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Papers by Yvonne Mascarenhas

X-ray absorption spectroscopy was used to probe the short-range structure in lanthanum-doped lead... more X-ray absorption spectroscopy was used to probe the short-range structure in lanthanum-doped lead titanate ceramics (Pb 1−x La x TiO 3 ) for x ranging from 0.0 to 0.30. A comparison of the XANES spectra and the X-ray diffraction (XRD) results indicates that the local structure around Ti atoms had a different compositional dependence. According to the XANES data, even for the sample containing 30% of lanthanum, for which the XRD analysis indicated the existence of a cubic structure, a local distortion around Ti atoms persisted. The intensity of the pre-edge feature of the PLT30 sample decreased by a factor of only two when compared with the lanthanum-free sample.

The existence of conducting islands in polyani-line films has long been proposed in the literatur... more The existence of conducting islands in polyani-line films has long been proposed in the literature, which would be consistent with conducting mechanisms based on hopping. Obtaining direct evidence of conducting islands, however, is not straightforward. In this paper, conducting islands were visualized in poly(o-ethoxyaniline) (POEA) films prepared at low pH, using Transmission Electron Mi-croscopy (TEM) and atomic force spectroscopy (AFS). The size of the islands varied between 67 and 470 Å for a pH = 3.0, with a larger average being obtained with AFS, probably due to the finite size effect of the atomic force mi-croscopy tip. In AFS, the conducting islands were denoted by regions with repulsive forces due to the double-layer forces. On the basis of X-ray diffraction (XRD) patterns for POEA in the powder form, we infer that the conducting islands are crystalline, and therefore a POEA film is believed to consist of conducting islands dispersed in an insulating, amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasi-one dimensional variable range hopping (VRH) mechanism.

Microporous and Mesoporous Materials, 2000

Na-Y zeolites ion exchanged with rare earth cations (Nd3+, Sm3+, Gd3+, Dy3+) were studied by X-ra... more Na-Y zeolites ion exchanged with rare earth cations (Nd3+, Sm3+, Gd3+, Dy3+) were studied by X-ray diffraction in order to locate the rare earth cations in the zeolite framework and the resulting changes in its structural properties. The results indicate that the rare earth cations dealuminate the framework differently. This is observed as a decrease in the values of the unit cell parameters, a0. This systematic decrease in a0 is related to the rare earth ionic radius and its coordination to the oxygen framework. The correlation between the Si/Al ratio obtained from the Fichtner-Schmittler equation and the ionic radius of the rare earth cations reveals that smaller ionic radii gives higher dealumination and smaller a0. This is related to hydrolysis constant cation. Samples treated with Dy3+ cations show a higher level of dealumination than those treated with the other cations (Sm3+, Gd3+, Nd3+). In order to characterize the dealumination process and magic angle spinning NMR measurements were attempted. Except for the Sm3+ treated sample, the Nd3+, Gd3+, Dy3+ samples could not have their tetrahedral and octahedral aluminum signal detected due to the high concentration of the paramagnetic ions with large effective number of Bohr magnetons.

Journal of Colloid and Interface Science, 2007

Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for th... more Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology-seen with atomic force microscopy and transmission electron microscopy-that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.

Materials Science Forum (278), 720-725 (1998)

AHfO(3) (A = Ca, Sr and Ba) belongs to perovskite family with general formula A(2+)B(4+)O(3). The... more AHfO(3) (A = Ca, Sr and Ba) belongs to perovskite family with general formula A(2+)B(4+)O(3). The crystal structure of CaHfO(3) (CH), SrHfO(3) (SH) and BaHfO(3) (BH) at room temperature (RT) is reported, combining the results of the Rietveld method refinements using X-ray and neutron powder diffraction data and PAC spectroscopy. The structures were refined by the Rietveld Method using DBWS9411 and GSAS programs, The refinement of SH using neutron and X-ray powder pattern indicates an orthorhombic Pnma symmetry at room temperature. The hyperfine parameters of PAC spectroscopy indicate that the structure has lower-than-cubic symmetry at RT, The structures of CH and BH were refined with the Pnma and Pm (3) over bar m space group respectively. The three compounds have near regular oxygen octahedra that are characteristic of perovskites of Glazer types a(+)a(-)a(-) and a(0)a(0)a(0), for which the distortion is better related to the tilting of the octahedra.

Acta crystallographica. Section E, Structure reports online, 2008

In the title compound, C(13)H(12)N(2)O(2)S, the dihedral angle between the two aromatic ring plan... more In the title compound, C(13)H(12)N(2)O(2)S, the dihedral angle between the two aromatic ring planes is 87.52 (12)°. The mol-ecule shows an intra-molecular N-H⋯O hydrogen bond. The crystal structure is stabilized by inter-molecular N-H⋯S and C-H⋯O hydrogen bonding.

Acta crystallographica. Section E, Structure reports online, 2008

The title compound, C(13)H(9)N(3)O(2)S, was synthesized from furoyl isothio-cyanate and 3-amino-b... more The title compound, C(13)H(9)N(3)O(2)S, was synthesized from furoyl isothio-cyanate and 3-amino-benzonitrile in dry acetone. The thio-urea group is in the thio-amide form. The thio-urea fragment makes dihedral angles of 3.91 (16) and 37.83 (12)° with the ketofuran group and the benzene ring, respectively. The mol-ecular geometry is stabilized by N-H⋯O hydrogen bonds. In the crystal structure, centrosymmetrically related mol-ecules are linked by two inter-molecular N-H⋯S hydrogen bonds to form dimers.

Acta Crystallographica Section E Structure Reports Online, 2008

Key indicators: single-crystal X-ray study; T = 150 K; mean (C-C) = 0.004 Å; R factor = 0.047; wR... more Key indicators: single-crystal X-ray study; T = 150 K; mean (C-C) = 0.004 Å; R factor = 0.047; wR factor = 0.117; data-to-parameter ratio = 13.6.

Plos One, 2013

This paper presents an industrial scale process for extraction, purification, and isolation of ep... more This paper presents an industrial scale process for extraction, purification, and isolation of epiisopiloturine (EPI) (2(3H)-

X-ray absorption spectroscopy was used to probe the short-range structure in lanthanum-doped lead... more X-ray absorption spectroscopy was used to probe the short-range structure in lanthanum-doped lead titanate ceramics (Pb 1−x La x TiO 3 ) for x ranging from 0.0 to 0.30. A comparison of the XANES spectra and the X-ray diffraction (XRD) results indicates that the local structure around Ti atoms had a different compositional dependence. According to the XANES data, even for the sample containing 30% of lanthanum, for which the XRD analysis indicated the existence of a cubic structure, a local distortion around Ti atoms persisted. The intensity of the pre-edge feature of the PLT30 sample decreased by a factor of only two when compared with the lanthanum-free sample.

The existence of conducting islands in polyani-line films has long been proposed in the literatur... more The existence of conducting islands in polyani-line films has long been proposed in the literature, which would be consistent with conducting mechanisms based on hopping. Obtaining direct evidence of conducting islands, however, is not straightforward. In this paper, conducting islands were visualized in poly(o-ethoxyaniline) (POEA) films prepared at low pH, using Transmission Electron Mi-croscopy (TEM) and atomic force spectroscopy (AFS). The size of the islands varied between 67 and 470 Å for a pH = 3.0, with a larger average being obtained with AFS, probably due to the finite size effect of the atomic force mi-croscopy tip. In AFS, the conducting islands were denoted by regions with repulsive forces due to the double-layer forces. On the basis of X-ray diffraction (XRD) patterns for POEA in the powder form, we infer that the conducting islands are crystalline, and therefore a POEA film is believed to consist of conducting islands dispersed in an insulating, amorphous matrix. From conductivity measurements we inferred the charge transport to be governed by a typical quasi-one dimensional variable range hopping (VRH) mechanism.

Microporous and Mesoporous Materials, 2000

Na-Y zeolites ion exchanged with rare earth cations (Nd3+, Sm3+, Gd3+, Dy3+) were studied by X-ra... more Na-Y zeolites ion exchanged with rare earth cations (Nd3+, Sm3+, Gd3+, Dy3+) were studied by X-ray diffraction in order to locate the rare earth cations in the zeolite framework and the resulting changes in its structural properties. The results indicate that the rare earth cations dealuminate the framework differently. This is observed as a decrease in the values of the unit cell parameters, a0. This systematic decrease in a0 is related to the rare earth ionic radius and its coordination to the oxygen framework. The correlation between the Si/Al ratio obtained from the Fichtner-Schmittler equation and the ionic radius of the rare earth cations reveals that smaller ionic radii gives higher dealumination and smaller a0. This is related to hydrolysis constant cation. Samples treated with Dy3+ cations show a higher level of dealumination than those treated with the other cations (Sm3+, Gd3+, Nd3+). In order to characterize the dealumination process and magic angle spinning NMR measurements were attempted. Except for the Sm3+ treated sample, the Nd3+, Gd3+, Dy3+ samples could not have their tetrahedral and octahedral aluminum signal detected due to the high concentration of the paramagnetic ions with large effective number of Bohr magnetons.

Journal of Colloid and Interface Science, 2007

Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for th... more Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology-seen with atomic force microscopy and transmission electron microscopy-that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.

Materials Science Forum (278), 720-725 (1998)

AHfO(3) (A = Ca, Sr and Ba) belongs to perovskite family with general formula A(2+)B(4+)O(3). The... more AHfO(3) (A = Ca, Sr and Ba) belongs to perovskite family with general formula A(2+)B(4+)O(3). The crystal structure of CaHfO(3) (CH), SrHfO(3) (SH) and BaHfO(3) (BH) at room temperature (RT) is reported, combining the results of the Rietveld method refinements using X-ray and neutron powder diffraction data and PAC spectroscopy. The structures were refined by the Rietveld Method using DBWS9411 and GSAS programs, The refinement of SH using neutron and X-ray powder pattern indicates an orthorhombic Pnma symmetry at room temperature. The hyperfine parameters of PAC spectroscopy indicate that the structure has lower-than-cubic symmetry at RT, The structures of CH and BH were refined with the Pnma and Pm (3) over bar m space group respectively. The three compounds have near regular oxygen octahedra that are characteristic of perovskites of Glazer types a(+)a(-)a(-) and a(0)a(0)a(0), for which the distortion is better related to the tilting of the octahedra.

Acta crystallographica. Section E, Structure reports online, 2008

In the title compound, C(13)H(12)N(2)O(2)S, the dihedral angle between the two aromatic ring plan... more In the title compound, C(13)H(12)N(2)O(2)S, the dihedral angle between the two aromatic ring planes is 87.52 (12)°. The mol-ecule shows an intra-molecular N-H⋯O hydrogen bond. The crystal structure is stabilized by inter-molecular N-H⋯S and C-H⋯O hydrogen bonding.

Acta crystallographica. Section E, Structure reports online, 2008

The title compound, C(13)H(9)N(3)O(2)S, was synthesized from furoyl isothio-cyanate and 3-amino-b... more The title compound, C(13)H(9)N(3)O(2)S, was synthesized from furoyl isothio-cyanate and 3-amino-benzonitrile in dry acetone. The thio-urea group is in the thio-amide form. The thio-urea fragment makes dihedral angles of 3.91 (16) and 37.83 (12)° with the ketofuran group and the benzene ring, respectively. The mol-ecular geometry is stabilized by N-H⋯O hydrogen bonds. In the crystal structure, centrosymmetrically related mol-ecules are linked by two inter-molecular N-H⋯S hydrogen bonds to form dimers.

Acta Crystallographica Section E Structure Reports Online, 2008

Key indicators: single-crystal X-ray study; T = 150 K; mean (C-C) = 0.004 Å; R factor = 0.047; wR... more Key indicators: single-crystal X-ray study; T = 150 K; mean (C-C) = 0.004 Å; R factor = 0.047; wR factor = 0.117; data-to-parameter ratio = 13.6.

Plos One, 2013

This paper presents an industrial scale process for extraction, purification, and isolation of ep... more This paper presents an industrial scale process for extraction, purification, and isolation of epiisopiloturine (EPI) (2(3H)-