Molecular Dynamics Simulations of Proton Conduction in Sulfonated Poly(phenyl sulfone)s

Full molecular dynamics was used to simulate separately the diffusion of naked protons and H₃O⁺ hydrated protons across sulfonated poly(phenyl sulfone)s. Simulations were carried out for wet membranes with the following characteristics:  ion-exchange capacity, 1.8 mequiv/g of dry membrane; water uptake, 10−30%; temperature range, 300−360 K. The diffusion coefficient of naked protons is nearly 1 order of magnitude higher than that of the hydrated protons for the membranes with the lower water uptake (10%). For the membranes with higher water uptake the ratio between the diffusion coefficients of the two particles reduces to about half an order of magnitude. The conductivity of the naked protons increases from 21.4 × 10⁻³ to 52.5 × 10⁻³ S/cm when the water uptake increases from 10% to 30%. For hydrated protons the conductivity increases from 1.54 × 10⁻³ to 7.57 × 10⁻³ S/cm. The conductivities obtained through simulations carried out at 300 K for the hydrated proton across membranes with water uptake 18% and 30% are roughly similar to those experimentally measured for a membrane with ion exchange capacity = 1.8 mequiv/g and water uptake = 24.3%. Simulated conductivities of both naked protons and hydrated protons follow Arrhenius behavior.This work was supported by the Comunidad de Madrid through the grant interfaces S-505/MAT-0227, Fondos Europeos de Desarrollo (FEDER), and Fondo Social Europeo (FSE). Financial support was also supplied by the Dirección General de Investigación Científica y Técnica (DGICYT) (grant MAT 2005-05648-C02-02)

Effect of time of annealing on gas permeation through coextruded linear low-density polyethylene (LLDPE) films

[EN] The effect of annealing on the permeation of oxygen, nitrogen, and carbon dioxide through coextruded linear low-density polyethylene (LLDPE) films is studied. The results indicate that the permeability coefficient P of nitrogen does not show a definite dependence on the time of annealing, ta, whereas for the other gases this parameter increases with ta. The analysis of the variation of the diffusion coefficient of O2 and N2 with ta indicates that D undergoes a sharp decrease from ta ) 0 to ta ) 2 h, but for larger times of annealing the diffusion parameter only undergoes a slight diminution; on the contrary, the diffusion coefficient of CO2 gradually decreases with increasing ta. The fact that annealing increases the solubility of the gases in the polymer films suggests that thermal treatments may favor the formation of microcavities or molecular packing defects in the crystalline amorphous interface that can accommodate individual site molecules without disturbing the natural dissolution process in the rubbery region of the polymer matrix. Finally, free volume theories are not sensitive enough to interpret the effect of annealing on the permeation characteristics of coextruded LLDPE films.This work was supported by the DGICYT through Grant PB95-0134-C02.Compañ Moreno, V.; Andrio, A.; Lopez, ML.; Alvarez, C.; Riande, E. (1997). Effect of time of annealing on gas permeation through coextruded linear low-density polyethylene (LLDPE) films. Macromolecules. 30:3317-3322. http://hdl.handle.net/10251/147741S331733223

Simulation and Experimental Studies on Proton Diffusion in Polyelectrolytes Based on Sulfonated Naphthalenic Copolyimides

This work describes proton transport in membranes cast from dimethyl sulfoxide solutions of polyelectrolytes obtained by polycondensation of 4,4′-diaminodiphenyl ether (ODA) and 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (ODADS) with 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), the moles of sulfonated diamine per mole of unsulfonated one being roughly 3/1. Pulsed field gradient (PFG) NMR studies reveal two kinds of water: water located in the pores of the membranes appearing in the range 5 to 1 ppm and a minor amount of water associated with the imide groups, appearing at 1 ppm. The diffusion coefficient of ¹H in the first type of water is about 2 orders of magnitude higher than that measured in the second type and in both cases the values of this parameter severely decrease as the water content of the membranes decreases. The diffusion coefficients of bare protons, hydronium ions and water in the membranes were calculated using molecular dynamics techniques. For membranes with low water content, the diffusion coefficient of ¹H is very close to the diffusion coefficients of water and hydronium ions obtained by simulation. At high concentrations the simulated values are higher than D(¹H). The simulated values obtained for the diffusion coefficients of hydronium ion and water for membranes equilibrated with water are fairly close to those estimated, respectively, from proton conductivity and osmotic measurements. This work suggests that the study of cation-exchange membranes in the acidic form using NMR, conductivity, and molecular dynamics simulation techniques provides useful information on how structure and water content affect transport processes in membranesThis work was supported by Comunidad de Madrid (CAM Project S-0505/MAT/0227) and the CICYT (Projects CTQ2005-04710/BQU, MAT2005-05648-C02-01, and MAT2007-63722)

Comparison Between the Conductivities of Protons Measured Experimentally with the Obtained by Molecular Dynamics Simulations in Sulfonated Polyphenyl Sulfones Membranes

Full Molecular Dynamics was used to simulate separately the diffusion of naked protons and H₃O⁺ hydrated protons across sulfonated polyphenyl sulfones, (sPS). The diffusion coefficient of naked protons is nearly one order of magnitude higher than that of the hydrated protons for the membranes with the lower water uptake (10%). The conductivities simulated at 300 K for the hydrated proton across membranes with water uptake 18% and 30 % are roughly similar to those both experimentally measured for the sPS4 membrane with ion exchange capacity = 1.8 eq/Kg in dry conditions and with water uptake = 24.3 %. The comparison between four sPS membranes shwon the strong dependence of conductivity with the water content into the membranes. In our study, the conductivity of sPS1 with a 3.1% water content decrease two order of magnitude respect the sPS4 with 24.3 of water content. Simulated conductivities of both naked protons and hydrated protons follow Arrhenius behavior.This work was supported by the Dirección General de Investigación Científica y Técnica (DGICYT), Grant MAT-2005-05648-C02-02, and from IMPIVA of Generalitat Valenciana through project IMCITA/2006/030 is gratefully acknowledged. The authors are also grateful to the Instituto de Tecnología Eléctrica (ITE) de la Universidad Politécnica de Valencia for the financial support

Simulations of Gas Transport in Membranes Based on Polynorbornenes Functionalized with Substituted Imide Side Groups

This paper studies the diffusive and sorption steps of several gases across membranes cast from poly(N-phenyl-exo,endo-norbornene-5,6-dicarboximide) chloroform solutions. Chains packing effects on gas transport was investigated by conducting a parallel study on the permeation characteristics of membranes cast from hydrogenated poly(N-phenyl-exo,endo-norbornene-5,6-dicarboximide) chloroform solutions. The permeability coefficients of several gases in the two membranes were measured finding that hydrogenation of the norbornene moieties decreases gas permeability. The transition states approach was used to determine the trajectories of the gases in the two types of membranes from which the diffusion coefficients were obtained. Monte Carlo techniques based on the Widom method were used to simulate gas sorption process as a function of pressure. The values of the solubility coefficients thus obtained undergo a relatively sharp drop at low pressures approaching to a constant value as pressure increases. With the exception of carbon dioxide, pretty good agreement between the experimental and simulated values of the permeability coefficient is found for the gases studied.This work was supported by Comunidad de Madrid (CAM projects: GR/MAT/0810/2004; S-0505/MAT/0227) and CICYT (projects: MAT-2005-05648-C02-01, CTQ2005-04710/BQU; MAT2004-01347)

Dielectric spectroscopy of natural rubber-cellulose II nanocomposites

[EN] Nanocomposite materials obtained from natural rubber (NR) reinforced with different amounts of cellulose II nanoparticles (in the range of 0 to 30 phr) are studied by dielectric spectroscopy (DS). For comparative purposes the pure materials, NR and cellulose, are also investigated. The dielectric spectra of the nanocomposites exhibit: (a) two overlapped ¿-relaxations associated respectively with the dynamic glass transitions of NR (faster process) and of the lipid present in NR; (b) a ß-relaxation associated with local chain dynamics of cellulose and (c) a relaxation process associated to the presence of traces of water in cellulose. The spectra exhibit conductivity phenomena at low frequencies and high temperatures. The samples were also studied in the dry state. An explanation is given concerning the cellulose effect on the dielectric properties of the dry and wet nanocomposites. © 2010 Elsevier B.V.All rights reserved.The authors gratefully acknowledge CICYT for Grant No. MAT2008-06725-C03-03 and Generalitat Valenciana for Grant No. ACOMP/2010/204.Ortiz Serna, MP.; Díaz Calleja, R.; Sanchis Sánchez, MJ.; Riande, E.; Numes, R.; Martins, A.; Visconte, L. (2011). Dielectric spectroscopy of natural rubber-cellulose II nanocomposites. Journal of Non-Crystalline Solids. 357(2):598-604. doi:10.1016/j.jnoncrysol.2010.06.044S598604357

Influence of the Water Content on the Diffusion Coefficients of Li⁺ and Water across Naphthalenic Based Copolyimide Cation-Exchange Membranes

The transport of lithium ions in cation-exchange membranes based on sulfonated copolyimide membranes is reported. Diffusion coefficients of lithium are estimated as a function of the water content in membranes by using pulsed field gradient (PFG) NMR and electrical conductivity techniques. It is found that the lithium transport slightly decreases with the diminution of water for membranes with water content lying in the range 14 < λ < 26.5, where λ is the number of molecules of water per fixed sulfonate group. For λ < 14, the value of the diffusion coefficient of lithium experiences a sharp decay with the reduction of water in the membranes. The dependence of the diffusion of lithium on the humidity of the membranes calculated from conductivity data using Nernst–Planck type equations follows a trend similar to that observed by NMR. The possible explanation of the fact that the Haven ratio is higher than the unit is discussed. The diffusion of water estimated by 1H PFG-NMR in membranes neutralized with lithium decreases as λ decreases, but the drop is sharper in the region where the decrease of the diffusion of protons of water also undergoes considerable reduction. The diffusion of lithium ions computed by full molecular dynamics is similar to that estimated by NMR. However, for membranes with medium and low concentration of water, steady state conditions are not reached in the computations and the diffusion coefficients obtained by MD simulation techniques are overestimated. The curves depicting the variation of the diffusion coefficient of water estimated by NMR and full dynamics follow parallel trends, though the values of the diffusion coefficient in the latter case are somewhat higher. The WAXS diffractograms of fully hydrated membranes exhibit the ionomer peak at q = 2.8 nm⁻1, the peak being shifted to higher q as the water content of the membranes decreases. The diffractograms present additional peaks at higher q, common to wet and dry membranes, but the peaks are better resolved in the wet membranes. The ionomer peak is not detected in the diffractograms of dry membranes.The authors acknowledge financial support provided by the DGICYT (Dirección General de Investigación Cientifíca y Tecnológica) through Grant MAT2011-29174-C02-02

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Relaxation response of polymers containing highly flexible side groups monitored by broadband dielectric spectroscopy

9 pages, 10 figures.The relaxation behavior of poly(5-acryloxymethyl-5-methyl-1,3-dioxacyclohexane), a polymer containing highly flexible side groups, is studied by broadband dielectric spectroscopy in the frequency and temperature ranges 10–1–109 Hz and 123–473 K, respectively. Above the glass transition temperature Tg the dielectric loss in the frequency domain exhibits a prominent absorption, followed in increasing order of frequencies by two secondary absorptions called and . At temperatures slightly higher than Tg, the relaxation is well separated from the , but as temperature increases overlapping between both relaxations augments forming an absorption in the vicinity of 420 K. This latter absorption displays a shoulder on its high-frequency side corresponding to the relaxation. The strength of the relaxation decreases with increasing temperature, eventually vanishing at the temperature at which the absorption is formed. The time retardation spectra of the isotherms are calculated and further used to facilitate the deconvolution of the overlapping relaxations. The fact that the temperature dependence of the relaxation also describes that of the absorption suggests that both relaxations have the same nature. It seems that as temperature increases, the relaxation feeds on the absorption until its complete disappearance. The relaxation, in turn, seems to increase at the expense of the process at high temperature.Peer reviewe