Antonio Martins Figueiredo Neto - Academia.edu (original) (raw)
Papers by Antonio Martins Figueiredo Neto
SPIE Proceedings, 2013
Lyotropic liquid crystals exhibiting nematic phases were obtained from the mixtures potassium lau... more Lyotropic liquid crystals exhibiting nematic phases were obtained from the mixtures potassium laurate/alkali sulfate salts (M 2 SO 4)/1-undecanol (UndeOH)/water and sodium dodecyl sulfate (SDS)/M 2 SO 4 /1-dodecanol (DDeOH)/water, where M 2 SO 4 represents the alkali sulfate salts being Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , Rb 2 SO 4 or Cs 2 SO 4. The birefringences measurements were performed via laser conoscopy. Our results indicated that cosmotropic and chaotropic behaviors of both ions and head groups are very important to obtain lyotropic biaxial nematic phase. To obtain the biaxial nematic phase, surfactant head group and ion present in lyotropic mixture have relatively opposite behavior, e.g. one more cosmotropic (more chaotropic) other less cosmotropic (less chaotropic) or vice versa.
Journal of the Optical Society of America B, 2002
We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals ... more We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals doped with ferrofluid. In these experiments, the sample is translated through the focal region of a focused Gaussian laser beam. The dependence of the far-field intensity on sample position due to intensity-dependent optical nonlinearities has been analyzed on the basis of the thermal-lens model of Gordon et al. and the Gaussian decomposition analysis of Sheik-Bahae et al. The thermal-lens model is nonlocal in space and time, whereas the Gaussian decomposition is predicated on a strictly local response. We compare the goodness of fit of the predictions of these models to experimental data, and we discuss limitations of these models in describing Z-scan experiments on systems with nonlocal response.
Liquid Crystals, 2012
Lyotropic liquid crystalline quaternary mixtures of potassium laurate (KL), potassium sulphate (K... more Lyotropic liquid crystalline quaternary mixtures of potassium laurate (KL), potassium sulphate (K 2 SO 4)/alcohol (n-OH)/water, with the alcohols having different number of carbon atoms in the alkyl chain (n), from 1-octanol to 1-hexadecanol, were investigated by optical techniques (optical microscopy and laser conoscopy). The biaxial nematic phase domain is present in a window of values of n = n KL ± 2, where n KL = 11 is the number of carbon atoms in the alkyl chain of KL. The biaxial phase domain got smaller and the uniaxial-to-biaxial phase transition temperatures shifted to the relatively higher temperatures on going from 1-nonanol to 1-tridecanol. Moreover, these new mixtures present high values of the birefringences comparing to other lyotropic mixtures. This result is expected to be related to the micellar shape anisotropy. Our results are interpreted assuming that alcohol molecules tend to segregate in the micelles in a way that depends on the relative value of n with respect to n KL. The larger the value of n, the more alcohol molecules tend to be located in the curved parts of the micelle, favoring the uniaxial nematic calamitic phase with respect to the biaxial and uniaxial discotic nematic phases.
The Journal of Chemical Physics, 1998
Nuclear magnetic resonance study of the internal magnetic field distribution in water base ionic ... more Nuclear magnetic resonance study of the internal magnetic field distribution in water base ionic and surfacted ferrofluids. [The Journal of Chemical Physics 109, 4670 (1998)]. Cecilia E. González, Daniel J. Pusiol, Antonio M. Figueiredo Neto, Máximo Ramia, Agnes. Bee. Abstract ...
Granular Matter, 2001
The first experimental evidence of director fluctuations in a micellar lyotropic liquid crystal, ... more The first experimental evidence of director fluctuations in a micellar lyotropic liquid crystal, studied by 1H spin-lattice relaxation rate, is reported. The system is constituted by the ternary mixture: potassium laurate/1-decanol/water. With the aim to test the slow dynamics, the experiment has been performed over a broad range of Larmor frequencies (2 × 103− 6.6 × 106 Hz), using fast field-cycling NMR relaxometry. The results evidence that in the nematic and isotropic mesophases and the poliphasyc region, director fluctuations are responsible for the spin-lattice relaxation dispersion in the low Larmor frequency range (5 Hz). By increasing the intermicellar water content, a crossover was found between a quasi-isotropic 3D director fluctuations behavior to a 2D pseudo-lamellar undulation fluctuations. In order to explain the higher frequency range (>105 Hz), two relaxation mechanisms are assigned: i) molecular reorientation by translational diffusion on the micellar surface, and ii) molecular exchange between the micelle and the bulk.
American Journal of Epidemiology, 1996
Physical activity pattern and its relation with cardiovascular risk factors was investigated in 1... more Physical activity pattern and its relation with cardiovascular risk factors was investigated in 1,402 men aged 69-90 years who participated in the 30-year follow-up survey of the Finnish (Eastern and Western Finland), Italian (Montegiorgio and Crevalcore), and Dutch (Zutphen) cohorts of the Seven Countries Study. Physical activity was assessed with a validated self-administered questionnaire designed for retired men. Total physical activity varied largely within cohorts. Median total reported physical activity ranged from 50 minutes/day in Montegiorgio to 89 minutes/day in Crevalcore. Walking, gardening, and bicycling together contributed more than 70% of total physical activity in all cohorts. Depending on the definition of physical inactivity, the estimated prevalence of inactivity varied between 5% and 33% in Zutphen and between 18% and 68% in Montegiorgio. Total physical activity was inversely associated with resting heart rate (r =-0.11, p < 0.001) and was positively associated with high density lipoprotein (HDL) cholesterol (r = 0.08, p < 0.01) in pooled data. These associations remained statistically significant after adjustment for age, cohort, smoki ig, body mass index, and alcohol intake. Total activity was not associated with total cholesterol, non-HDL cholesterol, blood pressure, or body mass index. The authors conclude that physical activity may have a beneficial effect on HDL cholesterol levels in elderly men. Walking, gardening, and bicycling contribute substantially to their physical activity pattern.
Exphe~~o meu~ mai6 ~ineeho6 aghadeeimento~ a Pho6a. Vha. Lia Queihoz do Amahal pela ~eguha e eomp... more Exphe~~o meu~ mai6 ~ineeho6 aghadeeimento~ a Pho6a. Vha. Lia Queihoz do Amahal pela ~eguha e eompetente ohientaç~o a e~te thabalho, bem eomo ~ ~ua amizade que ~e e~tende al~m do6 limite6 do eampo pho6i~~ional. Ã Pho6a.Vha. Ceeilia de Alvahenga Fheihe Pimentel, minha phimeiha pho6e66oha no TFUSP e inieiadoha na vida eieniZ 6iea no I n~tituto de Enehgia Atômiea., pela.6 valio6a6 di6eU66Õe6 no deeohheh do thaba.lho e amizade. Tanto ã Lia. quanto ã Ceeilia pela. minha aeeita.çã.o no Ghupo de Chi~ta.logha.6ia., em êpoea6 tuhbulenta~, bem eomo poh todo o e6fiohço di~pen6a.do na minha. eonthata.ção no In6tit~to de FZ~iea.
The Journal of Chemical Physics, 2000
Field cycling nuclear magnetic resonance relaxometry was used to study the slow molecular dynamic... more Field cycling nuclear magnetic resonance relaxometry was used to study the slow molecular dynamics in the nematics and isotropic phases and polyphasic region of the phase diagram in the thernary mixture: potassium laurate/1-decanol/water. The experiment has been performed over a broad range of Larmor frequencies (2×103−6.6×106 Hz). The first experimental evidence of director fluctuations in a micellar lyotropic nematic liquid
Physical review. E, Statistical, nonlinear, and soft matter physics, 2004
A new method, based on the measurement of the (23 )( )Na nuclei spin-spin NMR relaxation times ( ... more A new method, based on the measurement of the (23 )( )Na nuclei spin-spin NMR relaxation times ( T2 ), is proposed to investigate the shape of micelles in lyotropic nematic phases. We investigate the ternary lyotropic mixture of sodium dodecyl sulfate, 1-decanol, and water by using the NMR technique, measuring T2 in the two lyotropic uniaxial nematic phases. The characteristic relaxation time curves of each particular phase are analyzed by considering that they are constituted by a superposition of exponential decays with typical characteristic times: in a sense, a T2 spectroscopy. The analysis of the T2 dispersion profiles in both the uniaxial nematic calamitic and discotic phases indicates that our results can be interpreted in terms of the model of intrinsically biaxial micelles in all the nematic phases.
The Journal of Chemical Physics, 1998
A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, ... more A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, electrical measurements and 23Na NMR is reported with the aim to characterize the phase diagram of the ternary lyotropic mixture of sodium bis (2 ethylhexyl) sulfosuccinate, dodecanol, and water. One of the most interesting features of this phase diagram is the existence of a bicontinuous structure associated to an
Physica B: Condensed Matter, 2002
In a previous nuclear magnetic resonance (NMR) study we observed that the NMR spectra of water in... more In a previous nuclear magnetic resonance (NMR) study we observed that the NMR spectra of water in both surfacted and ionic ferrofluids are asymmetric and several orders of magnitude wider than the one of pure water. It has been proposed that this effect is produced by extremely strong magnetic field gradients in the intergrain volume and/or by surface interactions between the carrier liquid molecules and the grains surface. In the case of aqueous ionic ferrofluids the latter possibility should be interpreted as electric interactions between water (polar) molecules and the charges in the grain surface.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2002
A nuclear magnetic resonance study of protons and deuterons in the mesomorphic phases of the mice... more A nuclear magnetic resonance study of protons and deuterons in the mesomorphic phases of the micellar lyotropic mixture potassium laurate/1-decanol/heavy water is reported. The slow dynamical behavior of water molecules has been investigated with deuterons spin-lattice relaxation dispersion in the Larmor frequency range 10(3)<nu(L)<4.2x10(7) Hz. In order to compare relative behaviors additional T1 dispersion of micellar protons has been measured in the same compound, temperature, and Larmor frequency range. From the experimental behaviors, we conclude that in the nematic phases the water slow reorientational dynamics is closely related to the slow reorientation of the micellar aggregates. In addition, conventional deuterium nuclear magnetic resonance at nu(L)=4.2x10(7) Hz spectra has been measured at different places in the phase diagram. The line shapes show a quadrupolar splitting in nematic phases, meanwhile in the isotropic phase the spectral structure collapses in a singl...
A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, ... more A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, electrical measurements and 23Na NMR is reported with the aim to characterize the phase diagram of the ternary lyotropic mixture of sodium bis (2 ethylhexyl) sulfosuccinate, dodecanol, and water. One of the most interesting features of this phase diagram is the existence of a bicontinuous structure associated to an
Physical Review E, 2014
The Soret coefficient (S T ) of positively charged magnetic colloids was measured as a function o... more The Soret coefficient (S T ) of positively charged magnetic colloids was measured as a function of the nanoparticles' diameter. The Z-scan technique and the generalization of the thermal lens model proved to be a reliable technique to measure S T . We show that S T is negative and increases with the particle's diameter, being best described by a functional dependence of the type S T ∝ d 0 . Potentiometric and conductometric experiments show that the particle's surface charge decreases as the temperature increases, changing the electrostatic interaction between the nanoparticles. The temperature gradient imposed in the ferrofluid by the Gaussian laser beam leads to the formation of the particle's concentration gradient. The origin of this phenomenon is discussed in terms of the decrease of the particle's surface charge in the hottest region of the sample and the thermoelectric field due to the inhomogeneous distribution of hydrogenous ions present in the colloidal suspension.
The European Physical Journal E, 2011
SPIE Proceedings, 2013
Lyotropic liquid crystals exhibiting nematic phases were obtained from the mixtures potassium lau... more Lyotropic liquid crystals exhibiting nematic phases were obtained from the mixtures potassium laurate/alkali sulfate salts (M 2 SO 4)/1-undecanol (UndeOH)/water and sodium dodecyl sulfate (SDS)/M 2 SO 4 /1-dodecanol (DDeOH)/water, where M 2 SO 4 represents the alkali sulfate salts being Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , Rb 2 SO 4 or Cs 2 SO 4. The birefringences measurements were performed via laser conoscopy. Our results indicated that cosmotropic and chaotropic behaviors of both ions and head groups are very important to obtain lyotropic biaxial nematic phase. To obtain the biaxial nematic phase, surfactant head group and ion present in lyotropic mixture have relatively opposite behavior, e.g. one more cosmotropic (more chaotropic) other less cosmotropic (less chaotropic) or vice versa.
Journal of the Optical Society of America B, 2002
We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals ... more We carried out Z-scan measurements on lyotropic liquid crystals and on lyotropic liquid crystals doped with ferrofluid. In these experiments, the sample is translated through the focal region of a focused Gaussian laser beam. The dependence of the far-field intensity on sample position due to intensity-dependent optical nonlinearities has been analyzed on the basis of the thermal-lens model of Gordon et al. and the Gaussian decomposition analysis of Sheik-Bahae et al. The thermal-lens model is nonlocal in space and time, whereas the Gaussian decomposition is predicated on a strictly local response. We compare the goodness of fit of the predictions of these models to experimental data, and we discuss limitations of these models in describing Z-scan experiments on systems with nonlocal response.
Liquid Crystals, 2012
Lyotropic liquid crystalline quaternary mixtures of potassium laurate (KL), potassium sulphate (K... more Lyotropic liquid crystalline quaternary mixtures of potassium laurate (KL), potassium sulphate (K 2 SO 4)/alcohol (n-OH)/water, with the alcohols having different number of carbon atoms in the alkyl chain (n), from 1-octanol to 1-hexadecanol, were investigated by optical techniques (optical microscopy and laser conoscopy). The biaxial nematic phase domain is present in a window of values of n = n KL ± 2, where n KL = 11 is the number of carbon atoms in the alkyl chain of KL. The biaxial phase domain got smaller and the uniaxial-to-biaxial phase transition temperatures shifted to the relatively higher temperatures on going from 1-nonanol to 1-tridecanol. Moreover, these new mixtures present high values of the birefringences comparing to other lyotropic mixtures. This result is expected to be related to the micellar shape anisotropy. Our results are interpreted assuming that alcohol molecules tend to segregate in the micelles in a way that depends on the relative value of n with respect to n KL. The larger the value of n, the more alcohol molecules tend to be located in the curved parts of the micelle, favoring the uniaxial nematic calamitic phase with respect to the biaxial and uniaxial discotic nematic phases.
The Journal of Chemical Physics, 1998
Nuclear magnetic resonance study of the internal magnetic field distribution in water base ionic ... more Nuclear magnetic resonance study of the internal magnetic field distribution in water base ionic and surfacted ferrofluids. [The Journal of Chemical Physics 109, 4670 (1998)]. Cecilia E. González, Daniel J. Pusiol, Antonio M. Figueiredo Neto, Máximo Ramia, Agnes. Bee. Abstract ...
Granular Matter, 2001
The first experimental evidence of director fluctuations in a micellar lyotropic liquid crystal, ... more The first experimental evidence of director fluctuations in a micellar lyotropic liquid crystal, studied by 1H spin-lattice relaxation rate, is reported. The system is constituted by the ternary mixture: potassium laurate/1-decanol/water. With the aim to test the slow dynamics, the experiment has been performed over a broad range of Larmor frequencies (2 × 103− 6.6 × 106 Hz), using fast field-cycling NMR relaxometry. The results evidence that in the nematic and isotropic mesophases and the poliphasyc region, director fluctuations are responsible for the spin-lattice relaxation dispersion in the low Larmor frequency range (5 Hz). By increasing the intermicellar water content, a crossover was found between a quasi-isotropic 3D director fluctuations behavior to a 2D pseudo-lamellar undulation fluctuations. In order to explain the higher frequency range (&gt;105 Hz), two relaxation mechanisms are assigned: i) molecular reorientation by translational diffusion on the micellar surface, and ii) molecular exchange between the micelle and the bulk.
American Journal of Epidemiology, 1996
Physical activity pattern and its relation with cardiovascular risk factors was investigated in 1... more Physical activity pattern and its relation with cardiovascular risk factors was investigated in 1,402 men aged 69-90 years who participated in the 30-year follow-up survey of the Finnish (Eastern and Western Finland), Italian (Montegiorgio and Crevalcore), and Dutch (Zutphen) cohorts of the Seven Countries Study. Physical activity was assessed with a validated self-administered questionnaire designed for retired men. Total physical activity varied largely within cohorts. Median total reported physical activity ranged from 50 minutes/day in Montegiorgio to 89 minutes/day in Crevalcore. Walking, gardening, and bicycling together contributed more than 70% of total physical activity in all cohorts. Depending on the definition of physical inactivity, the estimated prevalence of inactivity varied between 5% and 33% in Zutphen and between 18% and 68% in Montegiorgio. Total physical activity was inversely associated with resting heart rate (r =-0.11, p < 0.001) and was positively associated with high density lipoprotein (HDL) cholesterol (r = 0.08, p < 0.01) in pooled data. These associations remained statistically significant after adjustment for age, cohort, smoki ig, body mass index, and alcohol intake. Total activity was not associated with total cholesterol, non-HDL cholesterol, blood pressure, or body mass index. The authors conclude that physical activity may have a beneficial effect on HDL cholesterol levels in elderly men. Walking, gardening, and bicycling contribute substantially to their physical activity pattern.
Exphe~~o meu~ mai6 ~ineeho6 aghadeeimento~ a Pho6a. Vha. Lia Queihoz do Amahal pela ~eguha e eomp... more Exphe~~o meu~ mai6 ~ineeho6 aghadeeimento~ a Pho6a. Vha. Lia Queihoz do Amahal pela ~eguha e eompetente ohientaç~o a e~te thabalho, bem eomo ~ ~ua amizade que ~e e~tende al~m do6 limite6 do eampo pho6i~~ional. Ã Pho6a.Vha. Ceeilia de Alvahenga Fheihe Pimentel, minha phimeiha pho6e66oha no TFUSP e inieiadoha na vida eieniZ 6iea no I n~tituto de Enehgia Atômiea., pela.6 valio6a6 di6eU66Õe6 no deeohheh do thaba.lho e amizade. Tanto ã Lia. quanto ã Ceeilia pela. minha aeeita.çã.o no Ghupo de Chi~ta.logha.6ia., em êpoea6 tuhbulenta~, bem eomo poh todo o e6fiohço di~pen6a.do na minha. eonthata.ção no In6tit~to de FZ~iea.
The Journal of Chemical Physics, 2000
Field cycling nuclear magnetic resonance relaxometry was used to study the slow molecular dynamic... more Field cycling nuclear magnetic resonance relaxometry was used to study the slow molecular dynamics in the nematics and isotropic phases and polyphasic region of the phase diagram in the thernary mixture: potassium laurate/1-decanol/water. The experiment has been performed over a broad range of Larmor frequencies (2×103−6.6×106 Hz). The first experimental evidence of director fluctuations in a micellar lyotropic nematic liquid
Physical review. E, Statistical, nonlinear, and soft matter physics, 2004
A new method, based on the measurement of the (23 )( )Na nuclei spin-spin NMR relaxation times ( ... more A new method, based on the measurement of the (23 )( )Na nuclei spin-spin NMR relaxation times ( T2 ), is proposed to investigate the shape of micelles in lyotropic nematic phases. We investigate the ternary lyotropic mixture of sodium dodecyl sulfate, 1-decanol, and water by using the NMR technique, measuring T2 in the two lyotropic uniaxial nematic phases. The characteristic relaxation time curves of each particular phase are analyzed by considering that they are constituted by a superposition of exponential decays with typical characteristic times: in a sense, a T2 spectroscopy. The analysis of the T2 dispersion profiles in both the uniaxial nematic calamitic and discotic phases indicates that our results can be interpreted in terms of the model of intrinsically biaxial micelles in all the nematic phases.
The Journal of Chemical Physics, 1998
A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, ... more A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, electrical measurements and 23Na NMR is reported with the aim to characterize the phase diagram of the ternary lyotropic mixture of sodium bis (2 ethylhexyl) sulfosuccinate, dodecanol, and water. One of the most interesting features of this phase diagram is the existence of a bicontinuous structure associated to an
Physica B: Condensed Matter, 2002
In a previous nuclear magnetic resonance (NMR) study we observed that the NMR spectra of water in... more In a previous nuclear magnetic resonance (NMR) study we observed that the NMR spectra of water in both surfacted and ionic ferrofluids are asymmetric and several orders of magnitude wider than the one of pure water. It has been proposed that this effect is produced by extremely strong magnetic field gradients in the intergrain volume and/or by surface interactions between the carrier liquid molecules and the grains surface. In the case of aqueous ionic ferrofluids the latter possibility should be interpreted as electric interactions between water (polar) molecules and the charges in the grain surface.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2002
A nuclear magnetic resonance study of protons and deuterons in the mesomorphic phases of the mice... more A nuclear magnetic resonance study of protons and deuterons in the mesomorphic phases of the micellar lyotropic mixture potassium laurate/1-decanol/heavy water is reported. The slow dynamical behavior of water molecules has been investigated with deuterons spin-lattice relaxation dispersion in the Larmor frequency range 10(3)<nu(L)<4.2x10(7) Hz. In order to compare relative behaviors additional T1 dispersion of micellar protons has been measured in the same compound, temperature, and Larmor frequency range. From the experimental behaviors, we conclude that in the nematic phases the water slow reorientational dynamics is closely related to the slow reorientation of the micellar aggregates. In addition, conventional deuterium nuclear magnetic resonance at nu(L)=4.2x10(7) Hz spectra has been measured at different places in the phase diagram. The line shapes show a quadrupolar splitting in nematic phases, meanwhile in the isotropic phase the spectral structure collapses in a singl...
A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, ... more A combined study of flow-induced optical birefringence, x-ray diffraction, optical observations, electrical measurements and 23Na NMR is reported with the aim to characterize the phase diagram of the ternary lyotropic mixture of sodium bis (2 ethylhexyl) sulfosuccinate, dodecanol, and water. One of the most interesting features of this phase diagram is the existence of a bicontinuous structure associated to an
Physical Review E, 2014
The Soret coefficient (S T ) of positively charged magnetic colloids was measured as a function o... more The Soret coefficient (S T ) of positively charged magnetic colloids was measured as a function of the nanoparticles' diameter. The Z-scan technique and the generalization of the thermal lens model proved to be a reliable technique to measure S T . We show that S T is negative and increases with the particle's diameter, being best described by a functional dependence of the type S T ∝ d 0 . Potentiometric and conductometric experiments show that the particle's surface charge decreases as the temperature increases, changing the electrostatic interaction between the nanoparticles. The temperature gradient imposed in the ferrofluid by the Gaussian laser beam leads to the formation of the particle's concentration gradient. The origin of this phenomenon is discussed in terms of the decrease of the particle's surface charge in the hottest region of the sample and the thermoelectric field due to the inhomogeneous distribution of hydrogenous ions present in the colloidal suspension.
The European Physical Journal E, 2011