. Mater. 2104, 16 /12,176-181;

18. Estimation of essential dielectric parameters in ferroelectric state of TGS Crystal, H.V. Alexandru, C. Mandru, R. Bacsei, C.P. Ganea, J. Optoelectron. Adv.Mater. 2014, 16(3/4): 457-462;

19. Peculiar aspects in ferroelectric transition of triglycine sulphate crystal, H.V. Alexandru, M. Pavelescu, C.P. Ganea,Ann. Acad. Rom. Sci. Phys. Ser. 4 (1),2014, 1-12;

20. Effects of the ionic association-dissociation and adsorption-desorption on the space charge polarization-a new theoretical approach, C.P. Ganea, Eur. Phys. J.Plus (2014) 129: art. No. 238 (12 pag.);

21. Estimation of essential dielectric parameters in ferroelectric state of TGS crystal, Alexandru, H. V.; Mindru, C.; Bacsei, R.; Ganea, C. P., JOAM, Volume: 16, Issue: 3-4, Pages: 457-462, 2014;

22. Polyester fabrics covered with ZNO particles: particle interaction with the surface shown by dielectric properties,Ganea CP, Frunza L, Zgura I, Preda N, Matei E, Frunza S, Digest Journal of Nanomaterials and Biostructures, DJNB Vol. 9, No. 4, 1493 – 1503, 2014;

23. Titanium dioxide layer deposited at low temperature upon polyester fabrics, Zgura, I.; Frunza, S.; Frunza, L.; C. P. Ganea et al. J. Optoelectron. Adv. Mater. Volume: 17  Issue: 7-8 Pages: 1055-1063, 2015;

24. Surface topography to reflectivity mapping in two-dimensional photonic crystals designed in germanium, Husanu, MA; Ganea, CP; Anghel, I; Florica, C; Rasoga, O; Popescu, DG; Applied Surface Science, 355, 1186-1191, 2015;

25. Correlation of optical reflectivity with numerical calculations for a twodimensional photonic crystal designed in Ge, Husanu, MA; Popescu, DG; Ganea, CP; Anghel, I; Florica, C; European Physical Journal D, 69, -, 2015;

26. Dielectric Properties of LDH-Type Layered Materials Containing Zn or Mg Ions: On the Non Monotonous Temperature Dependence of Relaxation Times,  Frunza, L; Frunza, S; Ganea, C P; Zgura, I; Neatu, F; Parvulescu, VI; Romanian Journal Of Information Science And Technology, 18, 312-328, 2015;

27. Dielectric and photoluminescence properties of Nd and Ga codoped-BaTiO3, prepared by sol-gel method, Cernea, M; Vasilescu, CA; Secu, M; Aldica, G; Surdu, A; Ganea, CP; Journal Of Materials Science-materials In Electronics, 27, 11371-11378, 2016;

28. Multi-wavelength Laser Irradiation of Be-C-W coatings, Avotina, L; Marcu, A; Porosnicu, C; Lungu, M; Stancalie, A; Ilie, AG; Ganea, CP; Savastru, D; Kalnacs, J; Lungu, CP; Kizane, G; Antohe, S; Digest Journal Of Nanomaterials And Biostructures, 11, 293-302, 2016;

29. Modeling the charge transfer at the electrode-ionic liquid interface in dielectric spectroscopy measurements,Ganea, CP; Journal of Molecular Liquids, 221, 422-433, 2016;

30. Dielectric spectroscopy in para-ferro transition of TGS, Ganea, C P; Mindru, C; Vineticu, N; Alexandru, HV; Ferroelectrics, 493, 165-171, 2016;

31. Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species, Frunza, Stefan; Frunza, Ligia; Ganea, Constantin Paul; et al./ Eur. Phys. J. Plus, Volume: 131 Issue: 1 Pages: 27-27, 2016;

32. Polyester Fabrics Covere with Amprphous Titanium Dioxide Layers Combinig Wettability Measurements and Photoinduced Hydrophulicity to assess their surface properties, Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Cotorobai, VF; Ganea, C P; Romanian Reports In Physics, 68, 259-269, 2016;

33. Wettability by water contact angle upon the surface of wool fabrics covered with oxide nanoparticles, Birzu, M; Frunza, L; Zgura, I; Cotorobai, V F; Ganea, C P; Preda, N; Enculescu, M;Digest Journal Of Nanomaterials And Biostructures, 12, 921-931, 2017;

34. Photocatalytic activity of wool fabrics deposited at low temperature with ZnO or TiO2 nanoparticles: Methylene blue degradation as a test reaction, Funza, L; Diamandescu, L; Zgura, I; Frunza, S; Ganea, CP; Negrila, CC; Enculescu, M; Birzu, M; Catalysis  Volume: 306, Pages: 251-259, 2018;

35. Synthesis and thermal, emission and dielectric properties of liquid crystalline Eu(III), Sm(III) and Tb(III) complexes based on mesogenic 4-pyridone ligands functionalized with cyanobiphenyl groups, Chiriac, L F.;Ganea P C.; Maximean D M; Pasuk I;Circu V, J. Mol. Liq. 290 (2019), 111184; DOI:10.1016/j.molliq.2019.111184;

Hirsh index: 7.

Author or Co-Author at 48 de ISI articles, 8 as first author or corresponding author;

Total citations without self-citations: 107. (01.11.2019)

 

Research projects

  1.  New advanced nanocomposites. Technological development and applications, PN-III-P1 -1.2-PCCDI-2017-0871, 2018-2020 - Researcher/team member;
  2. The usage of composite materials with graphene oxide for improving the performance of building and installation elements against fire action in order to ensure the protection of life in case of fire, PN-III-P1-1.2-PCCDI-2017-0350, 2018-2020 - Researcher/team member

Books

1. Laser Optofluidics in Fighting Multiple Drug Resistance, Editor Mihail Lucian Pascu, Cap. IX, Authors: L. Frunza, S. Frunza, C. P. Ganea, I. Zgura, Bentham Science eBooks

Patents

Patent application A01002/29-11-2018,Multilayer light sensor, Lorinczi Adam, Ganea Constantin Paul, Socol Gabriel, Zamfira Constantin Sorin, Cretu Nicolae Constantin, Popescu-Pelin Gianina Florentina, Matei Elena, Logofatu Constantin

Publications

1. Surface species of the nematic mixture E7 obtained by electrochemical insertion of Li+ ions
Authors: Baibarac, M; Zgura, I; Ganea, CP; Frunza, L

Published: APR 2023, EUROPEAN PHYSICAL JOURNAL E, 46, 26, DOI: 10.1140/epje/s10189-023-00280-z

We studied here the influence of Li+ ions on the benzene rings of nematic mixture E7, which is electrochemically adsorbed onto gold electrode surface, to highlight the ability of this mixture for the applications in the field of the rechargeable Li+-ion batteries. Raman spectra support the changes observed in electrochemical analyses while contact angle measurements show that wetting properties of E7 layer were modified after deposition of this mixture onto gold support and the doping with Li+ ions.
2. Surface species of nematic mixture E7 in hard confinement: spectroscopic investigations cannot distinguish among the E7 components interacting with the support surface
Authors: Frunza, L; Zgura, I; Ganea, CP; Loiko, VA; Manaila-Maximean, D

Published: 2023 MAR 1 2023, LIQUID CRYSTALS, DOI: 10.1080/02678292.2023.2182379

Properties of surface species of the nematic mixture E7 in contact with inorganic oxides (especially those containing more or less aluminium ions) are in detail investigated by infrared spectroscopy and thermogravimetry. The absorption infrared peaks were decomposed into Gaussian components, the procedure allowing an easier comparison with the behaviour of related composites. We worked at enough small concentrations of the E7 relatively to support this ratio permitting the (partial) elimination of the species belonging to the bulk. Species put here in evidence are species that are hydrogen bonded to the surface of OH groups, molecules randomly oriented on the surface, some species bonded by involvement of pi electrons of the CN group to the aluminium ions, thus implying a strong interaction to the support. Supramolecular assemblies of E7 molecules are thus followed up.
3. Columnar Liquid Crystals of Copper(I) Complexes with Ionic Conductivity and Solid State Emission
Authors: Circu, V; Ganea, CP; Secu, M; Manaila-Maximean, D; Marinescu, GC; Popescu, RG; Pasuk, I

Published: MAY 19 2023, MOLECULES, 28, 4196, DOI: 10.3390/molecules28104196

Two neutral copper(I) halide complexes ([Cu(BTU)(2)X], X = Cl, Br) were prepared by the reduction of the corresponding copper(II) halides (chloride or bromide) with a benzoylthiourea (BTU, N-(3,4-diheptyloxybenzoyl)-N '-(4-heptadecafluorooctylphenyl)thiourea) ligand in ethanol. The two copper(I) complexes show a very interesting combination of 2D supramolecular structures, liquid crystalline, emission, and 1D ionic conduction properties. Their chemical structure was ascribed based on ESI-MS, elemental analysis, IR, and NMR spectroscopies (H-1 and C-13), while the mesomorphic behavior was analyzed through a combination of differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and powder X-ray diffraction (XRD). These new copper(I) complexes have mesomorphic properties and exhibit a hexagonal columnar mesophase over a large temperature range, more than 100 K, as evidenced by DSC studies and POM observations. The thermogravimetric analysis (TG) indicated a very good thermal stability of these samples up to the isotropization temperatures and over the whole temperature range of the liquid crystalline phase existence. Both complexes displayed a solid-state emission with quantum yields up to 8% at ambient temperature. The electrical properties of the new metallomesogens were investigated by variable temperature dielectric spectroscopy over the entire temperature range of the liquid crystalline phase. It was found that the liquid crystal phases favoured anhydrous proton conduction provided by the hydrogen-bonding networks formed by the NH horizontal ellipsis X moieties (X = halide or oxygen) of the benzoylthiourea ligand in the copper(I) complexes. A proton conductivity of 2.97 x 10(-7) S.cm(-1) was achieved at 430 K for the chloro-complex and 1.37 x 10(-6) S.cm(-1) at 440K for the related bromo-complex.
4. Surface species of nematic mixture E7 in hard confinement: spectroscopic investigations cannot distinguish among the E7 components interacting with the support surface
Authors: Frunza, L; Zgura, I; Ganea, CP; Loiko, VA; Manaila-Maximean, D

Published: MAR 2023, LIQUID CRYSTALS, DOI: 10.1080/02678292.2023.2182379

Properties of surface species of the nematic mixture E7 in contact with inorganic oxides (especially those containing more or less aluminium ions) are in detail investigated by infrared spectroscopy and thermogravimetry. The absorption infrared peaks were decomposed into Gaussian components, the procedure allowing an easier comparison with the behaviour of related composites. We worked at enough small concentrations of the E7 relatively to support this ratio permitting the (partial) elimination of the species belonging to the bulk. Species put here in evidence are species that are hydrogen bonded to the surface of OH groups, molecules randomly oriented on the surface, some species bonded by involvement of pi electrons of the CN group to the aluminium ions, thus implying a strong interaction to the support. Supramolecular assemblies of E7 molecules are thus followed up.
5. Molecular dynamics of alkyl benzoate liquid crystals in the bulk state and in the surface layer of their composites with oxide nanopowders
Authors: Frunza, L; Zgura, I; Ganea, CP; Schonhals, A

Published: AUG 1 2022, JOURNAL OF MOLECULAR LIQUIDS, 359, 119374, DOI: 10.1016/j.molliq.2022.119374

This paper presents the results concerning monotropic nematic liquid crystals 4-pentylphenyl 40-alkyl benzoate (5PnB) (n = 3 or 5 carbon atoms in the alkyl chain). Their mesophase properties were supported by images of the polarized optical microscopy. Molecular dynamics in the bulk samples or in the composites prepared with aerosil A380 was investigated by broadband dielectric spectroscopy in a large temperature range, appropriately chosen. Thermo gravimetric and infrared investigations were additionally performed. The data were compared with those of structurally related nematics like cyanophenyl pentyl benzoates, which have a cyan group instead of the pentyl chain. The dielectric spectra of the bulk 3P5B and 5P5B demonstrate a dielectric behavior with several relaxation processes as expected for nematic liquid crystals. The temperature dependence of the relaxation rates (and of the dielectric strength) seems to have two distinguished regimes. Thus, in the isotropic state, at higher temperatures the data obey the Vogel-Fulcher-Tammann law, whereas an Arrhenius law is fitted at lower temperature, in a close similarity to the behavior of a constrained dynamic glass transition. Samples with a high density of silica (larger than 7 g aerosil/1 g of 5PnB) were prepared to observe a thin layer adsorbed on the particle surface; it was estimated that almost each guest 5PnB molecule interacts with the aerosil surface. For the composites only one main relaxation process is observed at frequencies much lower than those for the corresponding bulk, which was assigned to the dynamics of the molecules in the surface layer. Infrared spectroscopy shows that these molecules interact with the surface by the ester carbonyl group leading to the monolayer self-assembly at liquid-solid interface. We note once more the importance of the functional unit(s) for the interaction with the hydroxyl groups on the aerosil surface. (c) 2022 Elsevier B.V. All rights reserved.
6. Parameters in the ferroelectric phase of TGS
Authors: Alexandru, HV; Marinel, D; Mindru, C; Ganea, CP

Published: OCT 26 2021, FERROELECTRICS, 583, 124, DOI: 10.1080/00150193.2021.1980323

Polarization P(T) of triglycine sulfate (TGS) crystal shows distinct properties versus temperature, between 28 degrees C and the Curie point Tc. Carefully measured polarization versus temperature on several ranges is presented. The slopes on the curve P(T) on three temperature ranges between 28 divided by 46 degrees C appear quite normal, while near the Curie point (47 degrees C divided by Tc) behave abnormally, due to the domain walls. The relaxation time LOW, MIDDLE and HIGH appear very interesting. The MIDDLE relaxation time tau(M), between 40 divided by 46 degrees C behave like the HIGH relaxation time tau (H) between 47 and 48 degrees C and between -20 divided by 10 degrees C (25 KBT) similar to LOW relaxation time tau(L) (28K(B)T). The diagrams Cole-Cole of TGS are analyzed here for the first time. Roughly, several parameters change their slopes at 30, 42, and 47 degrees C. The values of epsilon '(H) and epsilon"(H) show about the same slope on the zones 42-47 degrees C and 30-42 degrees C. For the same zones, epsilon '(L) shows several increasing activation energies toward Curie point, except epsilon"(L) and R (L) whose activation energy decreases. Finally, we mention the opposite variation of the negative ordinate Y (CH), Y (CL) of both arcs Cole-Cole and of the radius R (H) and R (L).
7. Tetragonal-Cubic Phase Transition and Low-Field Dielectric Properties of CH3NH3PbI3 Crystals
Authors: Patru, RE; Khassaf, H; Pasuk, I; Botea, M; Trupina, L; Ganea, CP; Pintilie, L; Pintilie, I

Published: AUG 2021, MATERIALS, 14, DOI: 10.3390/ma14154215

The frequency and temperature dependence of dielectric properties of CH3NH3PbI3 (MAPI) crystals have been studied and analyzed in connection with temperature-dependent structural studies. The obtained results bring arguments for the existence of ferroelectricity and aim to complete the current knowledge on the thermally activated conduction mechanisms, in dark equilibrium and in the presence of a small external a.c. electric field. The study correlates the frequency-dispersive dielectric spectra with the conduction mechanisms and their relaxation processes, as well as with the different transport regimes indicated by the Nyquist plots. The different energy barriers revealed by the impedance spectroscopy highlight the dominant transport mechanisms in different frequency and temperature ranges, being associated with the bulk of the grains, their boundaries, and/or the electrodes' interfaces.
8. Adsorption, wicking behavior and photodegradation tests of Rhodamine B solution upon wool substrates
Authors: Frunza, L; Cotorobai, VF; Enculescu, M; Zgura, I; Ganea, CP; Birzu, M; Manaila-Maximean, D

Published: 2020, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGIES X, 11718, DOI: 10.1117/12.2572130

Behavior of some wool fabrics as such or functionalized with semiconductor nanoparticles against the photodegradation of Rhodamine B was investigated. The wool samples were commercially purchased, they were chosen to differ by the chemical nature of the yarns, by the size of the 2D texture elements and by the applied pretreatment. The samples were routinely characterized both in the original form and in the form coated with the oxide particles as well to consider the structure, the surface morphology and their changes due to dye deposition. Several techniques were routinely applied: optical microscopy, XRD, SEM, TGA, UV-Vis spectroscopy and FTIR-ATR. Data have shown that TiO2 layer has either an amorphous structure or is highly dispersed. Drops of Rhodamine B solution were deposited by sessile drop method. We have obtained optical images of the wet/colored spot during the radial wicking, collected with a usual camera. Image comparison was made by direct visualisation. The optical images of the spot on fabrics were taken immediately after the dye was applied, after the fabric was dried and afterwards, after the system illumination by UV-vis light as function of the time. The obtained final spots speak about the dye photodegradation in the studied cases.
9. Dielectric investigations on carbon nanotubes doped polymer dispersed liquid crystal films
Authors: Ganea, CP; Manaila-Maximean, D; Circu, V

Published: OCT 8 2020, EUROPEAN PHYSICAL JOURNAL PLUS, 135, DOI: 10.1140/epjp/s13360-020-00795-w

We obtained carbon nanotubes (CNTs) doped polymer dispersed liquid crystal (PDLC) films using the nematic E7 and polymethyl methacrylate, a composite that combines the benefic characteristic of the liquid crystals (LC) and carbon nanoparticles. The clearing temperatures recorded by differential scanning calorimetry for the PDLC blends were found to be lower than the value recorded for pure E7 LC mixture with no significant impact of the CNTs' concentration. Broadband dielectric spectroscopy (DS) measurements were performed in the (10(-1) / 107) Hz frequency range, in the temperature domain (280-350) K. From the DS study, a two order magnitude variation of the conductivity over the entire temperature range was observed. The presence of CNTs results in an increase of electrical conductivity, with increasing concentration. Because the loss tangent spectra have complex shapes, they were fitted using the generalized Havriliak-Negami functions, and the characteristic relaxation times were extracted. The dependency of the characteristic relaxation time on temperature was modeled using the Vogel-Fulcher-Tammann function, and it showed a temperature variation according to the Arrhenius law. The increase of the CNT concentration increases the activation energy of the molecular electric dipoles of the LC. The interface LC-polymer interactions influence the nematic to isotropic phase transition of the LC.
10. Molecular dynamics in bulk and surface species of cyanophenyl alkyl benzoates with 2, 3 and 7 carbon atoms in the alkyl chain: comparison in the whole homologous series
Authors: Frunza, S; Ganea, CP; Zgura, I; Frunza, L; Schonhals, A

Published: MAY 2 2020, LIQUID CRYSTALS, 47, 917, DOI: 10.1080/02678292.2019.1687768

Molecular mobility of cyanophenyl alkylbenzoates (CPnBs) (n = 2, 3, 7 - number of carbon atoms in the alkyl chain) in the bulk and in composites with aerosil A380 is investigated by broadband dielectric spectroscopy, while thermal analysis and infrared spectroscopy were applied to characterise the molecular species. The work completes preliminary results obtained for the members with n = 4 ... 6. An interaction by hydrogen bonding, between aerosil surface - OH groups and - CN or ester groups of the CPnB molecules takes place. It slows down the relaxation process as observed for related composites in comparison to the pure materials. The existence of two types of bonding might be the reason that Vogel temperature for the relaxation process in the surface layer does not show the odd-even effect. Temperature dependence of the relaxation rates for composites shows a crossover behaviour from a high to a low temperature regime. Moreover, the temperature dependence of the dielectric strength is unusual. As the loading degree is similar, comparison of the dielectric, spectroscopic and thermal data obtained here and with the results obtained for the composites with n = 4 ... 6 can be directly done. Increasing the number of the members of the homologous series confirms and hardens the preliminary conclusions.
11. (Ba,Sr)TiO3 solid solutions sintered from sol-gel derived powders: An insight into the composition and temperature dependent dielectric behavior
Authors: Patru, RE; Ganea, CP; Stanciu, CA; Surdu, VA; Trusca, R; Ianculescu, AC; Pintilie, I; Pintilie, L

Published: MAR 2020, CERAMICS INTERNATIONAL, 46, 4190, DOI: 10.1016/j.ceramint.2019.10.136

Single-phase Ba1-xSrxTiO3 (BST) perovskite ceramics with 0.3 <= x <= 0.4 were prepared from powders synthesized via sol-gel route. The compositions have the ferroelectric-paraelectric phase transition close to room temperature. At 20 degrees C the BST ceramics are ferroelectric for 0.3 <= x <= 0.35 and paraelectric for x = 0.375 and x = 0.40. The study follows the relation between the structural changes produced when increasing the Sr content and the dielectric properties at low intensity electric fields. It is found that the grain size and tetragonality decreases as the Sr content increases. Analyses of complex permittivity and impedance spectroscopy reveal the temperature and frequency dependencies of the dielectric properties. The phase transitions seem to be of first order for all compositions, with a thermal hysteresis that decreases with increasing the Sr content, fact attributed to the corresponding increase of the grain boundaries weight allowing a more efficient stress relaxation in the structure during the change of the symmetry from cubic to tetragonal. The diffusiveness degree during the phase transition is increasing with Sr content, suggesting some relaxor-type contribution attributed to smaller grain size. The ac conductivity follows the universal Jonscher law, with an ac component having the power parameter s independent of Sr content, and a dc component that it is thermally activated with an activation energy of about 0.7-0.77 eV attributed to oxygen vacancies acting as donor-like defects. The fit of impedance spectra at different temperatures and frequencies is obtained by using an equivalent circuit accounting the grains, grain boundaries, electrode interfaces and the local contributions produced by reorientation of defect dipoles or defect clusters. All the component circuits have significant variations around phase transitions. These are discussed in relation to structural changes occurring during transition and considering the changes in the distribution of various charges when polarization vanishes.
12. Effect of titanium oxide nanoparticles on the dielectric properties and ionic conductivity of a new smectic bis-imidazolium salt with dodecyl sulfate anion and cyanobiphenyl mesogenic groups
Authors: Ganea, CP; Circu, V; Manaila-Maximean, D

Published: NOV 1 2020, JOURNAL OF MOLECULAR LIQUIDS, 317, DOI: 10.1016/j.molliq.2020.113939

A new bis-imidazolium salt with two cyanobiphenyl groups and dodecyl sulfate counterion (BIC) was prepared by the metathesis reaction of the bromide salt with sodium dodecyl sulfate. The ILC shows at room-temperature a stable smectic A phase, confirmed by differential scanning calorimetry, polarized optical microscopy, and powder X-ray diffraction investigations. The ILC was doped with TiO2 nanoparticles, having a high specific area, in concentrations of 0.1%, 0.2%, 1% and 2%. Broadband Dielectric Spectroscopy spectra have been registered in the (10-1-107) Hz frequency range, and (250-330) K temperature domain. The study shows that at constant frequency, the conductivity increases with the temperature and dopant concentration. The characteristic times of the observed relaxation processes showed a temperature variation according to the Vogel-Fulcher-Tammann law. Higher values of characteristic times were calculated at the increase of the thickness of the sample. On the other hand, the increase of the concentration of TiO2 nanoparticles leads to a decrease of the characteristic relaxation times. In order to detectwhether the obtained high permittivity increase is due to the Maxwell-Wagner or Electrode Polarization (EP) type phenomena, studies were made on samples of the same concentration, but different thicknesses, and EP was assigned as the main cause of this dielectric constant variation. (C) 2020 Elsevier B.V. All rights reserved.
13. DENSITY OF ADSORBED SURFACE SPECIES FOR CYANOPHENYL ALKYL BENZOATES CONFINED TO AEROSIL A380: DEVELOPMENT OF THE EVALUATING ALGORITHM FOR ATTACHMENT BY TWO TYPES OF BONDS
Authors: Frunza, S; Frunza, L; Ganea, CP; Zgura, I; Schonhals, A

Published: 2019, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN-SERIES A-APPLIED MATHEMATICS AND PHYSICS, 81, 236, DOI:

We found previously how to estimate the density of the adsorbed surface species in the case of the molecules interacting to the oxide support surface by one type of bond. Here this algorithm is developed for the case of the molecules which can be bonded to the support surface by two types of bonds. The adsorption assumptions are similar to those considered in the case of only one type of bond. The calculation is exemplified for some composites of cyanophenyl alkylbenzoates (CPnBs) (n is the number of carbon atoms in the alkyl chain) interacting with Aerosil A380. The interaction takes place by hydrogen bonding between the -OH groups or the support and the functional groups of the CPnB molecules. The estimated values of the total surface density of CPnBs agree well with those found for the composites containing related but simpler molecules.
14. Impedance spectroscopy and electro-optic switching times of a liquid crystal-hydroxypropylcellulose network composite
Authors: Maximean, DM; Barar, A; Ganea, CP; Almeida, PL; Danila, O

Published: 2018, ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS, AND NANOTECHNOLOGIES IX, 10977, DOI: 10.1117/12.2326224

This paper presents electric and electro-optic studies conducted on a new composite, namely hydroxypropylcellulose network with liquid crystal fillings. The composite was manufactured using the electrospinning method, and deposited on indium tin oxide glass. In terms of electric characterization, the samples were subjected to impedance spectroscopy, their equivalent circuit model was deduced, and the corresponding electric parameters were computed based on the Cole-Cole diagrams and frequency plots of the two impedance components. In terms of electro-optic studies, the optical transmission of the sample under a varying steady-state alternative regime voltage was recorded, and the saturation threshold field was determined. Also, the switching times of the sample with respect to a step signal were determined.
15. Dielectric properties of a bisimidazolium salt with dodecyl sulfate anion doped with carbon nanotubes
Authors: Manaila Maximean, D; Circu, V; Ganea, CP

Published: JAN 16 2018, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 9, 174, DOI: 10.3762/bjnano.9.19

A new bisimidazolium salt with dodecyl sulfate as counterion has been designed and prepared. This salt shows a SmA phase that is stable at room temperature. The new ionic liquid crystal (ILC) was characterized by H-1 NMR, C-13 NMR and IR spectroscopy. Its liquid crystalline properties were analyzed by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) studies. The dielectric spectra of the ILC doped with different concentrations of carbon nanotubes (CNT) were recorded over a wide frequency and temperature range of 10(-1) to 10(7) Hz and 293-338 K, respectively. The values of the activation energy were found in the range of 0.46-0.61 eV; the characteristic time was obtained by fitting the spectra of the dielectric loss with the Havriliak-Negami functions. As a result of doping the ILC with CNT, the electric conductivity increases significantly. Ionic conductivity is dominant and it was indirectly observed through the electrode polarization (EP) effect. The very high dielectric permittivity values and the decrease of the electric conductivity at low frequencies confirm the presence of EP.
16. Wet chemical synthesis of ZnO-CdS composites and their photocatalytic activity
Authors: Zgura, I; Preda, N; Socol, G; Ghica, C; Ghica, D; Enculescu, M; Negut, I; Nedelcu, L; Frunza, L; Ganea, CP; Frunza, S

Published: MAR 2018, MATERIALS RESEARCH BULLETIN, 99, 181, DOI: 10.1016/j.materresbull.2017.11.013

The present study is focused on the wet chemical synthesis and the characterization of ZnO-CdS composites. The X-ray diffraction shows that the composites contain ZnO in hexagonal wurtzite structure and CdS in cubic phase. The scanning/transmission electron microscopy images reveal flower-like structures with different sizes depending on the CdS content. The optical investigations on composites reveal that the reflectance spectra disclose two thresholds of similar to 370 nm and similar to 460 nm associated with the ZnO and CdS, respectively. The photocatalytic activity measurements evidenced that the degradation efficiency of RhB in the presence of composites is higher comparatively with pristine ZnO, depending on the catalyst morphology, which varies with CdS content and the pH value of RhB solution. The electron paramagnetic resonance revealed the presence of the paramagnetic point defects in the samples. Thus, the wet chemical approaches are suitable for a large scale production of such ZnO-CdS composites having enhanced photocatalytic activity.
17. Conductivity losses in ferroelectric phase of TGS
Authors: Marinel, D; Alexandru, HV; Ganea, CP

Published: NOV-DEC 2018, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 20, 681, DOI:

Triglycine sulphate (TGS) is a crystal having a typical second order ferroelectric transition and the Curie point around 49 degrees C. It is quite easy to grow and to analyse its properties. Our TGS crystals were grown by slow solvent evaporation in paraelectric phase, around 54 degrees C, where no mechanical tensions due to ferroelectric domains were present. Dielectric properies of TGS crystals were continuously measured at a pace of 0.6 degrees C/min, starting from 65 degrees C, crossing down the Curie point until zero Celsius, on the frequency range 1 divided by 10(7) Hz. The two component of permittivity were measured and the parameters vs. temperature were estimated and analysed.
18. Photocatalytic activity of wool fabrics deposited at low temperature with ZnO or TiO2 nanoparticles: Methylene blue degradation as a test reaction
Authors: Frunza, L; Diamandescu, L; Zgura, I; Frunza, S; Ganea, CP; Negrila, CC; Enculescu, M; Birzu, M

Published: MAY 15 2018, CATALYSIS TODAY, 306, 259, DOI: 10.1016/j.cattod.2017.02.044

Different amounts of TiO2 and ZnO particles were deposited upon wool fabrics, which are among the less studied textiles. The materials were get from industry or were home made. Model samples for these oxide deposition and properties were also considered. Either sputtering or chemical sol-gel/electro less technique was respectively applied. The coated samples were then characterized structurally and morphologically, by XRD, SEM and XPS and were checked for photocatalytic properties. Both UV and vis light beams were used for irradiation. The photocatalytic experiments were performed by photodegradation of methylene blue in the PCC2 checker apparatus. The fabrics were firstly impregnated with the dye solution and then dried: self cleaning of the wool fabric samples took in fact place. Reflectance data in the visible spectral range of highest absorption band served for direct analysis of MB degradation. The photocatalytic properties of the coated fabrics increased much in comparison with the raw materials. The photocatalytic decolorization of methylene blue follows up a simple apparently first order kinetic equation in many studied cases. Thus it was demonstrated that MB decolorization can serve as a test reaction at least for self cleaning of fabrics. (C) 2017 Elsevier B.V. All rights reserved.
19. Filling in the voids of electrospun hydroxypropyl cellulose network: Dielectric investigations
Authors: Maximean, DM; Danila, O; Ganea, CP; Almeida, PL

Published: APR 23 2018, EUROPEAN PHYSICAL JOURNAL PLUS, 133, DOI: 10.1140/epjp/i2018-11997-8

Here we describe an organic electro-optic device, obtained using electrospun hydroxypropyl cellulose (HPC) polymer fibres and nematic liquid crystals (LC). Its working mechanism is similar to that of a classic polymer-dispersed liquid crystal (PDLC) device. The scanning electron microscopy of the HPC deposited fibres shows a mat of fibres with diameters in the nano and micron size range. Dielectric spectroscopy measurements allow the determination of the dependence of the dielectric constant and electric energy loss on frequency and temperature as well as the determination of the activation energy. The electro-optic study shows a very good optical transmission curve, with an "on"-"off" switching voltage of less than 1 V/mu m.
20. Electrical properties of a liquid crystal dispersed in an electrospun cellulose acetate network
Authors: Manaila Maximean, D; Danila, O; Almeida, PL; Ganea, CP

Published: JAN 15 2018, BEILSTEIN JOURNAL OF NANOTECHNOLOGY, 9, 163, DOI: 10.3762/bjnano.9.18

Electro-optical devices that work in a similar fashion as PDLCs (polymer-dispersed liquid crystals), produced from cellulose acetate (CA) electrospun fibers deposited onto indium tin oxide coated glass and a nematic liquid crystal (E7), were studied. CA and the CA/liquid crystal composite were characterized by multiple investigation techniques, such as polarized optical microscopy, dielectric spectroscopy and impedance measurements. Dielectric constant and electric energy loss were studied as a function of frequency and temperature. The activation energy was evaluated and the relaxation time was obtained by fitting the spectra of the dielectric loss with the Havriliak-Negami functions. To determine the electrical characteristics of the studied samples, impedance measurements results were treated using the Cole-Cole diagram and the three-element equivalent model.
21. WETTABILITY BY WATER CONTACT ANGLE UPON THE SURFACE OF WOOL FABRICS COVERED WITH OXIDE NANOPARTICLES
Authors: Birzu, M; Frunza, L; Zgura, I; Cotorobai, VF; Ganea, CP; Preda, N; Enculescu, M

Published: JUL-SEP 2017, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 12, 931, DOI:

Wetting properties of wool textiles were studied either for the raw samples or for those functionalized via covering them at low temperature with nanoparticles of titanium dioxide or zinc oxide. Oxygen plasma pretreatment was performed before deposition. Characterization used optical examination, scanning electron microscopy, infrared spectroscopy, thermogravimetry, X-ray diffraction. Wetting properties were tested under static conditions by estimating the water contact angle. The sessile drop method was applied. The deposited matter represents 3 to 8 wt%, covering rather uniformly the fiber surface. Treated samples show mostly lower values of contact angle than the pristine ones. Cassie-Baxter model is discussed in relation to the equilibrium contact angle of the support.
22. Dielectric spectroscopy in para-ferro transition of TGS
Authors: Ganea, CP; Mindru, C; Vineticu, N; Alexandru, HV

Published: MAR 15 2016, FERROELECTRICS, 493, 171, DOI: 10.1080/00150193.2016.1135687

Triglycine sulphate crystal (TGS) is one of the most studied ferroelectric materials, having a second order transition around 49 degrees C. The complex dielectric constant we have measured on the frequency range 1-10(7) Hz and on a large temperature range, in ferroelectric phase after the para - ferro transition. Temperature was monitored from room temperature to 65 degrees C, were for 30min it was kept constant and then was lowered down at a rate of 0.6 degrees C/min. Both component of permittivity were automatically registered. This study was focused on the dielectric relaxation processes. Three fundamental relaxation mechanisms (LF, MF, and HF) were found and analyzed with the Cole-Cole functions. The activation energy of these relaxation mechanisms have been estimated in the ferroelectric phase
23. Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species
Authors: Frunza, S; Frunza, L; Ganea, CP; Zgura, I; Bras, AR; Schonhals, A

Published: FEB 2 2016, EUROPEAN PHYSICAL JOURNAL PLUS, 131, DOI: 10.1140/epjp/i2016-16027-5

Surface layers have already been observed by broadband dielectric spectroscopy for composite systems formed by adsorption of rod-like cyanophenyl derivates as probe molecules on the surface of oxide particles. In this work, features of the surface layer are reported; samples with different amounts of the probe molecules adsorbed onto oxide (nano) particles were prepared in order to study their interactions with the surface. Thermogravimetric analysis (TGA) was applied to analyze the amount of loaded probe molecules. The density of the surface species n(s) was introduced and its values were estimated from quantitative Fourier transform infrared spectroscopy (FTIR) coupled with TGA. This parameter allows discriminating the composites into several groups assuming a similar interaction of the probe molecules with the hosts of a given group. An influence factor H is further proposed as the ratio of the number of molecules in the surface layer showing a glassy dynamics and the number of molecules adsorbed tightly on the surface of the support: It was found for aerosil composites and used for calculating the maximum filling degree of partially filled silica MCM-41 composites showing only one dielectric process characteristic for glass-forming liquids and a bulk behavior for higher filling degrees.
24. POLYESTER FABRICS COVERED WITH AMORPHOUS TITANIUM DIOXIDE LAYERS: COMBINING WETTABILITY MEASUREMENTS AND PHOTOINDUCED HYDROPHILICITY TO ASSESS THEIR SURFACE PROPERTIES
Authors: Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Cotorobai, VF; Ganea, CP

Published: 2016, ROMANIAN REPORTS IN PHYSICS, 68, 269, DOI:

Wettability properties of thin TiO2 amorphous layers obtained by sputtering or sol-gel onto polyester textile materials were investigated. Contact angle (CA) measurements by the sessile drop method were used to evaluate these properties. Comparison was performed with coated samples of related poly(lactic acid) material. The samples coated by sol gel have CAs a few degrees higher than those coated by sputtering. Wetting properties were conversely changed under alternate darkness/illumination conditions. Photoinduced hydrophilicity was observed even for these amorphous coating particles, being higher for sputtered samples than for sol gel ones.
25. Modeling the charge transfer at the electrode-ionic liquid interface in dielectric spectroscopy measurements
Authors: Ganea, CP

Published: SEP 2016, JOURNAL OF MOLECULAR LIQUIDS, 221, 433, DOI: 10.1016/j.molliq.2016.06.026

The phenomena occurring at the interface between the electrodes and a liquid with ionic conductivity is manifested specifically in the spectrum of the dielectric permittivity. The theoretical model of the electrode polarization (charge space polarization) is met in the dielectric spectroscopy measurements in which electrodes are conductors (allow transfer of electric charge) and the adsorption-desorption of ions occurs on their surface. A pair of ions with equal and opposite charge is considered. The ions are produced by the association dissociation of neutral molecules. We propope general boundary conditions (BCs) with charge transfer current which contains the adsorption-desorption parameters. The BCs and the basic equations of the Poisson-Nernst Planck model, i.e. transport equations of charge carriers and Poisson equation, are re-formulated through new variables. The mathematical problem is solved analytically. The results allow finding a criterion for choosing a general and simple admittance expression, thus using a unified approach for different cases. We show that the small" signal approximation is no longer needed, at least for modern dielectric spectroscopy equipment. The ions can be point-like or may have finite dimensions. For the last case a model of Stem compact layer with charge transfer is proposed, which allows to calculate the compact layer impedance. Finally we obtain the equivalent admittance of the physical system composed from metal electrodes and ionic liquid in the presence of the Stern layer and the space charge polarization. The limitations of the model are given by the hypothesis of "flat band" and the non-selective adsorption of ions. (C) 2016 Elsevier B.V. All rights reserved.
26. Dielectric Properties of LDH-Type Layered Materials Containing Zn or Mg Ions : On the Non Monotonous Temperature Dependence of Relaxation Times
Authors: Frunza, L; Frunza, S; Ganea, CP; Zgura, I; Neatu, F; Parvulescu, VI

Published: 2015, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 18, 328, DOI:

The electrical behavior of layered double hydroxides containing Al or Ga as the trivalent ions and Mg or Zn as bivalent ions was evaluated using broadband dielectric spectroscopy in a wide temperature range. Besides conduction effects a relaxation peak is observable at high frequencies which is assigned to the reorientational fluctuations of water molecules adsorbed on the oxide surface or in the interlayer voids. The Maxwell-Wagner-Sillars peak, superimposed to the conductivity phenomenon is observable at low frequencies. A non-monotonous temperature dependence of the relaxation rates of the relaxation process has been found. A quantitative description of this dependence was possible based on a model assuming two competing processes: rotational fluctuation of water molecules and formation of additional defects. Reasonable values for the characteristic parameters were obtained. Thus the water behavior in the studied layered oxides is similar to that observed for water in other porous materials. However, the activation energy of the rotational fluctuation, the pre exponential factor and the number of defects are higher whereas the value of the energy of defect formation is lower in the layered oxide materials than for water confined to nanoporous molecular sieves, porous glasses or in bulk ice.
27. Titanium dioxide layer deposited at low temperature upon polyester fabrics
Authors: Zgura, I; Frunza, S; Frunza, L; Enculescu, M; Florica, C; Ganea, CP; Negrila, CC; Diamandescu, L

Published: JUL-AUG 2015, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 17, 1063, DOI:

TiO2 deposition by sputtering or sol-gel techniques was applied onto less thermal stable polyester textiles and onto a related poly(lactic acid) material. The temperature of deposition and of the further treatment was low enough as allowed by the support nature. Structural and spectroscopic characterization of the raw and coated samples has been performed. TiO2 coated particles are amorphous as indicated by X-ray diffraction and scanning electron microscopy. Sputtered layers consist in aggregates randomly distributed on the substrate while the sol gel layers show a uniform coverage of nanoparticles having a mosaic-like structure. The morphology of the sputtered layers depends on the deposition pressure as well. The loading degree estimated on the basis of the thermogravimetric data is rather low (ca. 2%), but the fabric properties are much influenced by the deposition. Photocatalytic activity also present on the coated surfaces was evaluated in the methylene blue degradation. TiO2 layer is quite adherent as checked by an ultra-sonication method.
28. Correlation of optical reflectivity with numerical calculations for a two-dimensional photonic crystal designed in Ge
Authors: Husanu, MA; Popescu, DG; Ganea, CP; Anghel, I; Florica, C

Published: DEC 10 2015, EUROPEAN PHYSICAL JOURNAL D, 69, DOI: 10.1140/epjd/e2015-60478-7

A two dimensional photonic crystal (2DPhC) with triangular symmetry is investigated using optical reflectivity measurements and numerical calculations. The system has been obtained by direct laser writing, using a pulsed laser (lambda = 775 nm), perforating an In-doped Ge wafer. A lattice of holes with well-defined symmetry has been designed. Analyzing the spectral signature of PBGs recorded experimentaly with finite difference time domain theoretical calculations one was able to prove the relation between the geometric parameters (hole format, lattice constant) of the system and its ability to trap and guide the radiation in specific energy range. It was shown that at low frequency and telecommunication ranges of transvelsal electric modes photonic band gap occur. This structure may have potential aplications in designing photonic devices with applications in energy storage and conversion as potential alternative to Si-based technology.
29. Surface topography to reflectivity mapping in two-dimensional photonic crystals designed in germanium
Authors: Husanu, MA; Ganea, CP; Anghel, I; Florica, C; Rasoga, O; Popescu, DG

Published: NOV 15 2015, APPLIED SURFACE SCIENCE, 355, 1191, DOI: 10.1016/j.apsusc.2015.07.218

Light confinement in a two dimensional photonic crystal (2D PhC) with hexagonal symmetry is studied using infra-red reflectance spectromicroscopy and numerical calculations. The structure has been realized by laser ablation, using a pulsed laser (lambda = 775 nm), perforating an In-doped Ge wafer and creating a lattice of holes with well-defined symmetry. Correlating the spectral signature of the photonic gaps recorded experimentally with the results obtained in the finite difference time domain and finite difference frequency domain calculations, we established the relationship between the geometric parameters of the structure (lattice constants, shape of the hole) and its efficiency in trapping and guiding the radiation in a well-defined frequency range. Besides the gap in the low energy range of transversal electric modes, a second one is identified in the telecommunication range, originating in the localization of the leaky modes within the radiation continuum. The emerging picture is of a device with promising characteristics as an alternative to Si-based technology in photonic device fabrication with special emphasize in energy storage and conversion. (C) 2015 Elsevier B.V. All rights reserved.
30. Effects of the ionic association-dissociation and adsorption-desorption on the space charge polarization: A new theoretical approach
Authors: Ganea, CP

Published: OCT 28 2014, EUROPEAN PHYSICAL JOURNAL PLUS, 129, DOI: 10.1140/epjp/i2014-14238-4

A case where the electrode polarization occurs in dielectric spectroscopy measurements carried out on a liquid crystal cell in which there are paired ions with different transport properties in the presence of generation-recombination processes is discussed. The processes of adsorption/desorption take place at blocking electrode surfaces with different features. The theoretical approach consists in introducing new independent variables with simple significance and in reformulating the fundamental equation for the concentrations of charge carriers and Poisson equation for the electric field. The main purpose of the present mathematical method is to obtain a more convenient analytical expression of admittance and complex permittivity in a form that is easy to use for the interpretation of the experimental data. The expression of the admittance allows suggesting an equivalent electrical circuit according to the processes occurring in the sample volume and at the surface electrodes. The analytical form of the admittance highlights a distinctive term that is proportional to one adimensional parameter which estimates the relative effects of the bulk process in comparison with the interfaces process. Several cases are analyzed and for each an analytical expression is found. In some cases the formulas are available in a simple form.
31. POLYESTER FABRICS COVERED WITH ZNO PARTICLES: PARTICLE INTERACTION WITH THE SURFACE SHOWN BY DIELECTRIC PROPERTIES
Authors: Ganea, CP; Frunza, L; Zgura, I; Preda, N; Matei, E; Frunza, S

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1503, DOI:

Polyester fabrics modified with ZnO particles by electroless deposition were investigated by broadband dielectric spectroscopy in a parallel capacitor between 10(-2) and 10(7) Hz in a temperature interval from ca. 123 to 473 K. Textile samples were routinely characterized for the structure and interaction of the ZnO particles with the fiber surface. Since a textile fabric material is a mixture of air and fibers, the parameters taken into consideration should be called as effective ones. The deposition of ZnO particles lead to complex dielectric spectra and to the temperature dependence of the decomposed peaks following Arrhenius law.
32. Polyester fabrics coated with SiOx nanoparticles by vacuum deposition at small angle. Structural characterization and wetting properties
Authors: Frunza, L; Zgura, I; Enculescu, M; Frunza, S; Ganea, CP; Rasoga, O; Cotorobai, F; Dorogan, A

Published: JAN-FEB 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 181, DOI:

Vacuum deposition at small angle was successfully applied in deposition of SiOx particles onto polyester textile materials; this deposition is here presented in comparison with that upon other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of deposited samples has been performed and compared with that of the raw materials. The deposited particles are amorphous. Contact angle measurement by the sessile drop method, was used to study the wettability behavior of the investigated composite systems. The hierarchical roughness structure generates hydrophylic properties onto polyester fabrics and the other functionalized samples after deposition. The deposition technique was proven to be highly reproducible, easy scalable and cheap, allowing a wide range of applications.
33. Synthetic fabrics coated with zinc oxide nanoparticles by electroless deposition: Structural characterization and wetting properties
Authors: Frunza, L; Preda, N; Matei, E; Frunza, S; Ganea, CP; Vlaicu, AM; Diamandescu, L; Dorogan, A

Published: OCT 1 2013, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 51, +, DOI: 10.1002/polb.23346

Electroless deposition was successfully applied in developing crystalline particles of zinc oxide onto polyester textile materials; this deposition is here presented in comparison with other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of the raw and deposited samples has been performed. The structure of zinc oxide particles was that of wurtzite type as indicated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallites were 20-500 nm in diameter and up to 1 mu m in length. The grown particles cover the fibers not only on the fabric surface but in the textile depth. Contact angle measurement by the sessile drop method was used to study the wettability behavior of the investigated composite systems. The hierarchical roughness structure generates superhydrophobic properties onto polyester fabrics, for which water contact angles exceed 150 degrees. The other functionalized samples also become more hydrophobic after deposition. Cassie-Baxter model was found suitable to describe the behavior, though the fraction of surface occupied by the water-solid interface is high enough. The electroless deposition technique applied previously for cotton fabrics was once more proven to be highly reproducible, easy scalable, and cheap, allowing a wide range of applications. (c) 2013 Wiley Periodicals, Inc.
34. Electrode polarization and interface effects in liquid crystal systems with mobile ions: development of a model of bipolar diffusion
Authors: Ganea, CP

Published: APR 2013, CENTRAL EUROPEAN JOURNAL OF PHYSICS, 11, 511, DOI: 10.2478/s11534-013-0204-6

The influence of mobile ions on the results of impedance spectroscopy (dielectric spectroscopy) measurements performed on a liquid crystal cell using the new mathematical model recently described was investigated. This mathematical model reformulates the fundamental equation system of continuity for mobile charge carriers and the Poisson equation using new variables. One makes the following assumptions: ions have different mobilities and diffusion coefficients, there is no generation-recombination process, the equilibrium carrier concentrations are uniform and equal each other, the electrodes are either completely blocking or blocked with adsorption-desorption processes. The final result is the analytical expression of the equivalent admittance for the system, allowing to have a clearer picture of the mobile ions and of the processes that occur at the electrode interface influencing the dielectric behavior.
35. Pentylcyanobiphenyl as Test Molecule for the Acid Sites of Powdered Titanium(IV) Oxides: Sensitivity of Core Levels to the Local Structure
Authors: Ungureanu, F; Manea, AS; Frunza, L; Frunza, S; Ganea, CP; Cotorobai, F; Diamandescu, L; Schonhals, A

Published: 2012, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 562, 217, DOI: 10.1080/15421406.2012.697416

Pentylcyanobiphenyl was used successfully as a testmolecule to show the acid sites upon some commercial nanoscaled titanium dioxide materials. The surface interactions were investigated in detail using methods sensitive to the surface or to the bulk material, e. g., X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, and thermal analysis. Different oxidation states of surface Ti ions were revealed. Several species were found: the majority were bonded through the nitrogen lone pair of the cyano group, but bonding to the surface OH groups by benzene pi electrons might also appear. The N 1s lines of adsorbed 5CB were able to distinguish between Lewis acid and relatively weak Bronsted acid sites.
36. Oxidation activity of horseradish peroxidase hosted in molecular sieves: spectroscopic investigations show hindering of the enzyme activity
Authors: Frunza, L; Gheorghe, N; Ganea, CP; Eckelt, R; Kosslick, H

Published: FEB 2012, REACTION KINETICS MECHANISMS AND CATALYSIS, 105, 205, DOI: 10.1007/s11144-011-0408-y

Horseradish peroxidase immobilization inside molecular sieves with pores hexagonally structured as such or functionalized with copper ions is presented in comparison with the bidimensional immobilization onto aerosil A380 particles. Immobilization was performed under mild conditions that do not lead to enzyme denaturation. Guest-host interactions were pursued spectrophotometrically and by thermal analysis measurements. FTIR spectroscopy showed no major secondary structural change for the entrapped enzyme despite some influence of the support functionalization that can be supposed. The activity of the immobilized enzyme was tested in the oxidation of Alizarin Red S (ARS) with hydrogen peroxide. It was found that the dye oxidation is catalyzed by the enzyme in homogeneous reaction but the rate becomes much slower in heterogeneous catalytic processes with prepared catalysts. It seems that horseradish peroxidase immobilization in simple porous silica or alumino-silica post synthesis blocks the enzyme activity. In addition, copper ions make a stable complex with ARS hindering its oxidation as well.
37. Dielectric relaxation of pure TGS crystals
Authors: Mindru, C; Ganea, CP; Alexandru, HV

Published: JAN-FEB 2012, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 14, 162, DOI:

Pure triglycine sulphate crystals (TGS) show peculiar dielectric behavior in the ferroelectric phase, after crossing down the Curie point. Dielectric dispersion was investigated on the frequency range 1 Hz divided by 10 MHz. Temperature was changed at a sliding rate of 0.6 degrees C/minute, crossing up and down, several times, the Curie point between 65 degrees C and -120 degrees C. The second component of permittivity, drawn versus the frequency, shows two types of relaxation in the ferroelectric phase, with the characteristic time of tau(L) similar to 10(-3) sec and tau(H) similar to 10(-7) seconds. The first is recognized to be related with ferroelectric domain wall relaxation (domain cropping), although not clearly understood yet. The second one is ascribed to the "critical slowing down" effect, similar to the relaxation in the paraelectric phase, above T-C. A third, middle relaxation time, seems to be a sort of interaction of the two previously mentioned relaxation mechanisms. Papers from the literature, analyzing molecular dynamics and structural changes, could not correlate the flipping time similar to 10(-11) sec of the NH3 group of the glycine GI in the structure (the main responsible of the ferroelectric transition), with the mentioned relaxation times. Several aspects of the dielectric parameters evolution, related to the two relaxation processes on the large temperature range shall be analyzed and discussed.
38. NEW APPROACH OF THE AC ELECTRODE POLARIZATION DURING THE MEASUREMENTS OF IMPEDANCE SPECTRA
Authors: Ganea, CP

Published: 2012, ROMANIAN JOURNAL OF PHYSICS, 57, 675, DOI:

A mathematical approach for describing the influence of the ions dissolved in a liquid crystal on the impedance measurements is presented. New independent variables allow re-formulating the basic coupled differential equations of continuity and Poisson equation as well. The obtained forms are simpler than those used up to now. Illustrative examples are analyzed.
39. LIQUID CRYSTAL/COPOLYMER-CLAY NANOSTRUCTURED SYSTEMS: CONTRIBUTION TO THE CONDUCTIVITY OF THE ELECTRODE POLARIZATION
Authors: Ganea, CP; Manaila-Maximean, D

Published: 2011, UNIVERSITY POLITEHNICA OF BUCHAREST SCIENTIFIC BULLETIN-SERIES A-APPLIED MATHEMATICS AND PHYSICS, 73, 216, DOI:

The electrical conductivity of new nanocomposite systems liquid-ctystal/montmorillonite clay is performed using impedance spectroscopy. The dependence of the electrical conductivity on the frequency, temperature and bias voltage is obtained. The results referring to the alternative voltage influence allow getting more information on the conduction mechanism than the previous ones obtained under frequency and temperature influence. An important role has the polarization at the electrode-sample interface, both in continuous and alternative current. The electrode polarization effect on the electrical conductivity in dependence on the above mentioned parameters is also examined.
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