Specific Volume Changes Research Articles

Investigation of the pore texture of SnO2-CeO2 composite oxides

Gas adsorption techniques have been used to study the pore texture changes occurring in composite SnO2-CeO2 materials of varying Sn:Ce atom ratios on calcination at temperatures up to 1273 K. The data show that the uncalcined materials are largely microporous in nature, but changes in specific surface area, pore sizes and pore volume occur at an early stage in the calcination process with the formation of mesopores. However, significant changes occur at calcination temperatures >673 K at which point the mesopores are substantially reduced, and at 873 K and above the mean pore size increases greatly finally giving non-porous solids after calcination at 1273 K.

Tastes, structure and solution properties of D-glucono-1,5-lactone.

D-glucono-1,5-lactone differs from D-glucopyranose only in that it has a C = O group instead of CHOH group at carbon atom number one. The molecule therefore possesses an intact 3,4 alpha-glycol group and is sweet. However, it autohydrolyses in water solution at room temperature, forming D-gluconic acid and D-glucono-1,4-lactone. As the solution pH falls it becomes sweet-sour and eventually almost completely sour as the generated hydronium ions dominate both the solution properties and the taste perceptions elicited. It is shown that the ratio of generated hydronium ions to unchanged lactone accords with anticipated taste quality during the first 28 min of autohydrolysis. Changes in both apparent specific volume and apparent isentropic compressibility illustrate increasing solute-solvent interaction and increasing disturbance of water structure during the course of autohydrolysis. These changes are consistent with the concurrent sweet to sour change, but do not explain the weak bitterness which also accompanies them.

New phases induced by sucrose in saturated phosphatidylethanolamines: an expanded lamellar gel phase and a cubic phase

A new lamellar gel phase (L β) with expanded lamellar period was found at low temperatures in dihexadecylphosphatidylethanolamine (DHPE) and dipalmitoylphosphatidylethanolamine (DPPE) dispersions in concentrated sucrose solutions (1–2.4 M). It forms via a cooperative, relatively broad transition upon cooling of the L β gel phase of these lipids. According to the X-ray data, the transformation between L β and L β is reversible, with a temperature hysteresis of 6–10°C and a transition width of about 10°C. No specific volume changes and a very small heat absorption of about 0.05 kcal/mol accompany this transition. The L β−L β transition temperature strongly depends on the disaccharide concentration. From a value of about 10°C below the melting transition of DHPE, it drops by 25°C with decrease of sucrose concentration from 2.4 M to 1 M. The low-temperature gel phase L β has a repeat spacing by 8–10 Å larger than that of the L β gel phase and a single symmetric 4.2 Å wide-angle peak. It has been observed in 1. 1.25, 1.5 and 2.4 M solutions of sucrose, but not in 0.5 M of sucrose. The data clearly indicate that the expanded lamellar period of the L β phase results from a cooperative, reversible with the temperature, increase of the interlamellar space of the L β gel phase. Other sugars (trehalose, maltose, fructose, glucose) induce similar expanded low-temperature gel phases in DHPE and DPPE. The L β phase is osmotically insensitive. Its lamellar period does not depend on the sucrose concentration, while the lattice spacings of the L α, L β and H H phases decrease linearly with increase of sucrose concentration. Another notable sugar effect is the induction of a cubic phase in these lipids. It forms during the reverse H H−L α phase transition and coexists with the L α phase in the whole temperature range between the H H and L β phases. The cubic phase has only been observed at sucrose concentrations of 1 M and above. In accordance with previous data, sucrose suppresses the L α phase in both lipids and brings about a direct L β−H H phase transition in DHPE. A rapid, reversible gel-subgel transformation takes place at about 17°C in both DPPE and DHPE. Its properties do not depend on the sucrose concentration. The observed new effects of disaccharides on the properties of lipid dispersions might be relevant to their action as natural protectants.

The Volume and Compressibility Changes Associated with Protein Denaturation

Abstract The changes in the apparent specific volume and apparent specific adiabatic compressibility associated with thermal and chemical denaturations were studied for hen egg white lysozyme solution. No transition was found in the temperature dependence of the apparent quantities, whereas the addition of a certain amount of guanidine hydrochloride seems to decrease slightly the volume and compressibility.

The Very Long-Term Volume Recovery of Polycarbonate: Is Self-Retardation Finite?

The specific volume change of Bisphenol A polycarbonate was measured at room temperature for several years. The effects of formation conditions like cooling rate and pressure, the addition of low molecular additives, and injection molding and quenching were investigated. The volume shrinkage at long times was found to be much higher than extrapolated from short term measurements. A general pattern is observed in the volume recovery curves. They start with a small constant slope on the logarithmic time scale. After about 107 s a transition is observed to a much steeper slope. Whereas in the first section the characteristic increase in τeff is observed, the volume recovery during the transition can be fitted quite well with a single exponential. The sharp transition suggests that there is a long retardation time, which may represent the genuine α-relaxation. It also means that the self-retardation during physical aging is finite. The slope at long times (>107 s) scales with the distance from equilibrium, as extrapolated from measurements close to Tg. The cooling rate during vitrification affects the slope in the first zone only, while the formation pressure leads to a vertical shift of the curves. Addition of low molecular weight additives leads to a dramatic densification and accelerates the volume recovery.

Swelling of hydrophilic polymers. IV

AbstractThe swelling of five types of spherical crosslinked dextrans (Sephadex) that are either nonionic (G) or ionic [carboxymethyl (CM), sulphopropyl (SP), diethylaminoethyl (DEAE), and diethyl‐(2‐hydroxypropyl)aminoethyl (QAE)] in the same skeleton has been studied in water at different dissolved oxygen concentrations by microscopic observation and by dilatometry. The maximum specific volume, Vmax/V0 obtained by microscopic observation increased with the lowered dissolved oxygen concentration for each Sephadex. The change of the maximum specific volume was closely related to the changes of the dissolved oxygen concentrations. The maximum changes of the total volume took the larger negative values at the lower dissolved oxygen concentration. The effect of the difference in the dissolved oxygen on the change of the total volume with swelling was closely related to the viscosity B coefficient of the Jones‐Dole equation. From these results, we conclude that the structure of water on the inside of the gel differs from that on the outside of the gel. © 1995 John Wiley & Sons, Inc.

Thermal properties of A1203 in the melting region

The density and thermal expansion of alumina (99.99%) were studied in the liquid and solid states in the region of crystallization and melting by irradiating the samples with a narrow beam of gamma quanta. The temperature dependence of the density of strongly supercooled (by 220 K) alumina and the specific volume change on crystallization were determined. The results are compared with the data available in the literature.

Selective Adsorption of Lithium Ions from Molten Salt by Activated Alumina

Selective adsorption of lithium ions from molten NaNO3 containing a slight amount of lithium ions was examined using various inorganic adsorbents. Consequently, activated alumina was found to be the most promising adsorbent for adsorption of lithium ions because of its high recovery. Adsorption by activated alumina involved chemisorption with the activation energy of 70.7kJ/mol. It was confirmed that activated alumina showed high stability when mixed with molten salt because no changes of specific pore volume, surface area, or pore size distribution were observed throughout adsorption at high temperatures. Since the adsorption of lithium ions by activated alumina obeyed Freundlich's equation, it was found that the adsorption can be treated as that of lithium ions in dilute solution. The enrichment of lithium ions on activated alumina was much higher than that of sodium ions, indicating that the selective adsorption of lithium ions from molten salt by activated alumina is feasible.

Nucleation of ultrafine particles during reversible solid-solid phase transformation in oxides

We have studied the nucleation and growth processes that occur during the irreversible structural transformation of metastable oxide phases to their thermodynamically stable polymorphs. The transformations examined were: (i) cubic pyrochlore Pb2Ti2O6 (metastable) to tetragonal perovskite PbTiO3; (ii) hexagonal BaFe2O4 (metastable) to orthorhombic BaFe2O4; and (iii) orthorhombic stibiotantalite BiNbO4 (metastable) to triclinic BiNbO4. In each case the irreversible transformation was accompanied by a marked reduction in the particle size, which can be correlated to the change in the specific volume at the transition. Solids which undergo a relatively large change in specific volume during structural transformation can therefore be obtained in fine-particle form by controlled heating of their metastable polymorphs just above the transformation temperature.

The origin of the β transition and its influence on physical ageing

Volume dilatometry was used to explore the origin of the β transition ( T β ) and its influence on physical ageing. The results show that volume recovery does occur even at temperatures below T β , a phenomenon indicating the existence of molecular rearrangements and cooperative motions below this point. Lowering the ageing temperatures through T β progressively retards short-term molecular rearrangements and cooperative motions. Nonetheless, the T β quench does not incur any excess free-volume trapping, and its associated change in specific volume follows a linear relationship with respect to temperature. The existence of T β is time-dependent, which leads to the conclusion that the formation of T β has a kinetic origin.

Uniaxial compaction effects on soil physical properties in relation to soil type and cultivation

Disturbed soil samples, representing different textures and organic matter contents, were compressed uniaxially by a range of stresses and at varying water contents. Air permeability was measured immediately after compaction and tensile strength was measured after oven drying. The samples were taken from two soil types which had been subjected to three tillage treatments in a long-term field experiment and from the site of an experiment which compared the compaction caused by different tractor wheels. Within the range of practical interest, specific volume (i.e. the ratio of total volume to volume of solids) decreased with the log of applied stress and tensile strength increased linearly with applied stress. Specific volume also decreased with increasing water content at the time of compaction, whereas both tensile strength and air permeability increased. Soils with higher organic matter contents tended to have higher specific volumes and lower tensile strengths at a given water content and stress. The influence of water content on these properties upon compaction was less in soils of greater organic matter content. Similarly, the rate of increase of tensile strength with applied stress was less in soils of greater organic matter content. However, organic matter did not influence the relative change of specific volume with stress. In the tillage experiment, a stress applied in the laboratory of 100 kPa produced a specific volume similar to the average for ploughed soil in the field but 800 kPa was required to produce a specific volume similar to that obtained by direct drilling. A comparison with compaction values produced by vehicles in the field showed that a higher stress, by a factor of between 3 and 24, was required to reach the same specific volume in the laboratory as in the field. The tensile strength results indicated the susceptibility of the soils to clod formation and their ease of cultivation. Air permeability measurements gave some insight into the possible mechanics of compaction.

Process-Induced Stress and Deformation in Thick-Section Thermoset Composite Laminates

A study of process-induced stress and deformation in thick-section thermosetting composite laminates is presented. A methodology is proposed for predict ing the evolution of residual stress development during the curing process. A one- dimensional cure simulation analysis is coupled to an incremental laminated plate theory model to study the relationships between complex gradients in temperature and degree of cure, and process-induced residual stress and deformation. Material models are proposed to describe the mechanical properties, thermal and chemical strains of the thermoset resin during cure. These material models are incorporated into a micromechanics model to pre dict the effective mechanical properties and process-induced strains of the composite dur ing cure. Thermal expansion and cure shrinkage contribute to changes in material specific volume and represent important sources of internal loading included in the analysis. Tem perature and degree of cure gradients that develop during the curing process represent fun damental mechanisms that contribute to stress development not considered in traditional residual stress analyses of laminated composites. Model predictions of cure dependent epoxy modulus and curvature in unsymmetric graphite/epoxy laminates are correlated with experimental data. The effects of processing history (autoclave temperature cure cy cle), laminate thickness, resin cure shrinkage and laminate stacking sequence on the evo lution of process-induced stress and deformation in thick-section glass/polyester and graphite/epoxy laminates during cure are studied. The magnitude of process-induced residual stress is sufficient to mitiate transverse cracks and delammations. The results clearly indicate that the mechanics and performance of thick-section thermoset laminates are strongly dependent on processing history.

The density of liquid sulfur near the polymerization temperature

We have measured the density of liquid sulfur as a function of temperature near the polymerization temperature. We measure between 424 and 445 K, with a precision in density of 2×10−5 and an accuracy of 5×10−4. We see upward shifts of the density within 3 K of the polymerization temperature of about 8×10−4 with each cycle in temperature; these shifts could be due to the reaction of the sulfur with the quartz cell, or to the persistence of metastable polymeric forms of sulfur. Thus we consider the data from the first heating run to be the best, since the sample was then the purest. Our results differ from those in the literature in that, while we see a change in slope at the transition, we do not see a sharp minimum or a singularity. We compare our data to two models of the sulfur polymerization as a second order phase transition: the mean field model [A. V. Tobolsky and A. Eisenberg, J. Am. Chem. Soc. 81, 780 (1959)] and the n→0 magnet model [S. J. Kennedy and J. C. Wheeler, J. Chem. Phys. 78, 1523 (1983)]. Both models assume that the sulfur forms linear polymers which are in an ideal solution in monomeric sulfur, and that the thermal expansions of monomeric and polymeric sulfur are linear within the temperature range under consideration. For the most physically reasonable choice of thermodynamic parameters for the models, the mean field model describes the data better than does the n→0 model. The n→0 model is superior if the change of specific volume on polymerization is adjusted. One possible explanation is that sulfur belongs in the n=1 universality class, not in the n→0 class.

Flow Cytometric Analysis of Rhodamine 123 Fluorescence during Modulation of the Membrane Potential in Plant Mitochondria

The fluorescent dye rhodamine 123, which selectively accumulates in mitochondria based on the membrane potential, was used with flow cytometry to evaluate variations in activity of mitochondria isolated from plant tissues. In the presence of succinate and ATP, potato (Solanum tuberosum L.) tuber mitochondrial activity was affected by metabolic inhibitors and compounds that modify the membrane potential. The more uniform the mitochondrial population, the higher the observed membrane potential. The reactive population corresponds to the proportion of intact mitochondria (94-97%) defined by classic methods. Changes in the light-scattering properties are more related to internal modifications affecting the inner membrane-matrix system of the mitochondria during metabolic modulation than to specific volume change or outer membrane surface modifications. We tested our approach using an Arum maculatum preparation that contains three different types of mitochondria and demonstrated the validity of the light-scatter measurements to distinguish the alpha, beta, and [ill] mitochondria and to measure their ability to built up a membrane potential in the presence of succinate. These results demonstrate clearly that flow cytometric techniques using rhodamine 123 can be employed to study the activity in isolated plant mitochondria.

Hypoxaemia after nebulised salbutamol in wheezy infants: the importance of aerosol acidity.

The effect of nebulised iso-osmolar, preservative free, but acidic salbutamol solution was studied in 34 acutely wheezing infants aged 1-17 months. Transcutaneous oxygen pressure (TcPO2) and oxygen saturation (SO2) fell significantly during the first five minutes after nebulisation with further deterioration at 15-20 minutes. Ten of these infants were followed up for another two hours and showed slight improvement. Even after the second hour TcPO2 had not reached baseline values. Three months later the response to salbutamol and a placebo of equal acidity (pH 3.9) was studied in 11 infants from the same group, now free of symptoms. Lung function tests were included and showed no significant changes in specific conductance and volume corrected maximum expiratory flows (Vmax at functional residual capacity/thoracic gas volume). However, hypoxaemia occurred after the acidic placebo with a significant drop of TcPO2 (mean 0.9 kPa); SO2 decreased similarly but this did not reach significance. After salbutamol there was a further significant deterioration of mean TcPO2 (1.4 kPa) and of SO2. These results show that beside a possible pharmacological effect of salbutamol the acidity of the aerosol also induces hypoxaemia in infants.

On phase separation in high- and low-density polyethylene blends: 2. A working model

Some experimental evidence has recently been reported supporting the view of a phase-segregated melt in high-density/low-density polyethylene blends. Dispersive interaction between components makes it reasonable for segregation to occur. A simple model is proposed that allows one qualitatively to understand compatability as a function of the degree of branching. A critical branch content, ϵ c, below which compatibility is assured for all compositions, is predicted. The model is based on thermodynamic mixing concepts of lattice theory, assuming an increasing presence of holes with branching, according to specific-volume changes derived from X-ray data.

Phase Transitions of Urea Adducts with n-Paraffins under High Pressure

Abstract The temperatures of the phase transition between orthorhombic and hexagonal structures of the urea adducts with n-paraffins, n-CnH2n+2 (n = 14–44), have been measured by differential thermal analysis for the pressure range up to 250MPa. The transition temperatures increase both with pressure and with the number of carbon atoms of the guest paraffins. The increasing rate of the transition temperatures with pressure is about half of that of pure paraffin crystals. The pressure dependences of the lattice constants have also been measured by X-ray diffraction. The specific volume changes discontinuously at the transition pressure; the result suggests that the phase transition of the urea adducts with n-paraffins is a first-order one. Furthermore, the specific volume change at the transition pressure decreases with the number of carbon atoms of the guest paraffins; 3.4 × 10-6 m3/Kg for n = 16 and 2.1 × 10-6 m3/Kg for n = 44.

Dielectric properties of urea and acetamide in aqueous solution

The dielectric dispersion of urea and acetamide in aqueous solution can be reproduced fairly well by either two Debye relaxations or one Cole–Cole relaxation, with very little room for deciding in favour of one alternative or the other. There appears to be a small additional high-frequency relaxation in urea, revealed only in the measurements at 70 GHz. The amplitudes of the two Debye dispersions are compatible with a two-component water/solute model without ‘irrotational’ water or solute hydration. In keeping with this, the static relative permittivities of urea, acetamide and other amides (based on data from other sources) are analysed in terms of partial quantities whose values indicate changes in the electrical contributions of water and solute. In addition, a simple group-additivity model splitting the solute into apolar ‘holes’ and polar radicals provides a degree of rationalization in the static dielectric behaviour of various substituted amides. It is seen that concentrated urea, simple amides and N,N-dialkyl amides are all characterized by the very high permittivity of water, proportionately much larger than the accompanying changes of partial specific volume, enthalpy and entropy. It is suggested that the pronounced electrostatic modification of water may play a role in some of the disruptive effects of amides on proteins and viruses.

Structure and phase behavior of hydrated mixtures of L-dipalmitoylphosphatidylcholine and palmitic acid. Correlations between structural rearrangements, specific volume changes and endothermic events

Several new features of the phase diagram of L-dipalmitoylphosphatidylcholine (DPPC)/palmitic acid mixtures in excess water were established by means of static and time-resolved X-ray diffraction, densitometry and differential scanning calorimetry (DSC). At low temperatures, palmitic acid has a biphasic effect on the lamellar subgel phases: at concentrations below 5–6 mol%, it prevents formation of the DPPC subgel phase (L c ), while at higher contents (between about 40 and 90 mol%) another subgel phase (L c com) is formed as a result of lipid co-crystallization at 1 DPPC : 2 palmitic acid stoichiometry. A crystalline palmitic acid phase separates from L c com above 70–80 mol% of fatty acid. The L c com phase transforms into a lamellar gel phase (L β) in an endothermic transition centered at 38°C. At high temperatures, the mixtures form hexagonal liquid-crystalline phase (H II) in the region of 60–70 mol% and an isotropic phase (I) at 90–100 mol% of palmitic acid. No coexistence of H II phase with the fluid lamellar phase of DPPC was observed at intermediate compositions (20 and 50 mol% of palmitic acid) but rather formation of a complex phase with non-periodic geometry characterized by molten chains and a broad, continuous small-angle scattering band. No evidence for fluid phase coexistence was found also at compositions between H II and I phases. The L β-H II transition at 60–70 mol% of palmitic acids is readily reversible and two-state in both heating and cooling modes. It is characterized by the coexistence of initial and final phases with no detectable intermediates by time-resolved and static X-ray diffraction. The crystalline-isotropic transition in palmitic acid is two-state only in heating direction. On cooling, it is characterized by strong undercooling and gradually relaxing lamellar crystalline structures. The slowly reversible L c com-L β transition proceeds continuously through intermediate states. Although clearly discernible by both DSC and X-ray diffraction, it is not accompanied by specific volume changes.

Probing the Mechanisms of Macromolecular Recognition: the Cytochrome b 5 -Cytochrome C Complex

The specificity of complex formation between cytochrome b5 (cyt b5) and cytochrome c (cyt c) is believed to involve the formation of salt linkages between specific carboxylic acid residues of cyt b5 with lysine residues on cyt c. Site-directed mutagenesis was used to alter the specified acidic residues of cyt b5 to the corresponding amide analogues, which resulted in a lower affinity for complex formation with cyt c. The dissociation of the complex under high pressure resulted in specific volume changes, the magnitude of which reflected the degree of solvation of the acidic residues in the proposed protein-protein interface.