SUMMARY
Dissolution and precipitation processes modify the structure of the porous media at microscale which significantly affects the macroscopic properties of the media. These variations in the ...pore geometry result in changes in the hydraulic properties that control the groundwater flow, and also modify the electrokinetic properties associated to the displacement of electrical charges carried by the flow which originates the streaming potential. Under the hypothesis of a uniform dissolution or precipitation of the pores and based on the effective excess charge density approach, we present a physically based theoretical model for estimating the effective excess charge density as a function of time. The model is based on the assumption that the pore structure can be represented by an ensemble of capillary tubes with a smooth periodic variation of their radius and a fractal pore size distribution. The analytical expressions obtained to describe the effective excess charge density depend on the chemical parameters of the fluid and the petrophysical properties of the medium. In addition, the periodic variations assumed in the pore geometry represent a more realistic description of a porous medium than considering the pores as constant radii capillaries. These irregularities allow us to include the hysteresis phenomenon in the electrokinetic properties. The expressions of the proposed model have been tested with experimental data consisting of sets of effective excess charge density-effective saturation, permeability-effective saturation, porosity-time and permeability-time values. In all cases, the model is able to satisfactorily reproduce the behaviour of the data.
The self-potential (SP) method is a passive geophysical method that relies on the measurement of naturally occurring electrical field. One of the contributions to the SP signal is the streaming ...potential, which is of particular interest in hydrogeophysics as it is directly related to both the water flow and porous medium properties. The streaming current is generated by the relative displacement of an excess of electrical charges located in the electrical double layer surrounding the minerals of the porous media. In this study, we develop a physically based analytical model to estimate the effective excess charge density dragged by the water flow under partially saturated conditions. The proposed model is based on the assumption that the porous media can be represented by a bundle of tortuous capillary tubes with a fractal pore size distribution. The excess charge that is effectively dragged by the water flow is estimated using a flux averaging approach. Under these hypotheses, this new model describes the effective excess charge density as a function of saturation and relative permeability while also depending on the chemical and interface properties, and on petrophysical parameters of the media. The expression of the model has an analytical single closed-form which is consistent with a previous model developed from a different approach. The performance of the proposed model is then tested against previous models and different sets of laboratory and field data from the literature. The predictions of the proposed model fits fairly well the experimental data and shows improvements to estimate the magnitude of the effective excess charge density over the previous models. A relationship between the effective excess charge density and permeability can also be derived from the proposed model, representing a generalization to unsaturated conditions of a widely used empirical relationship. This new model proposes a simple and efficient way to model the streaming current generation for partially saturated porous media.
The thermal stability of blends obtained from the mixture of 4-dodecylbenzenesulfonic acid doped polyaniline (PANI(DBSA)) and a terpolymer of ethylene-propylene-5-ethylidene-2-norbornene (EPDM) by ...casting from organic solvents, was studied by thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) under nitrogen atmosphere. For the PANI(DBSA) complex and PANI(DBSA)/EPDM blends the TGA results showed more than one stage of degradation, of which the second (temperature range 380–520 °C) was observed to be the most significant. Apparently, in this stage, the simultaneous degradation of the bound dopant, the PANI and the elastomer occurred. The activation energy (
E) for the crosslinked blends was in the range 180–250 kJ mol
−1, higher values than those determined for pure components and non crosslinked blends which were in the range 150–210 kJ mol
−1. The
E values also indicated that the effects due to the PANI(DBSA) content and maleated EPDM were not significant and that the mechanism of degradation of both systems studied was associated with a random scission of the chain. The FTIR spectra for the PANI(DBSA)/EPDM crosslinked blend showed typical absorption bands associated with saturated and unsaturated hydrocarbons, water, carbon dioxide and nitrogen containing compounds.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The thermal stability of poly(
N-vinyl-2-pyrrolidone-co-methacrylic acid) copolymers was studied by thermogravimetry and infrared spectroscopy in inert atmosphere. The thermogravimetric curves ...suggested that the effective degradation of both systems occurred in the temperature range 350–500 °C with more than 60% mass loss. At this temperature, the activation energy was in the range 160–200 kJ mol
−1 (average values), suggesting that the degradation occurred by a random scission of the chain. The FTIR results indicated that the main volatile products of degradation are CO
2, CO and hydrocarbons (unsaturated structures) with low molecular weight. Pure PVP also showed the formation of NH
3 which was apparently suppressed in the copolymer by the formation of large amounts of CO
2 and CO. The results suggested that the thermal stability of the copolymers was essentially associated with the
N-vinyl-2-pyrrolidone monomer, losing stability when the percentage of methacrylic acid in the copolymer system was increased.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Studies on elemental analysis, Fourier transform infrared spectroscopy (FT-IR) and thermal decomposition (thermogravimetry, TG; and derivative thermogravimetry, DTG) of sedimentary fulvic (FA) and ...humic acids (HA) from marine, estuarine, lacustrine and terrestrial environments are presented. In general, H/C and N/C atomic ratios, as well as the infrared spectra, reflected the extent of the influence of algal and/or terrestrial organic matter sources on the samples, the aquatic (both, marine and freshwater) humic substances (HS) being richer in nitrogen and more saturated, than terrestrial materials. Comparison of properties of FA and HA from the same parent sediments showed that the latter are relatively richer in nitrogen and unsubstituted aliphatic chains and poorer in carboxylic groups. FT-IR spectra showed that the nitrogen present is mostly as forming part of amide groups. Concerning thermal degradation, two main steps were observed for all samples: the first, relative to the loss of moisture, being located between 40°C and 100°C and the second between 270°C and 440°C. FT-IR spectra of the samples which had been heated to 90°C, 400°C and 900°C showed that, upon heating, the carboxyl content decreases (especially for FA), the aliphaticity decreases and the aromaticity increases (especially for HA), indicating that the 270°C-470°C degradation step might be related to decarboxylation and unsaturation losses. In spite of this, both kinds of HS, were shown to be highly thermo-resistant materials retaining most of their typical original infrared spectral features, even after being heated to 400°C.
The effects of maleated ethylene propylene diene (EPDM-g-MA) on the thermal stability of polyamide/EPDM and polyamide/poly(ethylene terephthalate) (PET) systems were studied by thermogravimetric ...analysis and infrared spectroscopy in nitrogen. Based on the activation energy (
E) and reaction products, it is suggested that the thermal degradation of pure polyamide 12.10 (PA-12.10) and polyamide 6.10 (PA-6.10) occurred firstly by chain scission of the weakest C–N and –C(O)–NH bonds. The average value of
E for pure PA-12.10 was ca. 280 kJ mol
−1. In the binary and ternary blends, the decrease of
E to ca. 180–200 kJ mol
−1 indicated a more favourable degradation. For the systems containing PA-6.10,
E decreased from ca. 210 kJ mol
−1 (pure PA-6.10) to ca. 160 kJ mol
−1 in the ternary blends. The results suggest that the presence of EPDM-g-MA in the blend decreased the thermal stability of the polyamides.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The thermal degradation of 2-hydroxy-3-ionene chloride polymer (HICP) and 3,22-ionene bromide (3,22) was studied in nitrogen atmosphere by thermogravimetry (TG) and infrared spectroscopy (FTIR). For ...the two polymers, a different profile in the TG/DTG curves was observed which was probably associated with the structural and functional differences between HICP and 3,22. The
E-values decreased from 150 to 105 kJ mol
−1 for the HICP and increased from 110 to 140 kJ mol
−1 for the 3,22 in the same range of weight loss fraction. The observed behaviour in terms of the TG/DTG curves and the activation energy values suggested that the 3,22 is more stable thermally than the HICP. This conclusion was supported by the FTIR spectra of the residues and evolved gas products of degradation. The mechanism of degradation was apparently associated with the scission of weak bonds and random scission of the polymer chain. Evolved gas products such as CO
2 and NH
3 in HICP and unsaturated hydrocarbons in 3,22 confirm the above mechanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Two‐dimensional liquid chromatography separation (2‐DL), based on chromatofocusing for first dimension and hydrophobicity for second, can be used as a complementary method to two‐dimensional gel ...electrophoresis (2‐DE). A platform now available, ProteomeLab PF 2D provided by Beckman Coulter, (Fullerton, CA, USA), assembles these methods in automation. This system was applied to resolve large numbers of urine proteins. Reproducibility and sensitivity in protein resolution were evaluated in this study using urines collected from male blood donors. About 1000 peaks were detected at a pH range of 4.0–8.5 by applying 1 mg of proteins. Furthermore, the same fractions showing peaks with high absorbance intensities in second dimension were collected and subjected to matrix‐assisted laser desorption/ionization‐time of flight/mass spectrometry analysis for identification. The results showed that the 2‐DL provides high reproducibility of two‐dimensional protein map, and lends fractions to subsequent mass spectrometry analysis without the further need for extraction or solubilization of samples as required for spots excised from 2‐DE gels. In addition, this system also allows to separate particularly proteins with 40–9 kDa molecular weight.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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