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Dr. Eng. Malvina STROE

Scientific Researcher

Laboratory of Optical Processes in Nanostructured Materials

malvina[AT]infim[DOT]ro

Expertize

Education: 

2009-2012 - PhD in physics, Faculty of Physics, University of Bucharest, department of Optics, Spectroscopy, Plasma, Lasers;

2007-2009 – Master of Science (M.Sc); Engineering and Management of materials production, University Politehnica of Bucharest, Faculty of Science and Engineering of Materials;

2002-2007 - Dipl. Engineer; Chemistry; University Politehnica of Bucharest, Faculty of Applied Chemistry and Materials Science.

Career:

2018 December - prezent scientific researcher at National Institute of Materials Physics, Magurele, Romania

2009-2018 November - Research Assistant at National Institute of Materials Physics, Magurele, Romania

Publications

1. The influence of the functionalization of polystyrene and graphene oxide composites on the flammability characteristics: modeling with artificial intelligence tools
Authors: Anghel, I; Lisa, C; Curteanu, S; Preda, DM; Sofran, IE; Baia, M; Stroe, M; Paraschiv, M; Baibarac, M; Danciu, V; Cotet, LC; Baia, L

Published: 2024 FEB 3 2024, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, DOI: 10.1007/s10973-023-12869-9

This paper tackles the influence of the functionalization of polystyrene and graphene oxide (GO) composites on the flammability characteristics. A microscale combustion calorimeter (MCC) was used to experimentally determine the heat release capacity (HRC), the specific heat release rate (HRR) and the total heat released (THR). Neural models were designed that correlate the THR with a number of parameters related to the composition and type of flame retardant used, the heating rate, the amount of residue, the HRC, the peak heat release rate (PHRR), the temperature at the peak pyrolysis rate (TPHRR) and the time elapsed until the occurrence of the peak heat release rate (Time). The best results in the training, validation and testing stages were achieved with the neural model with 9 neurons in the input layer, 40 neurons in the hidden layer and one neuron in the output layer. This model was incorporated into an optimization procedure, based on a genetic algorithm, to establish the values of the input parameters used in the training of the neural networks, in order to generate a minimum THR value, which is the output parameter. Since the synthesis of polystyrene particles with different GO concentrations is costly, this research helps to reduce the number of experimental tests and allows to determine the best GO concentration by means of neural models and genetic algorithms.
2. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires
Authors: Stroe, M; Burlanescu, T; Paraschiv, M; Lorinczi, A; Matei, E; Ciobanu, R; Baibarac, M

Published: FEB 2023, MATERIALS, 16, 1742, DOI: 10.3390/ma16041742

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO2 nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO2 NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 degrees C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO2 NW sample contains TiO2 tetragonal anatase (A), cubic Ti0.91O (C), and orthorhombic Ti2O3 (OR), as well as monoclinic H2Ti3O7 (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4 degrees and 48 degrees belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4 degrees is explained to be a consequence of the interaction of TiO2 NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm(-1) and 3304-3315 cm(-1) from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO2 NW composites, respectively, with TiO2 NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO2 NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm(-1) and 635 cm(-1), which were assigned to the vibrational modes E-g in TiO2 A and E-g in H2Ti3O7 (ITiO2-A/I-H2Ti3O7), respectively, from 3.45 in TiO2 NWs to 0.94-0.96 in the TPU-TiO2 NW composites, which indicates that the adsorption of TPU onto TiO2 NWs involves an exchange reaction of TPU in the presence of TiO2 NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of TixO2x-mn, Ti2O3, and Ti0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO2 NW. After increasing the TiO2 NW concentration in the TPU-TiO2 NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO2 NW surface from 12.6 degrees to 32 degrees and 45.9 degrees, respectively, took place.
3. Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires
Authors: Stroe, M; Burlanescu, T; Paraschiv, M; Lorinczi, A; Matei, E; Ciobanu, R; Baibarac, M

Published: FEB 2023, MATERIALS, 16, 1742, DOI: 10.3390/ma16041742

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO2 nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO2 NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 degrees C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO2 NW sample contains TiO2 tetragonal anatase (A), cubic Ti0.91O (C), and orthorhombic Ti2O3 (OR), as well as monoclinic H2Ti3O7 (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4 degrees and 48 degrees belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4 degrees is explained to be a consequence of the interaction of TiO2 NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm(-1) and 3304-3315 cm(-1) from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO2 NW composites, respectively, with TiO2 NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO2 NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm(-1) and 635 cm(-1), which were assigned to the vibrational modes E-g in TiO2 A and E-g in H2Ti3O7 (ITiO2-A/I-H2Ti3O7), respectively, from 3.45 in TiO2 NWs to 0.94-0.96 in the TPU-TiO2 NW composites, which indicates that the adsorption of TPU onto TiO2 NWs involves an exchange reaction of TPU in the presence of TiO2 NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of TixO2x-mn, Ti2O3, and Ti0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO2 NW. After increasing the TiO2 NW concentration in the TPU-TiO2 NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO2 NW surface from 12.6 degrees to 32 degrees and 45.9 degrees, respectively, took place.
4. The Photoluminescence and Vibrational Properties of Black Phosphorous Sheets Chemically/Electrochemically Functionalized in the Presence of Diphenylamine
Authors: Baibarac, M., Burlanescu, T., Stroe, M., Smaranda, I., & Negrila, C.

Published: NOV 2022, Polymers, 21, 4479, DOI: 10.3390/polym14214479

In this work, new information concerning the optical properties of black phosphorus (BP) sheets chemically/electrochemically functionalized with diphenyl amine (DPA) and its macromolecular compound (poly(diphenylamine) (PDPA)) in the absence/presence of phosphotungstic acid (PTA) is reported. Raman scattering and FTIR spectroscopy studies indicate that the interaction of BP with PTA leads to the elimination of the PxOy layer onto the surface of the BP sheets. In the case of the chemical interaction of BP with DPA, the reaction product corresponds to DPA chemically functionalized BP sheets having an imino-phosphorane (IP) structure. The electrochemical oxidation of BP sheets chemically functionalized with DPA in the presence of PTA leads to an increase in the weight of P-N bonds as a consequence of the generation of PDPA doped with the PTA heteropolyanions, as shown by FTIR spectroscopy and Raman scattering. This process is evidenced by a shift of the Raman line from 362 cm(-1) to 378 cm(-1), assigned to the A(1g) mode. This change was explained by taking into account the compression of the layers containing P atoms, which is induced by PDPA macromolecular chains. The decrease in the intensity of the PL spectra of DPA as well as PDPA, in the presence of BP, indicates that BP acts as a PL quenching agent for these compounds. A preferential orientation of the PDPA doped with the PTA heteropolyanions on the surface of BP sheets is highlighted by the variation of the binding angle of the PDPA on the surface of BP sheets from 44.7 degrees to 39.9 degrees.
5. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane
Authors: Anghel, I; Lisa, G; Sofran, IE; Mitroi-Symeonidis, FC; Rusu, MM; Baia, M; Baia, L; Magyari, K; Danciu, V; Cotet, LC; Stroe, M; Baibarac, M

Published: 2021, JOURNAL OF POLYMER ENGINEERING, 41, 626, DOI: 10.1515/polyeng-2021-0071

In this study, polystyrene composites (PS-GO(f)) with variable concentration (0.5; 1; 2; 3; 4; and 5 wt%) of GO(f) were obtained through the in-situ polymerisation of the styrene in the presence of benzoyl peroxide and graphene oxide(GO) functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane(gamma-MPTS). For determining the morphological and structural particularities of polymeric composites transmission electron microscopy (TEM) measurements were performed. The influence of functionalized GO on thermal and combustion properties of polystyrene (PS)-based composite materials was determined through several methods: Thermogravimetry (TGA); derived thermogravimetry (DTG); microscale combustion calorimetry analysis (MCC); and chemical kinetic studies through TGA and MCC determinations at similar heating rates.
6. Optical, Structural, and Dielectric Properties of Composites Based on Thermoplastic Polymers of the Polyolefin and Polyurethane Type and BaTiO3 Nanoparticles
Authors: Baibarac, M; Nila, A; Smaranda, I; Stroe, M; Stingescu, L; Cristea, M; Cercel, RC; Lorinczi, A; Ganea, P; Mercioniu, I; Ciobanu, R; Schreiner, C; Garcia, RG; Bartha, C

Published: FEB 2021, MATERIALS, 14, DOI: 10.3390/ma14040753

In this work, new films containing composite materials based on blends of thermoplastic polymers of the polyurethane (TPU) and polyolefin (TPO) type, in the absence and presence of BaTiO3 nanoparticles (NPs) with the size smaller 100 nm, were prepared. The vibrational properties of the free films depending on the weight ratio of the two thermoplastic polymers were studied. Our results demonstrate that these films are optically active, with strong, broad, and adjustable photoluminescence by varying the amount of TPU. The crystalline structure of BaTiO3 and the influence of thermoplastic polymers on the crystallization process of these inorganic NPs were determined by X-ray diffraction (XRD) studies. The vibrational changes induced in the thermoplastic polymer's matrix of the BaTiO3 NPs were showcased by Raman scattering and FTIR spectroscopy. The incorporation of BaTiO3 NPs in the matrix of thermoplastic elastomers revealed the shift dependence of the photoluminescence (PL) band depending on the BaTiO3 NP concentration, which was capable of covering a wide visible spectral range. The dependencies of the dielectric relaxation phenomena with the weight of BaTiO3 NPs in thermoplastic polymers blends were also demonstrated.
7. Poly(Vinyl Chloride) Spheres Coated with Graphene Oxide Sheets: From Synthesis to Optical Properties and Their Applications as Flame-Retardant Agents
Authors: Baibarac, M; Stingescu, L; Stroe, M; Negrila, C; Matei, E; Cotet, LC; Anghel, I; Sofran, IE; Baia, L

Published: FEB 2021, POLYMERS, 13, DOI: 10.3390/polym13040565

A new method to obtain poly(vinyl chloride) (PVC) spheres, which consists of an interaction between commercial PVC grains and hexyl ethyl cellulose and lauroyl peroxide at a temperature of 60 degrees C, is reported. The addition of the graphene oxide (GO) sheets dispersed in dimethylformamide to the reaction mixture leads to the generation of composites made of PVC spheres coated with GO sheets. Scanning electron microscopy studies have demonstrated that this method allows for the transformation of PVC grains with sizes between 75 and 227 mu m into spheres with sizes varying from 0.7 to 3.5 mu m when the GO concentration in the PVC/GO composite mass increases from 0.5 to 5 wt.%. Our studies of Raman scattering and FTIR spectroscopy highlight a series of changes that indicate the appearance of ClCH=CH-, CH2=CCl-, and/or -CH=CCl- units as a result of PVC partial dehydrogenation. New -COO- and C-OH bonds on the GO sheet surfaces are induced during the preparation of PVC spheres coated with GO sheets. A photoluminescence (PL) band with a maximum at 325 nm is reported to characterize the PVC spheres. A PVC PL quenching process is demonstrated to be induced by the increase in the concentration of the GO sheets in the PVC/GO composite mass. The perspectives regarding the use of this composite as a flame-retardant material are also reported.
8. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles
Authors: Toulbe, N; Stroe, MS; Daescu, M; Cercel, R; Mogos, A; Dragoman, D; Socol, M; Mercioniu, I; Baibarac, M

Published: NOV 2020, NANOMATERIALS, 10, DOI: 10.3390/nano10112238

The influence of Ag and Au nanoparticles and reduced graphene oxide (RGO) sheets on the photodegradation of alpha-lipoic acid (ALA) was determined by UV-VIS spectroscopy. The ALA photodegradation was explained by considering the affinity of thiol groups for the metallic nanoparticles synthesized in the presence of trisodium citrate. The presence of excipients did not induce further changes when ALA interacts with Ag and Au nanoparticles with sizes of 5 and 10 nm by exposure to UV light. Compared to the Raman spectrum of ALA powder, changes in Raman lines' position and relative intensities when ALA has interacted with films obtained from Au nanoparticles with sizes between 5 and 50 nm were significant. These changes were explained by considering the chemical mechanism of surface-enhanced Raman scattering (SERS) spectroscopy. The photodegradation of ALA that had interacted with metallic nanoparticles was inhibited in the presence of RGO sheets.
9. Reduced Graphene Oxide Sheets as Inhibitors of the Photochemical Reactions of alpha-Lipoic Acid in the Presence of Ag and Au Nanoparticles
Authors: Toulbe, N'ghaya; Stroe, Malvina S; Daescu, Monica; Cercel, Radu; Mogos, Alin; Dragoman, Daniela; Socol, Marcela; Mercioniu, Ionel; Baibarac, Mihaela

Published: Nov 11 2020, , DOI: 10.3390/nano10112238

The influence of Ag and Au nanoparticles and reduced graphene oxide (RGO) sheets on the photodegradation of alpha-lipoic acid (ALA) was determined by UV-VIS spectroscopy. The ALA photodegradation was explained by considering the affinity of thiol groups for the metallic nanoparticles synthesized in the presence of trisodium citrate. The presence of excipients did not induce further changes when ALA interacts with Ag and Au nanoparticles with sizes of 5 and 10 nm by exposure to UV light. Compared to the Raman spectrum of ALA powder, changes in Raman lines' position and relative intensities when ALA has interacted with films obtained from Au nanoparticles with sizes between 5 and 50 nm were significant. These changes were explained by considering the chemical mechanism of surface-enhanced Raman scattering (SERS) spectroscopy. The photodegradation of ALA that had interacted with metallic nanoparticles was inhibited in the presence of RGO sheets.
10. Optical Properties of Composites Based on Graphene Oxide and Polystyrene
Authors: Stroe, M; Cristea, M; Matei, E; Galatanu, A; Cotet, LC; Pop, LC; Baia, M; Danciu, V; Anghel, I; Baia, L; Baibarac, MA

Published: MAY 2020, MOLECULES, 25, DOI: 10.3390/molecules25102419

In this work, new optical properties of composites based on polystyrene (PS) microspheres and graphene oxide (GO) are reported. The radical polymerization of styrene in the presence of benzoyl peroxide, pentane and GO induces the appearance of new ester groups in the PS macromolecular chains remarked through an increase in the absorbance of the infrared (IR) band at 1743 cm(-1). The decrease in the GO concentration in the PS/GO composites mass from 5 wt.% to 0.5 wt.% induces a diminution in the intensities of the D and G Raman bands of GO simultaneous with a down-shift of the D band from 1351 to 1322 cm(-1). These variations correlated with the covalent functionalization of the GO layers with PS. For the first time, the photoluminescent (PL) properties of PS/GO composites are reported. The PS microspheres are characterized by a PL band at 397 nm. Through increasing the GO sheets' concentration in the PS/GO composite mass from 0.5 wt.% to 5 wt.%, a PS PL quenching process is reported. In addition, in the presence of ultraviolet A (UVA) light, a photo-degradation process of the PS/GO composite having the GO concentration equal to 5 wt.% is demonstrated by the PL studies.
11. Morphological and structural investigation of the poly(Vinyl chloride) / graphene oxide composites
Authors: Stingescu, L., Cadar, C., Cotet, L.C., Baia, L., Saszet, K., Magyari, K., Mihis, A.G., Fort, C.I., Stroe, M., Matei, E., Nila, A., Anghel, I., Baia, M., Baibarac, M., Danciu, V.

Published: 2020, , DOI: 10.24193/subbchem.2020.3.19

The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 µm to 227 µm. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman glines situated in the spectral ranges 600- 650 and 2850-3000 cm-1 (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp2 to sp3. An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24° to 26° when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed. © 2020, Universitatea Babes-Bolyai, Catedra de Filosofie Sistematica. All rights reserved.
12. MORPHOLOGICAL AND STRUCTURAL INVESTIGATION OF THE POLY(VINYL CHLORIDE)/GRAPHENE OXIDE COMPOSITES
Authors: Stingescu, L; Cadar, C; Cotet, LC; Baia, L; Saszet, K; Magyari, K; Mihis, AG; Fort, CI; Stroe, M; Matei, E; Nila, A; Anghel, I; Baia, M; Baibarac, M; Danciu, V

Published: 2020, STUDIA UNIVERSITATIS BABES-BOLYAI CHEMIA, 65, 258, DOI: 10.24193/subbchem.2020.3.19

The morphological and structural properties of the poly(vinyl chloride)/graphene oxide (PVC/GO) composites are reported. By the mixture of the two constituents, the PVC/GO composite membranes with a concentration of the GO sheets varying from 0 wt.% to 0.5, 1, 2, 3, 4 and 5 wt.% were prepared. Using scanning electron microscopy (SEM) and the analysis of the atomic force microscopy (AFM) images we observed that as increasing the GO concentration in the PVC mass from 0 wt.% to 5 wt.%, the average surface roughness decreases from 235 mu m to 227 mu m. Using Raman scattering, we report that as increasing the GO concentration in the PVC mass, the ratio between the relative intensities of the Raman lines situated in the spectral ranges 600-650 and 2850-3000 cm(-1) (I600-650/I2850-3000) increases as a consequence of the change of GO carbon atoms hybridization from sp(2) to sp(3). An increase in the number of C-C bonds, simultaneous with the appearance of O-C=O bonds and the decrease of the chlorine concentration, when the GO concentration increases in the PVC weight is reported by X-ray photoelectron spectroscopy (XPS). The down-shift of the main diffraction signal from 24 degrees to 26 degrees when the GO concentration increases in the PVC/GO composite mass from 0 wt.% to 5 wt.%, confirms the incorporation of GO in the polymeric matrix and the modification of the original PVC sample structure. Using transmission electron microscopy (TEM), no agglomerations of the GO structures within the PVC/GO matrix contrast limit were observed.
13. Properties of textile and leather materials treated with new hybrid SiO2/TiO2/poly(2,2 '-bithiophene) nanocomposites
Authors: Chirila, L; Gaidau, C; Stroe, M; Baibarac, M; Stanca, M; Radulescu, DM; Radulescu, DE; Alexe, CA

Published: 2019, , DOI: 10.35530/IT.070.03.1634

The aim of this study was to investigate the influence of new hybrid composites of TiO2 or SiO2 nanoparticles with poly(2,2'-bithiophene) on 50% cotton/50% polyester fabric and sheep skin leather surface properties. The dispersion-based newly made nanocomposites were analyzed to determine conductivity, particle size, polydispersity and Zeta potential. The finished textile and leather materials were characterized in terms of functionalization treatments performance by: surface resistivity, water contact behaviour, physical-mechanical characteristics and photocatalytic properties. SEM analysis was used to investigate the distribution of nanoparticles on the textile and leather materials surface. Textile materials treated with SiO2/poly(2,2'-bithiophene) nanocomposite with concentration 98 wt% nanoparticles of SiO2 and leather treated with poly SiO2/poly(2,2'-bithiophene) nanocomposite with concentration of 95 wt% nanoparticles of SiO2 showed lower resistivity values, confirming the conductive properties of silica. The higher photodegradation efficiency of functionalized materials has been obtained for textile material treated with poly TiO2/(2,2'-bithiophene) with concentration of 95 wt% nanoparticles of TiO2 and for leather material treated with TiO2/poly(2,2'-bithiophene) with concentration of 98 wt% nanoparticles of TiO2, respectively.
14. Vibrational and photoluminescence properties of polydiphenylamine doped with silicotungstic acid heteropolyanions and their composites with reduced graphene oxide
Authors: Baibarac, M; Stroe, M; Fejer, SN

Published: MAY 15 2019, JOURNAL OF MOLECULAR STRUCTURE, 1184, 35, DOI: 10.1016/j.molstruc.2019.02.014

In this work, the influence of silicotungstic acid concentration on the diphenylamine (DPA) electro-polymerization in the absence and the presence of reduced graphene oxide (RGO) is studied. The optical properties of the composites based on polydiphenylamine (PDPA) doped with the H4SiW12O40 heteropolyanions and RGO are investigated by Raman scattering, IR absorption spectroscopy and photoluminescence (PL). The presence of RGO induces an up-shift of the oxidation maximum of the DPA, as a result of a covalent functionalization process of graphene sheets with the polymer in the doped state. The deposition of PDPA onto RGO sheets surface is confirmed by the Raman scattering studies. Regardless of the H4SiW12O40 concentration, an up-shift of the IR bands from 910 to 1014 cm(-1) to similar to 920 and 1022 cm(-1) is reported as a consequence of the compensation of positive charges of PDPA macromolecular chains with of the H4SiW12O40 heteropolyanions. An enhancement in the absorbance of the IR bands situated in the spectral range 750-1050 cm(-1) accompanied of a decrease in the relative intensity of the PL bands of PDPA and their composites with RGO, as increasing the H4SiW12O40 concentration, is reported. In the presence of RGO, a change in the PDPA PL spectra profile is also highlighted. (C) 2019 The Authors. Published by Elsevier B.V.
15. Electrochemical Synthesis of the Composites Based on Multi-Wall Carbon Nanotubes and Polypyrrole Doped with Phosphomolybdic Acid Heteropolyanions and Their Vibrational Properties
Authors: Baibarac, M; Serbschi, C; Stroe, M

Published: NOV 2018, INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, 13, 10526, DOI: 10.20964/2018.11.07

Using cyclic voltammetry, Raman scattering and infrared (IR) spectroscopy, new findings concerning the electrochemical synthesis of composites based on multi-wall carbon nanotubes (MWNTs) and polypyrrole (PPY) doped with H3PMo12O40 heteropolyanions are described in this report. To better understand the electrochemical mechanism behind the synthesis of these composites, the influence of the concentrations of pyrrole and the electrolytes of H3PMo12O40 and H2SO4 on the cyclic voltammogram profile is studied. The formation of PPY doped with H3PMo12O40 heteropolyanions onto the MWNT surface is demonstrated by complementary studies of Raman scattering and IR spectroscopy.
16. Exciton-phonon interaction in PbI2 revealed by Raman and photoluminescence studies using excitation light overlapping the fundamental absorption edge
Authors: Baibarac, M; Smaranda, I; Scocioreanu, M; Mitran, RA; Enculescu, M; Galatanu, M; Baltog, I

Published: OCT 2015, MATERIALS RESEARCH BULLETIN, 70, 772, DOI: 10.1016/j.materresbull.2015.06.012

Enhancement at low temperatures of the Raman scattering excited by laser light situated near the edge of the fundamental absorption band is often encountered when studying nanoscale structures. Theory devoted to this phenomenon has established that it originates in an exciton-phonon interaction process, known as the Frohlich interaction, Such a phenomenon was observed in PbI2. The experimental data conclude that the enhancement of the Raman emission results from: (i) an optical excitation near edge of fundamental absorption band; (ii) it is conditioned by the existence of excitonic PL; (iii) its occurrence is different over stokes and anti-stokes Raman branches as result of the different overlapping of the Raman spectral range and the excitonic PL band profile; and (iv) it appears more intense in micrometric powders or in bulk crystalline material. These data are interpreted as stimulated Raman effect resulting from the mixing of the pump laser light and the excitonic light. (C) 2015 Elsevier Ltd. All rights reserved.
17. Abnormal anti-Stokes Raman scattering and surface-enhanced infrared absorption spectroscopy studies of carbon nanotubes electrochemically functionalized with poly(2,2 '-bithiophene-co-pyrene)
Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Mevellec, JY; Lefrant, S

Published: AUG 1 2014, APPLIED SURFACE SCIENCE, 309, 21, DOI: 10.1016/j.apsusc.2014.04.114

A new composite material was synthesized via the electrochemical oxidation of 2,2'-bithiophene (BTh) and pyrene (Py) monomers dissolved in a solution of LiC1O(4) in CH3CN onto a working electrode of Au coated with a film of single-walled carbon nanotubes (SWNTs). The interaction of the poly(2,2'-bithiophene-co-pyrene) (PBTh-Py) with the SWNTs and the orientation of the copolymer on the working electrode were studied by anti-Stokes and Stokes Raman scattering and FTIR spectroscopy in the grazing-incidence angle reflection geometry. The Raman lines at 1464 and 1435 cm(-1), attributed to the symmetric stretching modes of the C=C bond in the quinoid and aromatic rings of the PBTh-Py copolymer, were observed when the working electrode is either a blank Au film or a Au support coated with a SWNT film. In the latter case, charge transfer occurs at the interface of the two constituents. This charge transfer leads to functionalization of the carbon nanotubes with the copolymer molecules. The presence of enhanced anti-Stokes Raman lines at -1461, -1435 and -1187 cm(-1) indicates a resonant optical excitation process of the PBTh-Py/SWNT composite. The FTIR spectra acquired under polarized light for the PBTh-Py copolymer electrosynthesized on a bare Au support reveal significant changes in the absorption bands situated in the spectral ranges of 1000-1150 and 1550-1650 cm(-1) that originate in the surface-enhanced IR absorption (SEIRA) processes. The functionalization of the SWNTs with the PBTh-Py copolymer is evidenced by the enhancement of the absorption of the FTIR bands at 793 and 846 cm(-1), which are assigned to the C S C deformation vibrational mode and the substituted benzene ring, respectively, due to the effects of steric hindrance that are induced for the copolymer molecules by the binding of carbon nanotubes. (C) 2014 Elsevier B.V. All rights reserved.
18. Spectroelectrochemical properties of the poly[(2,5-bisoctyloxy)-1,4-phenylenevinylene]/single-walled carbon nanotube composite
Authors: Baibarac, M; Baltog, I; Srnaranda, I; Ilie, M; Scocioreanu, M; Mevellec, JY; Lefrant, S

Published: SEP 2014, SYNTHETIC METALS, 195, 285, DOI: 10.1016/j.synthmet.2014.06.010

Using surface-enhanced Raman scattering (SERS) and photoluminescence (PL) studies, new data concerning the electrochemical oxidation both of poly[(2,5-bisoctyloxy)-1,4-phenylene-vinylene] (BO-PPV) and the BO-PPV/HIPCO single-walled carbon nanotubes (SWNTs) composite are presented in this paper. The SERS studies performed at the excitation wavelengths of 752 nm and 532 nm of the BO-PPV/SWNTs composite that ensure the resonant excitation of the semiconductor and metallic nanotubes, respectively, reveal that the mixing of the two constituents results, on the one hand, in an isolation of semiconducting nanotubes from the bundles containing both metallic and semiconducting tubes and, on the other hand, in a functionalization of metallic SWNTs with BO-PPV. The isolation of semiconducting SWNTs is demonstrated by the narrowing of the G band and the change of the ratio between the intensities of the Raman lines situated in the low-frequency range that are assigned to the radial breathing vibrational modes. An additional isolation of the semiconducting nanotubes from the SWNTs bundles is reported when an electro-oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2) V vs. Ag/AgCl. According to the Fourier transformed infra-red (FTIR) spectra and the SERS studies performed at an excitation wavelength of 1064 nm, the chemical interaction of BO-PPV with HIPCO SWNTs reveals a charge transfer between the two constituents that leads to the formation of BO-PPV covalently functionalized SWNTs. The BO-PPV luminescence quenching effect induced by the presence of SWNTs that consists of a change in the relative intensities of the three PL bands of the polymer peaked at 1.73 eV, 1.9 eV and 2.07 eV is due to the metallic tubes. The appearance of a new emission band at 2.32 eV was regularly observed when electrochemical oxidation of the BO-PPV/SWNTs composite was performed in the potential range of (0; +2) V. The PL band at 2.32 eV corresponds to ClO4- ions, which compensates the positive charges of BO-PPV generated during the electrochemical doping process. (C) 2014 Elsevier B.V. All rights reserved.
19. Photoluminescence decay time studies on ZnS in cubic and hexagonal phase and its mechanico-chemical interaction with polyaniline
Authors: Scocioreanu, M; Mihut, L; Baibarac, M; Baltog, I

Published: JUL 2013, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 250, 1431, DOI: 10.1002/pssb.201248234

We report new photoluminescence (PL) data generated by pulsed optical excitation on the composites achieved by a mechanico-chemical reaction between ZnS in the cubic (c) and wurtzite (w) phases and polyaniline-emeraldine base (PANI-EB). Under continuous and pulsed optical excitation, powders of the (w)ZnS and (w)ZnS/PANI-EB composites display PL with different spectral compositions. Contrary to expectations, the (c)ZnS and the (c)ZnS/PANI-EB composite displayed weak PL and decay time in the range of nanoseconds. This results from the great involvement of the surface states in nanometric powders which creates efficient channels for the non-radiative recombination of the carriers. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
20. Photoluminescence and Raman evidence for mechanico-chemical interaction of polyaniline-emeraldine base with ZnS in cubic and hexagonal phase
Authors: Scocioreanu, M; Baibarac, M; Baltog, I; Pasuk, I; Velula, T

Published: FEB 2012, JOURNAL OF SOLID STATE CHEMISTRY, 186, 223, DOI: 10.1016/j.jssc.2011.12.012

The mechanico-chemical interaction of a polyaniline-emeraldine base (PANI-EB) with ZnS in the cubic and wurtzite phases is studied by Raman spectroscopy and photoluminescence (PL). The results demonstrate that such an interaction leads to the formation of a PANI-salt and metallic Zn. Regardless of the structural form of the ZnS, the formation PANI-salt is indicated by a band in the Raman spectrum that shifts from 1162 to 1176 cm(-1) and the appearance of a new band at 1330 cm(-1) that indicates the protonated structure of a PANI-salt. The presence of the second product is determined by comparative PL studies performed on ZnS that has interacted mechanico-chemically with PANI-EB and metallic Zn powder. The variations of the PL spectra and their associated excitation spectra are explained as resulting from the charge collection processes that occur in the composite materials produced by the mechanico-chemical interaction between ZnS and PANI-EB or metallic Zn. (C) 2011 Elsevier Inc. All rights reserved.
21. Hybrid organic-inorganic materials based on poly(o-phenylenediamine) and polyoxometallate functionalized carbon nanotubes
Authors: Baibarac, M; Baltog, I; Smaranda, I; Scocioreanu, M; Lefrant, S

Published: JAN 31 2011, JOURNAL OF MOLECULAR STRUCTURE, 985, 218, DOI: 10.1016/j.molstruc.2010.10.044

The chemical polymerization of o-phenylenediamine (OPD) on single-walled carbon nanotubes (SWCNTs) in the presence of phosphomolybdic acid (H3PMo12O40 xH(2)O) has been studied by surface enhanced resonant Raman scattering (SERRS) spectroscopy. One demonstrates that an organic-inorganic hybrid composite of the type poly(o-phenylenediamine)/polyoxometallate-functionalized SWCNTs is produced by the chemical interaction between polyoxometallate-functionalized SWCNTs and poly(o-phenylenediamine) (POPD) doped with [H2PMo12O40](-) ions. According to TEM investigations, a result of the chemical interaction of SWCNT with H3PMo12O40 xH(2)O is the formation into the composite mass of tube fragments of shorter length, which behave like closed shell fullerenes since Raman fingerprint is given by lines situated at 240-275 and 1450-1472 cm(-1). The chemical polymerization of OPD on SWCNTs achieved in the absence of H3PMo12O40 xH(2)O leads to a covalent functionalization of the wall side of the tubes, which is revealed in Raman spectra, recorded at the excitation wavelength of 514 nm, by an enhancement of the lines associated with the tangential vibrational modes of SWCNTs. Using FTIR spectroscopy, significant hindrance steric effects are evidenced in the POPD/polyoxometallate-functionalized SWCNT composite. (c) 2010 Elsevier B.V. All rights reserved.
22. One-dimensional composites based on single walled carbon nanotubes and poly(o-phenylenediamine)
Authors: Baibarac, M; Baltog, I; Scocioreanu, M; Ballesteros, B; Mevellec, JY; Lefrant, S

Published: NOV-DEC 2011, SYNTHETIC METALS, 161, 2354, DOI: 10.1016/j.synthmet.2011.09.001

The direct mixing of aqueous ferric chloride and o-phenylenediamine (OPD) solution at room temperature in the absence and presence of carbon nanotubes (CNTs) has been used to prepare poly(o-phenylenediamine) (POPD) micro-fibers and composites of the type CNTs/POPD having nanotubes incorporated in polymer fiber mass. Using surface enhanced infrared absorption (SEIRA) spectroscopy significant modifications in the low frequency range of the polymer spectrum are revealed when Au is used as metallic support. Similar variations are reported for the POPD samples prepared by the electropolymerization of OPD onto rough Au electrode. A covalent functionalization of CNTs with POPD and a doping process of POPD with radical anions of CNTs is proved by surface enhanced resonant Raman scattering and SEIRA spectroscopy. The X-ray diffraction (XRD) studies indicate a high crystallinity both for POPD and CNTs/POPD composites prepared by chemical or electrochemical methods. (C) 2011 Elsevier B.V. All rights reserved.
23. Vibrational properties of the electrochemically synthesized polyindole/single-walled carbon nanotubes composite
Authors: Baibarac, M; Baltog, I; Scocioreanu, M; Lefrant, S; Mevellec, JY

Published: DEC 2009, SYNTHETIC METALS, 159, 2555, DOI: 10.1016/j.synthmet.2009.09.010

Electrochemical polymerization of indole in a LiClO4/CH3CN solution on a single-walled carbon nanotubes (SWNTs) film was studied by cyclic voltammetry, Raman scattering and FTIR spectroscopy. Comparing the cyclic voltammograms recorded on a blank Pt electrode with those obtained when carbon nanotubes films were previously deposited onto the Pt electrode, a down-shift of the indole reduction peak potential in the latter case was observed. Raman spectroscopy studies indicate that the electrochemical deposition of polyindole (PIN) onto the SWNT film results in a breaking of SWNT bundles into individual tubes. A covalent functionalization of SWNTs with PIN in the doped state is demonstrated by FTIR spectroscopy, when an increase in the intensity of the absorption band at 1045 cm(-1) is observed. Besides, Raman and FTIR studies performed on samples electrochemically prepared and thereafter post-chemically reacted with an NH4OH solution, indicate both a roping process of individual tubes with PIN as a binding agent and a strong steric hindrance effect. (C) 2009 Elsevier B.V. All rights reserved.
24. Textile Materials Treatment With Mixture of TiO2:N and SiO(2)Nanoparticles for Improvement of Their Self-Cleaning Properties
Authors: Mateescu, AO; Mateescu, G; Burducea, I; Mereuta, P; Chirila, L; Popescu, A; Stroe, M; Nila, A; Baibarac, M

Published: SEP 2020 , JOURNAL OF NATURAL FIBERS, DOI: 10.1080/15440478.2020.1818349

This study addresses the deposition with improved adhesion of TiO2:N/SiO(2)mixture, with different concentrations of the nano-powders (NPs) (1:0,5; 1:1 and 1:1,5) on 100% cotton fabrics. The characteristics of the deposited thin films were investigated by scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), Raman scattering, FTIR, and UV-VIS absorption spectroscopy. To improve the treatment durability to the external factors, the different crosslinking methods were used. Photocatalytic activity of functionalized textile fabrics was evaluated by determining the photodegradation efficiency of the methylene blue (MB) dye and forest juice, measuring the color difference of the irradiated samples compared with non-irradiated samples. Washing durability of the samples was achieved qualitatively by determining the photocatalytic activity remaining on the textile fabrics after 1 and 5 washing cycles. The samples treated with the mixture of TiO2:N/SiO(2)have demonstrated improved self-cleaning properties, the highest photocatalytic activity being obtained for the highest value of TiO2:N/SiO(2)NPs molar concentrations equal to 1:1.
25. Pyrolysis and combustion of polystyrene composites based on graphene oxide functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane
Authors: Anghel, I; Lisa, G; Sofran, IE; Mitroi-Symeonidis, FC; Rusu, MM; Baia, M; Baia, L; Magyari, K; Danciu, V; Cotet, LC; Stroe, M; Baibarac, M

Published: , JOURNAL OF POLYMER ENGINEERING, 2021, 626, DOI:

In this study, polystyrene composites (PS-GO(f)) with variable concentration (0.5; 1; 2; 3; 4; and 5 wt%) of GO(f) were obtained through the in-situ polymerisation of the styrene in the presence of benzoyl peroxide and graphene oxide(GO) functionalized with 3-(methacryloyloxy)-propyltrimethoxysilane(gamma-MPTS). For determining the morphological and structural particularities of polymeric composites transmission electron microscopy (TEM) measurements were performed. The influence of functionalized GO on thermal and combustion properties of polystyrene (PS)-based composite materials was determined through several methods: Thermogravimetry (TGA); derived thermogravimetry (DTG); microscale combustion calorimetry analysis (MCC); and chemical kinetic studies through TGA and MCC determinations at similar heating rates.
26. Textile Materials Treatment With Mixture of TiO2:N and SiO(2)Nanoparticles for Improvement of Their Self-Cleaning Properties
Authors: Mateescu, AO; Mateescu, G; Burducea, I; Mereuta, P; Chirila, L; Popescu, A; Stroe, M; Nila, A; Baibarac, M

Published: , JOURNAL OF NATURAL FIBERS, DOI: 10.1080/15440478.2020.1818349

This study addresses the deposition with improved adhesion of TiO2:N/SiO(2)mixture, with different concentrations of the nano-powders (NPs) (1:0,5; 1:1 and 1:1,5) on 100% cotton fabrics. The characteristics of the deposited thin films were investigated by scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), Raman scattering, FTIR, and UV-VIS absorption spectroscopy. To improve the treatment durability to the external factors, the different crosslinking methods were used. Photocatalytic activity of functionalized textile fabrics was evaluated by determining the photodegradation efficiency of the methylene blue (MB) dye and forest juice, measuring the color difference of the irradiated samples compared with non-irradiated samples. Washing durability of the samples was achieved qualitatively by determining the photocatalytic activity remaining on the textile fabrics after 1 and 5 washing cycles. The samples treated with the mixture of TiO2:N/SiO(2)have demonstrated improved self-cleaning properties, the highest photocatalytic activity being obtained for the highest value of TiO2:N/SiO(2)NPs molar concentrations equal to 1:1.
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