Heat Of Immersion In Water Research Articles

Cross-Linked Hydrogels Based on PolyNIPAAm and Acid-Activated Laponite RD: Swelling and Tunable Thermosensitivity.

The effects of acid activation of Laponite RD (Lap) on the structure and properties of activated Lap nanoparticles (aLap) and the properties of polyNIPAAm hydrogels physically cross-linked by aLap have been studied. The acid activation of Lap by the sulfuric acid was done using the concentration of sulfuric acid within the interval Ca = 0.525-14.58% for 10 h. For slightly activated samples (Ca ≤ 1.25 wt %), the significant increase of the specific surface area (by ≈1.56 times) was accompanied with a significant decrease in both the values of the specific heat of immersion in water and n-decane. However, the hydrophilic properties of all samples S0-S5 were still observed. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) data, Fourier transform infrared (FTIR) spectra, and X-ray diffraction (XRD) patterns demonstrated that the acid activation resulted in the destruction of the crystal lattice of Lap, leaching of magnesium and lithium, and formation of the amorphous phases. Moreover, the acid activation significantly affected aggregation and negative surface charges of the aLap faces in aqueous suspension. The effects of aLap on the swelling properties and cooperativity in the phase transitions of polyNIPAAm hydrogels cross-linked by aLap are also discussed. It was demonstrated that an increase in Ca resulted in a significant increase in the equilibrium degree of swelling of the hydrogels and a decrease in the hydrogel phase-transition temperature from the swollen phase to the shrunken phase.

Post-exercise hot water immersion elicites heat acclimation responses in endurance and recreational athletes. A systematic review and meta-analysis

Aims This meta-analysis aims to evaluate the effectiveness of heat acclimation (HA) via hot water immersion protocols and their effect on time trial (TT) performance, heart rate (HRE, HRM and HRTT), rectal temperature (Tre), Rate of perceived exertion (RPE), psychological stress index (PhSI), thermal comfort (Tcomf), thermal sensation (Tsen) and maximum oxygen uptake (Vo2max). Methods Pubmed, Scopus, Sportdiscus and Web of Science databases were used alongside the grey matter sites Google Scholar and Researchgate. The databases were then searched for randomised control trials and mixed-method design studies. Two RTCs, six repeated measure design studies and one randomised crossover design study were included after screening a total of 50 titles and 28 full-text articles. Sample sizes range from 1 - 13 with all participants having not participated in any form of heat training 6 months before their inclusion in the study. Results The mean difference (MD) for Heart rate (HR) was -9.1125 BPM (95% CI p = 0.026) and was considered to be statistically significant. The MD for Rectal temperature (Tre) effect size was -0.3814 Tre (°C) (95% CI; p = 0.05). The MD for sweat rate was 0.085; (96% CI; p = 0.0179) The changes in RPE, PhSI, Tcomf and Tsen were too small to be considered statistically significant. There was no significant difference between pre and post HA for Vo2max and PV. This meta-analysis implies that HA via HWI may improve tolerance to discomfort during heat exposure and thus subsequently improve physical performance during exercise in hot conditions. Conclusion The primary finding of this meta-analysis is that athletic performance is improved with post-exercise hot water immersion heat acclimation training. HWI HA protocols should focus on the following guidelines: 40-50 minutes of submaximal exercise (>65% of Vo2max) should be followed directly (within 10 minutes) by 40 minutes of hot water immersion at 40°C with the individual immersed up to their neck. The HA protocol should last between 6-9 days with a single bout of HWI every day for this period.

Silica-supported $$\hbox {Ni}_{{x}}\hbox {O}_{{y}}$$, $$\hbox {Zn}_{{x}}\hbox {O}_{{y}}$$ and $$\hbox {Mn}_{{x}}\hbox {O}_{{y}}$$ nanocomposites: physicochemical characteristics and interactions with water and n-decane

A series of \(\hbox {M}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}\) (where M = Ni, Zn and Mn) nanocomposites were synthesized at different \(\hbox {M}_{{x}}\hbox {O}_{{y}}\) contents (0.2, 1 and 3 mmol per 1 g \(\hbox {SiO}_{2})\) using a deposition method. The samples were characterized using nitrogen adsorption–desorption, X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy and photon correlation spectroscopy. The heat of immersion in water (\(Q_{\mathrm{w}})\) and n-decane (\(Q_{\mathrm{d}})\) were measured using a microcalorimetry method, and the corresponding values of the hydrophilicity index \(K_{\mathrm{h}}=Q_{\mathrm{w}}/Q_{\mathrm{d}}\) were analysed. The formation of \(\hbox {M}_{{x}}\hbox {O}_{{y}}\) on a silica surface leads to diminishing of the \(Q_{\mathrm{w}}\) and \(Q_{\mathrm{d}}\) values (calculated per 1 g of nanocomposites) because of the specific surface area reduction. However, the \(Q_{\mathrm{w}}\) values calculated per 1 \(\hbox {m}^{2}\) increase for \(\hbox {Zn}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}\) and \(\hbox {Mn}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}\) in comparison with the unmodified silica, and it remains unchanged for \(\hbox {Ni}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}\). Silica modification with \(\hbox {M}_{{x}}\hbox {O}_{{y}}\) significantly changes the pH dependence of zeta potential and affects the surface charge density. A shift of the isoelectric point \((\hbox {pH}_{\mathrm{IEP}})\) and a character of the zeta potential \(\zeta \)(pH) curve are affected by the \(\hbox {M}_{{x}}\hbox {O}_{{y}}\) phase, and \(\hbox {pH}_{{\mathrm{IEP}}}\) shifts toward higher values as follows Mn < Zn < Ni.

Silica-supported Ni and Co nanooxides: Colloidal properties and interactions with polar and nonpolar liquids

Binary and ternary mixed oxides composites (NiO/SiO2, Co3O4/SiO2, and NiO/Co3O4/SiO2) were synthesized using a method of solvate-stimulated modification of the fumed silica with Ni and Co nitrate hexahydrates for further thermal decomposition and formation of the crystalline NixOy, CoxOy or NixOy/CoxOy oxides. Synthesized composites were examined using IR spectroscopy, argon adsorption-desorption, microcalorimetry, and photon correlation spectroscopy. A two-stage method used for the synthesis of composites showed high potential in order to prepare ultra-dispersed solids with a high interfacial area of 246–255 m2/g, which is close to that of the initial fumed silica used as support. According to the results of the XRD analysis, 15 nm NiO and 14 nm Co3O4 crystallites were formed within the composite structure. As compared with the initial silica, the secondary particles (aggregates) of metal oxides in the aqueous medium have a large size of 100–180 nm while agglomerated particles are in the range from 1.1 to 1.3 μm. Hydrophilic properties of the synthesized composites are close to the initial silica, the hydrophilicity index varies from 2.4 to 2.6, according to the measured heats of immersion in water and n-decane.

Heats of immersion of hydroxyapatite and hydroxyapatite/fumed oxides composites in water and n-decane

The heat of immersion and surface properties of hydroxyapatite initial and modified (containing Ca, P, and CO32−) and composites with fumed oxides were examined using microcalorimetry. The microcalorimetric measurements showed a regular decrease in the heat of immersion in water per area unit with an increase in the specific surface area of samples. The nitrogen adsorption/desorption isotherms were used to estimate the textural characteristics of the materials studied.

The heat of immersion of modified silica in polar and nonpolar liquids

The influence of the degree of silica surface coverage by trimethylsilyl groups on the heat of immersion in various polar and nonpolar liquids has been investigated using microcalorimetry technique. The decrease of Gibbs free energy γ as a result of replacement a solid/gas interface with the solid/liquid is accompanied by the emission of heat, which value is determined by the intensity of the interaction of the molecules of liquid with the solid surface and area of interaction. The polarity of surface decreases due to substitution of polar silanol groups for the nonpolar trimethylsilyl (TMS) groups on the SiO2 surface, and consequently, the intensity of the interaction of this surface with polar and nonpolar substances changes. The heats of immersion of modified silica in polar triethylamine (TEA), 2-propanol, acetonitrile and water decrease almost linear with increasing degree of surface modification. The changes of heat of immersion of modified silica in nonpolar liquids are minor and may be associated with some decrease in the specific surface area of the samples owing to the synthesis. The heat of immersion in water is less than in hexane and decane at high degrees of surface modification with TMS groups (0.75 or higher), indicating the hydrophobic nature of the surface. The highest heat of immersion is observed for TEA, what is consistent with the specific interaction of a strong organic base TEA with surface silanol groups.

Influence of specific surface area of pyrogenic silicas on their heat of immersion in water and on their surface properties assessed using inverse gas chromatography

The heat of immersion and the surface properties of pyrogenic silicas were examined using microcalorimetry and inverse gas chromatography at finite concentration (FC-IGC). The microcalorimetric measurements showed a regular decrease of the heat of immersion, in water, per area unit with an increase in the surface areas. The desorption isotherms were established using FC-IGC. It is observed that BET constant value goes through a minimum, whereas the shapes of distribution function of the adsorption energies of isopropanol are changing. All results could be interpreted using a model of formation of the pyrogenic silica in the flame, which explains the change of surface functionality and geometry occurring around 200 m 2/g.

Silane modified fumed silicas and their behaviours in water: Influence of grafting ratio and temperature

The interaction of water with pyrogenic silica samples, modified by a controlled partial silylation with dimethyldichlorosilane, was studied by microcalorimetry, at 20 °C, 25 °C and 30 °C. Whatever the coverage ratio was, the heat of immersion in water does not vary significantly with the temperature, except one sample corresponding to a high grafting ratio that exhibit a high temperature dependence of the immersion heat. Two samples of quite the same molecular characteristics were examined by Si 29 NMR solid-state spectroscopy, which shows that the temperature dependence is related with a higher mobility of the grafted polydimethylsiloxane chains (PDMS). The temperature susceptibility could be attributed to the competition between adsorption of the grafts onto the silica surface and their association in the water phase favoured by the hydrophobic forces, a competition which is measurable only in case of long chain grafts.

Surface properties of dimethylsilylated silicas, assessed using IGC at finite concentration

The specific surface area of silicas samples modified by controlled silylation with dimethyldichlorosilane were assessed by inverse gas chromatography at finite concentration, using isopropanol and water as probes. If isopropanol assesses the whole residual free silica surface, water addresses only the more hydrophilic sites, present at the silica surface. It was also established that the heat of immersion in water of these silylated samples, in water measured by microcalorimetry, is clearly related to the residual free silica surface, delivered by IGC measurement.

Surface structure and properties of mixed fumed oxides

A variety of fumed oxides such as silica, alumina, titania, silica/alumina (SA), silica/titania (ST), and alumina/silica/titania (AST) were characterized. These oxides have different specific surface areas and different primary particle composition in the bulk and at the surface. These materials were studied by FTIR, NMR, Auger electron spectroscopy, one-pass temperature-programmed desorption with mass spectrometry control (OP TPDMS), microcalorimetry, and nitrogen adsorption. Nonlinear changes in the surface content of alumina in SA and AST and titania in ST and AST samples with increasing oxide content along with simultaneous changes in their specific surface area cause complex dependencies of the heat of immersion in water and desorption of water on heating on the structural parameters. Simultaneous analysis of changes in the surface phase composition, in the concentration of hydroxyls, and in the structural characteristics reveals that at a low content of the second phase the structural characteristics (e.g., S BET ) are predominant; however, at a large content of these oxides the phase composition plays a more important role.

Adhesion of solid particles to gas bubbles. Part 2: Experimental

In slurry bubble columns, the adhesion of solid catalyst particles to bubbles may significantly affect the G–L mass transfer and bubble size distribution. This feature may be exploited in design by modifying the hydrophilic or hydrophobic nature of the particles used. Previously we have proposed a generalised model, describing the adhesion of particles to G–L interface under stagnant conditions. In this work, we studied the adhesion of particles characterised by different degree of hydrophobicity and porosity: non-porous polystyrene and glass beads, unmodified and hydrophobised mesoporous silica, and activated carbon particles. Images recorded at high optical magnification show the particles adhering to gas bubbles individually or as aggregates. In aqueous media, higher liquid surface tension and particle surface hydrophobicity increase the adhesion strength and the tendency of particles to agglomerate, in agreement with the model. The adhesion of non-porous rough-surface particles to gas bubbles can be characterised by the receding contact angle. The advancing contact angle represents better the adhesion of the same particles to liquid droplets. We found that the “effective” contact angle of porous particles is much lower than an “intrinsic” contact angle calculated from the heat of immersion in water, or measured by sessile drop method. An equivalent contact angle derived from the Cassie rule explains the wetting behaviour of particles having the pores filled with liquid.

Partially hydrophobized silica supported Pd catalyst for hydrogenation reactions in aqueous media

The hydrophobic or hydrophilic nature of catalyst support materials may influence the reaction behaviour in three-phase catalytic oxidation or hydrogenation reactions in aqueous media. This may be attributed to the segregation or agglomeration behaviour of such support materials in water. We have systematically investigated the impact of surface hydrophobicity of silica supports during the catalytic hydrogenation of methyl acrylate in water. To this end, we deliberately varied the hydrophobicity of silica supported Pd catalysts by moderate silylation with dichlorodimethylsilane (DDMS). A range of materials was prepared in this way, with three-phase contact angles up to 90°, in order to allow the water to fill the catalyst pores. Hydrophobic silica supported catalysts were either prepared by silylation of hydrophilic mesoporous silica followed by incipient wetness impregnation of the support with H 2PdCl 4 solution (a), or by the reverse procedure (b). This way of rendering the support more hydrophobic leads to an increased three-phase contact angle, lower heat of immersion in water and lower heat of water vapour adsorption. These factors induce a more pronounced adhesion of particles to gas bubbles. During the hydrogenation of methyl acrylate in aqueous media, hydrophobic Pd/silica catalysts show higher activity than similar hydrophilic Pd/silica catalyst. The catalyst prepared by the route (a) shows the highest activity also as result of better Pd dispersion on the hydrophobic support.

Calorimetric and Spectroscopic Studies of Water Adsorption onto Alkaline Earth Fluorides

Interactions between the surfaces of alkaline earth fluorides (CaF2, SrF2 and BaF2) and water molecules were investigated by calorimetric and spectroscopic methods. The exposed surfaces of the alkaline earth fluoride samples, with which the (100) crystalline plane is mainly associated, were found to be fully covered with strongly adsorbed water molecules, resulting in characteristic IR bands at 3684, 2561, 1947 and 1000 cm−1, respectively. This surface was homogeneous towards further water adsorption. The strongly adsorbed water molecules were almost completely desorbed from the surface on evacuating the sample up to 473 K. The heat of immersion in water also increased with increasing pretreatment temperature; this may be attributed to surface rehydration of the alkaline earth fluorides. The state of the surface changed drastically as the pretreatment temperature was increased and stabilized towards incoming water molecules. Thus, the surface formed after evacuation at temperatures greater than 473 K was resistant to hydration even after immersion in water at room temperature. This surface was relatively heterogeneous towards water adsorption, although it behaved homogeneously towards argon adsorption. These facts indicate that strongly adsorbed water molecules appear to be somewhat specific towards the adsorption of further incoming water molecules. The adsorption properties of the (100) plane of alkaline earth fluorides towards water and argon molecules depend strongly on both the electrostatic field strength and the extent of rehydration of the alkaline earth fluoride surface.

Surface characterisation of sic powder by heat of immersion in water

surface characterisation of sic powder by heat of immersion in water

Characterization of surface conditions of non oxide ceramic powders by heat of immersion in water

Characterization of surface conditions of non oxide ceramic powders by heat of immersion in water

Characterization of Surface Conditions of Silicon Nitride Powders by Heat of Immersion in Water

Characterization of Surface Conditions of Silicon Nitride Powders by Heat of Immersion in Water

Liquid phase microcalorimetry applied to evaluate surface polarity of MCM-41 type aluminosilicates

Three calorimetric methods have been used to evaluate the surface polarity of three MCM-41 materials characterised by different Si:Al ratios (referred to as SiAl xC14, where x is the moles of Si:Al ratio, and 14 the chain length of the surfactant template). In the liquid phase, the heats of adsorption of 1-butanol from n-heptane and the heats of immersion in water, n-heptane and formamide were compared with the corresponding heat values obtained for two reference solids, viz. silica XOB015 and alumina. Surface (internal) energy of all MCM-41 samples appeared to be smaller than that of any reference solid, the differences being more marked in the case of alumina. In the gas phase, the combination of ammonia gas adsorption and mirocalorimetry measurements was used to evaluate the number and strength of acidic surface sites. With the exception of SiAl8C14, which contains 46% of strongly acidic sites, SiC14 and SiAl32C14 have low surface acidity. The broad distribution of adsorption energy values indicates the energetic heterogeneity of the acidic sites. Incorporating Al into the silicate matrix caused the surface polarity of the materials to increase.

シリカ粉体表面に加熱生成されたシロキサンの水およびアルコールに対する反応性

Reactivities of siloxane bridge formed by thermal treatment of fine silica powder surfaces for water and several aicohols were studied quantitatively. Aerosil 200 as a fine silica powder was thermally treated in vacuum, in the temperature range from 25 to 500°C for 4hrs. The heats of immersion in water of heated silica have a broad maximum at about 300°C. The results of immersional heat suggested that rehydroxylation of siloxane on surface of thermally treated silica dose not completely restore the surface to its original condition. The interesting result obtained by Grignard's reagent test was that the siloxanes, in the all of heat-treated silica, were rehydroxylated by exposure to saturated water vapor for 12hrs. This result was also substantiated by change in the spectra of FT-IR and 29Si CP/MAS NMR. In conclusion, rehydroxylation of siloxane was observed by the heat-treatment ranging from 200 to 500°C. However, for the surfaces treated above 300°C, the reaction rate of rehydroxylation decreased. On the other hand, significant reactions were not observed on a few alcohols.

Influence of thermal treatment on the structure of calcium hydroxyapatite

Synthetic calcium hydroxyapatite, Ca10(PO4)6(OH)2 (CaHap), prepared by a wet method was evacuated at various temperatures up to 900°C and the influence of thermal treatment on the structure of this material was investigated by FTIR, determination of concentration of surface P–OH groups, adsorption of H2O and heat of immersion in water. The number of surface P–OH groups was 2.6 groups nm−2 and the ionic ratio of surface HPO42− to H2PO4− was 31:69. The surface P–OH groups were essentially dehydroxylated by outgassing above 400°C to produce surface P–O–P species. The heat of rehydroxylation per one P–O–P group was determined to be 1.43×10−16 J group−1. When outgassed above 600°C, CaHap was rehydrated via the reaction: (1−x)Ca10(PO4)6(OH)2+3xβ-Ca3(PO4)2+xH2O→Ca10−x(P2O7)x(PO4)6−2x(OH)2.

Adsorption-energetic and IR spectroscopic studies of NH4 natrolite

The ammonium form of natural zeolite, natrolite, obtained by vapor phase ion exchange is similar to calcium-containing zeolites of the natrolite group in its de- and rehydration characteristics and the heats of immersion in water. The adsorption capacity and the heat of immersion in water are maximum after evacuation of the zeolite at 200 °C. The irreversible sintering of NH4 natrolite occurs above 200 °C (up to 45% at 500 °C), accompanied by the formation of hydroxyl groups.