Papers by Edvaldo Sabadini
Química Nova, 2001
Recebido em 30/5/00; aceito em 28/5/01 HEATING IN MICROWAVE OVENS/ DEVELOPING OF BASIC CONCEPTS. ... more Recebido em 30/5/00; aceito em 28/5/01 HEATING IN MICROWAVE OVENS/ DEVELOPING OF BASIC CONCEPTS. The microwave oven became a common domestic equipment, due mainly to the short time spent to heat foods. One of the most interesting characteristics of the microwave oven is the selective heating. Different from the conventional oven, where the heating is not selective, the heating by microwave depends on the chemical nature of the matter. Many Students of Chemistry have no knowledge of the principles involved in this selective heating, in spite of the daily microwave oven use. The heating by microwave is feasible for chemistry courses. In discussions about the microwave absorption by the matter it is possible to explore chemical properties like: heat capacity, chemical bound, molecular structure, dipole moments, polarization and dielectric constant. This paper presents the basic principles involved in the microwave heating. It is proposed a simple and inexpensive experiment that could be developed in general chemistry courses, to illustrate the relationship between heating and the chemical properties of some solvents. Experiments to check the power of the microwave oven are also proposed.
Estudo das relaxações de polimeros utilizando sondas luminescentes
Algumas relaxacoes de polimeros orgânicos foram estudadas utilizando sondas luminescentes dispers... more Algumas relaxacoes de polimeros orgânicos foram estudadas utilizando sondas luminescentes dispersas nos polimeros. Foram estudados os seguintes polimeros: poliestireno, poliacetato de vinila, polipropileno, polietileno de baixa densidade e polietileno glicol-600. Utilizamos o antraceno e a benzofenona dispersos nestes polimeros para analisar a dependencia com a temperatura das emissoes de fluorescencia dessas sondas luminescentes. Para isso, foi necessario realizar um estudo das propriedades fotofisicas destas substâncias dispersas nas matrizes, sendo caracterizados: os tipos de emissao, a mudanca nos processos fotofisicos causados pelas interacoes com as matrizes e a formacao de agregados. O estudo da dependencia com a temperatura da intensidade de fluorescencia do antraceno disperso nos polimeros permitiu que se determinasse a temperatura da relaxacao vitrea (transicao vitrea) do polietileno glicol-600, que envolve o movimento micro-browniano de aproximadamente 50 unidades metilenicas da cadeia do polimero. Esta relaxacao pode ser observada devido a diferenca nas propriedades luminescentes do antraceno isolado na matriz e forma cristalina, que e formada apos essa relaxacao. As relaxacoes que envolvem o movimento de pequenos grupos dos polimeros nao foram observadas utilizando esta sonda fluorescente. Estas relaxacoes foram obtidas atraves da dependencia com a temperatura da intensidade de fosforescencia da benzofenona dispersa nos polimeros, observando-se uma diminuicao abrupta da intensidade de fosforescencia na regiao da relaxacao resultante de uma mudanca no processo fotofisico da sonda fosforescente. O mecanismo desta mudanca foi discutido, podendo envolver uma desativacao por formacao de exciplexos (relaxacao no poliestireno) e/ou destivacao por colisao de oxigenio molecular com a sonda (todas os polimeros). Com esta sonda foi possivel se determinar a temperatura para: a rotacao do grupo fenila no poliestireno (relaxacao g); a relaxacao de grupos metoxi pertencentes a impurezas copolimerizadas com o poliaceta- to de vinila: a reorientacao de grupos metilas da polipropileno; a relaxacao de algumas unidades metilenicas pertencentes a cadeia do polietileno (relaxacao g) e a relaxacao g no polietileno glicol, que envolve a movimento de 3 a 4 grupos metilenicos pertencentes a cadeia principal desse polimero. Abstract
O uso de RMN para estudar a estrutura da água em interfaces e sistemas coloidais
O modelo de dois sitios, utilizado nos estudos de relaxacao do solvente em solucoes de carboidrat... more O modelo de dois sitios, utilizado nos estudos de relaxacao do solvente em solucoes de carboidratos, pode ser transposto de forma satisfatoria para solucoes de polimeros hidrofilicos. Polimeros que possuem hidrogenios labeis, isto e, que possuem hidrogenios disponiveis para troca quimica com os hidrogenios da agua, causam aumento da taxa de relaxacao spin-spin do solvente, R2, em relacao ao valor obtido para a agua pura O efeito torna-se mais intenso na medida em que a concentracao dos polimeros aumenta. Polimeros que nao possuem hidrogenios labeis nao alteram significativamente o R2 do solvente, pois o mecanismo de troca quimica nao e estabelecido. A relaxacao do solvente pode ser usada para estudar o processo de transicao sol-gel em sistemas polimericos. Conforme o gel e formado, as moleculas de agua comecam a ser confinadas e a taxa de relaxacao do solvente aumenta significativamente. A estrutura de hidrogeis supramoleculares formados entre PEG e a-CD, a qual possui uma cavidade ...
Dinâmica interacional de soluções binárias álcool-água e poli(etileno glicol)-água por ressonância magnética nuclear
O entendimento do comportamento de solucoes aquosas de alcoois e poli(etileno glicois) e de inter... more O entendimento do comportamento de solucoes aquosas de alcoois e poli(etileno glicois) e de interesse do ponto de vista fundamental e aplicado. Visando ampliar o conhecimento sobre as interacoes intermoleculares entre estes dois componentes em misturas binarias com agua, foram desenvolvidos estudos com alcoois monohidroxilados ? metanol, etanol, 1-propanol, 2-propanol e terc-butanol ? e com poli(etileno glicol) de massa molar media 200, 300, 400 e 600 g mol-1. Os estudos foram desenvolvidos em toda a faixa de concentracao a 25 °C. As solucoes foram estudadas atraves de correlacoes entre propriedades macroscopicas, especificamente a viscosidade, com propriedades moleculares medidas atraves de ressonância magnetica nuclear (relaxometria e coeficiente de difusao). As medidas neste caso foram baseadas no atomo de hidrogenio e foram realizadas no dominio do tempo (20 MHz) e no dominio da frequencia (500 MHz). Para as solucoes alcool-agua, o tamanho da cadeia alquilica e a estrutura molecular do alcool sao fundamentais nas interacoes intermoleculares e, consequentemente, nas propriedades macroscopicas observadas. Cadeias alquilicas maiores favorecem as interacoes hidrofobicas e a formacao de microheterogeneidades em meios aquosos, enquanto que, em alcoois menores, as interacoes alcool-agua sao predominantes. Observa-se que as medidas macroscopicas e microscopicas seguem a mesma tendencia ate certa fracao molar de agua, na qual o limite em que a estrutura tetraedrica dos arranjos de moleculas de agua ainda e preservada. A partir deste ponto, para todos os alcoois as propriedades divergem. No caso das misturas binarias agua-poli(etileno glicol), as propriedades macroscopicas e microscopicas seguem a mesma tendencia em todo regime de concentracao. A principal alteracao no comportamento destas propriedades e observada na transicao do regime diluido para o semidiluido, definido como o ponto em que as moleculas de poli(etileno glicol) comecam a se tocar. A transicao ocorre em uma concentracao EO/H2O (numero de segmentos EO por moleculas de agua em solucao) que independe do tamanho do PEG. Abstract
The study of solutions to enhance oil recovery has been widely used, mainly due to large amount o... more The study of solutions to enhance oil recovery has been widely used, mainly due to large amount of oil that remains in reservoirs after primary and secondary recoveries. Solutions with good potential to recovery must have some specific characteristics such as low water/oil interfacial tension and a moderate viscosity to improve the efficiency of the oil swept. The fluid-rock and oil-rock interactions are of great importance concerning the total oil recovered. Therefore, studies involving wettability of rock surfaces are essential [1]. A traditional method of analysis, which is considered as standard to measures the wettability is the Amott test, however, this method spends too much time and sample preparation [2]. This study analyzes rock wettability using the technique of Low Field Nuclear Magnetic Resonance (low-field NMR). This is based on the relaxation rates of the magnetization of water and/or oil molecules, free or bounded at the surface of the pores of the rock [3]. The tech...
Reologia e estabilidade de micelas gigantes
A formacao, estabilidade e aplicacoes das micelas gigantes tem sido amplamente estudadas. Estes s... more A formacao, estabilidade e aplicacoes das micelas gigantes tem sido amplamente estudadas. Estes sistemas sao muito interessantes devido ao seu comportamento reologico similar aos polimeros. Porem, as micelas gigantes sao especies supramoleculares mantidas por ligacoes nao-covalentes, portanto, sob alta turbulencia, podem resistir a degradacao mecânica, alem de promoverem reducao de atrito hidrodinâmico devido ao efeito Toms. Neste estudo, a formacao e estabilidade das micelas gigantes formadas pela combinacao de surfatantes cationicos e diferentes compostos aromaticos, foram estudadas sistematicamente. A reducao de atrito foi observada medindo o torque aplicado a solucao para manter a turbulencia. A temperatura do sistema foi progressivamente aumentada, mostrando o ponto especifico em que as micelas gigantes sao termicamente destruidas. Baseado neste estudo foi possivel estabelecer a ordem em termos de estabilidade: acido orto-hidroxicinâmico (OHCA) ~ salicilato > tosilato > a...
Composição de fluido de perfuração e seu uso na perfuraçao de poços de petróleo e gás
Refere-se a presente invencao a uma composicao de fluido de perfuracao que compreende uma solucao... more Refere-se a presente invencao a uma composicao de fluido de perfuracao que compreende uma solucao aquosa de pH acido emulsionada em oleo, utilizada na operacao de perfuracao para contribuir para o aumento da taxa de penetracao em rochas reativas a acidos, tipicas do cenario do pre-sal brasileiro e seu uso na perfuracao de pocos de petroleo e gas.
Static acid dissolution of carbonate outcrops investigated by 1H NMR and X-ray tomography
The success of oil and gas exploration in carbonate reservoirs demands better strategies. Concern... more The success of oil and gas exploration in carbonate reservoirs demands better strategies. Concerning the step of acid stimulation, the understanding of the nature of the carbonate matrices and their response to the acids can contribute for improvements of this process. We report a study about the reactivity of six different carbonate rocks with aqueous solutions of hydrochloric (HCl) and acetic (HAc) acids. The reactivity of the samples was determined by measuring the mass loss of the carbonate samples during the acid dissolution process. The results demonstrate that the dolomitization of the matrices is the main factor to decrease the kinetic of dissolution. Based on visual inspection, and micro-computed tomography, it was observed that the cylindrical outcrops with low dolomitization present different patterns of morphological dissolution upon HCl or HAc. For HCl, homogenous radial dissolution is observed, producing a smooth surface, while for HAc, the radial structure is practica...
Estudo do impacto de gotas usando redutores de atrito hidrodinamico
O fenomeno do "splash" tem levantado interesse desde muito tempo atras, principalmente ... more O fenomeno do "splash" tem levantado interesse desde muito tempo atras, principalmente pela beleza das estruturas produzidas pelo impacto de uma gota contra uma superficie liquida. Como o "splash" ocorre num curto intervalo de tempo (milisegundos), e necessario uma tecnica rapida para se conseguir imagens. Utilizando uma câmera CCD e um programa de digitalizacao de imagens, este trabalho tem o objetivo de estudar as modificacoes morfologicas do "splash" quando o liquido contem um agente redutor de atrito hidrodinâmico: a presenca de pequenas quantidades de polimeros em solucao (ppm), provoca consideravel reducao de atrito, quando a mesma e submetida a escoamento turbulento. Atraves das imagens das estruturas do "splash", foi possivel estudar o efeito do polimero poli(oxido de etileno), PEO, o mais eficiente agente redutor de atrito hidrodinâmico, sobre as estruturas do "splash", bem como os efeitos relacionados as energias potencial ...
Dissolved Air Flotation as potential new mechanism for intestinal parasite diagnosis in feces
Acta Tropica
The parasitological examination of feces is recommended for the laboratory diagnosis of intestina... more The parasitological examination of feces is recommended for the laboratory diagnosis of intestinal parasites due to its practicality, low-cost, and moderate diagnostic sensitivity. Dissolved Air Flotation (DAF) is an efficient technical principle used in other areas to separate dispersed solids. This study sought the preliminary evaluation of a proof-of-concept prototype as a tool for detecting species of parasites by adjusting DAF. Two DAF prototype units were developed to evaluate microbubbles' generation amidst fecal suspension and parasites' capture. For this evaluation, samples were screened and processed by the TF-Test technique (Control) and simultaneously by DAF device. The dimensional and attachment characteristics in the formation of the microbubbles were evaluated, and the percentage of parasitic recovery in floated and not-floated regions compared by Student's t-test. The second prototype unit proved to be more efficient in forming microbubbles with diameters between 34 and 170µm. The flotation tests showed a recovery of 73.27%, 58.12%, 37.85%, and 91.89% for Ascaris lumbricoides, Hymenolepis diminuta, Giardia duodenalis, and Strongyloides stercoralis, respectively. This study confirmed the selective interaction between microbubbles and parasite eggs and larvae during the flotation process using the DAF principle for the first time through imaging.
Mechanism for enhanced oil recovery from carbonate reservoirs by adding copper ions to seawater
Fuel
Urea induces (unexpected) formation of lamellar gel-phase in low concentration of cationic surfactants
Journal of Colloid and Interface Science
Inulin gelled emulsion as a fat replacer and fiber carrier in healthier Bologna sausage
Food Science and Technology International
The effects of gelled emulsions (GE) used as animal fat replacers in terms of the nutritional, te... more The effects of gelled emulsions (GE) used as animal fat replacers in terms of the nutritional, technological, and sensory properties of Bologna sausages during 60 days of chilled storage have been studied. Samples with GE added exhibited a fat reduction of 31%. Sausages with GE had higher values of L* and lower values of a* compared to the control. Harder sausages were obtained by the addition of GE. Higher lipid oxidation rates were found with increasing amounts of GE in the reformulated products. In addition, the relaxation time was not affected by the reformulation. All samples were deemed acceptable by consumer tests. However, CATA (Check-all-that-apply) tests showed that Bolognas formulated with partial or total pork fat replaced with GE were described as rubbery, not very spicy and firm, appeared to be dry and opaque, and had an aftertaste. Chilled storage significantly affected the Thiobarbituric Acid Reactive Substances (TBARS) values and slightly affected the pH values, tex...
Using inulin‐based emulsion gels as fat substitute in salt reduced Bologna sausage
Journal of the Science of Food and Agriculture
BACKGROUND A high-fiber emulsion gel (EG) containing inulin, soy protein isolate, and soybean oil... more BACKGROUND A high-fiber emulsion gel (EG) containing inulin, soy protein isolate, and soybean oil was applied as animal fat replacer in reduced salt and fat Bologna sausage containing mechanically deboned chicken meat (MDCM), pork meat, and pork back fat. Technological and microbiological properties were evaluated for 60 days at 4 °C. RESULTS A reduction of 11-34% and 35-45% of fat and sodium were obtained in reformulated products, respectively. An increase in fiber content and polyunsaturated fatty acid was noticed in the formulations with EG. The addition of EG in Bologna increased L* values and reduced a* values comparing to control treatment. Microstructural properties of sausages exhibited a denser network with the presence of EG. A softer, more elastic, cohesive and resilient samples with a higher intensity of lipid oxidation (p < 0.05) were observed in EG added sausages. The NMR data shows that the presence of EG recovers the matrix that has been weakened due to reduction of fat and salt. Sensory evaluation showed that the incorporation of the emulsion gels resulted in acceptable scores. CONCLUSION These results suggest that inulin based emulsion gel is a potential fat substitute for developing healthier meat products, with better fatty acids composition and stable to chilled storage. This article is protected by copyright. All rights reserved.
Probing the Formation of Wormlike Micelles Formed by Cationic Surfactant with Chlorobenzoate Derivatives
Langmuir
The energy released when tetradecyltrimethylammonium bromide (C14TAB) is combined with different ... more The energy released when tetradecyltrimethylammonium bromide (C14TAB) is combined with different derivatives of chlorobenzoates in an isothermal titration calorimeter (ITC) allows a direct evaluation of the spontaneity of the threading of the aromatic anions into the micellar palisade. The comparison between the enthalpimetric curves with the one for viscosity of the solutions, hydrodynamic radii of the aggregates (DLS experiments) and fraction of aromatic anions incorporated (DOSY experiments), allows the establishment of the variations of enthalpy with formation, growing and decreasing of the wormlike micelles (WLM). The formation of WLM with C14TAB is very favored (very exothermic) for titrations of chlorobenzoate derivatives which present the chlorine atom in the positions 3 or 4 of the aromatic ring. However, the aggregation is highly unfavorable if the chlorine is at the position 2 of the chlorobenzoate. According to the results, it was demonstrated the high potential of the ITC to determine critical concentrations and the energies associated with the aggregation of a cationic surfactant and aromatic anions for the formation of WLM.
Solubility and molar enthalpy of solution of sucralose in H2O and D2O
Fluid Phase Equilibria
Abstract The solubility of sucralose, a chlorinated derivate of sucrose was measured for the firs... more Abstract The solubility of sucralose, a chlorinated derivate of sucrose was measured for the first time in D2O over a range of temperatures. The results are important to verify the effect of substitution of OH by Cl in the structure of sucrose and the consequent interaction with the heavy water molecules. Our findings indicated that in the temperature range measured, the solubility of sucralose in D2O is 23.3% lower than in H2O. Based on such measurements, the dissolution Gibbs free energy, enthalpy and entropy were then determined. The values of solubility and the mentioned thermodynamic parameters were compared to the ones for sucralose in H2O. Beside the determination of dissolution enthalpy by using the van't Hoff Equation, this thermodynamic property was also measured for the two solvents in an isoperibol solution-reaction calorimeter.
Host-guest interaction into the cage of a supramolecular iron-organic complex – Is the process enthalpically or entropically- driven?
The Journal of Chemical Thermodynamics
Abstract We report a calorimetric study of the binding in aqueous solution of some guests (dichlo... more Abstract We report a calorimetric study of the binding in aqueous solution of some guests (dichloromethane, furan, tetrahydrofuran, 1,4- dioxane and tetrahydropyran) with the cage of the supramolecular iron-organic host Fe 4 II L 6 4 - , where L is formed by 2-formylpyridine and 4,4′-diaminobiphenyl-2,2′-disulfonic acid. This supramolecular iron-organic host has a tetrahedral structure with a cage capable to complex specific guests. The study was carried out by using an isothermal titration calorimeter, allowing the determination of the binding constants between some of the guests with Fe 4 II L 6 4 - . Depending on the molecular nature of the guests their incorporation can be fast or very slow. In this latter case, the rate of energy released during the process was used to determine the kinetic constant for the assemblage between the guests with Fe 4 II L 6 4 - . For the cases of fast encapsulation, the correspondent values for Δ H 298 0 , Δ HG 298 0 and Δ S 298 0 were determined and the thermodynamic driven force was elucidated.
Two different pathways for assembling bis-urea in benzene and toluene
Journal of molecular modeling, Jan 7, 2018
The thermodynamic stability of assemblies formed by a bis-urea-based supramolecular polymer, 2,4-... more The thermodynamic stability of assemblies formed by a bis-urea-based supramolecular polymer, 2,4-bis(2-ethylhexylureido)toluene (EHUT), was investigated in solutions using either benzene or toluene as the solvent. Starting from a higher temperature in which EHUT was soluble in both solvents, molecules spontaneously self-organized into tubular assemblies upon cooling and these assemblies were stable in a wide range of temperatures. However, the systems followed different paths below a specific temperature: while the supramolecular polymer remained stable in toluene, EHUT molecules underwent precipitation in benzene. The causes for these different behaviors were explored by molecular dynamics simulations, which provided support for stronger enthalpic stabilization of the tubular assemblies in toluene as compared to benzene. This stabilization was due mainly to the better interaction energy of trapped toluene molecules instead of benzene ones. For both cases, lowering the temperature m...
Effect of the Hydrophobic Tail of a Chiral Surfactant on the Chirality of Aggregates and on the Formation of Wormlike Micelles
Langmuir
The micellization of chiral enantiopure surfactants, dodecyl- N, N-dimethyl- N-( S)-(1-phenyl)eth... more The micellization of chiral enantiopure surfactants, dodecyl- N, N-dimethyl- N-( S)-(1-phenyl)ethylammonium bromide and hexadecyl- N, N-dimethyl- N-( S)-(1-phenyl)ethylammonium bromide, was investigated by circular dichroism spectroscopy and isothermal titration calorimetry. The formation of wormlike micelles (WLMs) upon the addition of sodium salicylate to the aqueous solutions of the surfactant was observed only in the case of hexadecyl- N, N-dimethyl- N-( S)-(1-phenyl)ethylammonium bromide. The presence of WLMs was assessed by cryogenic transmission electron microscopy, rheology, and isothermal titration calorimetry experiments, and their supramolecular chirality was investigated by circular dichroism spectroscopy. Depending on the length of the hydrophobic tail, molecular chirality is transferred into a different chiral supramolecular trait. Our findings demonstrate that hydrophobic interactions by controlling the organization and functions of self-assemblies also control the transcription of the chiral information from molecules to complex supramolecular systems.
Rheological and calorimetric study of alkyltrimethylammonium bromide-sodium salicylate wormlike micelles in aqueous binary systems
Journal of colloid and interface science, 2018
It is known that additives like glycerol and sucrose lead to the swelling of aqueous bilayer Lα p... more It is known that additives like glycerol and sucrose lead to the swelling of aqueous bilayer Lα phases. The swelling of the Lα phases can be explained by the increase of the refractive index of the mixed solvent, which lowers the van der Waals attraction between the bilayers. Afterwards, the undulation forces between the bilayers can push them apart. This hypothesis was previously extended to wormlike micelles (WLM) of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal). These types of self-assembly structures have viscoelastic properties, and the zero shear viscosity of these solutions is dependent on the molar ratio NaSal/CTAB, R. At R = 0.6, R = 1.0 and R ≈ 2.6 the viscosity goes, respectively, through a maximum, a minimum and another maximum. These viscosities can be explained by differences in relaxation mechanisms predominant in each region. Similarly to what is observed to bilayer Lα phases, the additives would change the interaction between the WLM, affecting...
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Papers by Edvaldo Sabadini