Transport Properties Of Polymers Research Articles

Probing the Free Volume in Polymers by Means of Positron Annihilation Lifetime Spectroscopy.

Positron annihilation lifetime spectroscopy (PALS) is a valuable technique to investigate defects in solids, such as vacancy clusters and grain boundaries in metals and alloys, as well as lattice imperfections in semiconductors. Positron spectroscopy is able to reveal the size, structure and concentration of vacancies with a sensitivity of 10-7. In the field of porous and amorphous systems, PALS can probe cavities in the range from a few tenths up to several tens of nm. In the case of polymers, PALS is one of the few techniques able to give information on the holes forming the free volume. This quantity, which cannot be measured with macroscopic techniques, is correlated to important mechanical, thermal, and transport properties of polymers. It can be deduced theoretically by applying suitable equations of state derived by cell models, and PALS supplies a quantitative measure of the free volume by probing the corresponding sub-nanometric holes. The system used is positronium (Ps), an unstable atom formed by a positron and an electron, whose lifetime can be related to the typical size of the holes. When analyzed in terms of continuous lifetimes, the positron annihilation spectrum allows one to gain insight into the distribution of the free volume holes, an almost unique feature of this technique. The present paper is an overview of PALS, addressed in particular to readers not familiar with this technique, with emphasis on the experimental aspects. After a general introduction on free volume, positronium, and the experimental apparatus needed to acquire the corresponding lifetime, some of the recent results obtained by various groups will be shown, highlighting the connections between the free volume as probed by PALS and structural properties of the investigated materials.

Design of Polymeric Membranes for Air Separation by Combining Machine Learning Tools with Computer Aided Molecular Design

The growing importance of the membrane-based air separation processes results in an increasing demand for suitable polymeric membrane structures. This has spurred the interest in designing polymer structures for O2/N2 separation by employing a systematic approach. In this work, a computer-aided molecular design (CAMD)-based framework was developed to identify promising structures of polymers that can be used for air separation. To incorporate constraints in CAMD, the rough set-based machine learning (RSML) method was implemented to establish predictive models for the physical and transport properties of polymer owing to its interpretability. The deterministic rules generated from RSML would be interpreted scientifically reflecting the structure–property relationship to ensure that the molecules generated were feasible according to a scientific point of view. The most prominent rules selected were then integrated as constraints in CAMD. The relevant properties in this framework comprised of glass transition temperature (Tg), molar volume (Vm), cohesive energy (Ecoh), O2 permeability and O2/N2 selectivity. The solutions from CAMD optimisation were demonstrated in case studies. Results indicated the capability of a novel approach in identifying potential polymeric membrane candidates for air separation application that meet the permeability and selectivity requirements.

Hybrid Microporous Polymeric Materials with Outstanding Permeability and Increased Gas Transport Stability: PTMSP Aging Prevention by Sorption of the Polymerization Catalyst on HCPS.

The influence of hyper-crosslinked polystyrene (HCPS) MacronetTM MN200 on the gas transport properties and aging of the highly permeable glassy polymer poly(1-trimethylsilyl-1-propyne) (PTMSP) was studied and analyzed in detail. The gas transport characteristics of dense PTMSP membranes containing 0–10.0 wt % HCPS were studied. It was shown that the introduction of a small amount of HCPS into the PTMSP matrix led to a 50–60% increase of the permeability coefficients of the material for light gases (N2, O2, CO2) and slowed down the deterioration of polymer transport properties over time. The lowest reduction in gas permeability coefficients (50–57%) was found for PTMSP containing HCPS 5.0 wt % after annealing at 100 °C for 300 h. It was found that HCPS sorbed residues of tantalum-based polymerization catalyst from PTMSP. In order to investigate the influence of catalysts on transport and physical properties of PTMSP, we purified the latter from the polymerization catalyst by addition of 5 wt % HCPS into polymer/chloroform solution. It was shown that sorption on HCPS allowed for almost complete removal of tantalum compounds from PTMSP. The membrane made of PTMSP purified by HCPS demonstrated more stable transport characteristics compared to the membrane made of the initial polymer. HCPS has a complex effect on the aging process of PTMSP. The introduction of HCPS into the polymer matrix not only slowed down the physical aging of PTMSP, but also reduced chemical aging due to removal of active reagents.

Interfacial thermal transport properties of polyurethane/carbon nanotube hybrid composites

Although polymers have been used in a wide range of applications in everyday life, their extremely low thermal conductivity severely impedes their applicability in the fields of energy-efficient buildings and microelectronics. Pioneering researchers have proposed carbon nanotubes (CNTs) that can remarkably improve the overall thermal transport properties of polymers by functioning as great thermally conductive fillers. However, the interfacial thermal transport mechanisms between CNT and polymer are complex and not fully understood. To clarify this issue, the interfacial thermal conductance (G) of a representative single-walled CNT (SWCNT)/polymer interface, specifically CNT/polyurethane (PU), was studied in detail by molecular dynamic simulation. Two different hybrid CNT/PU structures were constructed and the corresponding G values were 0.163 MW m−2 K−1 and 1.062 MW m−2 K−1. This significant enhancement in the G value can primarily be attributed to the increase in the length of SWCNTs and in the number of PU molecular chains. The vibrational densities of states of phonon spectrum indicate that the carbon and oxygen atoms in the PU molecular chains are favorable for interfacial thermal transport. The radial distribution function and interaction energy demonstrate the distribution characteristics of the PU molecular chains and also verify the accuracy of the simulation.

BEYOND THE SPHERICAL APPROXIMATION: ELONGATED FREE VOLUME HOLES IN RUBBERS: A POSITRON ANNIHILATION STUDY

ABSTRACT The free volume fraction, a key parameter for the understanding of mechanical and transport properties of polymers, has been evaluated in a fluoroelastomer and a cis-polyisoprene rubber by means of positron annihilation lifetime spectroscopy and dilatometry. The evaluation showed that the assumption of elongated holes allows one to get a very good agreement between the free volume fraction experimentally determined and the theoretical expectation based on the lattice-hole model. On the other hand, systematic discrepancies are found using the spherical approximation. Moreover, the average hole size is found to be correlated to the effective bond length leff, a parameter connected to reptation motions and largely independent of the polymer structure. The result sheds some light on conformational statistics for the most flexible linear polymers that approach Gaussian chain behavior.

Synthesis and Study of Gas Transport Properties of Polymers Based on Macroinitiators and 2,4-Toluene Diisocyanate.

Nowadays, block copolymers hold great promise for the design of novel membranes to be applied for the membrane gas separation. In this regard, microporous block copolymers based on a macroinitiator with an anionic nature, such as potassium-substituted block copolymers of propylene oxide and ethylene oxide (PPEG) and 2,4-toluene diisocyanate (TDI), were obtained and investigated as effective gas separation membranes. The key element of the macromolecular structure that determines the supramolecular organization of the studied polymers is the coplanar blocks of polyisocyanates with an acetal nature (O-polyisocyanate). In the present research, the influence of the content of peripheral polyoxyethylene (POE) blocks in PPEG on the supramolecular structure processes and gas transport characteristics of the obtained polymers based on PPEG and TDI was investigated. According to the study of polymers if the POE block content is 15 wt %, the polyoxypropylene segments are located in the internal cavity of voids formed by O-polyisocyanate blocks. When the POE block content is 30 wt %, the flexible chain component forms its own microphase outside the segregation zone of the rigid O-polyisocyanate blocks. The permeability for polar molecules, such as ammonia or hydrogen sulfide, significantly exceeds the permeability values obtained for non-polar molecules He, N2 and CH4. A relatively high permeability is also observed for carbon dioxide. At the same time, the content of POE blocks has a small effect on the permeability for all studied gases. The diffusion coefficient increases with an increase in the POE block content in PPEG for all studied gases.

Synthesis and properties of a series of quinoxaline-based copolymers: an example to understand the effect of the structure of the mainchain and sidechain on the charge transport ability of the polymers

This paper systematically studied the influence of mainchain and sidechain variations on optical, electronic and charge transport properties of polymers.

Controlling aggregation and crystallization of solution processed diketopyrrolopyrrole based polymer for high performance thin film transistors by pre-metered slot die coating process

The organic semiconductors have attracted much attention for plastic electronics due to their good solution processability, low temperature deposition, and compatible with large-area printing technology. The charge transport properties of polymer based field effect transistors are limited by their amorphous domains and weakly interaction between polymer chains. In this study, antisolvent like methanol is introduced to promote polymer chain aggregation, and slot die coating is used to finely tune the film morphology. The effects of anti-solvent introduction and slot die coating process on the device performance, e.g. charge transport, surface morphology, and solid state packing, were investigated in details. By optimizing the antisolvent ratio and polymer chain aggregation, the charge transport properties of the polymer devices were observed to be significantly improved. An average charge carrier mobility of 3.76 cm2 V−1 s−1 and a maximum mobility of 4.10 cm2 V−1 s−1 were achieved under optimized conditions. The controlling the aggregation degree by combining the mixed solvent system and slot die coating technique provides a convenient and practical approach to achieve high performance polymer field effect transistor.

Chain Dynamics, Relaxation Times, and Conductivities of Bithiophene--Acene Copolymers Measured Using High Frequency Saturation Transfer EPR.

We present a study to probe the formation of localized aromatic sextets and their effects on the charge transport properties in polymers with acene cores. Bithiophene-acene copolymers containing benzene, naphthalene, or anthracene as acene cores were synthesized using Yamamoto polymerization. Drop-casted polymer films were chemically doped and analyzed using high frequency saturation transfer EPR (HF ST-EPR), a method which has proven useful in the study of conducting polymers. The spin-spin and spin-lattice relaxation times were determined for these polymers at low temperatures (4 to 20 K) and used to obtain inter- and intrachain spin diffusion rates and conductivities. Similar interchain spin diffusion rates were seen across all polymer systems; however, anthracene containing polymer poly(hexylTTATT) was found to have the largest intrachain spin diffusion rate. The poly(hexylTTATT) intrachain spin diffusion rate may be artificially high if the anthracene ring restricts the diffusion of spin to the hexylated quaterthiophene segment in poly(hexylTTATT) whereas the spins diffuse through the acene cores in the benzene and naphthalene derivatives. Alternatively, as both the spin diffusion rates and conductivities vary unpredictably with temperature, it is possible that the π-electron localization previously seen in the anthracene core could be relieved at lower temperatures.

Mass transfer considerations in solid-liquid two-phase partitioning bioreactors: a polymer selection guide

BACKGROUND Selection of polymers for two-phase partitioning bioreactors (TPPBs) has been focused primarily on predicting a polymer's affinity for the target molecule. Although the extent to which a polymer absorbs a solute is important, the rate of uptake/release must be sufficiently rapid such that a TPPB is not mass transfer limited. This work focused on developing a guide to identify combinations of polymer diffusivities and diffusional path lengths that will ensure a TPPB is not limited by substrate delivery. RESULTS TPPB systems limited by substrate delivery yielded linear growth, while biologically limited systems exhibited exponential growth. Release rates of phenol from various polymer phases increased as polymer diffusivity increased, or as diffusional path length (polymer bead size) decreased. A polymer selection guide was developed identifying combinations of polymer diffusivity and bead size that will ensure a TPPB is not mass transfer limited, for a desired maximum substrate consumption rate. CONCLUSION In selecting polymers for TPPB applications, solute affinity (extent of uptake) has been relatively well characterized using first principles methods, and the present work has now ‘completed the picture’ by providing a description of polymer transport properties (diffusivity and diffusional path length) to be able to generate a guide for selecting polymers. © 2015 Society of Chemical Industry

Thermal Properties of Polymethyl Methacrylate Composite Containing Copper Nanoparticles.

Thermal functional Materials have wide applications in thermal management fields, and inserting highly thermal conductive materials is effective in enhancing thermal conductivity of matrix. In this paper, copper nanoparticles were selected as the additive to prepare polymethyl methacrylate (PMMA) based nanocomposite with enhanced thermal properties. Uniform copper nanoparticles with pure face-centered lattice were prepared by liquid phase reduction method. Then, they were added into PMMA/N, N-Dimethylmethanamide (DMF) solution according to the different mass fraction for uniform dispersion. After DMF was evaporated, Cu-PMMA nanocomposites were gained. The thermal analysis measurement results showed that the decomposition temperature of nanocomposites decreased gradually with the increasing particle loadings. The thermal conductivity of the Cu-PMMA nanocomposites rose with the increasing contents of copper nanoparticles. With a 20 vol.% addition, the thermal conductivity was up to 1.2 W/m · K, a 380.5% increase compared to the pure PMMA. The results demonstrate that copper nanoparticles have great potential in enhancing thermal transport properties of polymer.

Technology Focus: Heavy Oil (March 2015)

Technology Focus This past year witnessed significant activity and growth related to heavy-oilfield developments worldwide, and this was accompanied by a record number of SPE paper submissions on related topics. This feature article highlights several technical focus areas identified in this new literature set. On the basis of field experience, operators have recognized the importance of developing and implementing technologies that improve inflow conformance to facilitate uniform steam-chamber development along steam-assisted-gravity-drainage (SAGD) production wells. Several papers describe the development, testing, and field piloting of completions that incorporate various types of inflow-control de vices (ICDs). While most of these consider passive or autonomous control de vices, one paper describes the installation and early performance of an intelligent-well-completion system with full surface activation and control of the ICDs in an SAGD well. Technical challenges associated with sand control, erosion, scaling, and plugging also must be addressed as these various systems evolve and their use continues to grow. Significant attention was also given to solvent-based recovery methods with more than three dozen papers on various aspects of modeling, experimental evaluation, and field piloting of different solvent recovery schemes. This work contributes to the understanding of the complex chemical and physical processes involved in applying such recovery methods in different reservoirs and thus will assist operators in the effective screening, design, and commercial implementation of these techniques. As an example, another paper offers insights to the simulation community on methodological aspects of modeling hybrid steam/solvent processes. The exploitation of offshore heavy-oil reservoirs continued to be a focus for operators in many regions. The literature describes comprehensive appraisal and development planning programs as well as various studies and field pilots undertaken to screen/evaluate alternative primary- and enhanced-recovery methods (including polymer floods and various thermal processes) for these applications. One paper outlines the strategies pursued to address the challenges involved in developing a high-viscosity heavy-oil reservoir in the North Sea. Additional focus areas include advanced simulation techniques, new polymer developments and field applications, reservoir characterization and recovery surveillance, recovery strategies for fractured carbonate reservoirs, thermal-well design and integrity, caprock integrity, rock- and fluid-property determination, artificial-lift performance and reliability, and in-situ-combustion and electrical-heating recovery methods. The additional-reading papers and many others on these topics can be found in the OnePetro library. With the decline in oil price and typical product differentials, the current year will be particularly challenging for heavy-oil operations. However, as in the past, these conditions also create opportunities for technology development and deployment to improve operational performance and efficiency, and this should remain a priority for the industry. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 172850 Polymer Flooding for Extraheavy Oil: New Insights on the Key Polymer Transport Properties in Porous Media by F. Rodriguez, Paris Diderot University, et al. SPE 169678 Maximizing Steam-Project Value in South Oman Through Flexible Development Phasing and Integrated Reservoir Surveillance by S.M. Al-Hinai, Petroleum Development Oman, et al. SPE 172889 Maximizing the Profitability of Extraheavy-Oil Wells With Cyclic Steam Injection in the Samaria Neogeno Field by Using Injection Profiles Logged Under Extreme Temperatures by Ezequiel A. Isidro Torres, Pemex, et al. SPE 170109 A Case Study in the Application of Bitumen Geochemistry for Reservoir Characterization in SAGD Development by J.N. Sereda, Suncor Energy, et al. SPE 169513 Case Study: Steam-Injection Step-Rate Tests Run in the Shallow Low- Permeability Diatomite Formation, Orcutt Oil Field, Careaga Lease, Santa Barbara County, California by Ramon Elias, Santa Maria Energy, et al.

Controlling polymer translocation and ion transport via charge correlations.

We develop a correlation-corrected transport theory in order to predict ionic and polymer transport properties of membrane nanopores under physical conditions where mean-field electrostatics breaks down. The experimentally observed low KCl conductivity of open α-hemolysin pores is quantitatively explained by the presence of surface polarization effects. Upon the penetration of a DNA molecule into the pore, these polarization forces combined with the electroneutrality of DNA sets a lower boundary for the ionic current, explaining the weak salt dependence of blocked pore conductivities at dilute ion concentrations. The addition of multivalent counterions to the solution results in the reversal of the polymer charge and the direction of the electroosmotic flow. With trivalent spermidine or quadrivalent spermine molecules, the charge inversion is strong enough to stop the translocation of the polymer and to reverse its motion. This mechanism can be used efficiently in translocation experiments in order to improve the accuracy of DNA sequencing by minimizing the translocation velocity of the polymer.

Controlling Conformations of Diketopyrrolopyrrole-Based Conjugated Polymers: Role of Torsional Angle

Transport of charge carriers through conjugated polymers is strongly influenced by the presence and distribution of structural disorders. In the present work, structural defects caused by the presence of torsional angle were investigated in a diketopyrrolopyrrole (DPP)-based conjugated polymer. Two new copolymers of DPP were synthesized with varying torsional angles to trace the role of structural disorder. The optical properties of these copolymers in solution and thin film reveal the strong influence of torsional angle on their photophysical properties. A strong influence was observed on carrier transport properties of polymers in organic field-effect transistors (OFET) device geometry. The polymers based on phenyl DPP with higher torsional angle (PPTDPP-OD-TEG) resulted in high threshold voltage with less charge carrier mobility as compared to the polymer based on thiophene DPP (2DPP-OD-TEG) bearing a lower torsional angle. Carrier mobility and the molecular orientation of the conjugated polymers were correlated on the basis of grazing incidence X-ray scattering measurements showing the strong role of torsional angle introduced in the form of structural disorder. The results presented in this Article provide a deep insight into the sensitivity of structural disorder and its impact on the device performance of DPP-based conjugated polymers.

Thermoelectric Potential of Polymer-Scaffolded Ionic Liquid Membranes

Organic thin films have been viewed as potential thermoelectric (TE) materials, given their ease of fabrication, flexibility, cost effectiveness, and low thermal conductivity. However, their intrinsically low electrical conductivity is a main drawback which results in a relatively lower TE figure of merit for polymer-based TE materials than for inorganic materials. In this paper, a technique to enhance the ion transport properties of polymers through the introduction of ionic liquids is presented. The polymer is in the form of a nanofiber scaffold produced using the electrospinning technique. These fibers were then soaked in different ionic liquids based on substituted imidazolium such as 1-ethyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium bromide. This method was applied to electrospun polyacrylonitrile and a mixture of polyvinyl alcohol and chitosan polymers. The ion transport properties of the membranes have been observed to increase with increasing concentration of ionic liquid, with maximum electrical conductivity of 1.20 × 10−1 S/cm measured at room temperature. Interestingly, the maximum electrical conductivity value surpassed the value of pure ionic liquids. These results indicate that it is possible to significantly improve the electrical conductivity of a polymer membrane through a simple and cost-effective method. This may in turn boost the TE figures of merit of polymer materials, which are well known to be considerably lower than those of inorganic materials. Results in terms of the Seebeck coefficient of the membranes are also presented in this paper to provide an overall representation of the TE potential of the polymer-scaffolded ionic liquid membranes.

The Entropic Cost of Polymer Confinement

The confinement of a polymer into a small space is thermodynamically unfavorable because of the reduction in the number of conformational states. The entropic penalty affects a variety of biological processes, and it plays an important role in polymer transport properties and in microfluidic devices. We determine the entropic penalty for the confinement of elastic polymer of persistence length P in the long-chain limit. We examine three geometries: (1) parallel planes separated by a distance d (a slit); (2) a circular tube of diameter d; and (3) a sphere of diameter d. We first consider infinitely thin (ideal) chains. As d/P drops from 100 to 0.01, TΔS rises from ∼5 × 10(-4) kT to ∼30 kT per persistence length for cases (1) and (2), with the entropic penalty for case (2) being consistently about twice that for case (1). TΔS is ∼5 kT per persistence length for confinement to a sphere when d = P, about twice the value predicted by mean field theory. For all three geometries, in the limit d/P ≫ 1, the asymptotic behavior of ΔS vs d is consistent with the d(-2) behavior predicted by theory. In the limit d/P ≪ 1, the scaling of ΔS for slits and tubes is also consistent with earlier predictions (d(-2/3)). Finally, we treat volume exclusion effects, examining chains of diameter D > 0. Confinement to a narrow slit or tube (d/P ≪ 1) has the same entropic penalty as that for an ideal chain in a slit or tube with d' = d - D; in the weak confinement regime (d/P ≫ 1), the entropic penalties are significantly larger than those for infinitely thin chains. When a chain of finite diameter is forced into a sphere or other closed cavity, the entropic confinement penalty rises without limit because there are no configurations available to the chain once its volume exceeds that of the cavity.

Spin transport in poly(metalarenylsilane)

We focused on the spin transport properties of polymers containing ferrocene and the related transition-metal-benzene sandwich compound (metal = Cr and V) with a silicon bridge such as poly(ferrocenylsilane) and poly(metalarenylsilane). As a model system, a sulfur-substituted oligomer was put on gold electrodes via the sulfur-gold interaction. Spin transport between the two gold electrodes was calculated using a non-equilibrium Green’s function formalism and density functional theory. We have found that the oligomer containing Cr or V atoms exhibited an almost perfect spin filter behavior in which all the 3dz2 orbitals contributed to the electron transport.

Theory Design of Two Polymer Donors for Organic Heterojunction Solar Cells

A highly efficient organic solar cell needs a copolymer as donor possessing low-band gap, high open-circuit voltage (Voc), good charge transfer at donor-acceptor (D-A) interface, and good transport properties in polymers. As the first step towards this goal, we constructed two polymers (PBnDT-HTAZ and PBnDT-6CNTAZ) incorporating benzodithiophene (BnDT) as the electron-rich units and either 1H-benzo(d)(1,2,3)triazole (HTAZ) or 1H-benzo(d)(1,2,3)triazole-6-carbonitrile (6CNTAZ) as the electron-deficient unit. The designed PBnDT-6CNTAZ was introduced a cyano in the electron-deficient unit. PBnDT-HTAZ and PBnDT-6CNTAZ as donors and (6,6)-phenyl C61-butyric acid methyl ester (PC60BM) as an ac- ceptor in hetero-organic solar cell, as well as the D-A complexes are investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) in this work. The electronic properties, optical absorption properties, intramolecular and intermolecular charge transfer, exciton binding energy of two polymers and corresponding D-A com- plexes are discussed. By means of Marcus theory, the exciton-dissociation, charge-recombination rate of D-A complex at the D-A interface, and the hole-transport rate of polymer donors are studied. According to the computational results, it indicates that the two polymers have strong and wide absorption peaks in visible region, as well as strong intramolecular charge trans- fer and intermolecular charge transfer for corresponding D-A complex. The designed PBnDT-6CNTAZ possesses lower the energy of the highest occupied molecular orbital (HOMO) so that PBnDT-6CNTAZ exhibits larger open-circuit voltage and better ability of antioxidant in comparison with PBnDT-HTAZ. The two polymers corresponding D-A complexes have small exciton binding energy. The PBnDT-6CNTAZ has good ability of charge transfer and larger hole-transport rate in compari- son to PBnDT-HTAZ. It is thus clear that incorporating cyano in polymer (PBnDT-6CNTAZ) have an important impact on performance of organic solar cell. Therefore, we can infer that PBnDT-6CNTAZ may be a potential donor material of bulk heterojunction solar cells. The present calculated results demonstrated a first attempt of providing a theoretical model for the introduction of electron-deficient groups in copolymer donors. These results may provide a structural guideline for optimiz- ing chemical construction of copolymer donors to improve the performance of bulk heterojunction solar cells. Our computa- tional models and conclusions can be applied to design and predict other new polymer donors. Keywords organic solar cell; donor-acceptor complex; benzotriazole; charge transfer

Water transport and clustering behavior in homopolymer and graft copolymer polylactide

Polylactide is a bio-based and biodegradable polymer well-known for its renewable origins. Water sorption and clustering behavior in both a homopolymer polylactide and a graft copolymer of polylactide was studied using the quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) technique. The graft copolymer, poly(1,5-cyclooctadiene-co-5-norbornene-2-methanol-graft-d,l-lactide), contained polylactide chains (95wt.%) grafted onto a hydrophobic rubbery backbone (5wt.%). Clustering is an important phenomenon in the study of water transport properties in polymers since the presence of water clusters can affect the water diffusivity. The HCC method using the thermal power signals and Van’t Hoff's law were both employed to estimate the water sorption enthalpy. Sorption enthalpy of water in both polymers was determined to be approximately −40kJ/mol for all water activity levels. Zimm–Lundberg analysis showed that water clusters start to form at a water activity of 0.4. The engaged species induced clustering (ENSIC) model was used to curve fit sorption isotherms and showed that the affinity among water molecules is higher than that between water molecules and polymer chains. All the methods used indicate that clustering of water molecules exists in both polymers.

Coarse-Grained Simulations of Penetrant Transport in Polymer Nanocomposites

We report the results of coarse-grained simulations of the transport of penetrants in polymer nanocomposite materials. This work was motivated by recent experimental results in the context of conductivity and barrier properties of polymer nanocomposites. We adopt a coarse-grained simulation formalism which is suitable for studying issues surrounding the transport of ions, large gas molecules and probes in polymer nanocomposite systems. The results presented focuses on two issues: (i) the role of polymer interfacial layers and (ii) the influence of polymer matrix dynamics upon the transport properties of polymer–nanoparticle mixtures. Our results indicate that in our model the penetrant transport properties are dominated by the “filler” effect, in which the particles act as obstructions for the penetrant diffusion. Interfacial effects, which are driven by the polymer–particle interactions play a role, but their impact is shown to be less important than the filler effect. A second outcome of our work is a d...