Species Distribution in Bicontinuous Phase Systems for Enhanced Oil Recovery Probed by Single-Sided NMR.

Multiphase aqueous-organic systems where a bicontinuous phase is in equilibrium with an excess organic and aqueous phase find various applications in industry. These systems─also known as Winsor III─are complex not only for the different phases that develop therein but also because they are multicomponent systems. In this work, we explore for the first time the use of a benchtop low-field single-sided NMR to determine the species distribution in Winsor III systems. The proposed methodology provides information at macroscopic and microscopic levels. In particular, we show the use of single-sided NMR to determine the phases' dimensions and the species distribution in a polymer-based bicontinuous system. The phases' dimensions and limits can be resolved with micrometric precision and are indicative of the bicontinuous phase stability. The species distribution is determined by means of spatially resolved NMR relaxation and diffusion experiments. It was observed that the salinity of the aqueous phase also impacts the species distribution in the bicontinuous system. Experiments show that the additive and the polymer are mainly located in the bicontinuous phase. As the salinity of the aqueous phase increases, the amount of organic components in the bicontinuous phase decreases as a consequence of the species distribution in the system. This influences the total amount of recovered organic liquid from the organic phase. The information is obtained in a relatively fast experiment and is relevant to the system's possible applications, such as enhanced oil recovery (EOR). This methodology is not only circumscribed to its application in EOR but can also be applied to the study of any emulsion or microemulsion systems without sample size or geometry constraints.

Comparison of experimental times in T1-D and D-T2 correlation experiments in single-sided NMR.

Diffusion-relaxation correlation experiments in nuclear magnetic resonance are a powerful technique for the characterization of fluid dynamics in confined geometries or soft matter, in which relaxation may be either spin-spin (T2) or spin-lattice (T1). The general approach is to acquire a set of bidimensional data in which diffusion is codified by the evolution of the magnetization with either Hahn or stimulated echoes (STE) in the presence of a constant magnetic field gradient. While T2 is codified by a Carr-Purcell-Meiboom-Gil (CPMG) sequence, T1 is either encoded by saturation or inversion-recovery methods. In this work, we analyse the measurement time of diffusion-relaxation times in single-sided NMR and show that T1-D acquisition is always shorter than D-T2. Depending on the hardware characteristics, this time reduction can be up to an order of magnitude. We present analytical calculations and examples in model porous media saturated with water and in a dairy product.

Single-shot velocity mapping by rewinding of velocity encoding with Echo-Planar Imaging.

The ability of single-shot NMR imaging methods to follow the time evolution of a velocity distribution within an object is strongly limited by the phase errors accumulated as velocity maps are acquired. In the particular case of Carr-Purcell based sequences combined with Echo Planar Imaging acquisition, phase accumulates through subsequent images, hampering the possibility to acquire several velocity maps, which would be useful to determine transient behavior. In this work, we propose the use of a rewinding velocity encoding module applied after the acquisition of each image during the CPMG echo train. In this way, the first velocity module imparts a velocity dependent phase prior to the image acquisition and the second pair cancels this phase out before the next refocusing radiofrequency pulse is applied. The performance and limits of this method are studied by acquiring 100 images of a co-rotating Couette cell over a period of 1.6 s as a function of the rotation speed. The method is applied to determine the kinematic viscosity of a water/alcohol mixture, which is a relevant topic in many physical, chemical and biological processes.

Flow-Pattern Characterization of Biphasic Electrochemical Cells by Magnetic Resonance Imaging under Forced Hydrodynamic Conditions.

The fluid dynamics of a liquid|liquid system inside a four-electrode electrochemical cell were studied by velocimetry magnetic resonance imaging (MRI) and flow propagator measurements. To characterize this system fully, three different cell configurations operating at two rotational frequencies were analyzed. Quantitative information about the stability of the liquid|liquid interface and the dynamics of the organic phase were determined. The NMR spectroscopy results were in agreement with the electrochemical measurements performed by using the same experimental setup.

Environmental Topology and Water Availability Modulates the Catalytic Activity of ß-Galactosidase Entrapped in a Nanosporous Silicate Matrix.

In the present work we studied the catalytic activity of E. coli ß-Gal confined in a nanoporous silicate matrix (Eß-Gal) at different times after the beginning of the sol-gel polymerization process. Enzyme kinetic experiments with two substrates (ONPG and PNPG) that differed in the rate-limiting steps of the reaction mechanism for their ß-Gal-catalyzed hydrolysis, measurements of transverse relaxation times (T2) of water protons through 1H-NMR, and scanning electron microscopy analysis of the gel nanostructure, were performed. In conjunction, results provided evidence that water availability is crucial for the modulation observed in the catalytic activity of ß-Gal as long as water participate in the rate limiting step of the reaction (only with ONPG). In this case, a biphasic rate vs. substrate concentration was obtained exhibiting one phase with catalytic rate constant (kcA), similar to that observed in solution, and another phase with a higher and aging-dependent catalytic rate constant (kcB). More structured water populations (lower T2) correlates with higher catalytic rate constants (kcB). The T2-kcB negative correlation observed along the aging of gels within the 15-days period assayed reinforces the coupling between water structure and the hydrolysis catalysis inside gels.

Structure characterization of the non-crystalline complexes of copper salts with native cyclodextrins.

The characterization of non-crystalline complexes is particularly difficult when techniques like X-ray diffraction or NMR cannot be used. We propose a simple procedure to characterize the physicochemical properties of amorphous new coordination compounds between cyclodextrins (CD) and Cu(2+) salts, by means of the integration of the information provided by several techniques including elemental analysis, flame atomic absorption, TGA, UV-Vis diffuse reflectance, colorimetry, FT-IR and EPR. On the basis of these procedures, we suggest geometrical and structural approximations resulting in an octahedral or distorted octahedral geometry with diverse positions for the metallic centre. According to the EPR spectrum, only one of the complexes may have rhombic symmetry. We also analyzed enthalpy-entropy compensation and the isokinetic effect. In addition, general trends in thermal stability, spectroscopic properties and inclusion in the cavity were analysed. This complete characterization methodology becomes essential for their future application as catalysts.

Enhanced Surface Interaction of Water Confined in Hierarchical Porous Polymers Induced by Hydrogen Bonding.

Hierarchical porous polymer systems are increasingly applied to catalysis, bioengineering, or separation technology because of the versatility provided by the connection of mesopores with percolating macroporous structures. Nuclear magnetic resonance (NMR) is a suitable technique for the study of such systems as it can detect signals stemming from the confined liquid and translate this information into pore size, molecular mobility, and liquid-surface interactions. We focus on the properties of water confined in macroporous polymers of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)] with different amounts of cross-linkers, in which a substantial variation of hydroxyl groups is achieved. As soft polymer scaffolds may swell upon saturation with determined liquids, the use of NMR is particularly important as it measures the system in its operational state. This study combines different NMR techniques to obtain information on surface interactions of water with hydrophilic polymer chains. A transition from a surface-induced relaxation in which relaxivity depends on the pore size to a regime where the organic pore surface strongly restricts water diffusion is observed. Surface affinities are defined through the molecular residence times near the network surface.

Unusual temperature-induced swelling of ionizable poly(N-isopropylacrylamide)-based microgels: experimental and theoretical insights into its molecular origin.

In the traditional view of temperature-driven volume phase transitions in PNIPAM-based microgel solutions, a monotonic and sharp decrease in the particle size occurs upon heating the solution to above the volume phase transition temperature (VPTT). However, at sufficiently high microgel concentrations and under low salt conditions, our dynamic light scattering experiments reveal an unexpected non-monotonic evolution of the particle size when increasing the solution temperature. These findings show that poly(N-isopropylacrylamide-co-methacrylic acid) (P(NIPAM-co-MAA)) microgels swell upon heating the solution in the temperature range where NIPAM is water-soluble (i.e., below the VPPT). Further heating the microgel solution leads to microgel collapse as typically observed at temperatures above the VPTT. This novel behavior depends on the particle and salt concentration. We have observed the expected monotonic temperature-response of P(NIPAm-co-MAA) microgel solutions at low particle density and high salt concentration. To gain insights into the molecular origin of the unusual behavior of these microgel solutions, we have combined nuclear magnetic resonance studies and molecular-level theoretical calculations of the system. A delicate balance between inter-particle steric compressions and intra-microgel physical interactions and chemical equilibria determines the size of these microgels. Both steric compression, due to finite density, and hydrogen bond formation in the interior of the microgels favors a more compact particle. On the contrary, at the pH of the experiments the acid-base equilibrium constrains the polymer charge to increase, which favors particle swelling due to intra-microgel electrostatic repulsions. This interplay between physical interactions and chemical equilibria occurring at the nanometer length-scale determines the unusual thermal-induced swelling of P(NIPAM-co-MAA) microgels.

Evaporation kinetics in swollen porous polymeric networks.

NMR is a fast, nondestructive, and noninvasive technique that can provide information about the pore structure of macroporous polymer beads and the dynamics of liquids confined in them. In this work, we describe the study of the pore structure of the macroporous polymer of ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate [poly(EGDMA-co-HEMA)] in the dry but also in the swollen state by measuring relaxation times of liquids contained in the polymer network. The results show that the pore architecture differs from the dry to the soaked state. The behavior of polar liquids during evaporation and deswelling dynamics is monitored and described. An internal migration of water from the swollen polymer mesh into expanding pores takes place. With this procedure it is possible to obtain information about the microscopic morphology behavior of the matrix during evaporation and deswelling. This information is of great interest with the aspect of possible and future applications for these types of materials.

Determination of volatile organic compounds of Tagetes filifolia Lag. (Asteraceae) from Córdoba (Argentina) using HS-SPME analysis / Determinación de compuestos orgánicos volátiles de Tagetes filifolia Lag. (Asteraceae) proveniente de Córdoba (Argentina) utilizando análisis por HS-SPME

A headspace solid-phase microextraction (HS-SPME) method followed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC–FID) are described for the analysis of volatile compounds in Tagetes filifolia Lag. The composition of the total aerial parts of the plant (whole plant) and the inflorescences, leaves and stems were studied separately using HS-SPME. As a result, 54 compounds were determined, of which 47 were identified. The major components observed in this analysis were trans-anethole and estragole. The HS-SPME method used for the analysis of volatile compounds of T. filifolia is simple, fast, effective, free from the use of solvents, and permits by an analysis of small amounts of samples to achieve better results in terms of the determination of the composition than those reported in the literature for the analysis of essential oil.

Se realizó el análisis de los componentes volátiles de Tagetes filifolia Lag. utilizando el método de microextracción en fase sólida del espacio de cabeza con análisis posterior por cromatografía de gases acoplada a espectrometría de masas y por cromatografía de gases con detección por ionización de llama. Se estudio la composición de la planta entera así como también la de las inflorescencias, hojas y tallos por separado empleando el método de HS-SPME. Como resultado, se determinaron 54 compuestos de los cuales 47 fueron identificados. Los componentes mayoritarios observados en este análisis fueron: trans-anetol y estragol. El método de HS-SPME utilizado para el análisis de los compuestos volátiles de T. filifolia es simple, rápido, efectivo, libre de la utilización de solventes, y permitió mediante el análisis de pequeñas cantidades de muestra alcanzar mejores resultados en cuanto a la determinación de la composición, que los reportados en literatura para el análisis del aceite esencial.

Determination of volatile organic compounds of tagetes Argentina Cabrera (Asteraceae) using HS-SPME analysis / Determinación de compuestos orgánicos volátiles de tagetes Argentina Cabrera (Asteraceae) utilizando análisis por HS-SPME

A headspace solid-phase microextraction (HS-SPME) method followed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID) is described for the analysis of volatile compounds in Tagetes argentina Cabrera. The composition of the totality of the aerial parts of the plant (whole plant) and the inflorescences, leaves and stems was studied separately using HS-SPME. As a result, 53 compounds were determined, of which 39 were identified. The major components were: cis-tagetenone, trans-tagetenone, trans-tagetone and cis-tagetone.Using a much smaller amount of samples, a shorter extraction time and a very simple procedure, the HS-SPME method can achieve similar or better results than those obtained by EO analysis. In conclusion, the HS-SPME method is simple, rapid, effective and free of solvent, and can be used for the analysis of volatile compounds in samples of different populations of T. Argentina.

Se realizó el análisis de los componentes volátiles de T. argentina Cabrera utilizando el método de micro-extracción en fase sólida del espacio de cabeza con análisis posterior por cromatografía de gases acoplada a espectrometría de masas y por cromatografía de gases con detección por ionización de llama. Se estudio la composición de la totalidad de las partes aéreas de la planta (planta entera) como así también de las inflorescencias, hojas y tallos por separado empleando el método de HS-SPME. Como resultado, se determinaron 53 compuestos de los cuales 39 fueron identificados. Los componentes mayoritarios fueron: cis-tagetenona, trans-tagetenona, trans-tagetona and cis-tagetona. Utilizando una muy pequeña cantidad de muestra, un corto periodo de tiempo y un procedimiento muy simple se lograron similares o mejores resultados a aquellos reportados mediante el análisis del aceite esencial. En conclusión, el método de HS-SPME es simple, rápido, efectivo, libre de la utilización de solventes y puede ser fácilmente implementado para el análisis de componentes volátiles provenientes de muestras de diferentes poblaciones de T. Argentina.

Phytochemistry of Tagetes minuta L. (Asteraceae) from Córdoba, Argentina: comparative study between essential oil and HS-SPME analyses / Fitoquímica de Tagetes minuta L. (Asteraceae) originario de Córdoba, Argentina: estudio comparativo entre análisis del aceite esencial y análisis por HS-SPME

A headspace solid-phase microextraction (HS-SPME) method followed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC–FID) is described for the analysis of volatile compounds in Tagetes minuta L. Five types of SPME commercial fibers including PA, PDMS, CAR-PDMS, PDMS–DVB and DVB–CAR–PDMS were investigated and the best extraction was achieved with the mixed fiber DVB–CAR–PDMS. Parameters for HS-SPME in terms of equilibrium time of HS, fiber exposition time and extraction temperature were also investigated. Additionally, the composition of inflorescences, leaves and stems was also studied separately by HS-SPME. As a result, 68 compounds were determined and 53 were identified. A comparison was made between results obtained by HS-SPME–GC–MS and steam distillation of essential oil of the aerial parts of the plant. In both analyses, the major components were: cis-tagetenone and trans-tagetenone. Using much smaller samples, a shorter extraction time and a simpler procedure, the HS-SPME method can achieve similar results to those obtained by EO analysis. In conclusion, the HS-SPME method is simple, rapid, effective and free of solvent, and can be used for the analysis of volatile compounds in samples of different populations of T. minuta.

Se realizó el análisis de los componentes volátiles de T. minuta L. utilizando el método de micro-extracción en fase sólida del espacio de cabeza con análisis posterior por cromatografía de gases acoplada a espectrometría de masas y por cromatografía de gases con detección por ionización de llama. Se estudiaron cinco tipos de fibras comerciales que incluyeron a PA, PDMS, CAR-PDMS, PDMS–DVB y DVB–CAR–PDMS y se estableció que la fibra de DVB–CAR–PDMS es la que posee mejor comportamiento en el proceso de extracción. Se determinó el efecto del tiempo de equilibrio del espacio de cabeza, de la temperatura de extracción y del tiempo de exposición de la fibra sobre el proceso de HS-SPME. Adicionalmente, también se estudio por separado la composición de inflorescencias, hojas y tallos empleando el método de HS-SPME. Como resultado de este estudio se determinaron 68 componentes de los cuales 53 fueron identificados. Por otra parte se realizó una comparación de los resultados HS-SPME con el análisis del aceite esencial obtenido de las partes aéreas de la planta. En ambos casos, los componentes mayoritarios fueron: cis-tagetenona y trans-tagetenona. Utilizando una muy pequeña cantidad de muestra, un corto periodo de tiempo y un procedimiento más simple se lograron similares resultados a los obtenidos mediante el análisis del aceite esencial. En conclusión, el método de HS-SPME desarrollado es simple, rápido, efectivo y libre de la utilización de solventes, puede ser fácilmente implementado para el análisis de componentes volátiles provenientes de muestras de diferentes poblaciones de T. minuta.

Synthesis of amphiphilic dendrons and their interactions in aqueous solutions with cetyltrimethylammonium p-toluenesulfonate (CTAT).

In this work, we report synthesis and rheology of an interesting structured fluid based on the self-assembly of amphiphilic dendrons and wormlike micelles. Two amphiphilic dendrons were synthesized by the combination of aliphatic chains and polar dendritic heads. They showed different degrees of hydrophobicity and formed micelles in aqueous solution at critical micelle concentrations (CMC) of 25 and 125 ppm. The dendrons were soluble in water up to a concentration of approximately 1200 ppm, and produced no measurable increase in the viscosity of the solvent. The rheology of solutions of mixtures of each dendron with cetyltrimethylammonium p-toluenesulfonate (CTAT, a cationic surfactant) was characterized in simple shear flow. In the concentration range in which CTAT forms semidilute solutions of wormlike micelles, dendron addition produced a substantial synergy in zero-shear rate viscosity. Parallel-plate oscillatory shear measurements demonstrated that the CTAT/dendron mixtures are significantly more elastic than CTAT solutions. The viscosity synergy occurs at dendron concentrations lower than their CMC, and it is stronger for the more hydrophobic dendron. This suggests that the interactions between dendrons and wormlike micelles are basically hydrophobic, which implies attachment of dendron micelles to wormlike CTAT micelles in a manner similar to micellization of surfactants on polyelectrolytes.

Chemical and physicochemical characteristics of humic acids extracted from compost, soil and amended soil.

In order to gain understanding about how "HA-like substances" from organic amendments may change some properties in the soil solution, the knowledge of chemical and physicochemical characteristics (charge development, acid-base behavior and heterogeneity) should be known. The aim of this research were (i) to study the elemental and functional composition, (ii) to determine charge behavior, acid-base properties (apparent dissociation constant and buffer capacity) and (iii) to evaluate heterogeneity of humic acids (HA) isolated from municipal solid waste compost (MWC) and from the corresponding MWC-amended soil, in comparison to those of the unamended soil HA using potentiometric titration and differential scanning potentiometry (DSP). Potentiometric titration and the first derivative of -Q versus pH (negative charge development versus pH) curves could be used to determine proton-affinity distribution and the chemical heterogeneity of the HA as well as the average pK(app) and buffer capacity in a wide range of pH. Differential scanning potentiometry allows determination of the pK(app) values in a narrower range of pH than potentiometric titrations and is another simple methodology to study acid-base behavior of HA. DSP allows us to determine seven different pK(app) values for HA-S and HA-E and four different pK(app) for HA-C. Each one of these values corresponds to known acidic groups that can be present in the macromolecule of HA.