Role Of Free Volume Research Articles

The role of free volume, hydrogen bonds, and crosslinks on physical aging in polymers of intrinsic microporosity (PIMs)

Physical aging rates strongly correlate with the initial free volume of microporous polymers. Introducing hydrogen bonds and crosslinks can reduce the initial free volume and significantly impact gas separation selectivity over time.

Insight into the role of free volume in irradiation resistance to discoloration of lead‐containing plexiglass

AbstractLead‐containing plexiglass is prepared successfully via copolymerization of lead‐methacrylate (Pb(MAA)2 and the acrylic monomer such as methyl methacrylate, methyl acrylate, ethyl acrylate, and butyl acrylate. The results show that as‐prepared plexiglass has good photons shielding performance and resistance to the discoloration induced by radiation (10 kGy γ‐ray), and the alteration of shielding performance can be well described by the Monte Carlo Code simulations (MCNP5). Using two plasticized systems, the external‐plasticized one with various n‐octanoic acid concentrations and the internal‐plasticized one with different acrylic monomer, as the target samples, it is found that free volume plays dominant role in the irradiation resistance via the positron annihilation lifetime spectroscopy and electron paramagnetic resonance characterizations. The larger the free volume, the greater the quenching probability of free radicals during irradiation. Because the primary type of radiation‐induced color centers are annealable color centers, the effect of annealing of irradiation‐induced discoloration of lead‐containing plexiglass is remarkable. Differing from common treatments of improving irradiation resistance, the increased free volume via plasticization gives plexiglass good resistance to discoloration. This study discloses valuable information around improving irradiation shielding performance and resistance to the radiation‐induced discoloration for the plexiglass‐based materials.

Role of free volume in mechanical behaviors of side chain lcp grafted products of high density polyethylene

Role of free volume in mechanical behaviors of side chain lcp grafted products of high density polyethylene

Role of free volumes and segmental dynamics on ion conductivity of PEO/LiTFSI solid polymer electrolytes filled with SiO2 nanoparticles: a positron annihilation and broadband dielectric spectroscopy study.

The limited ionic conductivity of polymer electrolytes is a major issue for their industrial application. Enhancement of ionic conductivity in the poly(ethylene oxide), PEO, based electrolyte has been achieved by loading passive nanofillers such as SiO2 nanoparticles (NPs). To investigate the role of modifications in free volume characteristics and the polymer chain dynamics induced by the loading of passive fillers on the ionic conductivity of the PEO based ternary electrolyte, a systematic investigation has been carried out using positron annihilation and broadband dielectric spectroscopy. As a result of interfacial interactions, the loading of SiO2 NPs alters the semi-crystalline morphology of PEO resulting in a higher crystallinity at lower loadings due to the surface confinement of PEO chains, and the formation of smaller PEO crystallites at higher loadings due to interparticle nanoconfinement. These modifications are accompanied by a decrease in free volume fraction at the lowest loading (0.5 wt%) followed by an increase at higher loadings (≥2.0 wt%). The Almond-West formalism considering two different universalities in different temperature and frequency ranges has been used to explain the ion-conduction process at different NP loadings. The Li ion conductivity is observed to be maximum for a 5.0 wt% loading of SiO2 NPs. The enhancement in ionic conductivity is observed to be directly correlated with the free volume characteristics and segmental dynamics of the PEO matrix, confirming their role in ion transport in polymer electrolytes.

Blends based on biodegradable poly(caprolactone) with outstanding barrier properties for packaging applications: The role of free volume and interactions

In order to improve the poor barrier properties of poly(caprolactone) (PCL) this polymer was blended with poly(hydroxy ether of bisphenol A) (PH). The thermal properties, as well as the free volume of the system were analysed. The incorporation of PH significantly reduces the permeability of poly(caprolactone) to oxygen, carbon dioxide and water vapour. This reduction is linked to the free volume fraction, the thermal properties and the balance of interactions between polymers and penetrants. The outstanding results obtained allow to expand the applications of poly(caprolactone) in the packaging sector. The aim of this work is to achieve a better understanding of the factors that are involved in the barrier character improvement of poly(caprolactone) that could be extended to other biodegradable polymers.

Role of free volume in molecular mobility and performance of glassy polymers for corrosion-protective coatings

ABSTRACTGlassy polymer coatings on metal substrates rely on their mechanical, physical, and transport properties for corrosion protection. These properties are influenced by free volume between polymer chains that plays a critical role in coating performance. Free volume permits local segmental mobility that affects mechanical properties, such as yield and adhesion, and also permits diffusion of small molecules (water, ions, and oxygen) through the coating to the substrate. Fractional free volume is calculated from the specific volume and Bondi group contribution theory for the occupied volume. Free volume distribution (free volume element size and number) is measured by positron annihilation lifetime spectroscopy (PALS) using the ortho-positronium (oPs) probe, which detects free volume elements in glassy polymer coatings. The oPs probe is sensitive to phenomena that affect both the mechanical and barrier properties of coatings including physical ageing, water sorption, and plasticisation, making PALS a suitable allied testing method for corrosion-protective coatings.

Role of free volumes in conducting properties of GO and rGO filled PVA-PEDOT:PSS composite free standing films: A positron annihilation lifetime study

In this paper, we demonstrate the preparation of the polymer composite films of poly (vinyl alcohol) (PVA) – poly (3, 4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) blend filled with synthesized Graphene oxide (GO) and reduced Graphene oxide (rGO) by solvent casting technique. The X-ray diffraction (XRD) studies confirmed the changes in crystallinity upon incorporation of the Graphene. The differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) depicted the variation in chain mobility and thermal stability of the GO/rGO filled composites. The scanning electron microscope (SEM) and atomic force microscope (AFM) studies affirm the uniform dispersion of fillers in the polymer matrix. The mechanical properties such as the Young's modulus and tensile strength are enhanced after the insertion of fillers. The impedance data is fitted with the equivalent circuit model and the obtained impedance parameters execute the variation in bulk conductivity with increase in wt.% of filler and is maximum at 5 wt.% GO/rGO addition. Positron annihilation lifetime spectroscopy (PALS) is effectively used to investigate the molecular packing and hence free volume properties of the composites. The o-Ps lifetime and hence, the size of the free volume is initially decreased due to shrinkage of free volume and enhanced at 10 wt.% loading, attributed to the increased agglomeration of the additives. The decrease in the lifetime τ2 and increase in the intensity I2 at lower filling is attributed to the created small size defects. The variation in the free volume is corroborated by other experimental observations such as XRD, DSC and electrical conductivity.

Micromechanical analysis of molecular orientation in high-temperature creep of polycarbonate

The molecular orientation of bisphenol-A polycarbonate (PC) was determined by the in-situ wide-angle X-ray diffraction (WAXD) measurement during high-temperature creep. The resulting creep and WAXD data were used to analyze the coupled deformation of macro-continuum and micro-structure. A four elements viscoelastic model was introduced to fit the creep results and describe the time-dependent orientation in creep. The delayed elastic stress was regarded as an assessment of molecular orientation, and two dashpots in the model were used to analyze the physical meanings of retardation time, which helped to understand the mechanism of molecular orientation and the role of free volume and stress on the viscoelastic parameters. A threshold range of free volume was proposed to interpret the change regularity of retardation time, delayed elastic modulus and coefficient C. The delayed elastic stress can be successfully used in assessing the orientation. Our work provides a deeper insight into the evolution of molecular orientation induced by high-temperature creep.

Plasticity Mechanism for Glassy Polymers: Computer Simulation Picture

This review summarizes the data published over the past two and a half decades on the mechanism of plastic deformation of bulk isotropic linear glassy polymers in uniaxial tension, compression, and shear at low deformation temperatures (Тdef < 0.6Тg) and moderate loading rates. The main attention is focused on studies concerning the numerical computer simulations of plasticity of organic polymer glasses. The plastic behavior of glassy polymers at nano-, micro-, and macrolevels in the range of macroscopic strains up to ≈100% is discussed. Plasticity mechanisms are compared for organic, inorganic, metallic, polymer, and nonpolymer glasses with different chemical structures and types of interparticle interactions. The general common mechanism of plasticity of glassy compounds, the nucleation of plasticity carriers in them, and the structure of such carriers and their dynamics are covered. Within the framework of the common plasticity mechanism, the specific features of deformation in glassy polymers are analyzed. Specifically, the participation of conformational transformations in macromolecules in the deformation response of polymer glasses, change in intensity of the yield peak with the thermomechanical prehistory of the sample, and the role of van der Waals interactions in the accumulation of excess potential energy by the sample under loading are considered. The role of free volume and structural and dynamic heterogeneities in the plasticity of glasses is also discussed.

Positronium Lifetimes and Gas Permeation in Aquivion® for Fuel Cells

Variations of ortho-positronium (o-Ps) lifetime and gas permeability of the Aquivion® E8705 membrane were studied as functions of temperature under vacuum and relative humidity at room temperature. When the temperature was varied between 0 and 100 °C in vacuum, the hole volume of Aquivion® E8705, deduced from the ortho-positronium lifetime, gradually increased. However, when the relative humidity was changed at room temperature, the hole volume was essentially unchanged. Good linear correlations between the logarithm of permeabilities of O2 and H2 and reciprocal hole volume at different temperatures indicates the importance role of free volume in gas permeation in dry Aquivion® E8705. However, for hydrated Aquivion® E8705 the permeability less depends on hole volume.

Role of free volume in strain softening of as-cast and annealed bulk metallic glass

Plasticity in amorphous alloys is associated with strain softening, induced by the creation of additional free volume during deformation. In this paper, the role of free volume, which was a priori in the material, on work softening was investigated. For this, an as-cast Zr-based bulk metallic glass (BMG) was systematically annealed below its glass transition temperature, so as to reduce the free volume content. The bonded-interface indentation technique is used to generate extensively deformed and well defined plastic zones. Nanoindentation was utilized to estimate the hardness of the deformed as well as undeformed regions. The results show that the structural relaxation annealing enhances the hardness and that both the subsurface shear band number density and the plastic zone size decrease with annealing time. The serrations in the nanoindentation load-displacement curves become smoother with structural relaxation. Regardless of the annealing condition, the nanohardness of the deformed regions is ∼12–15% lower, implying that the prior free volume only changes the yield stress (or hardness) but not the relative flow stress (or the extent of strain softening). Statistical distributions of the nanohardness obtained from deformed and undeformed regions have no overlap, suggesting that shear band number density has no influence on the plastic characteristics of the deformed region.

Physical and Mechanical Behavior of Polymer Glasses. VI. the Role of Free Volume

For various polymer glasses, the temperature-induced recovery of residual deformation was studied. The ratio between the low-temperature and high-temperature recovery components is controlled by the difference between deformation temperature and glass transition temperature T g of polymer samples independently of their chemical structure. This ratio correlates with polymer macroscopic mechanical characteristics such as elastic modulus and yield stress. Experimental results were treated in terms of the dynamics of segmental mobility within different structural sublevels with different packing densities. To correlate this mechanical response with the structural state of glassy polymers, positron annihilation lifetime spectroscopy (PALS) was used. For different polymer glasses, the microscopic segmental mobility and resultant macroscopic mechanical properties were shown to be controlled only by the development of the adequate free volume content which depends on the difference between testing temperature and T g . These results allowed us to propose the general correlation between microstructure, microscopic molecular mobility, and Macroscopic mechanical behavior of polymer glasses.

On the role of free volume in pick-off annihilation and positronium chemical reactions

Free volume effects are important for positronium formation, pick-off annihilation and chemical reactions. The relation between the long-lived component intensity and the number of defects is considered for the case of selective localization of positrons and positronium in ordered and disordered sites of plymers. Positronium lifetimes for the large pores (r≥1 nm) are discussed. In positronium chemical reactions recent results show crucial role of the bubble parameters in liquids.

Auger electron spectroscopy studies of interdiffusion in electrodeposited amorphous NiP alloys

AbstractThe effect of annealing on the Auger electron depth profiles of electrodeposited amorphous Ni100‐yPy/Ni100‐xPx (15 &lt; x &lt; 32 at.%, y &gt; x) thin film couples is studied at temperatures in the range 190–280 °C. Diffusion coefficients are evaluated by means of the Boltzmann–Matano method. The composition dependence of diffusion coefficients is explained by the role of free volumes in amorphous materials on interdiffusion.

On the volume dependence of viscosity of some magmatic silicate melts

Density and viscosity measurements of three melts of volcanic rock composition (basalt and andesite) at low temperatures were carried out to understand the role of free volume in the viscous behavior of a magma and to estimate the flow unit in the melts. The data combined with literature data suggest the following conclusion: free-volume theory is not applicable to these silicate melts; the relation between viscosity and the inverse of free volume does not yield a straight line in a wide temperature range from the glass-transion temperature to 1550°C. However, two depolymerized melts, diopside and Oki-Dozen alkali basalt (OAB), yield almost linear relationships. Thus, the free-volume theory should hold to a fairly good approximation for these two melts. Based on this approximation, the radius of flow unit for diopside melt was calculated to be about 4.7 A, and that for Oki-Dozen alkali basalt to be about 4.2 A. The three-dimensional silicate anions which may correspond to the flow unit are Si14O3514− and Si16O4016− for diopside melt, and Si10O2510− and Si12O3012− for OAB melt. The temperature effect on the initial slope of the viscosity-pressure relation has also been examined in the frame of free-volume theory. It was concluded that the relative increase of the initial slope of the relation with increasing temperature might be caused by the increase of free volume.

The role of free volume in the twisted intramolecular charge transfer (TICT) emission of dimethylaminobenzonitrile and related compounds in rigid polymer matrices

The amount of free volume present in a polymer matrix represents a driving force toward twisted intramolecular charge transfer (TICT) emission of p-dimethylaminobenzonitrile (DMABN) and related compounds. The intensity of the TICT band for these compounds in PVC (poly(vinyl chloride), PVA (poly(vinyl alcohol)), PHEMA (poly(hydroxyethyl methacrylate)) and PMMA (poly(methyl methacrylate)) was found to increase in this order, which is consistent with the increased free volume present in the same sequence. This rules out specific solute-solvent interactions as being responsible for the TICT emission in PVA polymer matrices.

Role of free volume in the viscous behavior of magma.

In the present study, the effects of free volume on the viscous behavior of magmatic melts are discussed on the basis of free-volume theory. The most important conclusion is that the change of viscosity with temperature, pressure, and composition is related approximately to the change of free volume in the melts. It has been found that an increase of temperature and mafic components induces an increase of free volume in magmatic melts, and it is well known that they also tend to cause a decrease of viscosity. The relation between free volume and viscosity is interpreted as a reflection of the greater ease of movement of constituent units in melts that have more interstitial space. Pressure effects on viscosity are also interpreted as fundamentally based on the change of free volume. Melts having an abundance of free volume at 1 atm are depolymerized melts and show an increase of viscosity with pressure owing to a decrease of free volume. On the other hand, in polymerized melts having a small free volume at low pressures, the controlling process of viscous flow is not the change of free volume but making or breaking of bonds between constituent units of the melt. Sharma et al. (1979) suggested on the basis of Raman spectroscopy that the decrease of viscosity of polymerized melts at high pressures was caused by deformation of constituent unit accompanying the weakening of Si-O-Si bond. Our explanation of the behavior of polymerized melts is in harmony with their interpretation.

134. Role of free volume in the effect of pressure on viscous flow of magma(Abstracts of Papers Presented at the Spring Meeting of the Society)

134. Role of free volume in the effect of pressure on viscous flow of magma(Abstracts of Papers Presented at the Spring Meeting of the Society)

The role of free volume in the formation of macroradicals during the radiolysis of polymers

A process, based on a free-volume model, is discussed for the formation of macroradicals during the radiolysis of polymers. At high pressures, the free volume in polymers is reduced and this leads primarily to a reduction in the radiation yield of end macroradicals formed during the scission of the polymer chain. In PTEE, the minimum volume necessary for the exit of end macroradicals from a cage is approximately 45 A ̊ 3 and that for the exit of a fluorine atom, approximately 2 A ̊ 3 . The radiation yield of macroradicals is decreased in polymers that have been treated beforehand at high pressures. The formation of microporosities in PTEE leads to an increase in the radiation yield of macroradicals.

Selected aspects of photochemistry in polymer media

Abstract A number of selected aspects of the reciprocal interactions of polymers with excited solutes or polymer-bound chromophores are given. The role of free volume, glass-transition temperature (Tg), microscopic viscosity, and polarity or environments to which excited molecules are exposed is emphasized in order to illustrate possible manners in which the photophysical, photochemical, and subsequent chemistries can be influenced. Many of these factors can affect several monomolecular and bimolecular processes encountered in the sensitization of photocrosslinkable polymers: the photophysics of the sensitizer, energy transfer to the reactive sites on the polymer, and the formation of crosslinks. In fact, the triplet yields of aroylnaphthothiazole derivatives, a widely used class of sensitizers, are considerably higher in the more viscous polymeric matrices. These 0. in the polymer approach, however, a value of only ca. 0.7. As a result a search for more efficient triplet sensitizers led to a new class of compounds: 5- and 7-substituted 3-ketocoumarins. As a model for study of the bimolecular processes in polymers, we chose exciplex and excimer probes. The following conclusions were drawn: 1. Several exciplex and excimer emissions in polymeric media are considerably shifted to shorter wavelengths as compared with the maxima measured in fluid media, indicating that interactions are impaired in polymeric matrices. 2. Emissions from the polymer matrix above the glass-transition temperature are similar in wavelength and temperature dependence thereof to those observed in fluid solutions. 3. Improper orientation of the reactants in polymers is responsible for the shift observed in excimer emission and for a part or all of the shift in exciplex emissions. 4. Little if any difference is observed between exciplex emissions in polymers of low and moderate macroscopic polarities. This may be attributed to two causes: a) Due to improper orientation the dipole moment of the exciplex in the polymer is expected to be smaller and, therefore, less solvation energy can be gained. b) The segmental motion of the polymer required to properly solvate the complex is probably too slow at room temperature compared with the lifetime of the exciplex. 5. Bichromophoric molecules, which form exciplexes in fluid media, fail to reach an exciplex configuration when dissolved in polymers.