Specific Free Volume Research Articles

Modified Free Volume Theory for Self-Diffusion of Small Molecules in Amorphous Polymers

Diffusion of small molecules in amorphous polymers near the glass transition is a topic of interest for a variety of technological applications. Within this study, the free volume theory (FVT) of Vrentas and Duda as a predictive tool for estimating self-diffusion coefficients is extended by suggesting modifications to certain aspects of this model. These modifications encompass the description of the free volume of the mixture, the viscosity–diffusivity interplay, and the energetics of the diffusion. To support the derived modifications, they are exercised on the diffusion of three active ingredients in polyvinylpyrrolidone. The results are partly compared with experimental data based on dielectric spectroscopy as well as secondary ion mass spectrometry (adopted from the literature). Concerning the specific hole free volume, an approach for describing nonideal mixtures achieved by means of estimating the mixtures’ Vogel temperature at each composition is proposed. Moreover, a new fragility-dependent parameter, ξ1, is introduced into the main equation of the FVT model, which brings the model in harmony with the fractional Stokes–Einstein (F-SE) relation at the pure diffusant limit, hence improving its predictions at higher diffusant mass fractions. Furthermore, the F-SE equation is employed to describe the pre-exponential factor as well as the effective molar jump energy at the pure diffusant extreme. The resulting molar energy is subsequently combined with an empirically obtained effective energy at the pure polymer limit and weighted according to a quadratic expression analogous to the cohesive energy of a solution. In conclusion, the modified FVT model discussed in this study presents a fully predictive platform for describing diffusion in polymers and offers an extended temperature and compositional applicability range compared to the original version of FVT. This model is expected to be applicable to the diffusion of small molecules, which are commensurate in size with typical segments of the polymer.

Effect of gelatin on the solubility and diffusivity of normal pentane in the poly (vinyl alcohol)/Gelatin blends

In this work, we investigated the effect of Gelatin on the solubility and diffusivity of normal pentane in poly (vinyl alcohol) (PVA)/Gelatin (Gel) blends. The processibility of PVA was enhanced after adding the gelatin as plasticizer to PVA which gelatin could extend the process widow of PVA with destroying the hydrogen bonding of the polymer matrix. Therefore, the PVA/Gel blends with different concentrations were prepared by simple solution-casting method. The intermolecular suitable interactions in PVA/Gel blends were confirmed using the FTIR, XRD and SEM/EDX analyzes. In the following, the effect of various factors like temperature, pressure and gelatin content on the thermodynamic parameters like specific free volume, solubility and diffusivity was investigated. It was shown that there was a relationship between the specific free volume of the blends with the solubility and diffusivity of normal pentane in blends. The specific free volume of blends was determined by applying the PVT data and the Sanchez-Lacombe (SL) equation of state, in which it was enhanced with increasing of the temperature and gelatin in blends, respectively. Also, the solubility and diffusivity of normal pentane in samples were determined by the magnetic suspension balance (MSB) system. The results presented that the solubility and diffusivity of n-pentane improved with increasing of gelatin content in blend, pressure and temperature decrement, respectively.

Enhanced proton conductivity and stability of Ba-deficient BaCe0.8Y0.2O3-δ

A-cation deficiency has a significant impact on the properties of proton-conducting perovskites (ABO3), depending on factors such as the ionic radius, concentration of dopant and degree of substoichiometry of the A-site cation. Here, we focus on the influence of Ba deficiency on the structure, stability and partial electrical conductivities of the perovskite BaCe0.8Y0.2O3-δ (BCY20). Neutron powder diffraction is employed to determine a monoclinic symmetry (space group I2/m) for Ba0.95Ce0.8Y0.2O3-δ (B95CY20), with greater distortion and specific free volume than BCY20. Confocal Raman microscopy integrated with atomic force microscopy and X-ray diffraction confirm improved resistance to carbonate formation in the Ba-deficient material. Electrical conductivity is also greater for B95CY20 in both wet and dry oxidising and moderate reducing conditions, reaching ≈1.4 and 1 S m−1 in dry conditions of O2 and N2, respectively, at 600 °C. Partial conductivities determined by a defect-chemistry-based method indicate that proton conductivity is dominant in wet air for temperatures <700 °C and greater for B95CY20 (≈0.95 S m−1 at 600 °C) in comparison to BCY20 (≈0.58 S m−1 at 600 °C), with an associated hydration enthalpy of −128 kJ mol−1. Mixed oxide ionic-electronic conductivity dominates in dry oxidising conditions and, again, is greater for Ba substoichiometric material.

Kinetic Regularities of Crystallization of Nanocomposites Based on Clinoptilolite and Ethylene-Hexene Copolymer

The paper presents the results of experimental studies of the crystallization process of nanocomposites based on clinoptilolite and an ethylene-hexene copolymer. The temperature dependence of the specific volume and free volume was investigated by the method of dilatometric measurements. In accordance with the theory of Avrami, the kinetic regularity of the isothermal crystallization process at the temperature of the first-order phase transition has been studied. The mechanism and type of crystal growth for the initial polymer matrix and nanocomposites are determined.

Integral evaluation of granular activated carbon at four stages of a full-scale WWTP deodorization system

Odor emissions from wastewater treatment plants (WWTPs) have always been a public concern. In this work, the physico-chemical, olfactometric and textural characterization of granular active carbon (GAC) used by an urban WWTP as a deodorization system, as well as the chromatographic quantification of the retained odoriferous compounds, have been carried out. These techniques have allowed an integral evaluation of the contaminated GAC and the characterization of the retained gaseous emission from four different stages of the wastewater treatment (pretreatment header: GAC-1; sand and fat removal: GAC-2; sludge thickening: GAC-3; sludge dehydration: GAC-4). A larger amount and variety of retained odoriferous compounds were found in GAC samples from the wastewater line deodorization (GAC-1 and GAC-2) after the same operation time (one year), GAC-1 being the adsorbent bed that retained the highest mass of volatile compounds (approximately 150μg/g GAC). Furthermore, some variables such as the removed specific odor concentration and free micropore volume were inversely correlated (R2=0.9945). The analysis of odor contribution showed that sulfur-containing compounds were the major odor contributors (61–97%). However, hydrogen sulfide cannot be considered a key odorant in this particular WWTP, since the elimination of this compound does not reduce the significant contribution of other (organic) sulfur compounds to the global odor (especially dimethyl disulfide). Consequently, multi-technical analysis might be a suitable alternative to better understand odor removal by GAC adsorption.

Electrical properties and conduction mechanisms of K, Ga co-substituted Na0.5Bi0.5TiO3 ferroelectrics

Ferroelectric Na0.5Bi0.5TiO3 has potential in exhibiting oxide-ion conductive characteristics at higher temperatures due to their high leakage current. In this study, K+ and Ga3+ co-doped Na0.5Bi0.5TiO3 ceramics are synthesized using the conventional solid-state reaction method, and their conduction mechanism and electrical performance are investigated. The compounds with dominant oxygen-ion conduction are identified and their stability in the presence of nitrogen is analyzed. The bulk conductivity of the ceramics is improved by decreasing the concentration of K+ associated with an enhanced Na/K–O vibration. Excess K+ dopants hinder oxygen vacancy migration owing to the attraction effect on oxygen vacancies VO•• and A-site acceptor KBi'', and narrow the oxygen vacancy migration channel. The oxygen vacancy concentration, tolerate factor, specific free volume, relaxation parameter, and critical radius are used to discuss the conductive properties. The results demonstrate that an appropriate amount of K+ and Ga3+ doping promotes the oxide-ionic conductivity, which is helpful for tailoring the electrical properties of Na0.5Bi0.5TiO3-based oxygen-ion conductors.

Catalytic behavior of ABO3 perovskites in the oxidative coupling of methane

Herein, we attempted to identify the active sites behavior of perovskite catalysts in the oxidative coupling of methane (OCM) reaction, using ten types of ABO3 perovskite catalysts with different structural properties according to their A and B site elements. The results showed that the catalyst surface lattice oxygen species are responsible for the selective conversion of methane. In particular, surface lattice oxygen species with moderate binding energies selectively catalyzed the OCM to produce C2 hydrocarbons. The surface oxygen vacancies, resulting from the reaction of lattice oxygen and CH4, were refilled with adsorbed surface oxygen and bulk lattice oxygen species. This oxygen cycle was closely related to the oxygen ion conductivity of perovskites, which could be determined based on their structural factors, such as the tolerance factor and the specific free volume. Accordingly, a facile oxygen cycle resulted in a high CH4 conversion during this reaction. Finally, we concluded that the lattice oxygen properties and the oxygen ion conductivity of perovskite catalysts are key factors in determining the catalytic activity and should, therefore, be precisely controlled for the systematic design of efficient OCM catalysts.

Samples of Ba1-xSrxCe0.9Y0.1O3-δ, 0 < x < 0.1, with Improved Chemical Stability in CO2-H2 Gas-Involving Atmospheres as Potential Electrolytes for a Proton Ceramic Fuel Cell.

Comparative studies were performed on variations in the ABO3 perovskite structure, chemical stability in a CO2-H2 gas atmosphere, and electrical conductivity measurements in air, hydrogen, and humidity-involving gas atmospheres of monophase orthorhombic Ba1−xSrxCe0.9Y0.1O3−δ samples, where 0 < x < 0.1. The substitution of strontium with barium resulting in Ba1−xSrxCe0.9Y0.1O3−δ led to an increase in the specific free volume and global instability index when compared to BaCe0.9Y0.1O3−δ. Reductions in the tolerance factor and cell volume were found with increases in the value of x in Ba1−xSrxCe0.9Y0.1O3−δ. Based on the thermogravimetric studies performed for Ba1−xSrxCe0.9Y0.1O3−δ, where 0 < x < 0.1, it was found that modified samples of this type exhibited superior chemical resistance in a CO2 gas atmosphere when compared to BaCe0.9Y0.1O3−δ. The application of broadband impedance spectroscopy enabled the determination of the bulk and grain boundary conductivity of Ba1−xSrxCe0.9Y0.1O3−δ samples within the temperature range 25–730 °C. It was found that Ba0.98Sr0.02Ce0.9Y0.1O3−δ exhibited a slightly higher grain interior and grain boundary conductivity when compared to BaCe0.9Y0.1O3−δ. The Ba0.95Sr0.05Ce0.9Y0.1O3−δ sample also exhibited improved electrical conductivity in hydrogen gas atmospheres or atmospheres involving humidity. The greater chemical resistance of Ba1−xSrxCe0.9Y0.1O3−δ, where x = 0.02 or 0.05, in a CO2 gas atmosphere is desirable for application in proton ceramic fuel cells supplied by rich hydrogen processing gases.

Ba0.95Ca0.05Ce0.9Y0.1O3 as an electrolyte for proton-conducting ceramic fuel cells

Comparative studies of the physicochemical and electrochemical properties of BaCe0.9Y0.1O3 and Ba0.95Ca0.05Ce0.9Y0.1O3 sintered ceramics are described. The orthorhombic (Pnma) space group was determined for both investigated samples within the temperature range 25–800 °C, using the X-ray diffraction method. A decrease in the cell volume of Ba0.95Ca0.05Ce0.9Y0.1O3 compared to that of BaCe0.9Y0.1O3 was observed within the investigated temperature range.It was found that the partial substitution of calcium for barium, resulting in Ba0.95Ca0.05Ce0.9Y0.1O3, caused an increase in specific free volume and global instability index compared to the original composition BaCe0.9Y0.1O3. Improvement of the chemical resistance of Ba0.95Ca0.05Ce0.9Y0.1O3 in a CO2 gas atmosphere was observed. It was found that Ba0.95Ca0.05Ce0.9Y0.1O3 exhibited a slightly lower level of electrical conductivity than BaCe0.9Y0.1O3 in air as well as in ArH2 gas atmospheres.The greater chemical resistance of Ba0.95Ca0.05Ce0.9Y0.1O3 in a CO2 gas atmosphere enhances the suitability of the modified material as an electrolyte for fuel cells with proton-conducting ceramics. The electrochemical response of the interface (La0.60Sr0.40)0.95Co0.20Fe0.80O3−δ|Ba0.95Ca0.05Ce0.9Y0.1O3 was also investigated within the applied potential range from −0.05 to −0.5 V in SOFC mode as well as from 0.05 to 0.5 V in SOEC mode); it was found that the current reached a fairly stable value over time.

Crystalline phases and oxygen permeation properties of mixed conductive (La, Ca)FeO3-δ

A typical mixed conductive oxide with high oxygen permeability is La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF), which is applicable to oxygen separation membrane and to cathodes for solid oxide fuel cells. However, Sr and Co included in the LSCF lower its stability when kept at elevated temperatures. La1-xCaxFeO3-δ(LCF) is a good candidate of mixed conductive oxides with no Sr and Co ions. This study investigated systematic details of crystalline phase, electrical conductivity, and oxygen permeability as functions of the Ca content in the LCF. The x = 0.3–0.4 samples with perovskite structure reveal higher electrical conductivity and higher oxygen permeation flux JO2 among the investigated LCF. Particularly, the JO2 of the x = 0.35 and 0.4 are higher than that of the LSCF, proposing that the samples replace the LSCF. Larger specific free volumes in x = 0.3–0.4 are a possible main reason for higher vacancy mobility, resulting in higher JO2.

Scandium Doping Effect on a Layered Perovskite Cathode for Low-Temperature Solid Oxide Fuel Cells (LT-SOFCs)

Layered perovskite oxides are considered as promising cathode materials for the solid oxide fuel cell (SOFC) due to their high electronic/ionic conductivity and fast oxygen kinetics at low temperature. Many researchers have focused on further improving the electrochemical performance of the layered perovskite material by doping various metal ions into the B-site. Herein, we report that Sc3+ doping into the layered perovskite material, PrBaCo2O5+δ (PBCO), shows a positive effect of increasing electrochemical performances. We confirmed that Sc3+ doping could provide a favorable crystalline structure of layered perovskite for oxygen ion transfer in the lattice with improved Goldschmidt tolerance factor and specific free volume. Consequently, the Sc3+ doped PBCO exhibits a maximum power density of 0.73 W cm−2 at 500 °C, 1.3 times higher than that of PBCO. These results indicate that Sc3+ doping could effectively improve the electrochemical properties of the layered perovskite material, PBCO.

Influence of A-site off-stoichiomety on grain conductivity and oxygen relaxation behavior of Na0.5Bi0.5TiO3 ceramics

The electrical performances and relaxation behaviors of the Na0.525Bi0.475TiO2.975 and Bi-deficient Na0.51Bi0.48TiO2.975 sample were investigated. The grain conductivity of the Na0.525Bi0.475TiO2.975 sample is able to reach 1.51 × 10−3 S/cm at 673 K. In the temperature range of measurement, the grain conductivity of the Bi-deficient Na0.51Bi0.48TiO2.975 sample is lower than that of the Na0.525Bi0.475TiO2.975 sample. By the internal friction and dielectric relaxation spectrum, the activation energy and relaxation time at infinite temperature were determined as (0.82 eV, 2.47 × 10−14 s), (0.67 eV, 5.82 × 10−12 s) and (0.85 eV, 5.8 × 10−13 s), (0.52 eV, 2.55 × 10−10 s) for the Na0.525Bi0.475TiO2.975 and Na0.51Bi0.48TiO2.975 samples at the different temperature regions. In the Na0.525Bi0.475TiO2.975 compound, there is larger specific free volume, higher mobile oxygen vacancy content and better oxygen vacancy mobility, which cause the higher grain conductivity in the Na0.525Bi0.475TiO2.975 compound. To some extent, by the Bi-deficient method, oxygen vacancies can be introduced into the Na0.51Bi0.48TiO2.975 compound and the grain conductivity may be improved, but the other side of Bi-deficiency harms the oxygen vacancy diffusion capacities in the Na0.5Bi0.5TiO3 compound.

Role of Filler Porosity and Filler/Polymer Interface Volume in Metal-Organic Framework/Polymer Mixed-Matrix Membranes for Gas Separation.

Metal-organic frameworks (MOFs) and inorganic fillers are frequently incorporated into mixed-matrix membranes (MMMs) to overcome the traditional trade-off in permeability ( P) and selectivity for pure organic polymer membranes. Therefore, it is of great interest to examine the influence of porous and nonporous fillers in MMMs with respect to the possible role of the polymer-filler interface, that is, the void volume. In this work, we compare the same MOF filler in a porous and nonporous state, so that artifacts from a different polymer-filler interface are excluded. MMMs with the porous MOF aluminum fumarate (Al-fum) and with a nonporous dimethyl sulfoxide solvent-filled aluminum fumarate (Al-fum(DMSO)), both with Matrimid as polymer, were prepared. Filler contents ranged from 4 to 24 wt %. Gas separation performances of both MMMs were studied by mixed gas measurements using a binary mixture of CO2/CH4 with gas permeation following the theoretical prediction by the Maxwell model for both porous and nonporous dispersed phase (filler). MMMs with the porous Al-fum filler showed increased CO2 and CH4 permeability with a moderate rise in selectivity upon increasing filler fraction. The MMMs with the nonporous Al-fum(DMSO) filler displayed a reduction in permeability while maintaining the selectivity of the neat polymer. A linear dependence of log P versus the reciprocal specific free fractional volume (sFFV) rules out a significant contribution from a void volume. The sFFV includes the free volume of the polymer and the MOF, but not the polymer-filler interface volume (so-called void volume). The sFFV for the MMM was calculated between 0.23 cm3/g for a 24 wt % Al-fum/Matrimid MMM and 0.12 cm3/g for a 24 wt % Al-fum(DMSO)/Matrimid MMM. The negligible effect of an interface volume is supported by a good matching of theoretical and experimental density of the Al-fum and Al-fum/(DMSO) MMMs which gave a specific void volume below 0.02 cm3/g, often even below 0.01 cm3/g.

Demonstrating the Influence of Physical Aging on the Functional Properties of Shape-Memory Polymers.

Polymers that allow the adjustment of Shape-Memory properties by the variation of physical parameters during programming are advantageous compared with their counterparts requiring synthesis of new material. Here, we explored the influence of hydrolytic (physical) aging on the Shape-Memory properties of the polyetherurethane system Estane, programmed in repeated thermomechanical cycles under torsional load. We were able to demonstrate that physical aging occurred through water adsorption influencing the existing free volume of the samples as well as the functional properties of Estane. Dynamic Mechanical Thermal Analysis determined the glass transition temperatures of dry and hydrolytically aged samples. According to our results, Estane takes up to 3 wt % water for two weeks (at an ambient temperature of θ = 20 °C). The glass transition temperatures of dry samples decreased within this period from 55 to 48 °C as a consequence of a plasticization effect. Next, for both samples, six subsequent thermomechanical cycles under torsional loading conditions were performed. We were able to confirm that hydrolytically aged samples showed higher shape recovery ratios of Rr ≥ 97%, although dry samples revealed better shape fixity values of about 98%. Moreover, it was observed that the shape fixity ratio of both dry and hydrolytically (physically) aged samples remained almost unchanged even after six successive cycles. Besides this, the shape recovery ratio values of the aged samples were nearly unaltered, although the shape recovery values of the dry samples increased from Rr = 81% in the first cycle to 96% at the end of six repeated cycles. Further, the evolution of the free volume as a function of temperature was studied using Positron Annihilation Lifetime Spectroscopy. It was shown that the uptake of two other organic solvents (acetone and ethanol) resulted in much higher specific free volume inside the samples and, consequently, a softening effect was observed. We anticipate that the presented approach will assist in defining design criteria for self-sufficiently moving scaffolds within a knowledge-based development process.

Evaluation of UiO‐66 metal organic framework as an effective sorbent for Curcumin's overdose

Metal organic frameworks (MOFs) UiO‐66 (UiO stands for University of Oslo) and NH2‐UiO‐66 were prepared and characterized as sorbent (antidotal agents) for curcumin (CUR) adsorption. The structure of products were characterized by X‐ray powder diffraction (XRD), Field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), Attenuated Total Reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR), and N2 adsorption–desorption measurements. FESEM showed NH2‐UiO‐66 displayed symmetrical crystals with triangular base pyramid morphology, with the particle size around 100 nm and uniform size distribution. Adsorption capacities of CUR/MOFs with different mass ratios in the feed were investigated in the present study, and this investigation revealed that when the CUR/MOFs with mass ratio was around 0.4, the absorption capacity of NH2‐UiO‐66 had tended to maximum. Although, functionalization reduced the specific surface area and free volume, introducing polar amine groups could improve the affinity of NH2‐UiO‐66 respect to CUR. Kinetic studies showed that the kinetic data are well fitted with the pseudo‐ second‐order model. MTT assay revealed that MOFs at the concentration range of 0–560 μg/ml had no cytotoxic effect on the Human Foreskin Fibroblast normal cell line (HFF‐2). These results suggest that these MOFs could be safe as sorbent for adsorb CUR from the body.

Impedance and dielectric relaxation spectroscopy studies on the calcium modified Na0.5Bi0.44Ca0.06TiO2.97 ceramics

Na0.5Bi0.44Ca0.06TiO2.97 ceramics were synthetized by conventional solid-state reaction. XRD measurement analysis shows that the Na0.5Bi0.44Ca0.06TiO2.97 sample is the single perovskite structures. The oxide ion conductivity of the Na0.5Bi0.44Ca0.06TiO2.97 sample was investigated by AC impedance spectroscopy measurement. The bulk conductivity of Na0.5Bi0.44Ca0.06TiO2.97 sample can arrive at 2.22×10-4 S/cm at 573 K in air atmosphere. By changing measuring temperature of dielectric frequency spectroscopy measurement, the activation energy E and pre-exponential factor τ0 are E= 0.81 eV, τ0=1.5×10-13 s for Na0.5Bi0.44Ca0.06TiO2.97 sample, respectively. Judging from the relaxation parameters, the dielectric loss peaks correspond to oxide ion via vacancies diffusion in Na0.5Bi0.44Ca0.06TiO2.97 sample. Compared with the same dopant amount Na0.5Bi0.5Ti0.94Mg0.06O2.94 compound, the better oxygen vacancy mobility and larger specific free volume Vsf might be responsible for the favourable oxide ion conductivity in the Na0.5Bi0.44Ca0.06TiO2.97 sample, indicating that calcium modified Na0.5Bi0.5TiO3 materials are promising for intermediate-temperature solid electrochemical devices.

Structural, electrical and dielectric properties of Bi-doped Pr0.8-xBixSr0.2MnO3 manganite oxides prepared by sol-gel process

The aim of this paper is to investigate the structural, electrical and dielectric properties of Pr0.8-xBixSr0.2MnO3 (x = 0, 0.05 and 0.1) perovskite materials. Our samples were synthesized by sol-gel route and characterized by X-ray powder diffraction at room temperature. It has been demonstrated that they crystallize in the orthorhombic perovskite system with Pnma space group. As x varies from 0 to 0.1, the MnO bond length and the unit cell volume increases. Consequently, the bandwidth describing the overlap between the Mn3d and O2p orbital is reduced and this affects physical properties. The studied samples were also characterized by complex impedance spectroscopy in a wide range of temperature and frequency. DC conductance results show that doping by Bi suppresses the metal behavior observed at low temperatures in the parent compound. The conductivity decreases when increasing the concentration of Bi due to the reduction of the specific free volume. AC conductivity measurements were split in two parts: The metallic region is well described by the classical Drude model and the semiconductor one was well fitted by the universal Jonscher power law. Results show that the conduction mechanism is described by non-overlapping small polaron tunneling (NSPT) model. Besides, the Cole-Cole plots which are fitted by adequate equivalent circuits show the contributions of grain and grain boundaries in the conduction mechanism. At high temperatures, the total conductivity tends to be governed by grains. Dielectric results show that the Pr0.75Bi0.05Sr0.2MnO3 sample has better dielectric properties than Pr0.7Bi0.1Sr0.2MnO3. Dielectric loss is analyzed by Giuntini theory and correlated with conduction losses. The energy required for carriers to jump over the potential barriers is determined.

Fluid dynamics and thermodynamics as a unified field theory

We study the problem of consistency of equations of continuum dynamics (using the Euler equations and the continuity equation as examples) and thermodynamic equations of state (for the specific free energy, entropy, and volume). We propose a variant of the Hamiltonian formulation of a model that combines the fluid dynamics of a potential flow of a compressible fluid or gas and local equilibrium thermodynamics into a unified field theory. Thermodynamic equations of state appear in this model as second-class constraint equations. As a consistency condition, there arises another second-class constraint requiring that the product of density and temperature should be independent of time. The model provides an in-principle possibility of finding the time dependence of the specific entropy of the arising dynamical system.

Extended studies on molecular interactions of SDBS and DTAB in aqueous solutions of amino acid at T = 293.15–313.15 K

The volumetric properties for this mixture of amino acid–surfactant system have already been discussed in an earlier published article, but to go further into the details on molecular interactions, different acoustical parameters viz. relative association (RA), intermolecular free length (Lf), molar sound number ([U]), specific acoustic impedance (Z), free volume (Vf), molar volume (Vm), internal pressure (πi) and molar cohesive energy (MCE) have been evaluated from the parent data of density, speed of sound and viscosity. The variation of these parameters with concentration of surfactant helps us in understanding the nature and extent of interactions present among the molecules in the mixture. The effect of amino acid concentrations on the micellization behavior of these surfactants has also been discussed through these parameters.

Thermodynamic Properties and Free Volume Analyses of Polycarbonates by a Combined Experimental and Molecular Simulation Method

A combined experimental and computational approach is applied to amorphous polycarbonates (PCs) to link the macroscopic behavior and molecular features. The Simha–Somcynsky equation of phase (EOS) provides a more accurate description than the Tait EOS for describing the pressure–volume–temperature (PVT) relationship and thermal expansivity. The relationship between the specific volume and the hole free volume was investigated using PVT measurements, positron annihilation lifetime spectra, and molecular dynamics (MD) techniques, to examine the correlations between changes in the behavior of specific volume and molecular packing. We found that the specific volume and hole free volume have linear relationships with temperature. However, the occupied volume displayed remarkable compressibility. The analyses revealed that the PC with side methyl groups and long C–Si bonds contributed to the formation of large free volume. The MD results validate the effectiveness of molecular simulation techniques in designing materials at the molecular level.