Increase In Specific Volume Research Articles

Two energy scales in YbInCu4 from specific heat in high magnetic fields

Metallic YbInCu4 undergoes a first-order valence transition at 42K, where the specific volume increases by 0.5% upon cooling. It is believed that the valence transition is driven by band structure effects that help quench Yb localized moments via a Kondo mechanism. The known phase diagram indicates that the transition can be suppressed with external magnetic fields. We used an adiabatic calorimeter to measure the specific heat in the high-field phase of the material. Data obtained in magnetic fields up to 50T show an enhanced Sommerfeld coefficient and anomalies in the specific heat that are compatible with a much depressed Kondo temperature. Our data indicate quite different energy scales in the low-field and high-field phases of YbInCu4.

Effect of Retrograded Waxy Corn Starch on Bread Staling

Waxy corn starch pastes (10%) were stored at 5 °C for up to 35 days, and the powder specimens of retrograded starches thus obtained were added to wheat flour for bread baking at a level of 5%. The effect of retrograded starch on the staling of bread was determined. The loaf which contained retrograded waxy corn starch, which was prepared by storing the 10% paste at 5 °C for 7 days, showed an increase in specific volume and the results of the sensory evaluation showed that it was very acceptable. During the storage of bread, the increase in firmness and decrease in degree of gelatinization were suppressed by adding retrograded waxy corn starch. The moisture content of bread crumbs did not relate to firmness. Added retrograded waxy corn starch decreased the final viscosity of flour. The crystalline region of retrograded waxy corn starch used for bread baking included longer chains from amylopectin which in raw starch occurred in the amorphous region.

Waterlike anomalies for core-softened models of fluids: two-dimensional systems.

We use molecular-dynamics simulations in two dimensions to investigate the possibility that a core-softened potential can reproduce static and dynamic anomalies found experimentally in liquid water: (i) the increase in specific volume upon cooling, (ii) the increase in isothermal compressibility upon cooling, and (iii) the increase in the diffusion coefficient with pressure. We relate these anomalies to the shape of the potential. We obtain the phase diagram of the system and identify two solid phases: a square crystal (high-density phase) and a triangular crystal (low-density phase). We also discuss the relation between the anomalies observed and the polymorphism of the solid. Finally, we compare the phase diagram of our model system with experimental data, noting especially the line of temperatures of maximum density, the line of pressures of maximum diffusion constant, and the line of temperatures of minimum isothermal compressibility.

Solvent sorption effects on the structure and properties of PP/Rodrun blends

Toluene, carbon tetrachloride, and tetrahydrofuran sorption and desorption by polypropylene (PP) and PP/thermotropic liquid crystal polymer (Rodrun) blends with 20 and 40% Rodrun contents were studied as well as the effects of the solvent presence on the structure and mechanical properties. The rate of sorption and desorption and the solvent content at the equilibrium were higher in the blends than in pure PP. This was attributed to microcracking in the PP matrix induced by the presence of Rodrun. Taking into account the very low permeability of Rodrun to the solvents of this work, and the increase in specific volume of the blends as a result of sorption, sorption-induced additional microcracking, partially in the form of debonding of the dispersed Rodrun phase, is also believed to occur. Plasticization was the main effect on mechanical properties. The partially irreversible effect of sorption on the mechanical properties agrees with the proposed partial debonding and weak solvent resistance of these blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1090–1100, 2000

Plastic behavior of monoclinic polypropylene under hydrostatic pressure in compressive testing

The plastic deformation of monoclinic isotactic polypropylene is studied in compressive testing with particular attention to the effect of hydrostatic pressure up to 300 MPa, in the temperature range 20–60°C. The coefficients of the Coulomb criterion are fairly consistent with those assessed from the comparison of the tensile and compressive yield stresses at atmospheric pressure, in the same temperature range. The high friction coefficient of polypropylene is ascribed to a strain-induced order-to-disorder transition from the monoclinic to the smectic form accompanied by an increase of specific volume. This local and transient phase change is assumed to result from the mobile conformational chain defects that govern the elementary mechanism of plasticity in the crystalline phase of polypropylene consisting of 3/1 helix chains. A comparative discussion is made with polyethylene that displays a much lower friction coefficient. The dislocation-based approach that is proposed in relation to the viscoelastic relaxation processes provides a new insight into the molecular grounds of the elementary mechanism of plasticity of polypropylene. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1241–1247, 1999

Plastic behavior of monoclinic polypropylene under hydrostatic pressure in compressive testing

The plastic deformation of monoclinic isotactic polypropylene is studied in compressive testing with particular attention to the effect of hydrostatic pressure up to 300 MPa, in the temperature range 20–60°C. The coefficients of the Coulomb criterion are fairly consistent with those assessed from the comparison of the tensile and compressive yield stresses at atmospheric pressure, in the same temperature range. The high friction coefficient of polypropylene is ascribed to a strain-induced order-to-disorder transition from the monoclinic to the smectic form accompanied by an increase of specific volume. This local and transient phase change is assumed to result from the mobile conformational chain defects that govern the elementary mechanism of plasticity in the crystalline phase of polypropylene consisting of 3/1 helix chains. A comparative discussion is made with polyethylene that displays a much lower friction coefficient. The dislocation-based approach that is proposed in relation to the viscoelastic relaxation processes provides a new insight into the molecular grounds of the elementary mechanism of plasticity of polypropylene. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1241–1247, 1999

Effect of freezing rate on the thermal, mechanical and physical aging properties of the glassy state in frozen sucrose solutions

The freezing of foods containing significant quantities of sugar and other carbohydrate-based systems involves the removal of water (plasticizer) as ice crystals leading to the complex formation of a metastable amorphous (unfrozen) phase. A study was undertaken using differential scanning calorimetry (DSC) and thermal mechanical analysis (TMA) to characterize the influence of freezing rate on the formation and stability of the glassy state in freeze-concentrated sucrose solutions. Two thermal transitions were evident upon warming these solutions, denoted T Tr1 and T Tr2 in this study. Rapidly frozen systems exhibited concentration-dependent thermal behaviour ( T Tr1on and T Tr2 values and level of devitrification) and reduced mechanical resistance to structural flow (TMA). The physical aging behaviour was freezing-rate-dependent (greater excess enthalpy for rapid freezing) and showed maximum excess enthalpy values in good agreement with T Tr1 DSC measurements under the various treatments. Annealing at −35°C for 60 min following slow freezing resulted in the greatest increase in T Tr1, up to −40°C (DSC), and an increase in specific volume below T Tr2 suggesting that the T′ g occurred in this temperature range. The freezing rate had a substantial influence on the resulting stability and formation of frozen systems which attest to the importance of kinetic variables in understanding food freezing.

Rejuvenation of epoxy glasses subjected to uniaxial compression

Two epoxy networks, differing significantly in their glass transition temperatures ( T gs), were subjected to uniaxial compression tests in the glassy state (20°C). One of the systems was based on the diglycidyl ether of bisphenol-A (DGEBA) cured with ethylenediamine (EDA). The other one was based on an epoxidized novolac (EPN) cured with 4,4′-diaminodiphenyl sulfone (DDS). Both systems were physically aged by specific thermal treatments. The endothermic enthalpy relaxation peak, characteristic of aged glasses, could be erased at temperatures well below T g by large mechanical deformations, i.e. close to the incipient strain hardening level in uniaxial compression tests. This phenomenon, which was accompanied by an increase in specific volume, constitutes a clear manifestation of rejuvenation produced by large mechanical stimuli. The validity of statements presenting an opposite point of view is also discussed.

Effects of crosslinking on physical properties of phenol–formaldehyde novolac cured epoxy resins

AbstractTo clarify the relationship between crosslinking density and physical properties of phenol–formaldehyde novolac cured epxy resin and factors governing their physical properties, we studied various properties of cured resins having different crosslinking densities. The resins were prepared with various curing accelerators and raw epoxy resins having different molecular weights. We found that as the crosslinking density of a cured resin increases, glass transition temperature (Tg) rises and the relaxation time becomes longer. Furthermore, in the rubbery region, the coefficient of linear thermal expansion drops and the elastic modulus become larger, while, in the glassy region, the coefficient of linear thermal expansion, specific volume, water absorption, diffusion coefficient, and permeability all increase but the elastic modulus becomes smaller. The WLF analysis on the relaxation behaviors of typical cured resin showed that cured resin with a higher crosslinking density decreases in the fractional free volume. This behavior is completely opposite from the relationship predicted from the temperature dependency of specific volume. While the coefficient of thermal expansion of free volume decreases as the crosslinking density increases for the cured resin, it coincides well with the tendency predicted from the difference in coefficient of cubic thermal expansion in the rubbery and glassy regions of each cured resin. That the free volume obtained from WLF analysis shows a relationship opposite to the predicted free volume as based on the temperature dependency of specific volume is explained as follows: Namely, the free volume obtained from the WLF analysis is a hole free volumeVhwhich contributes to fluidity andVhdecreases with the crosslinking density. On the other hand, the free volume predicted from the specific volume is a sum of the interstitial free volumeViandVh.Viincreases with the crosslinking density and thisViincrease exceeds the decrease ofVh. Therefore, the free volume predicted from the specific volume increases with the crosslinking density. Consequently, the influence of free volume on the relationship between the crosslinking density and physical properties of cured resin can be interpreted as follows. As the crosslinking density increases on cured resins,Tgrises, the relaxation time is lengthened, and the coefficient of linear thermal expansion becomes smaller in the rubbery region because, as the crosslinking density increases,Vhdecreases. Since crosslinking density increases on cured resins, the coefficient of linear thermal expansion, water absorption, diffusion coefficient, and permeability become larger, and the elastic modulus becomes smaller in the glassy region because, as the crosslinking density increases,Viincreases and, accordingly, molecular chain packing becomes looser; i.e., the specific volume increases. © 1993 John Wiley & Sons, Inc.

Interpretation of density and conductivity measurements in the liquid-crystal phases of the cesium pentadecafluorooctanoate-water system and its implication for the structure of the lamellar phase.

It has recently been argued [P. Photinos and A. Saupe, Phys. Rev. A 41, 954 (1990)], on the basis of density measurements (as measured by a vibrating densitometer) and the observation of long relaxation times in both these and electrical conductivity measurements, that the nematic-to-lamellar transition in the cesium pentadecafluorooctanoate(CsPFO)--water system involves a significant change in the aggregate structure, probably a transformation from discotic (disk-shaped) micelles to continuous lamellae. With a view to distingushing between these conclusions and previous ones, by the present authors [N. Boden et al., J. Phys. (Paris) 47, 2135 (1986)], which suggested the transition solely involves the onset of translational order without significant changes in micellar structure, we have made a comparison of the densities of a CsPFO${\mathrm{\ensuremath{-}}}^{2}$${\mathrm{H}}_{2}$O (w=0.406) sample as measured by both a vibrating densitometer and a classical dilatometer. The densitometer measurements exhibit discontinuities at both the isotropic-to-nematic and the nematic-to-lamellar transitions: at the isotropic-to-nematic transition, the specific volume increases by 7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ ${\mathrm{cm}}^{3}$ ${\mathrm{g}}^{\mathrm{\ensuremath{-}}1}$ of solution, a result at variance with a predicted decrease of 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}7}$ ${\mathrm{cm}}^{3}$ ${\mathrm{g}}^{\mathrm{\ensuremath{-}}1}$ as calculated from the previously reported pressure dependence of the isotropic-to-nematic transition temperature [M. R. Fisch, S. Kumar, and J. D. Litster, Phys. Rev. Lett. 57, 2830 (1986)]; a large increase in specific volume is also observed at the nematic-to-lamellar transition.No such changes are, however, detectable in the dilatometer experiments. This has led us to conclude that the excess specific volumes characterizing the nematic and lamellar phases in the densitometer experiments must be associated with some nonequilibrium state of the sample, induced by the vibration of the sample container. These effects are specific to the liquid-crystal phases, not to the isotropic solution phase, and must therefore arise because of the long-range structural organization of the former. It appears that the vibrating densitometer cannot be used to measure densities of amphiphilic liquid-crystal phases. Hysteresis and long relaxation times observed in electrical conductivity measurements in the lamellar phase are associated with partial focal conic textures; they do not arise from changes in aggregate structure.

Changes in free volume and mechanical properties of PVC films incurred by quenching and aging

Abstract Using a specially constructed microbalance for hydrostatic weighing, the specific volume increase due to rapid quenching (∼500°C/sec) and the subsequent densification from physical aging have been observed for PVC thin films. The more severe the quench through its glass transition temperature (Tg), the greater is the free-volume content. Isobaric volume recovery at higher temperatures has further been investigated by volume dilatometry. Within the experimental time scale, aging of relaxing molecular rearrangements for PVC films takes place as a linear function of logarithmic aging time at temperatures far below Tg. When aging temperatures approach Tg, however, the isothermal volume contraction becomes nonlinear. The observed volumetric results follow the wellknown phenomena of physical aging. The changes in molecular mobility during quenching and aging have further been explored by means of tensile creep and stress-strain to failure. All results reflect that a relatively small change in free volu...

A subtransition in a phospholipid with a net charge, dipalmitoylphosphatidylglycerol.

Suspensions of dipalmitoylphosphatidylglycerol (DPPG) have been analyzed by differential scanning calorimetry, equilibrium and differential scanning dilatometry, and X-ray diffraction techniques. After the DPPG suspensions are stored several days at 2 degrees C, a new phase transition is observed at a lower temperature than either the main transition or the pretransition. This subtransition has an enthalpy of about 6 kcal/mol and occurs at about 20 degrees C, the exact temperature depending on the buffer used. The lipid partial specific volume increases by 0.035 mL/g upon warming through the subtransition. X-ray diffraction patterns from suspensions in the subgel phase contain orders of a lamellar repeat and several additional sharp and broad wide-angle reflections between 8 and 2 A. As the water content in the specimen is reduced, the lamellar repeat period decreases, whereas the spacings and intensities of these additional wide-angle reflections are unchanged. These data indicate that on incubation at 2 degrees C the lipid molecules crystallize in the plane of each bilayer. X-ray experiments also show that this subgel phase converts to the normal L beta' gel phase above the subtransition.

16KhSN high-strength steel in various structural conditions and with various deformation conditions

1. Drawing and reducing of 16KhSN steel with degrees of 0–60% leads to an increase in yield strength σy from 300 to 680 MPA and in tensile strength σt from 500 to 860 MPa and a reduction in the reduction of area ψ from 72 to 57%, in the elongation δ from 30 to 9%, in the work for limiting deformation Af from 1020 to 940 MJ/m3, and in the strain-hardening factor from 0.177 to 0.080. 2. The influence of hardening heat treatment (harden from 930°C and temper at 350°C) on the mechanical properties of 16KhSN steel is similar to the influence of work hardening, but the strength properties of this steel after heat treatment increase to a greater degree than after deformation, σy to 1080 MPa, σt to 1280 MPa, and Af to 1660 MJ/m3. 3. As a result of cold plastic deformation of 16KhSN steel by drawing or reducing, the density decreases (by 0.41% with degrees of deformation of e=60%). The increase in specific volume is an indication of the "loosening" of the material in work hardening and is caused by the occurrence of submicro- and microscopic cracks and microdistortions. 4. The intense decrease in plasticity of the steel in the work-hardened condition with an increase in the index of the stressed state (i.e., in the volume of the path of tension) and the increase in the notch sensitivity πψ from 0.160 to 0.575 are related to the presence of discontinuities in the structure of the material.

Selecting the size of pipes carrying hot gas to defrost evaporators

The selection of correct pipe size for carrying hot gas to defrost evaporators is an important factor in conserving energy by such practices as maintaining low condensing pressures. The correct size will ensure that the resultant increase in specific volume of the hot gas that occurs at low pressures does not cause prohibitive pressure drops in the pipes. The way in which hot gas flow rates during defrost affects the pipe size selection is discussed together with the influence of saturation temperature.

Pressure-volume-temperature behavior of several synthetic rubbers

Abstract The pressure-volume-temperature (P-V-T) relations were studied for cis-1,4-polybutadiene, cis-l,4-polyisoprene, and poly(styrene-butadiene) in the pressure range of 1 to 8000 kg/cm2 at 10 to 50°C. The specific volume of cis-1,4-polybutadiene and cis-1,4-polyisoprene decreased with increasing pressure and abruptly decreased at a certain pressure (low-pressure break). Above this pressure, the specific volume decreased smoothly with increasing pressure and then decreased abruptly again (high-pressure break). The compressibilities below and above the low-pressure break were of the order of 10−5 (kg/cm2)−1 up to the high-pressure break. Above the high-pressure break, the compressibilities reduced to the order of 10−6 (kg/cm2)−1. The P-V isotherms for poly(styrenebutadiene) showed only the high pressure break. An abrupt increase in specific volume occurred in the isobaric measurements for cis-l,4-polyisoprene at a pressure and temperature corresponding to the high-pressure break in the isotherms. From the temperature shift of the low-pressure break and the behavior of radiation-induced crosslinking with pressure, the low-pressure break was concluded to be due to partial crystallization. The high-pressure break was concluded to be due to the transition from liquid to densified glass, judging from the fact that the high-pressure break existed in poly(styrenebutadiene) and the result of isobaric measurements in cis-1,4-polyisoprene.

The effects of the crystallinity and crystal size on the physical transitions of polypropylene

Abstract The results of experimental expansion tests carried out on polypropylene (PP) samples having different,crystallinities and the same crystal size, or vice versa, or both these parameters differing, were made in the temperature range from - 100 to +200°C. These showed the melting temperature to be independent of crystallinity and to be determined by the crystal size. The glass temperature depends on the crystallinity and the average linear dimension of the crystals. A change in the melting range and the increase in specific volume during melting are both functions of the original crystallinity of the sample.

Shock Compression of Foamed Graphite

Conventional high-explosive techniques have been used to determine the principal Hugoniots of two graphite foams for stresses up to about 190 kbar. The initial densities of the foams were 0.55 and 0.68 gm/cm3. Hugoniot data for each foam fall into two distinct domains, depending on the amplitude of the input shock wave. Continuous free-surface velocity measurements on the foam surfaces indicate that shock waves in the lower stress domains have two-wave structures. The inherent irregularity of the surfaces of the foams, however, prevented exact measurement of the properties of these two-wave structures. Results of further experiments which were designed to study loading and unloading from shocked states in the foam are consistent with the two-wave picture in the lower stress domains and also show that single shock waves exist in the higher stress domains. Data in the higher stress domains show an increase in specific volume with increasing stress. This ``bending back'' of the Hugoniot is attributed to increases in thermal energy which occur in the compression process. Estimates of Grüneisen's parameter have been made for the higher stress domains, where voidless states are believed to exist. The values obtained for Grüneisen's parameter as well as the general behavior of the Hugoniots suggest that the graphite-to-diamond phase transition occurs at the higher stresses.

Properties and Structure of Elastomers

Abstract The glass transition temperatures of high molecular weight poly (vinyl n-alkyl ethers) decrease with increasing length of the n-alkyl group. On lengthening the n-alkyl group, 14 per cent of the specific volume increase is free volume. Branching or substitution in the alkyl group of the polymer increases the Tg value. A comparison of poly (vinyl n-alkyl ethers) and polymers of normal α-olefins shows that an ether group and a methylene group in the side chain are equivalent in influencing the glass transition temperature. We have varied systematically the side chain alkyl group in poly (vinyl alkyl ethers) and evaluated at 3 different temperatures the influence of these variations on the dynamic properties of the vulcanizates of these polymers. The relative position of the curves, relating dynamic resilience to dynamic modulus of these polymers, is generally in the order of their glass transition temperatures. The dynamic mechanical property data on poly (vinyl n-pentyl ether) and poly (vinyl 2-ethylhexyl ether), which have the same glass transition temperature, fall on a common curve characteristic of the temperature of measurement. Apparently, the Tg is a major factor in correlating the dynamic mechanical behavior of these elastomers. The size and shape of the alkyl group appear to be reflected primarily in their effect on the Tg. Polysulfidic crosslinks are not essential for the attainment of high tensile strength in natural rubber vulcanizates cured with a sulfur-diphenylguanidine system. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted a curve of tensile strength as a function of 300 per cent modulus for the control samples.

Properties and structure of elastomers

AbstractA study of the effect of structure on the dilatometric glass transformation temperatures, Tg, of poly(vinyl alkyl ethers) of reasonably high molecular weight showed that the Tg values of poly(vinyl n‐alkyl ethers) decrease with increasing length of the n‐alkyl group from methyl to n‐octyl. On lengthening the n‐alkyl group, 14% of the specific volume increase is free volume. Branching of the alkyl group of the polymer increased the Tg value. A comparison of poly (vinyl n‐alkyl ethers) and polymers of normal a‐olefins showed that the ether group and methylene group in side chains are equivalent in influencing the glass transformation temperatures. The side chain alkyl group in poly(vinyl alkyl ethers) was varied systematically and the influence of these variations on the dynamic mechanical properties of their vulcanizates was evaluated at 31, 60, and 98°C, The relative position of the curves, relating the dynamic resilience to the dynamic modulus of these polymers, was approximately in the order of their glass transformation temperatures. Dynamic mechanical property data on poly(vinyl n‐pentyl ether) and poly(vinyl 2‐ethylhexyl ether), which have the same Tg values, fall on a common curve characteristic of the test temperature. Apparently, the Tg is a major factor in correlating the dynamic mechanical behavior of these elastomers. The size and shape of the alkyl group appear to be reflected primarily in their effect on the Tg. A direct approach was made for testing an existing hypothesis on the requirement of labile crosslinks for attaining high tensile strength in rubber vulcanizates. This direct approach involved the modification of the labile polysulfidic crosslinks already in existence in natural rubber‐sulfur‐diphenylguanidine vulcanizates to relatively less labile disulfidic or nonlabile monosulfidic crosslinks by reaction with triphenylphosphine. It was demonstrated that highly labile polysulfidic crosslinks are not essential for achieving high tensile strength in natural rubber vulcanizates. Data for the samples which had lost significant amounts of polysulfidic crosslinks by reaction with triphenylphosphine fitted the tensile strength versus 300% modulus curve for the control samples.