Mass fractal characteristics of wet sonogels as determined by small-angle x-ray scattering and differential scanning calorimetry

Low density silica sonogels were prepared from acid sonohydrolysis of tetraethoxysilane. Wet gels were studied by small-angle x-ray scattering (SAXS) and differential scanning calorimetry (DSC). The DSC tests were carried out under a heating rate of 2 degrees C/min from -120 degrees C up to 30 degrees C. Aerogels were obtained by CO(2) supercritical extraction and characterized by nitrogen adsorption and SAXS. The DSC thermogram displays two distinct endothermic peaks. The first, a broad peak extending from about -80 degrees C up to practically 0 degrees C, was associated to the melting of ice nanocrystals with a crystal size distribution with pore diameter ranging from 1 or 2 nm up to about 60 nm, as estimated from Thomson's equation. The second, a sharp peak with onset temperature close to 0 degrees C, was attributed to the melting of macroscopic crystals. The DSC incremental nanopore volume distribution is in reasonable agreement with the incremental pore volume distribution of the aerogel as determined from nitrogen adsorption. No macroporosity was detected by nitrogen adsorption, probably because the adsorption method applies stress on the sample during measurement, leading to a underestimation of pore volume, or because often positive curvature of the solid surface is in aerogels, making the nitrogen condensation more difficult. According to the SAXS results, the solid network of the wet gels behaves as a mass fractal structure with mass fractal dimension D=2.20 +/- 0.01 in a characteristic length scale below xi=7.9 +/- 0.1 nm. The mass fractal characteristics of the wet gels have also been probed from DSC data by means of an earlier applied modeling for generation of a mass fractal from the incremental pore volume distribution curves. The results are shown to be in interesting agreement with the results from SAXS.

Cationic liposomes in mixed didodecyldimethylammonium bromide and dioctadecyldimethylammonium bromide aqueous dispersions studied by differential scanning calorimetry, nile red fluorescence, and turbidity

The thermotropic phase behavior of cationic liposomes in mixtures of two of the most investigated liposome-forming double-chain lipids, dioctadecyldimethylammonium bromide (DODAB) and didodecyldimethylammonium bromide (DDAB), was investigated by differential scanning calorimetry (DSC), turbidity, and Nile Red fluorescence. The dispersions were investigated at 1.0 mM total surfactant concentration and varying DODAB and DDAB concentrations. The gel to liquid-crystalline phase transition temperatures (T-m) of neat DDAB and DODAB in aqueous dispersions are around 16 and 43 degrees C, respectively, and we aim to investigate the T-m behavior for mixtures of these cationic lipids. Overall, DDAB reduces the T-m of DODAB, the transition temperature depending on the DDAB content, but the T-m of DDAB is roughly independent of the DODAB concentration. Both DSC and fluorescence measurements show that, within the mixture, at room temperature (ca. 22 degrees C), the DDAB-rich liposomes are in the liquid-crystalline state, whereas the DODAB-rich liposomes are in the gel state. DSC results point to a higher affinity of DDAB for DODAB liposomes than the reverse, resulting in two populations of mixed DDAB/DODAB liposomes with distinctive phase behavior. Fluorescence measurements also show that the presence of a small amount of DODAB in DDAB-rich liposomes causes a pronounced effect in Nile Red emission, due to the increase in liposome size, as inferred from turbidity results.

Raman scattering, differential scanning calorimetry and Nd3+ spectroscopy in alkali niobium tellurite glasses

Alkali niobium tellurite glasses have been prepared and some of their properties measured by differential scanning calorimetry and Raman scattering. The vitreous domain was established in the pseudo ternary phases diagram for the system TeO2-Nb2O5-(0.5K(2)O-0.5Li(2)O). Raman scattering shows that for samples in the TeO2 rich part of the phase diagram the vitreous structure is composed essentially of (TeO4) units connected by the vertices, as in the alpha-TeO2 crystal. The addition of alkali and niobium oxides causes depolymerization to occur with structures composed essentially of (TeO3) and (NbO6) units. Samples with the composition (mol%) 80TeO(2)-10Nb(2)O(5)-5K(2)O-5Li(2)O, stable against crystallization, were prepared containing up to 10% mol Nd3+. The addition of this oxide increases the rigidity of the vitreous network shifting characteristic temperatures to higher temperatures. For the 10% Nd3+ sample amorphous phase separation is assumed to exist from the observation of two glass transition temperatures. Spectroscopic properties such as Judd-Ofelt Omega(lambda) intensity parameters, radiative emission probabilities, and induced emission cross sections were calculated. From these results and also from the emission quenching observed as a function of Nd3+ concentration, we suggest that these glasses could be utilized in optical amplifying devices. (C) 1999 Elsevier B.V. B.V. All rights reserved.

Interaction between poly(ethylene glycol) and C12E8 investigated by dynamic light scattering, time-resolved fluorescence quenching, and calorimetry

Dynamic light scattering (DLS), time-resolved fluorescence quenching (TRFQ), and isothermal titration microcalorimetry have been used to show that, in dilute solution, low molecular weight poly(ethylene glycol) (PEG, M-w = 12 kDa) interacts with the nonionic surfactant octaethylene glycol n-dodecyl monoether, C12E8, to form a complex. Whereas the relaxation time distributions for the binary C12E8/water and PEG/water systems are unimodal, in the ternary mixtures they may be either uni- or bimodal depending on the relative concentrations of the components. At low concentrations of PEG or surfactant, the components of the relaxation time distribution are unresolvable, but the distribution becomes bimodal at higher concentrations of either polymer or surfactant. For the ternary system in excess surfactant, we ascribe, on the basis of the changes in apparent hydrodynamic radii and the scattered intensities, the fast mode to a single micelle, the surface of which is associated with the polymer and the slow mode to a similar complex but containing two or three micelles per PEG chain. Titration microcalorimetry results show that the interaction between C12E8, and PEG is exothermic and about 1 kJ mol(-1) at concentrations higher than the CMC of C12E8. The aggregation number, obtained by TRFQ, is roughly constant when either the PEG or the C12E8 concentration is increased at a given concentration of the second component, owing to the increasing amount of surfactant micelles inside the complex.

Differential scanning calorimetry, x-ray diffraction and F-19 nuclear magnetic resonance investigations of the crystallization of InF3-based glasses

Results of differential scanning calometry (DSC), x-ray diffraction (XRD), and F-19 nuclear magnetic resonance (NMR) of InF3-based glasses, treated at different temperatures, ranging from glass transition temperature (T-g) to crystallization temperature (T-c), are reported. The main features of the experimental results are as follows. DSC analysis emphasizes several steps in the crystallization process. Heat treatment at temperatures above T-g enhances the nucleation of the first growing phases but has little influence on the following ones. XRD results show that several crystalline phases are formed, with solid state transitions when heated above 680 K, the F-19 NMR results show that the spin-lattice relaxation, for the glass samples heat treated above 638 K, is described by two time constants. For samples treated below this temperature a single time constant T-1 was observed. Measurements of the F-19 spin-lattice relaxation time (T-1), as a function of temperature,made possible the identification of the mobile fluoride ions. The activation energy, for the ionic motion, in samples treated at crystallization temperature was found to be 0.18 +/- 0.01 eV. (C) 1998 American Institute of Physics.

Thermo-optical characterization of tellurite glasses by thermal lens, thermal relaxation calorimetry and interferometric methods

In this work the thermal lens, thermal relaxation calorimetry and interferometric methods are applied to investigate the thermo-optical properties of tellurite glasses (in mol%: 80TeO(2)-20 Li2O(TeLi), 80TeO(2)-15Li(2)O-5TiO(2) (TeLiTi-5) and 80TeO(2)-10Li(2)O-10TiO(2) (TeLiTi-10)). Thermal diffusivity, thermal conductivity, specific heat and the temperature coefficients of refractive index, optical path length, thermal expansion and electronic polarizability were determined. The use of three independent methods was useful for a complete characterization of the studied tellurite glasses. In addition, our results showed that the thermal expansion coefficient and the temperature coefficient of the optical path length (dS/dT) were significantly modified with the introduction of titanium, which may be relevant for the application of these glasses in the photonic area. (c) 2006 Elsevier B.V. All rights reserved.

H-bonding in entrapped water in poly(o-methoxyaniline): Results from a differential scanning calorimetry study

Differential scanning calorimetry (DSC) was used to investigate entrapped water in poly(o-methoxyaniline) (POMA) in powder form. Two endothermic peaks were attributed to removal of water molecules that were adsorbed with distinct energies. By obtaining thermograms at various heating rates, we succeeded in applying Kissinger's approaches to estimate activation energies for the water adsorbed. The values obtained were ca. 25 and 53 kJ/mol, which correspond to H-bonding interactions, probably at the amine and imine centers of POMA, respectively. (C) 2005 Elsevier B.V. All rights reserved.

Calorimetry, Morphometry, Oxidative Stress, and Cardiac Metabolic Response to Growth Hormone Treatment in Obese and Aged Rats

This study investigated the effects of growth hormone therapy on energy expenditure, lipid profile, oxidative stress and cardiac energy metabolism in aging and obesity conditions. Life expectancy is increasing in world population and with it, the incidence of public health problems such as obesity and cardiac alterations. Because growth hormone (GH) concentration is referred to be decreased in aging conditions, a question must be addressed: what is the effect of GH on aging related adverse changes? To investigate the effects of GH on cardiac energy metabolism and its association with calorimetric parameters, lipid profile and oxidative stress in aged and obese rats, initially 32 male Wistar rats were divided into 2 groups (n = 16), C: given standard-chow and water; H: given hypercaloric-chow and receiving 30 % sucrose in its drinking water. After 45 days, both C and H groups were divided into 2 subgroups (n = 8), C + PL: standard-chow, water, and receiving saline subcutaneously; C + GH: standard-chow, water, and receiving 2 mg/kg/day rhGH subcutaneously; H + PL: hypercaloric-chow, 30 % sucrose, receiving saline subcutaneously; H + GH: hypercaloric-chow, 30 % sucrose, receiving rhGH subcutaneously. After 30 days, C + GH and H + PL rats had higher body mass index, Lee-index, body fat content, percent-adiposity, serum triacylglycerol, cardiac lipid-hydroperoxide, and triacylglycerol than C + PL. Energy-expenditure (RMR)/body weight, oxygen consumption and fat-oxidation were higher in H + GH than in H + PL. LDL-cholesterol was highest in H + GH rats, whereas cardiac pyruvate-dehydrogenase and phosphofrutokinase were higher in H + GH and H + PL rats than in C + PL. In conclusion, the present study brought new insights on aging and obesity, demonstrating for the first time that GH therapy was harmful in aged and obesity conditions, impairing calorimetric parameters and lipid profile. GH was disadvantageous in control old rats, having undesirable effects on triacylglycerol accumulation and cardiac oxidative stress.

Phase behavior of synthetic amphiphile vesicles investigated by calorimetry and fluorescence methods

The understanding of biological membranes may be improved by investigating physical properties of vesicles from natural or synthetic amphiphiles. The application of vesicles as mimetic agents depends on the knowledgment of their structure and properties. Vesicles having different curvature and size may be obtained using different preparation protocols. We have used differential scanning calorimetry (DSC) and steady-state fluorescence to investigate the gel to liquid-crystal phase transition of vesicles prepared by sonication (SUV) and non-sonication (GUV) of the synthetic dioctadecyldimethylammonium bromide (DODAB) in aqueous solution. DSC thermograms for a non-sonicated dispersion show a well-defined pre- and main transition corresponding to two narrow peaks at 36 and 45°C in the first upscan, while in a second upscan, only the main peak was observed. The sharpness of the peaks indicate a cooperative phase behavior for GUV. For a sonicated DODAB dispersion, the first upscan shows a third peak at 40.3°C, whereas for the second upscan the peaks are not well-defined, indicating a less cooperative phase behavior. Alternatively, the fluorescence quantum yield (Φ f) and the anisotropy (r) of trans, trans, trans-1-[4-(3-carboxypropyl)-phenyl]-6-[4-butylphenyl]-1,3,5-hexatriene (4H4A) and the ratio I 1/I 3 of the first to the third vibronic peaks of the pyrene emission spectrum as function of temperature are used as well to describe the phase behavior of DODAB sonicated and non-sonicated dispersions. It is in good agreement with the DSC results that the cooperativity of the thermotropic process is diminished under sonication of the DODAB dispersion, meaning that sonication changes from homogeneous to heterogeneous populations of the amphiphile aggregates. The pre- and main transitions obtained from these techniques are in fairly good accord with results from the literature.

Maturity degree of composts from municipal solid wastes evaluated by differential scanning calorimetry

Differential scanning calorimetry (DSC) in association with chemical analysis was applied to assess the maturity reached by the organic fraction of Municipal Solid Wastes (MSW) subjected to composting processes with manual and fixed aeration and sampled at different composting times. Thermograms showed that the difference in the treatments, i.e., the manual aeration and the fixed aeration, had no relevant effect on the stabilization and maturation of OM in the substrates. Common thermal effects observed were: a low temperature endotherm assigned to dehydration and/or loss of peripheral polysaccharides chains; a medium temperature exotherm assigned to loss of peptidic structures, and a high temperature exotherm assigned to oxydation and polycondensation of aromatic nuclei of the molecule. Results obtained suggest that in the experimental conditions used, a shorter time of composting (about 30 d) appears adequate, in order to limit the extended mineralization of OM, whereas a prolonged composting time (up to 132 d) would produce a compost of poor quality with high ash content and low OM content.

Estimation of the metabolic equivalent (MET) of an exercise protocol based on indirect calorimetry

Objective: This study aimed to determine the energy expenditure (EE) in terms of caloric cost and metabolic equivalents (METs) of two sessions of an exercise protocol. Methods: Fifteen subjects (51.0 ± 5.5years) performed the exercise sessions (80min), which were composed by (warming, walking and flexibility exercises; Session A) and (warming, walking and local muscular endurance exercises; Session B). Heart hate (HR) was measured during each part of the sessions. In laboratory environment, maximal oxygen consumption (VO2max) and oxygen uptake in rest and exercise conditions (using mean HR obtained in classes) were measured on different days, using indirect calorimetry. Exercise METs were obtained by dividing VO2 in exercise (mL.kg-1.min-1) by VO2 in rest (mL.kg-1.min-1). The EE of the exercises was calculated by the formula: MET x Weight(kg) x Time(min)/60. The results were analyzed by ANOVA with Tuckey post hoc test (p < 0.05). Results: One MET for this group was 2.7 ± 0.1mL.kg-1.min-1. The mean METs of exercises were 4,7 ± 0,8 (warming), 5,8 ± 0,9 (walking) and 3,6 ± 0,7 (flexibility) on session A, and 4,6 ± 1,2 (warming), 5,6 ± 1,0 (walking) and 4.8 ± 1,0 (local muscular endurance exercises) on Session B. The training sessions showed similar energy cost (A: 398 ± 86.72 kcal and B: 404 ± 38.85 kcal; p > 0,05). None of activities were classified into vigorous intensity (> 7 METs). There were no differences on VO2 between walking (15,6 ± 2,8 or 15,4 ± 2,6 mL.kg-1.min-1) and local muscular endurance exercises (13,2 ± 2,9 mL.kg-1.min-1), although both were higher (p > 0.05) than flexibility exercises (10.1 ± 2.2 mL.kg-1.min-1). Conclusion: The proposed protocol achieves the physical activity needed by healthy adults to improve and maintain health, by their structure, moderate intensity, duration, frequency and caloric expenditure.