Surface Enthalpy Research Articles

Thermodynamic and aggregation properties of aza- and imino-substituted gemini surfactants designed for gene delivery

Improving the efficiency of gene delivery by using non-viral vectors is currently an area of considerable research interest. Novel derivatives of gemini surfactants having aza- (12-5N-12, 12-7N-12, 12-8N-12) and imino- (12-7NH-12) substituted spacer groups and C12 tails have been designed to improve DNA transfection. Physicochemical characterization of micelle and interfacial properties of these cationic compounds are reported. The effect of these substitutions on the aggregation properties of the gemini surfactants is discussed in the context of results for the 12-s-12 and 12-EOx-12 gemini series, previously reported in the literature. Aza substitution results in a spacer of intermediate hydrophobicity to the above series, reflected by the magnitude of both the critical micelle concentrations and head group areas. Enthalpy and apparent molar volume of micellization data illustrate the differences in the aggregation properties that result from the bulkier and more hydrophobic aza-substituent in the spacer as compared to an ether oxygen (for the 12-EOx-12 series) containing spacer. The 12-7N-12 and 12-8N-12 compounds show aberrant features in the surface tension and enthalpy of dilution results that are not observed for the 12-5N-12 and 12-7NH-12 compounds. Premicelle association is considered to be a source of this behaviour.

TiO2Stability Landscape: Polymorphism, Surface Energy, and Bound Water Energetics

The energetics of pure-phase rutile nanorods and spherical anatase nanoparticles have been studied by high-temperature drop solution calorimetry in 3Na2O·4MoO3 solvent at 975 K and water adsorption calorimetry in a wide range of particle sizes (surface area) from 6 to 40 nm (5−270 m2/g). The calorimetric surface enthalpies for rutile and anatase, calculated as 2.22 ± 0.07 and 0.74 ± 0.04 J/m2, respectively, are in general agreement with Ranade et al.'s results (Proc. Natl. Acad. Sci. U.S.A., 2002, 99, 6476), although their numerical values are somewhat different because of impurities and unaccounted bound water in the previous work. This study supports the energy crossovers previously proposed for the TiO2 polymorphs. The energetics of water adsorption were measured using a commercial Calvet microcalorimeter coupled with a gas dosing system. This permitted the calculation of differential and integral enthalpies of water adsorption that characterize how tightly water binds to rutile and anatase surfaces and the calculation of adsorption entropies, which reflect the surface mobility of adsorbed water. The integral enthalpy of tightly bound water (relative to liquid H2O standard state) is −18 kJ/mol for anatase and −40 kJ/mol for rutile. As seen previously for Al2O3, the TiO2 polymorphs with higher surface energy bind water more tightly. The calculated entropy changes for the adsorption of water on TiO2 are more negative than the entropy changes for the condensation of gaseous water to hexagonal ice. This finding suggests highly restricted mobility of molecules adsorbed at initial stages of adsorption (low coverage) and, possibly, dissociative adsorption on both rutile and anatase surfaces. However, nanoparticles contain both tightly bound water and loosely bound water. The latter is characterized by energetics of bulk water. The stabilizing water contribution to the overall energy of the system makes the hydrated nanophase samples more stable. The recommended transformation enthalpy for bulk anatase to bulk rutile is −1.7 ± 0.9 kJ/mol.

Enthalpy of water adsorption and surface enthalpy of lepidocrocite (γ-FeOOH)

Lepidocrocite (γ-FeOOH) appears to be thermodynamically metastable with respect to goethite (α-FeOOH) and yet the former phase forms and persists both in nature and laboratory. Here we show that the thermodynamic factors relevant to these observations cannot be dismissed, although kinetics undoubtedly plays a significant role in the formation and preservation of metastable phases. To understand the relationships of the FeOOH polymorphs in the bulk and nanoscale, we investigated the energetics of lepidocrocite nanoparticles. We measured enthalpy of water adsorption and enthalpy of formation of lepidocrocite samples with surface area of 42–103 m 2/g. Having both quantities measured allowed us to calculate the surface enthalpy for a water-free surface of this phase as 0.62 ± 0.14 J/m 2 and the energy of a relaxed (hydrated) surface as 0.40 ± 0.16 J/m 2. Our measurements show that a portion of the adsorbed water (∼40% under laboratory conditions) is chemisorbed (strongly bound) with enthalpy of adsorption of −65.8 ± 2.6 kJ/mol of H 2O relative to vapor (or −21.8 ± 2.6 kJ/mol relative to liquid water). The standard enthalpy of formation from elements for a hypothetical lepidocrocite with nominal composition FeOOH and zero surface area is −552.0 ± 1.6 kJ/mol. Our results demonstrate that when considering the thermodynamic properties of iron oxides in the environment, a conclusive statement about their stability cannot be made without specifying the particle size of individual phases.

Densities, surface tensions, and derived surface thermodynamics properties of (trimethylbenzene + propyl acetate, or butyl acetate) from T = 298.15 K to 313.15 K

Densities ( ρ) for binary systems of (1,2,4-trimethylbenzene, or 1,3,5-trimethylbenzene + propyl acetate, or butyl acetate) were determined at four temperatures (298.15, 303.15, 308.15, and 313.15) K over the full mole fraction range. The excess molar volumes ( V E) calculated from the density data show that the deviations from ideal behaviour in the systems (all being positive, excepting 1,2,4-trimethylbenzene + butyl acetate system) become more positive with the temperature increasing. Surface tensions ( σ) of these binary systems were measured at the same temperatures (298.15, 303.15, 308.15, and 313.15) K by the pendant drop method, the surface tension deviations ( δσ) for all system are negative, and decrease with the temperature increasing. The V E and δσ are fitted to the Redlich–Kister polynomial equation. Surface tensions were also used to estimate surface entropy ( S σ ) and surface enthalpy ( H σ ).

Surface Tension of Liquid Fluorocompounds

This work aims at studying the surface tension of some linear, cyclic, aromatic, and α-substituted perfluorocarbons. Despite its fundamental interest, information about this property for these compounds is scarce, and the available data are old and present strong discrepancies among each other. The measurements were carried out in the temperature range (283 to 327) K with the Du Nouy ring method. The analysis of the experimental data shows that the molecular structure is an important factor in the surface behavior of the studied compounds since the aromatic fluorocompounds present the highest surface tensions, followed by the cyclic and substituted fluorocompounds. The linear n-perfluoroalkanes exhibit the lowest surface tension values, slightly increasing with the carbon number. The surface thermodynamic functions such as surface entropy and enthalpy were derived from surface tension values and are also reported. The experimental data were compared against the Faizullin correlation, and it is shown that ...

Energetics of Bulk and Nano-Akaganeite, β-FeOOH: Enthalpy of Formation, Surface Enthalpy, and Enthalpy of Water Adsorption

Akaganeite, β-FeOOH, is a commonly occurring ferric mineral in the environment and is a sorbent, ion exchanger, and catalyst. It is often fine-grained (nanophase) and frequently contains excess water. Its enthalpy of formation was studied by solution calorimetry in aqueous HCl. The enthalpy of water adsorption was studied by a new calorimetric technique combining a Calvet microcalorimeter and an automated gas dosing system, used for surface adsorption measurements. Akaganeite samples with surface areas of 30−280 m2/g were used. Sample characterization was performed by X-ray powder diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, Brunauer−Emmett−Teller method, scanning electron microscopy, and transmission electron microscopy. Surface enthalpy and enthalpy of water adsorption are reported for the first time. By adsorbing water, akaganeite decreases its effective surface enthalpy from 0.44 J/m2 to 0.34 J/m2. The enthalpy of formation of akaganeite can vary by 10−12 kJ/mol as a function of the surface area. The standard enthalpy of formation of akaganeite with zero surface area was refined and is −554.7 ± 1.9 kJ/mol. Thus, the standard enthalpy of formation and surface enthalpy of akaganeite are between those of goethite and lepidocrocite. The more metastable the polymorph, the lower its surface energy.

Surface Tension of the 4-Methyl-2-Pentanone/Ethyl Benzoate Binary System in the Temperature Range from 278.15 to 308.15K

Surface tensions (σ) and densities (ρ) of 4-methyl-2-pentanone/ethyl benzoate binary mixtures have been measured over the entire composition range at 278.15, 288.15, 298.15, and 308.15 K. Values of the excess surface tensions (σE) and excess molar volumes (VE) have been calculated. The σE and VE values were fitted by to the Redlich–Kister polynomial equation and the Ak coefficients have been derived. The standard deviations between the calculated and the experimental excess properties have also been derived. The surface tension values have been further used to calculate the surface entropies (SS) and surface enthalpies (HS) per unit surface area. The lyophobicity (β) and the surface mole fractions (x1S) of the surfactant 4-methyl-2-pentanone have been derived using the extended Langmuir model. The obtained results are discussed from the viewpoint of the existence of specific interactions between unlike molecules in the bulk region and the surface.

Thermodynamic investigation of N, N-dimethylformamide/toluene binary mixtures in the temperature range from 278.15 to 293.15 K

Densities ( ρ), surface tensions ( σ), and absolute viscosities ( η) of binary mixtures of N, N-dimethylformamide (DMF) with toluene have been measured over the entire composition range at the temperatures (278.15, 283.15, and 293.15) K. The excess molar volumes ( V E), the excess surface tensions ( σ E), the deviations in viscosity (Δ η), and the excess free energies of activation of the viscous flow (Δ G ∗E) have been calculated. The excess thermodynamic properties V E, σ E, Δ η, and Δ G ∗E were fitted to the Redlich–Kister polynomial equation, and the A k coefficients as well as the standard deviations between the calculated and experimental values have been derived. The surface tension values have been further used to calculate the surface entropy ( S S) and surface enthalpy ( H S) per unit surface area. The lyophobicity ( β) and the surface mole fraction ( x 2 S ) of the surfactant toluene have been also derived using the extended Langmuir model. The results obtained are discussed from the viewpoint of the existence of interactions between the components in the bulk and the surface.

Direct measurements of water adsorption enthalpy on hafnia and zirconia

A commercial surface area analyzer and Calvet-type microcalorimeter were combined for measurements of heats of gas–solid interactions, providing enhanced resolution, flexibility, and throughput compared to conventional methods. Integral adsorption enthalpies for half monolayer coverage on HfO2 and ZrO2 surfaces were found to be in the range −130–190 and −110–170kJ per mole of gaseous H2O for differently prepared monoclinic phases and −70 and −90kJ∕mole for tetragonal phases from precipitation. The surface enthalpy for anhydrous tetragonal ZrO2 was derived as 1.23±0.04J∕m2 from water adsorption and high-temperature solution calorimetry data.

Entrapment of Organic Solutes by the Water Cage in the Nanochannel of MCM-41

The effect of MCM-41 on the ESR spectrum of an aqueous spin probe solution was observed. The sharp ESR spectrum turns into a rather broad characteristic one leaving a sharper signal as the minor component, immediately after the addition of MCM-41 powder to the system. This observation indicates that MCM-41 traps the solute molecule into the nanochannel by letting the solvent water form a rather stable molecular cage, since the ESR line shape indicates that the nitroxide radical undergoes anisotropic rotation without being adsorbed on the wall. Thermodynamic parameters for this process are estimated from the temperature dependencies of the trapping efficiency. This process is explained in terms of the surface enthalpy of the liquid specifically intensified in the nanospace.

Viscoelasticity and Metastability Limit in Supercooled Liquids

A supercooled liquid is said to have a kinetic spinodal if a temperature Tsp exists below which the liquid relaxation time exceeds the crystal nucleation time. We revisit classical nucleation theory taking into account the viscoelastic response of the liquid to the formation of crystal nuclei and find that the kinetic spinodal is strongly influenced by elastic effects. We introduce a dimensionless parameter lambda, which is essentially the ratio between the infinite frequency shear modulus and the enthalpy of fusion of the crystal. In systems where lambda is larger than a critical value lambda(c) the metastability limit is totally suppressed, independently of the surface tension. On the other hand, if lambda<lambda(c) a kinetic spinodal is present, and the time needed to experimentally observe it scales as exp([omega/(lambda(c)-lambda)2], where omega is roughly the ratio between surface tension and enthalpy of fusion.

Surface tension and related thermodynamic parameters of alcohols using the Traube stalagmometer

An apparatus was devised using the Traube Stalagmometer for the determination of the surface tension of the alcohols methanol, ethanol, propan-1-ol and butan-1-ol. Measurements were made under atmospheric pressure at temperatures between 288.15 K and 313.15 K. The surface tension values were correlated with temperature and surface thermodynamic parameters, namely surface entropy and surface enthalpy, were also calculated. The results obtained are in agreement with the literature and they are promising for the use of this low cost arrangement for accurate measurement of surface tension. Surface tension values were obtained with a maximum error of 0.5 mN m−1 and a maximum standard deviation of 0.8 mN m−1. We recommend this arrangement for students in advanced university courses and it can also be used for research work.

Genesis and maintenance of &amp;quot;Mediterranean hurricanes&amp;quot;

Abstract. Cyclonic storms that closely resemble tropical cyclones in satellite images occasionally form over the Mediterranean Sea. Synoptic and mesoscale analyses of such storms show small, warm-core structure and surface winds sometimes exceeding 25ms-1 over small areas. These analyses, together with numerical simulations, reveal that in their mature stages, such storms intensify and are maintained by a feedback between surface enthalpy fluxes and wind, and as such are isomorphic with tropical cyclones. In this paper, I demonstrate that a cold, upper low over the Mediterranean can produce strong cyclogenesis in an axisymmetric model, thereby showing that baroclinic instability is not necessary during the mature stages of Mediterranean hurricanes.

Surface Tension of Dilute Solutions of Linear Alcohols in Benzyl Alcohol

The surface tensions of binary mixtures of 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, and 2-pentanol in benzyl alcohol were measured over the temperature range of (20 to 50) °C using a platinum ring method. The surface entropies and surface enthalpies of the mixtures were obtained. The surface tension of the binary mixtures decreases with increasing linear alcohol content. The surface tension of the mixtures was fitted by a polynomial equation, and fitting parameters are presented.

Surface Tensions of Dilute Solutions of Cycloheptanol in Ethylene Glycol

Surface properties (surface entropy, surface enthalpy, and surface composition) of dilute solutions of cycloheptanol in ethylene glycol were obtained by using of surface tension measurements at various temperatures. Surface excess values and surface mole fractions were obtained from the Gibbs equation and the extended Langmuir model, respectively. The results show that cycloheptanol is surface-active in ethylene glycol. The lyophobicity of cycloheptanol decreases with increasing temperature.

Surface enthalpy of goethite

AbstractHigh-temperature oxide-melt solution calorimetry and acid-solution calorimetry were used to determine the heat of dissolution of synthetic goethite with particle sizes in the range 2–75 nm and measured surface areas of 30–273 m2/g (27–240 × 103 m2/mol). Sample characterization was performed using X-ray diffraction, Fourier transform infrared spectroscopy, the Brunauer, Emmett and Teller method and thermogravimetric analysis. Water content (structural plus excess water) was determined from weight loss after firing at 1100°C. Calorimetric data were corrected for excess water assuming this loosely adsorbed water has the same energetics as bulk liquid water. The enthalpy of formation was calculated from calorimetric data using enthalpies of formation of hematite and liquid water as reference phases for high-temperature oxide-melt calorimetry and using enthalpy of formation of lepidocrocite for acid-solution calorimetry. The enthalpy of formation of goethite can vary by 15–20 kJ/mol as a function of surface area. The plot of calorimetric data vs. surface area gives a surface enthalpy of 0.60±0.10 J/m2 and enthalpy of formation of goethite (with nominal composition FeOOH and surface area = 0) of −561.5±1.5 kJ/mol. This surface enthalpy of goethite, which is lower than values reported previously, clarifies previous inconsistencies between goethite-hematite equilibrium thermodynamics and observations in natural systems.

Surface thermodynamic functions of dilute solutions of methylcyclohexanols in ethylene glycol

Surface thermodynamic functions (surface entropy, surface enthalpy, and surface composition) of dilute solutions of 2-, 3-, and 4-methylcyclohexanol in ethylene glycol were obtained using surface tension measurements at various temperatures. Surface excess values and surface mole fractions were obtained from Gibbs equation and extended Langmuir model respectively. The results show that all methylcyclohexanols are surface active in ethylene glycol. The lyophobicity of solutes decreases with increasing temperature. The presence of a maximum point in the surface entropy diagram in all systems is explained by the formation of clathrate-like solvates at the surface of these systems.

Equilibrium Surface Tensions of Benzyl Alcohol + Ethylene Glycol Mixtures

The paper presents the properties of mixtures of benzyl alcohol and ethylene glycol at the liquid/air interface. The properties were studied by surface tension measurements carried out at as a function of the mole fraction of benzyl alcohol at temperatures between (20 and 50) °C. It was shown that at constant temperature by the addition of benzyl alcohol the surface tension decreases and at constant composition by the increasing of temperature the surface tension decreases linearly. The surface entropies and enthalpies were calculated from experimental data. The surface composition of the mixture at a low concentration of benzyl alcohol was obtained from the extended Langmuir model. Values of the excess surface tension for mixtures were calculated and show a negative deviation from ideality.

Energy Crossovers in Nanocrystalline Zirconia

The synthesis of nanocrystalline powders of zirconia often produces the tetragonal phase, which for coarse‐grained powders is stable only at high temperatures and transforms into the monoclinic form on cooling. This stability reversal has been suggested to be due to differences in the surface energies of the monoclinic and tetragonal polymorphs. In the present study, we have used high‐temperature oxide melt solution calorimetry to test this hypothesis directly. We measured the excess enthalpies of nanocrystalline tetragonal, monoclinic, and amorphous zirconia. Monoclinic ZrO2 was found to have the largest surface enthalpy and amorphous zirconia the smallest. Stability crossovers with increasing surface area between monoclinic, tetragonal, and amorphous zirconia were confirmed. The surface enthalpy of amorphous zirconia was estimated to be 0.5 J/m2. The linear fit of excess enthalpies for nanocrystalline zirconia, as a function of area from nitrogen adsorption (BET) gave apparent surface enthalpies of 6.4 and 2.1 J/m2, for the monoclinic and tetragonal polymorphs, respectively. Due to aggregation, the surface areas calculated from crystallite size are larger than those measured by BET. The fit of enthalpy versus calculated total interface/surface area gave surface enthalpies of 4.2 J/m2 for the monoclinic form and 0.9 J/m2 for the tetragonal polymorph. From solution calorimetry, the enthalpy of the monoclinic to tetragonal phase transition for ZrO2 was estimated to be 10±1 kJ/mol and amorphization enthalpy to be 34±2 kJ/mol.

기능성 어육단백질의 젤화 특성과 산업적 응용-1. 가열변성 중 화학결합에 미치는 pH의 영향

The effect of pH on surface hydrophobicity, sulfhydryl group, infrared spectrum, SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) pattern and enthalpy was investigated in recovered protein from mackerel and frozen blackspotted croaker by alkaline processing. Hydrophobic residue in myofibrillar protein exposed to the surface of protein, and hydrophobic interaction were the highest around 6. The surface hydrophobicity was different between myofibrillar protein and myofibrillar protein including sarcoplasmic protein (recovered protein). The peak at 1636 c was increased with pH, and the recovered protein was unfolded in alkali pH. Difference of surface and total sulfhydryl group at pH 7.0 and 10 was comparative high, and decrease of surface sulfhydryl group indicated formation of S-S bonds. Mackerel and frozen blackspotted croaker in alkaline pH showed bands of polymerized myosin heavy chain on SDS-PAGE pattern. The transition temperatures of recovered protein were 33.1, 44.3 and 65.5. Gelation of recovered protein from alkali processing was estimated by increase of -sheet structure by pH treatment, S-S bonds by oxidation of surface sulfhydryl group in heating, polymerization of myosin heavy chain in order.r.