Amount Of Free Volume Research Articles

Mobility and solubility of antioxidants and oxygen in glassy polymers. III. Influence of deformation and orientation on oxygen permeability

The mobility of small molecules in a glassy polymer is largely determined by the amount of free volume present in the material. The amount of free volume can be altered by changing the physical state of the polymer. Plastic deformation under compression reduces this amount, whereas the application of a tensile stress increases it. Furthermore, orientation of a polymer introduces an anisotropy in the free volume. The change in free volume was monitored by oxygen permeation experiments. A clear correlation was found between the draw ratio, plastic deformation and stress on the one hand and oxygen permeability on the other. Since the mobility of oxygen is an important parameter for the stabilisation of a polymer against oxidation, the physical state of the polymer can have a significant influence on the service life of the product.

Oxygen‐barrier properties of polyethylene terephthalate modified with a small amount of aromatic comonomer

AbstractThe oxygen‐barrier properties of amorphous copolyesters based on ethylene terephthalate with 10%, or less, of an acid comonomer were examined. Comonomer units were isophthalate, phthalate, 1,5‐naphthalate, 1,8‐naphthalate, 2,6‐naphthalate, 1,8‐anthracenate, 2,6‐anthracenate, and 2,7‐pyrenate. Even 2.5 mol % comonomer significantly affected the permeability. Linear comonomers decreased the permeability. In contrast, small amounts of a kinked comonomer increased the permeability. However, increasing the amount of kinked comonomer further (gradually) decreased permeability P below that of polyethylene terephthalate. Generally, comonomer affected solubility S less than diffusivity D; therefore, changes in P reflected primarily changes in D. The solubility and diffusivity depended on copolymer composition in accordance with static and dynamic free‐volume concepts of gas permeability in glassy polymers. The solubility correlated with the amount of free volume, as determined by the glass‐transition temperature. This study also explored the relationship of dynamic free volume, which determines D, to thermally accessible segmental motions of the polymer chain. The effect of comonomer on D correlated with the intensity of the gauche component of the subambient γ relaxation. Changes in the fraction of gauche‐glycol conformations resulting from copolymerization were confirmed by Fourier transform infrared spectroscopy. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1900–1910, 2001

Oxygen‐barrier properties of copolymers based on ethylene terephthalate

AbstractThe oxygen‐barrier properties of amorphous polyethylene terephthalate‐based copolymers with various acid comonomers were examined. The incorporation of increasing amounts of isophthalate, phthalate, or naphthalate gradually reduced the permeability P toward the low values obtained for the corresponding homopolymers. The permeability of poly(ethylene 3,4′‐bibenzoate) homopolymer was only slightly lower than that of polyethylene terephthalate, and the copolymers correspondingly exhibited a very gradual decrease in P as the amount of 3,4′‐bibenzoate (3,4′BB) increased. In contrast, copolymerization with the linear isomer, 4,4′BB, produced a substantial increase in P. Generally, comonomer affected the solubility S less than the diffusivity D, and therefore changes in P reflected primarily changes in D for the polymers studied. The diffusivity and solubility depended on the copolymer composition in accordance with static and dynamic free‐volume concepts of gas permeability in glassy polymers. The solubility S correlated with the amount of free volume as determined by the glass‐transition temperature. Correlation of the diffusivity D with the magnitude of the subambient γ relaxation identified dynamic free volume with thermally activated conformational changes and segmental motions. Correspondence in the activation energy confirmed the relationship. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1889–1899, 2001

Supersoftening of transverse phonons inZr41Ti14Cu12.5Ni10Be22.5bulk metallic glass

Acoustic properties and low-temperature specific heat of ${\mathrm{Zr}}_{41}{\mathrm{Ti}}_{14}{\mathrm{Cu}}_{12.5}{\mathrm{Ni}}_{10}{\mathrm{Be}}_{22.5}$ alloy in glassy, fully crystallized and equilibrium crystalline states have been investigated. It is found that a large amount of free volume is quenched in the bulk metallic glass (BMG) which is obtained at a low-cooling rate, even fully crystallization cannot remove all the free volume from the alloy. A supersoftening of long-wavelength transverse acoustic phonons in the BMG relative to its equilibrium crystalline state is observed. The origins for the phenomenon are discussed. The finding has significance for understanding of the glassy state as well as the excellent glass forming ability of the glass forming alloy.

Studies on the free volume and the volume expansion behavior of amorphous polymers

In order to estimate the free volume contribution on the volume change, we investigated the relationship between the volume expansion behavior by Pressure–Volume–Temperature measurement apparatus and the free volume behavior by Positron Annihilation Lifetime Spectroscopy for some amorphous polymers. From these results, the free volume fraction of the amorphous polymers was calculated by assuming that the core volume increases at a constant rate with temperature. It was found that the amount of free volume was not constant even in the glassy state and it played a very important role in the volume expansion.

Structural relaxation and plastic flow in amorphous La 50Al 25Ni 25

The tensile deformation of amorphous La 50Al 25Ni 25 is studied in an extensive set of tensile tests at temperatures just below the glass transition temperature. Depending on the pre-annealing treatment, in many cases strain softening occurs during the tensile tests. Only in the case of a very short pre-annealing treatment does apparent strain hardening occur. After deformation, up to ε=0.3, all samples are tested by differential scanning calorimetry, which reveals that the glass transition peak depends on the temperature and strain rate during the tensile test, but not on the pre-annealing treatment. The entire set of experimental evidence can adequately be explained by the free volume concept. The conclusion is that during plastic deformation additional free volume is created as compared with thermal equilibrium, and the structure reaches a temperature and strain rate dependent steady state of disorder, i.e. amount of free volume. A quantitative description of this process, which should be envisaged as the production of a small amount of free volume during each flow event, is presented.

Positronium-salt interactions and ionic conductivity in poly(2-hydroxyethyl methacrylate) gel electrolytes

The effects of copolymerization of poly(2-hydroxyethyl methacrylate) with oligo-(ethylene glycol) dimethacrylates (OEDs) on the ionic conductivity of the gel electrolyte copolymers was investigated. A series of HEMA-OED cross-linked copolymers were produced with the number of ethylene glycol units varying between zero (uncross-linked) and nine. The conductivity of samples containing distilled and deionized water (DDIW) and 1 M KBr electrolytes was characterized by AC impedance measurements. The relationship between the amount of water/salt solution contained within the gel electrolytes and resultant conductivity is investigated and discussed with reference to the free volume in the system. The free-volume characteristics were probed by positron annihilation lifetime spectroscopy (PALS), and the influence of free volume and the amount of water/solution in the gels on conductivity discussed. The results indicate a positive correlation between the amount of mobile conducting phase and the available free volume in the system, with the amount of conducting phase present matched by a proportionate amount of free volume in the gel. The system showed evidence of orthopositronium (oPs) inhibition in the ion containing samples when compared with the DDIW samples. Slight differences in the oPs pickoff rate recorded in DDIW and KBr solution are attributed to microviscosity differences between the two fluids, rather than oPs quenching.

エネルギーフィルタ透過電子顕微鏡によるポリエチレンのナノメータ領域の密度分布推定法の検討

One-dimensional mass-thickness distribution of polyethylene specimen was estimated with an energy-filtering TEM for unstained specimen with suitable calibration points using lamella information as calibration data. Possibility to estimate the free volume ratio distribution and therefore the possibility of free volume distribution itself becomes realistic. volume ratio is the average free volume amount along the electron beam line across TEM specimen and it is not free volume distribution itself. We need proper definition of Free Volume Distribution for further development.

Creation of free volume in amorphous Pd 40Ni 40P 20 during high temperature deformation

The deformation of amorphous Pd 40Ni 40P 20 is investigated as a function of temperature and strain rate. The free volume is used as a measure for the state of structural relaxation, and its influence on the material's mechanical properties is investigated using Differential Scanning Calorimetry (DSC) traces as a measure for the frozen-in amount of free volume after heat treatment and deformation. It is found that amorphous Pd 40Ni 40P 20, when preannealed into its metastable equilibrium state, shows a large strain softening effect when deformed at temperatures close to the glass transition temperature. It is shown that the strain softening is caused by the creation of additional free volume due to the deformation, and that the material reaches a new, strain-rate dependent equilibrium state. In order to understand this effect, the free volume theory is used as a starting point to investigate the mechanism by which deformation in metallic glasses occurs.

Preparation and glass transition temperatures of elastomeric PolyHIPE materials

Highly porous elastomeric PolyHIPE materials have been prepared by polymerisation of the continuous phase of high internal phase emulsions (HIPEs) containing styrene, divinylbenzene and varying amounts of either 2-ethylhexyl acrylate or the corresponding methacrylate monomer. The glass transition temperatures of the resulting copolymers were investigated by differential scanning calorimetry (DSC). For each series,Tg was found to vary non-linearly with copolymer composition. By consideration of the comonomer unit sequencing along the polymer backbone, as deduced from reactivity ratios, the relationship between Tg and composition in each case has been qualitatively explained. Comparison between experimental results and values calculated using an entropic approach have been made. It is thought that the (meth)acrylate comonomers reduce the overall Tg by three mechanisms: by introducing large amounts of free volume, due to their bulky side groups; by providing a much higher degree of flexibility to the polymer chains; and by reducing the proportion of adjacent styrene units, which display particularly unfavourable steric interactions.

Characterization of static and dynamic properties of a low-density polyethylene. Evidence for translocation of fluorescent probes upon stretching and determination of relaxation processes at the mesoscopic level

Fluorescence from anthracene guest molecules (AN) has been used to study secondary α, β and γ relaxation processes in unstretched and stretched low density polyethylene (LDPE) in the temperature range 15–400 K. The LDPE was characterized by several different techniques. It contains about 4 vinylidene, vinylene and vinyl type CC bonds and about 320 CH3 groups per 10 000 CH2 units. The unstretched polymer is 31% crystalline and has a melting point, Tm, of 109°C. The 5x stretched polymer is 51% crystalline and Tm = 110°C. Although the degree of crystallinity of the films suffers a large change upon macroscopic stretching, the melting temperature (determined by d.s.c. and fluorescence spectroscopy) and the relaxation temperatures do not. However, plots of total fluorescence intensity or fluorescence intensity ratios at different wavelengths vs temperature indicate that dynamic processes involved with the excited singlet states of anthracene are dependent upon polymer stretching. These results, in combination with others obtained previously, suggest that stretching reduces the average amount of free volume at guest sites and induces a translocation of anthracene molecules toward sites at the crystalline-amorphous interfaces.

Photo-isomerization of polymer monolayers and multi-layers on water

The kinetics of trans-cis photo-isomerization of azo-dye-functionalized polymer films deposited at the air-water interface is studied by optical second harmonic generation. The azo dyes are found to isomerize with two distinct rate constants depending on their local environment. For the first polymer monolayer absorbed on water, isomerization occurs with roughly the same rate as in dilute solutions. For polymers deposited above this monolayer, the reaction rate is nearly two orders of magnitude slower, resembling that in a bulk polymer film. Environmental differences leading to the difference in the amount of free volume is presumably responsible for the two different reaction rates.

The calorimetric glass transition of amorphous Pd 40 Ni 40 P 20

The calorimetric glass transition in amorphous Pd 40Ni 40P 20 was measured in a series of Differential Scanning Calorimetry (DSC) experiments. Especially the exact shape and position of the glass-transition peak were examined after different pre-annealing treatments of the sample and at different heating rates. The experimental results are in good agreement with a kinetic model of the glass transition. In particular, we found strong support for the existence of an equilibrium state when amorphous Pd 40 Ni 40 P 20 is heated above its glass transition, and derived that the shape and position of glass-transition peak of amorphous Pd 40 Ni 40P 20 at a given heating rate depends on a single structure parameter, in this paper designated as the average amount of free volume. The kinetics of free-volume changes are fully in agreement with results from viscosity measurements and speed-of-sound measurements. In order to obtain a good agreement between the model calculations and the experimental DSC curves, heat effects from chemical ordering were included in the calculations and the thermal delay of the measurement device was modelled with a simple RC-model.

Packing density and gas permeability of copolyimides containing bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride constituent

AbstractPacking density and gas permeability of two copolyimide series containing an alicyclic monomer, bicyclo[2,2,2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA), and a fluorinated monomer, hexafluoroisopropylidene,2,2‐bis(phthalic acid anhydride) (6FDA), were measured. Incorporation of a rigid BCDA segment in 6FDA polyimides either increases gas permeability or improves gas selectivity, depending on the base 6FDA polyimide. In the case of the highly gas permeable 6FDA polyimide, introduction of BCDA further increases gas permeability despite a loss in the amount of free volume. In the moderately gas permeable 6FDA polyimide, on the other hand, the introduction improves gas selectivity. © 1995 John Wiley & Sons, Inc.

Physical properties of epoxy and free volume evaluated by positron annihilation spectroscopy

The macroscopic physical properties of commercially available bisphenol -A epoxy resins cured by acid anhydride in which amount of the plasticizer, polypropyleneglycol was changed systematically have been measured and were compared with the amount of free volume evaluated by the positron annihilation technique. The lifetime and the intensity of orthopositronium were used to evaluate the amount of the free volume in the epoxy resins. It was found that up to the certain amount of plasticizer, the amount of the free volume did not increase so much and then showed the marked increase. The close correlations were found between the amount of the free volume and the macroscopic physical properties such as hardness and specific volume

Molecular-dynamics simulation of stress relaxation on a triangular lattice.

Simulations were performed using the method of molecular dynamics for ideal lattices and for lattices with defects generated by three different procedures. Curves of relaxation of stress \ensuremath{\sigma} vs logarithmic time t were obtained. In agreement with experimental results, the simulated curves exhibit three regions: initial, nearly horizontal, starting at ${\mathrm{\ensuremath{\sigma}}}_{0}$; central, descending approximately linearly; and final, corresponding to the internal stress ${\mathrm{\ensuremath{\sigma}}}_{\mathit{i}}$ as defined by Li. The existence of the central linear part has been predicted by a cooperative theory. In agreement with the theory, the slope of the simulated central part is proportional to the initial effective stress ${\mathrm{\ensuremath{\sigma}}}_{0}^{\mathrm{*}}$=${\mathrm{\ensuremath{\sigma}}}_{0}$-${\mathrm{\ensuremath{\sigma}}}_{\mathit{i}}$. The central part extends over approximately one decade of ${\mathrm{log}}_{10}$t for ideal lattices but over several decades for lattices with defects. High values of the imposed strain \ensuremath{\varepsilon} correspond to low internal stresses ${\mathrm{\ensuremath{\sigma}}}_{\mathit{i}}$, and vice versa. Stress relaxation is mainly due to deformations that occur in the vicinity of the defects, hence the process is related to the defect concentration and the amount of free volume ${\mathit{v}}^{\mathit{f}}$. Collective response of atoms in groups is observed. The origin of the defects does not seem to influence the relaxation.

Glass Transition Temperatures Studied by MD Simulation of Some Alkali Metasilicates

Abstract Molecular dynamics simulation of some alkali metasilicates (M2SiO3, M = Li, Na, K) was performed to compare glass transition temperatures, Tg , defined in various ways. The potential parameters derived from ab initio MO calculations were used and found to reproduce the inflection of V-T relation on cooling the system. The Tg defined by the inflection point corresponds well to that defined by geometrical changes of coordination polyhedra found in previous work. The self-diffusion coefficients of the alkali ions in higher temperature regions were shown to be related to the amount of free volume in these systems.

On the amount of free volume in gas–polymer mixtures

Using sorption and dilatation data, the molar volumes of CO 2 and CH 4 that are inaccessible for diffusion were determined for silicone rubber. These values were used to calculate the mobile gas concentration for CO 2 and CH 4 in glassy polycarbonate assuming that an iso-free-volume state exists below the T g . The analysis presented here suggests an alternative view of the concept of partial immobilization that is independent of the dual mode sorption model. Those molecules that contribute to maintaining the iso-free-volume glassy state are mobile while those that do not are completely immobile

Internal Plasticization of Granular Rice Starch by Hydroxypropylation: Effects on Phase Transitions Associated with Gelatinization

AbstractThe effects of hydroxypropylation on phase transitions associated with gelatinization of granular rice starch were studied by differential scanning calorimetry. At a 1:1 starch/water ratio, a progressive shift of the biphasic gelatinization endotherms to lower temperatures as well as a broadening and shortening of the G endotherm with increasing molar substitution were observed, indicating increased internal plasticization and destabilization of the amorphous regions of the starch granules. The overall enthalpy of gelatinization was also reduced. Hydroxypropyl groups, which are attached to starch molecules primarily in the amorphous regions of the starch granules, behave as flexible side chains. The motion of these side chains creates a large amount of free volume, thereby lowering the glass transition and crystallite melting temperatures associated with starch gelatinization. The modified starch granules may thus be viewed as internally plasticized polymer resins which are more easily gelatinized than the unmodified starch.

Chain relaxation capability and service life of polymeric materials

AbstractBehavior of polymers in creep, stress relaxation, stress‐strain curve determination, impact tests and under dynamic periodic loads are analyzed. Rapid crack propagation and slow crack propagation are considered in relation to service performance and life time. All essential aspects of mechanical behavior of polymeric materials and components have a common denominator: competition between chain relaxation capability (CRC) and destructive processes. For a given force (magnitude, rate, direction, duration) the outcome of this competition depends largely on the amount of free volume.