Influence Of Free Volume Research Articles

Microstructure and barrier properties of reactive compatibilized PLA/PA11 blends investigated by positron annihilation lifetime spectroscopy

Poly(lactic acid)/polyamide11 (PLA/PA11) blends were prepared by reactive blending with multifunctional epoxy oligomer as compatibilizer, and the compatibility of PLA and PA11 was improved. The compatibilization, toughness mechanisms, and rheological behavior of PLA/PA11 blends were studied. Positron annihilation lifetime spectroscopy (PALS) was used to study the free volume and interfacial compatibility of the compatibilized blends. Moreover, the influence of free volume and void volume on the barrier properties of the blend films was discussed. The glass-transition temperature and storage modulus of PLA in the compatibilized PLA/PA11 blends decreased, and the rheological behavior in the blends changed from liquid-like to solid-like at low-frequency. This finding showed that the interfacial compatibility between PLA and PA11 improved, and the material properties underwent a rigid-to-tough transition. PALS analysis further showed the improved interfacial compatibility of the multifunctional epoxy reactive compatibilizer reduced the free-volume pores and increased the number of free-volume pores. The entanglement degree of the molecular-chain segment in the compatibilized blend system increased, and the volume of free-volume pore decreased. The reactively compatibilized PLA/PA11 blend had excellent oxygen and water barrier properties, and its oxygen transmissibility and water-vapor diffusion coefficient greatly decreased. Therefore the reactive compatible PLA/PA11 blends had potential application and research value as packaging-barrier film materials.

Effect of cast temperature, size and annealing condition on the serrated flow during nano-indentation of Zr-based bulk metallic glasses

The present work deals with mechanical properties of five multicomponent Zr-based bulk metallic glasses: Zr58Cu22Fe2Ag6Al12, Zr58Cu22Fe4Ag4Al12, Zr58Cu22Fe4Co4Al12, Zr58Cu22Fe8Al12, and Zr58Cu22Ag8Al12, using nano-indentation technique at very low loading rate (80 μN/s). Zr-based glasses exhibit serrated flow during nano-indentation, manifested as a stepped load-displacement curve. Systematic study on the influence of free volume and nanocrystallization on shear band formation by varying the casting temperature and cross-section of the Zr58Cu22Fe2Ag6Al12, and annealing above and below glass transition temperature of the Zr58Cu22Co4Fe4Al12 alloy is carried out. Analysis of the experimental data has revealed that higher casting temperature and larger casting cross-section cause partial crystallization, which decreases the hardness by promoting multiple shear band formation. However, hardness of the annealed glasses with similar fraction of nanocrystalline phases increases due to the reduction of free volumes as confirmed through electron diffraction studies in transmission electron microscope. Moreover, both free volume and nanocrystalline phase are found to have significant influence on the mechanical properties of bulk metallic glasses investigated in the present study.

Nanoindentation response of Cu–Ti based metallic glasses: Comparison between as-cast, relaxed and devitrified states

Cu36Ti34Zr22Ni8 glassy ribbons were synthesized by melting spinning. The effects of annealing treatments on the microstructure and mechanical properties of this alloy are investigated. Annealing below the crystallization temperature induces a reduction of free volume, as evidenced by differential scanning calorimetry. Annealing at sufficiently high temperatures promotes the formation of stable CuTi, NiTi and Zr–Ti–Cu phases. The as-spun alloy exhibits high hardness (H>8GPa), moderate reduced Young's modulus (Er≈90GPa) and good wear resistance. These properties are enhanced after thermal treatments (H>13GPa and Er≈140GPa are achieved in the fully crystallized sample). The mechanical hardening is accompanied with an increase of the elastic recovery. The influence of free volume on these annealing-induced changes in the mechanical properties is discussed.

Influence of free volume and medium-range order on the deformation response of rapidly solidified and bulk Zr-based (Zr52Ti6Al10Cu18Ni14) metallic glass

Free volume and medium-range order (MRO) present in rapidly solidified ribbons (RSRs) and bulk metallic glasses (BMGs) of Zr52Ti6Al10Cu18Ni14 have been probed by high resolution electron microscopy, fluctuation microscopy, positron annihilation and differential scanning calorimetry. In the as-solidified condition, RSRs showed higher free volume and lower MRO in comparison to BMGs. Within BMGs, the central regions showed higher MRO and lower free volume than the peripheral regions. Uniform deformation of BMGs and RSRs modified their structures, where in, free volume increased in the former and reduced in the latter. These changes in structures led to work hardening in RSRs and work softening in BMGs. Such behaviour could be explained by invoking a concept of critical free volume in the glass phase. For samples (in as-solidified condition) having free volume higher than the critical value, free volume decreased with deformation and showed work-hardening behaviour. In contrast, the work softening behaviour was noticed in samples having free volume lower than the critical free volume.

Clay Intercalation and its Influence on the Morphology and Transport Properties of EVA/Clay Nanocomposites

Nanocomposite membranes based on poly-(ethylene-co-vinyl acetate) copolymer (18% vinyl acetate content)and two different organomodified clays have been prepared by mechanical mixing using two roll mill method. The morphology of the nanocomposites was investigated using small angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The mechanical and thermal studies were also performed using universal testing machine and differential scanning calorimeter, respectively. Samples with low filler content showed excellent dispersion of layered silicates resulting in a partially exfoliated structure. The diffusion and transport of organic solvents through the membranes have been investigated in detail as a function of clay content, nature of solvent and clay, and temperature in the temperature range of 28−70 °C. The influence of free volume on the transport properties of the membranes was studied using positron annihilation lifetime spectroscopy. The solvent uptake was minimum for composites with 3 wt % of filler, and it get increased with increasing filler content, which is presumably due to aggregation of clay filler at higher loading. The transport phenomenon was found to follow an anomalous mode. Activation parameters were estimated, and the molar mass between cross-links was calculated. Finally, the experimental transport data were compared with theoretical predictions. (Less)

Development of an EOS based on lattice cluster theory for pure components

In many industrial applications, like tissue fabric production, osmotic separation, but also tissue engineering in medical laboratories, the knowledge of polymer behaviour is of vital importance. This behaviour is partially well known, but often the underlying mechanisms are not understood to a degree, which would make a prediction of polymer behaviour possible based on short and long chain branching, as well as general architecture. The Lattice Cluster Theory (LCT) of Freed and co-workers makes it possible to describe the influence of molecules’ architecture on the free energy of mixtures containing them. As possible functional groups (e.g. acidic groups) or permanent dipole or multi-pole moments are not accounted for by the LCT, this article will deal with linear and branched alkanes in order to test its applicability on the calculation of thermodynamic properties of these common compounds. To model the influence of pressure on phase behaviour, the LCT is transformed to a lattice gas equation of state. As is usual in lattice gas theories, the influence of free volume, and hence density will be modelled by the introduction of a non-interacting species of the size of one lattice site (hole). This approach yields the Lattice Cluster Theory Equation of State (LCT-EOS). The LCT-EOS pure component parameters are fit to the experimental data of several n-alkanes. Using only these parameters, fit to linear alkanes, the vapour pressure of a branched alkane is predicted accurately.

Influence of Clay Content and Amount of Organic Modifiers on Morphology and Pervaporation Performance of EVA/Clay Nanocomposites

Poly(ethylene-co-vinyl acetate)/organically modified clay nanocomposites were prepared using different clay loadings and by varying the amount of organic modifier. The morphology of the nanocomposites was investigated using small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SAXS results displayed intercalation of polymeric chains between the silicate layers in all the cases. The interlayer distance varies slightly between the series. TEM images showed a better dispersion of the clay platelets at lower loading for both series of samples. The pervaporation performances of membranes were analyzed using a chloroform/acetone mixture. Membranes displayed high selectivity. The influence of feed composition on pervaporation was analyzed. The nanoclay content and the influence of free volume on pervaporation performance were also investigated in detail. A drop in selectivity and an increase in permeation rate were observed at higher clay loadings.

Influence of free volume on magnetoelastic coupling in iron-based amorphous alloys

In this paper, the influence of structural relaxation on magnetoelastic coupling in iron-based amorphous alloys is carefully examined. In order to change free volume content, the as-quenched samples were annealed for 1 h at temperatures corresponding to the structural relaxation. Magnetostriction measurements were carried out at room temperature using the infrared magnetodilatometer. It was shown that both the parallel magnetostriction coefficient λ∥ and the perpendicular magnetostriction coefficient λ⊥ decrease with decreasing free volume content, whereas the saturation magnetostriction λS (proportional to λ∥−λ⊥) remains constant. In contrast, the volume magnetostriction ω strongly depends on free volume content and follows the relation ω∝ m2 (where m is the reduced magnetization). Moreover, it was confirmed that λS can be attributed to one-ion spin correlations, short range in nature.

Influence of free volume on the mechanical properties of epoxy based composites: A correlation study

AbstractEpoxy resins need toughening for enhancement of their usage in various applications. The commonly used rubber for toughening epoxies is silicones. In the present study, the effect of Amine containing silicones (ACS) as modifiers and hollow micro sphere such as cenospheres as fillers on DGEBA epoxy resin is studied. To understand the microstructure and its influence on the mechanical properties, free volume measurements have been carried out using Positron Annihilation Lifetime spectroscopy (PALS). The positron results indicate that the mechanical properties like tensile strength and modulus have a significant dependence on free volume. Attempts to correlate the available free volume with chain mobility and mechanical properties have led to the the general belief that any process, which reduces free volume, increases tensile strength and similar change in tensile modulus. From positron data it was observed that both free volume hole size, Vf and fractional free volume, Fv decreases as the cenospheres wt% increased up to 30 wt% and a slight increase thereafter in the siliconized epoxy composite. The tensile strength of cenospheres filled composite shows moderate increase of about 17.5% while an opposite trend is observed in fractional free volume which is on the expected lines. However tensile modulus exhibits behaviour different from tensile strength. This may be possibly due to low density of the fillers and the also the characteristics of epoxies as far as mechanical properties are concerned. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Free Volume on Damping Properties for CIIR and CIIR/PEA Investigated by Positron

The effect of the free volume on damping properties for CIIR (Chlorinated isoprene-isobutylene rubber) and CIIR/PEA (polyethylacrylate) were investigated by positron annihilation lifetime spectroscopy and DMA, respectively. The DMA results indicate that the tanδ peaks of CIIR and CIIR/PEA both have very broad covering temperature range. The tanδ peak of CIIR/PEA shifts to higher temperature region which indicates that the CIIR/PEA has better damping property in high temperature region that CIIR. From PALS results, we found that the lifetime of o-Ps in CIIR and CIIR/PEA both exhibit broad glass transition. It is interestingly that the glass transition region of CIIR/PEA also shifts to higher temperature than CIIR. This character of the free-volume is well in agreement with the damping properties obtained by DMA. It indicates that the free volume has close relationship with damping mechanism for CIIR and CIIR/PEA.

Morphology and transport characteristics of poly(ethylene- co-vinyl acetate)/clay nanocomposites

Poly(ethylene- co-vinyl acetate)/clay nanocomposite membranes were prepared with different clay loadings. The morphology of the nanocomposites was investigated using X-ray diffraction technique and transmission electron microscopy. The dispersion of layered silicates decreased with increasing filler loading. Samples with low filler content showed excellent dispersion of layered silicates resulting in a partially exfoliated structure. The transport characteristics of aromatic hydrocarbons through the nanocomposite membranes were studied by the simple sorption gravimetric analysis in the temperature range 28–70 °C and the results were compared with unfilled membranes. The solvent uptake nature of the nanoclay filled polymer samples was found to be much reduced. The solvent uptake was minimum for composites with 3 wt% of filler and increased with increasing filler content, which is presumably due to aggregation of clay filler at higher loading. The influence of free volume on the transport properties of the membranes was studied using positron annihilation lifetime spectroscopy. The transport phenomenon was found to follow an anomalous mode. Activation parameters were estimated and the molar mass between crosslinks was calculated using Flory–Rehner Theory. The experimental data were compared with theoretical predictions.

Influence of free volume on the mechanical properties of Epoxy/poly (methylmethacrylate) blends

Positron lifetime measurements have been performed to investigate the free volume dependence of the mechanical properties of Epoxy/poly methyl methacrylate (PMMA) blends of varying composition of PMMA (2.5, 5, 7.5, 10, 12.5, 15, and 17.5 wt%). The mechanical properties of the blends have been evaluated according to the (ASTM) standard. The positron results indicate that the mechanical properties like tensile strength and surface hardness have a significant dependence on the free volume of the blends. It is also found that the blends of the present study show positive deviation from the familiar linear additivity rule suggesting the immiscible nature of the blends. Further, up to 5-wt% of PMMA in the blend, an increase in relative fractional free volume correlates well with a decrease of tensile strength.

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.

Description of Phase Behavior of Polymer Blends by Different Equation-of-State Theories. 1. Phase Diagrams and Thermodynamic Reasons for Mixing and Demixing

A comparison has been made between the Sanchez-Lacombe equation-of-state theory and the theory of Patterson for describing the phase behavior of various polymer blends. Phase diagrams have been determined as well as PVT data, in order to determine the reduction parameters of the polymers used. With these data the phase diagrams were simulated applying these two theories. Furthermore, the cause of compatibility or incompatibility, i.e., the influence of free volume and enthalpic effects were investigated. Both theories show surprisingly similar behavior with respect to the mentioned properties.

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.

High‐conversion polymerization. VII. A definition of the explosive region and the influence of free volume on it

AbstractThe easily observed autoacceleration of free radical Polymerization is defined as the explosive region and an arbitrary but quantitative definition of it is made. Using this definition it is shown that the explosive regions of solution polymerizations of methyl methacrylate occur at constant values of the product of polymer concentration times (molecular weight)1/2. This upholds the concept that polymer entanglements control the termination reaction in this region. It is also shown that this region does not, as previously suggested, occur at a constant value of free volume, but that free volume does play a role in determining the rate of termination at a given level of chain entanglements.