We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide... more We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-hydroxysuccinimide methacrylate (NMS) by reversible addition–fragmentation chain transfer (RAFT) polymerization. To control the polymer composition, the faster reacting monomer (NMS) was added slowly to the reaction mixture beginning 30 min after initating the polymerization (ca. 16% HPMA conversion). One RAFT agent, based on azocyanopentanoic acid, introduced a –COOH group to the chain at one end. Use of a different RAFT agent containing a 4-amino-1,8-naphthalimide dye introduced a UV–vis absorbing and fluorescent group at this chain end. The polymers obtained had molecular weights of 30 000 and 20 000, respectively, and contained about 30 mol% NMS active ester groups.
This study investigated the combined effects of commercial electroplating additives on the proper... more This study investigated the combined effects of commercial electroplating additives on the properties of nickel electrodeposits. Pieces of carbon steel were electroplated in a Hull cell, using the Watt’s bath with different concentrations of additives and different times of deposition according a 25-1 fractional factorial design. Three response variables, namely brightness, roughness and charge transfer resistance were studied. Several synergistic and antagonistic interactions between the studied factors were found and briefly discussed on a physical basis. Principal Component Analysis (PCA) revealed that clustering in PC-space can be associated with morphological characteristics of the coatings.
This work describes the characterization of DCNPPV films obtained electrochemically over differen... more This work describes the characterization of DCNPPV films obtained electrochemically over different substrates like Pt, Au, ITO and Al. This characterization was performed by infrared (IR), UV-Visible (UV-Vis) and fluorescence (Fl) spectroscopy and by cyclic voltammetry measurements (CV). The obtained results has demonstrated that the formed films present a hight purity grade in all studied substrates, just like was observed in the IR spectra that shown only the characteristics bands of this polymer. The UV-Vis, Fl and CV characterization revealed that this material presents a hight electron affinity value of 3.45 eV. This fact possibilitated that the organic electronic devices formed with this polymer and Al used like cathod electrode, could present a lower electron injection barrier. It was also observed that the solvent used to the electropolymerization process can modulate the nucleation and growth mechanism for the polymeric layer formation.
Design and production of α-MnO 2 structures over carbonaceous material is considered as potential... more Design and production of α-MnO 2 structures over carbonaceous material is considered as potential strategy for improving electrochemical performance of supercapacitors. This study describes the development of a simple method for hydrothermal synthesis of a composite material with directly anchoring α-MnO 2 over a nanographite matrix. The nanographite matrix was obtained by electrochemical exfoliation of graphite rods (from depleted Leclanché batteries) and characterized by X-ray diffraction (XRD), Raman spectroscopy and field emission gun-scanning electron microscopy (FEG-SEM). The obtained results indicated that nanographite produced presented low levels of defects with a mild oxidized surface. This nanographite was used as anchoring base for producing MnO 2 particles, using the developed hydrothermal procedure. For paralleling, pure MnO 2 particles were also produced in same conditions. The prepared materials were characterized by XRD, Raman spectroscopy and FEG-SEM. XRD patterns proved formation of α-MnO 2 for pure and composite materials. Morphological characterization indicated the formation of nanoneedles in both situations; however, in the composite the α-MnO 2 was produced as smaller nanoneedles homogeneously spread over the nanographite surface. Raman spectra showed that the desired composition was achieved. Electrochemical characterization showed that the adopted strategy was successful in producing materials with improved pseudocapacitive performance, high reversibility, presenting specific capacitance of 279.8 F g −1 and coulombic efficiency of 99.7%.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015
ABSTRACT Manipulation of polymeric films at the molecular level can be appropriate to improve the... more ABSTRACT Manipulation of polymeric films at the molecular level can be appropriate to improve the properties of optoelectronic devices. In this paper, the copolymer poly(2,5-dicyano-p-phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV) was spread on the air-water interface forming Langmuir films. The monolayers were investigated with surface pressure-area isotherms, and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The monomolecular films were then transferred to solid supports through the Langmuir-Blodgett (LB) technique, and characterized by PM-IRRAS and atomic force microscopy, with the viability of the film as an optical device investigated with fluorescence spectroscopy. The immobilization of this copolymer on solid supports as LB films provided a molecular architecture with control of their molecular properties, which may have applications for the production of optoelectronic devices.
Abstract This manuscript presents the electrochemical impedance spectroscopy study regarding the ... more Abstract This manuscript presents the electrochemical impedance spectroscopy study regarding the influence of the pH and the range of the applied potential on the IR drop of polyaniline – Gum arabic/graphene oxide (PANI-GA/GOx) electrodes modified by the Layer-by-Layer technique. Using the equivalent circuit modeling methodology, it was discussed the IR drop dependence on parameters such as series and charge-transfer resistances and the double-layer capacitance. Series resistance related to the (PANI-GA/GOx) film conductivity showed to be very influenced by the pH, where a lower value of pH favored the protonation of the polyaniline-based film, increasing the overall conductivity leading to lower values of IR drop. Moreover, the IR drop also showed to be dependent on the range of the applied potential, reflecting in a change at the electrode/electrolyte interface, where an increase at the charge-transfer resistance was found at higher potentials, probably due to the pernigraniline state of PANI.
Trisubstituted thiazoles were synthesized and studied for their antimicrobial activity and suppor... more Trisubstituted thiazoles were synthesized and studied for their antimicrobial activity and supported by theoretical calculations. In addition, MIC, MBC and MFC were also tested. Moreover, the present study was analyzed to scrutinize comprehensive structure-activity relationships. In fact, LUMO orbital energy and orbital orientation was reliable to explain their antibacterial and antifungal assay. Amongst the tested compounds, tri-methyl-substituted thiazole compound showed higher antimicrobial activity and low MIC value due to highest LUMO energy.
We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide... more We describe the synthesis of an end-functionalized copolymer of N-(2-hydroxypropyl)methacrylamide (HPMA) and N-hydroxysuccinimide methacrylate (NMS) by reversible addition–fragmentation chain transfer (RAFT) polymerization. To control the polymer composition, the faster reacting monomer (NMS) was added slowly to the reaction mixture beginning 30 min after initating the polymerization (ca. 16% HPMA conversion). One RAFT agent, based on azocyanopentanoic acid, introduced a –COOH group to the chain at one end. Use of a different RAFT agent containing a 4-amino-1,8-naphthalimide dye introduced a UV–vis absorbing and fluorescent group at this chain end. The polymers obtained had molecular weights of 30 000 and 20 000, respectively, and contained about 30 mol% NMS active ester groups.
This study investigated the combined effects of commercial electroplating additives on the proper... more This study investigated the combined effects of commercial electroplating additives on the properties of nickel electrodeposits. Pieces of carbon steel were electroplated in a Hull cell, using the Watt’s bath with different concentrations of additives and different times of deposition according a 25-1 fractional factorial design. Three response variables, namely brightness, roughness and charge transfer resistance were studied. Several synergistic and antagonistic interactions between the studied factors were found and briefly discussed on a physical basis. Principal Component Analysis (PCA) revealed that clustering in PC-space can be associated with morphological characteristics of the coatings.
This work describes the characterization of DCNPPV films obtained electrochemically over differen... more This work describes the characterization of DCNPPV films obtained electrochemically over different substrates like Pt, Au, ITO and Al. This characterization was performed by infrared (IR), UV-Visible (UV-Vis) and fluorescence (Fl) spectroscopy and by cyclic voltammetry measurements (CV). The obtained results has demonstrated that the formed films present a hight purity grade in all studied substrates, just like was observed in the IR spectra that shown only the characteristics bands of this polymer. The UV-Vis, Fl and CV characterization revealed that this material presents a hight electron affinity value of 3.45 eV. This fact possibilitated that the organic electronic devices formed with this polymer and Al used like cathod electrode, could present a lower electron injection barrier. It was also observed that the solvent used to the electropolymerization process can modulate the nucleation and growth mechanism for the polymeric layer formation.
Design and production of α-MnO 2 structures over carbonaceous material is considered as potential... more Design and production of α-MnO 2 structures over carbonaceous material is considered as potential strategy for improving electrochemical performance of supercapacitors. This study describes the development of a simple method for hydrothermal synthesis of a composite material with directly anchoring α-MnO 2 over a nanographite matrix. The nanographite matrix was obtained by electrochemical exfoliation of graphite rods (from depleted Leclanché batteries) and characterized by X-ray diffraction (XRD), Raman spectroscopy and field emission gun-scanning electron microscopy (FEG-SEM). The obtained results indicated that nanographite produced presented low levels of defects with a mild oxidized surface. This nanographite was used as anchoring base for producing MnO 2 particles, using the developed hydrothermal procedure. For paralleling, pure MnO 2 particles were also produced in same conditions. The prepared materials were characterized by XRD, Raman spectroscopy and FEG-SEM. XRD patterns proved formation of α-MnO 2 for pure and composite materials. Morphological characterization indicated the formation of nanoneedles in both situations; however, in the composite the α-MnO 2 was produced as smaller nanoneedles homogeneously spread over the nanographite surface. Raman spectra showed that the desired composition was achieved. Electrochemical characterization showed that the adopted strategy was successful in producing materials with improved pseudocapacitive performance, high reversibility, presenting specific capacitance of 279.8 F g −1 and coulombic efficiency of 99.7%.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015
ABSTRACT Manipulation of polymeric films at the molecular level can be appropriate to improve the... more ABSTRACT Manipulation of polymeric films at the molecular level can be appropriate to improve the properties of optoelectronic devices. In this paper, the copolymer poly(2,5-dicyano-p-phenylene-vinylene)-co-(p-phenylene-vinylene) (DCN-PPV/PPV) was spread on the air-water interface forming Langmuir films. The monolayers were investigated with surface pressure-area isotherms, and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS). The monomolecular films were then transferred to solid supports through the Langmuir-Blodgett (LB) technique, and characterized by PM-IRRAS and atomic force microscopy, with the viability of the film as an optical device investigated with fluorescence spectroscopy. The immobilization of this copolymer on solid supports as LB films provided a molecular architecture with control of their molecular properties, which may have applications for the production of optoelectronic devices.
Abstract This manuscript presents the electrochemical impedance spectroscopy study regarding the ... more Abstract This manuscript presents the electrochemical impedance spectroscopy study regarding the influence of the pH and the range of the applied potential on the IR drop of polyaniline – Gum arabic/graphene oxide (PANI-GA/GOx) electrodes modified by the Layer-by-Layer technique. Using the equivalent circuit modeling methodology, it was discussed the IR drop dependence on parameters such as series and charge-transfer resistances and the double-layer capacitance. Series resistance related to the (PANI-GA/GOx) film conductivity showed to be very influenced by the pH, where a lower value of pH favored the protonation of the polyaniline-based film, increasing the overall conductivity leading to lower values of IR drop. Moreover, the IR drop also showed to be dependent on the range of the applied potential, reflecting in a change at the electrode/electrolyte interface, where an increase at the charge-transfer resistance was found at higher potentials, probably due to the pernigraniline state of PANI.
Trisubstituted thiazoles were synthesized and studied for their antimicrobial activity and suppor... more Trisubstituted thiazoles were synthesized and studied for their antimicrobial activity and supported by theoretical calculations. In addition, MIC, MBC and MFC were also tested. Moreover, the present study was analyzed to scrutinize comprehensive structure-activity relationships. In fact, LUMO orbital energy and orbital orientation was reliable to explain their antibacterial and antifungal assay. Amongst the tested compounds, tri-methyl-substituted thiazole compound showed higher antimicrobial activity and low MIC value due to highest LUMO energy.
Uploads
Papers by Jarem Garcia