Transport Properties Of Poly Research Articles

Preparation of composite membranes by means of plasma polymerization of tiophene

The structure and the charge transport properties of poly(ethylene terephthalate) track membranes modified in a thiophene plasma were studied. It was found that polymer deposition on the surface of a track membrane via the plasma polymerization of thiophene results in composite membranes that, in the case of the formation of a semipermeable layer, exhibit conductivity asymmetry—rectifying effect—in electrolyte solutions. It was shown that chemical doping with iodine or photo-oxidation of the polymer layer produced in plasma leads to alteration in the electrochemical properties of plasma-modified membranes.

Synthesis, Electrical, Electronic and Charge Transport Properties of Poly(aniline‐co‐p‐toluidine)

Copolymers of aniline with p‐toluidine were synthesized for different molar ratios of the respective monomers in acid medium. The electrical conductivity, charge transport and spectral characteristics upon incorporation of p‐toluidine units into the polyaniline backbone were investigated. The electrical conductivity of the copolymers showed frequency dependence which became more prominent with an increase in the number of p‐toluidine units in the polyaniline backbone. A direct relationship between the frequency dependence and electron localization was observed in the copolymers. Electronic spectra showed blue shifts in the π→π*and benzenoid→quinoid transitions revealing a decrease in the extent of conjugation in the copolymers. The protonated forms of the copolymers were soluble in DMSO giving polaron band around 400 nm. The decrease in electrical conductivity was attributed to the greater electron localizations as revealed from the broader ESR signals. Temperature dependence of electrical conductivity showed that charge transport was mainly through variable range hopping though a mixed conduction behavior was observed at higher temperature range.

Dimensionality-induced effects on transport properties of poly(G)–poly(C)

We consider a ladder model of DNA for addressing the relation between the transport properties and electronic structure and the interbase coupling in poly(G)–poly(C). Based on the negative eigenvalue theorem and transfer matrix method, the density of states and current–voltage characteristics are evaluated, and an expression for the dependence of the band gap on intra- and inter-strand nucleobase couplings is proposed. There exists a semiconducting-metallic transition in poly(G)–poly(C) by modulating the interbase coupling, and the physical nature is traced back to dimensionality-induced effects. Our results provide possibility for interpreting a variety of transport behaviors observed in DNA molecules.

Synthesis and properties of poly(ether urethane) membranes filled with isophorone diisocyanate-grafted carbon nanotubes

A three-step surface treatment of multi-walled carbon nanotubes (MWCNTs) was used to enhance the mechanical and transport properties of poly(ether urethane) (PEU) film. The original MWCNTs were first carboxylated via a mixture of sulfuric and nitric acids to obtain MWCNT grafted to a –COOH group (MWCNT-COOH), then further hydroxylated via thionyl chloride and 1,6-hexanediol to obtain MWCNT grafted to 1,6-hexanediol (MWCNT-OH), and finally treated via isophorone diisocyanate (IPDI) to obtain MWCNT grafted to IPDI (MWCNT-IPDI), which had a similar structure to the hard segments of PEU. Fourier-transform infrared spectroscopy revealed that the functional group –IPDI was successfully grafted onto MWCNTs. Then the prepared MWCNT-IPDI was blended with PEU in a tetrahydrofuran solution to obtain the final transparent MWCNT-IPDI/PEU membranes. All the membranes were characterized by Instron, DMA, DSC and water vapor permeability (WVP). The results showed a remarkable enhancement of mechanical properties and glass-transition temperature of the hard-segments of PEU by adding only small amount of MWCNT-IPDI. For example, the tensile strength was increased from 26.2 MPa for pure PEU to 42 MPa for composites containing 0.3 wt% of MWCNT-IPDI, and the storage modulus was improved from 1500 MPa for pure PEU to 2350 MPa for composites containing 0.5 wt% of MWCNT-IPDI. Very interestingly, a largely improved WVP of PEU film has been achieved by mixing with MWCNT-IPDI. The WVP was increased from 646 g/m 2 24 h for the pure PEU to 856 g/m 2 24 h for the composites containing 0.3 wt% of MWCNT-IPDI, and to 1180 g/m 2 24 h for the composites containing 0.8 wt% of MWCNT-IPDI.

Effects of epoxy treatment of organoclay on structure, thermo-mechanical and transport properties of poly(ethylene terephthalate- co-ethylene naphthalate)/organoclay nanocomposites

Poly(ethylene terephthalate- co-ethylene naphthalate) (PETN) nanocomposites containing two different organoclays, Cloisite 20A and 30B, were prepared by melt intercalation using an extruder. The organoclays was treated with epoxy monomer to further improve the polar interactions with PETN matrix. The morphological, thermal-mechanical, mechanical and gas barrier characteristics of the nanocomposites were evaluated using several characterization tools. It is found that the Cloisite 30B had better interactions with PETN and was more uniformly dispersed within PETN than Cloisite 20A. Epoxy treatment of Cloisite 30B organoclay resulted in improvements in d-spacing between silicate layers, thermo-mechanical and tensile properties, as well as thermal stability, processing and gas barrier characteristics of the PETN/30B nanocomposites. These results suggest that the epoxy acted as the compatibilizer as well as the chain extender, improving the chemical interactions between PETN and organoclay, while discouraging the macromolecular mobility of polymer chains in the vicinity clay particles. The implications and the mechanisms behind these observations are discussed.

Effect of supermolecular structure on transport phenomenon in polymeric membranes

In this paper a correlation between the transport properties of poly(methyl-4-pentene-l) membranes and the supermolecular structure of polymer is demonstrated. The orientation of the amorphous regions induced by semicrystallinity results in the appearance of the constrained and unconstrained amorphous structures. The concept of two amorphous fractions in the semicrystalline system is applied in order to better explain the transport phenomenon. Both types of amorphous fractions were found and two structural relaxations were distinguished. It was shown that the transport phenomena depended on both the free volume and the mobility of the segments creating the supermolecular structure of the membrane. The results of positron annihilation lifetime spectroscopy (PALS), calorimetric measurements (DSC) and mechanical spectroscopy (DMTA) are presented for the chosen membranes. It is tempting to believe that we should distinguish the both fractions of the amorphous phase to give better description of relaxation and transport phenomenon. Moreover, new formula and new approach to the transport process of molecules through the membrane will advance the theoretical understanding of such a process. These new concepts will also allow the better modelling of the membranes for utility purpose. Summary and analysis of the experimental data pertinent to the free volume approach are presented.

Charge carrier transport properties of poly (9,9-dioctylfluorene) thin films

Charge carrier transport properties of hole-only devices based on poly(9,9-dioctylfluorene) (PFO) are investigated in terms of dark current-voltage (I-V) measurements. The built-in potential (V bi ) of the devices is determined by photovoltaic measurements. A power-law I-V relationship, I V m (m > 2), is found above the Ohmic region. Space-charge-limited current theory for exponential localized-state distributions can be applied to the interpretation of such behavior by taking account of V bi .

Charge transport in disordered organic field-effect transistors

AbstractThe transport properties of poly(2,5-thienylene vinylene) (PTV) field-effect transistors (FET) have been investigated as a function of temperature under controlled atmosphere. In a disordered semiconductor as PTV the charge carrier mobility, dominated by hopping between localized states, is dependent on the charge carrier density. The transfer characteristics of PTV FET have been modeled considering the distribution of charge carriers and mobility over the accumulation channel. Good agreement with the experimental data is obtained.

Gas sorption and transport in side-chain crystalline and molten poly(octadecyl acrylate)

The gas sorption and transport properties of poly(octadecyl acrylate) are described for the semi-crystalline and molten states. The change in permeability upon traversing the melting point, or permeation switch, was observed to be as high as two orders of magnitude depending on the penetrant. Analysis of gas transport is explained using the Michaels and Bixler model for semi-crystalline polyethylene. This analysis shows chain immobilization of the amorphous phase by surrounding crystals to play a significant role in describing the penetrant-dependent permeation switch in this side-chain crystalline polymer. Traditional two-phase models describing crystallites as impenetrable barriers with no effect on amorphous phase properties may explain solubility in this system but do not describe diffusion. The dependence of transport parameters on polymer composition, e.g. side-chain length, is also discussed.

Effect of H-bond active sites on transport properties of poly(ethylene oxide) dissolved in its monomers: Shear viscosity and diffusion coefficient studies

The possibility of dissolving poly(ethylene oxide) [PEO:H–(O–CH2–CH2)n–OH] in its monomeric liquid ethylene glycol [EG:H–(O–CH2–CH2)–OH] represents the only way to verify the complex polymer–monomer interactions, through the OH end groups, resulting in the scaling law R∝Nν. We report viscosity results, in conjunction with photon correlation spectroscopy data, on different molecular weight PEO samples, in a wide range of concentrations, dissolved in EG. In order to distinguish among various interaction mechanisms, we also studied PEO dissolved in EG monomethyl ether [EGmE:CH3–(O–CH2–CH2)–OH] and EG dimethyl ether [EGdE:CH3–(O–CH2–CH2)OCH3], the latter not having in its chemical structure OH hydroxylic groups available to give rise to hydrogen bond interactions. In particular, the quality (good-theta-poor) of the solvents has been analyzed by verifying the well-known Mark–Houwink–Sakurada scaling law and the effects of the polymer–solvent interactions on the coils diffusive properties.

Effect of Doping Level and Morphology on the Transport Properties of Poly(4,4′-Dipentoxy-2,2′-Bithiophene)

The transport properties of the title conducting polymer (polyET2), synthesized using two different supporting electrolytes, have been studied over a wide range of electrochemical doping levels. The Hall mobility of the material is found to be sensitive to both the carrier concentration and the molecular order, decreasing as a function of the free carrier concentration, and becoming greater with increasing molecular order. The mobilities achieved with this method are the highest so far known for this kind of material. A conduction model based on overlapping cation states is proposed.

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997

Gas transport and structural features of sulfonated poly(phenylene oxide)

The effect of ionomer structure on gas transport properties of membranes was investigated. For this purpose physical and transport properties of poly(phenylene oxide) (PPO) and its sulfonated derivative (SPPO) were compared. SPPO has a more rigid structure and a lower free volume, which determines low gas permeability and high permselectivity. Gas transport properties of two types of SPPO—PPO composite membranes with top layers prepared from solutions in methanol or N,N-dimethylacet-amide (DMA) were investigated. The use of SPPO solution in DMA leads to the formation of membranes with higher gas permeability. It was shown that DMA is a morphologically active solvent for SPPO. Strong complexes of SPPO with DMA are formed in solution and retained upon transition into the condensed state. The plasticizing effect of DMA on SPPO determines the high gas permeability of the membranes and is in agreement with their mechanical properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1439–1443, 1997

Effect of the bathing electrolyte concentration on the charge transport process at poly(o-aminophenol) modified electrodes. An ac impedance study

The effects of ionic strength and film thickness on the transport properties of poly(o-aminophenol) (POAP) film electrodes were studied by impedance spectroscopy. The dependences of the characteristic impedance quantities (Warburg coefficient, resistance and redox capacitance at low frequency) on these external variables were interpreted on the basis of two models: a transmission line and a modified electron hopping model. Analysis of experimental data by means of the transmission line model allowed us to separate the charge transport process within the film in terms of electronic and ionic contributions represented by the diffusion constants. Dc and Dx, respectively. Application of the electron hopping model only gave an effective diffusion coefficient, Dcff. The diffusion coefficients Dc and Dx, in the first case, and Deff in the second case, depend upon the ionic strength and film thickness. Moreover, Deff is very close to Dc. This proves that charge propagation is dominated by electron transport in this polymer.

Gas sorption and transport in poly(tertiary-butyl methacrylate)

Gas sorption and transport properties of poly(tertiary-butyl methacrylate) (PtBMA) have been measured at 35°C and are compared with prior results for poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), and poly(ethyl methacrylate) (PEMA). The t-butyl substitution increases the gas permeability as a result of increases in both diffusivity and solubility coefficients; however, the ideal selectivity for a given gas pair may increase or decrease depending upon the methacrylate polymer to which it is compared. Poly(t-butyl methacrylate) does not show plasticization by CO 2 up to 10 atm of CO 2. The effect of t-butyl substitution on gas permeability observed here for the methacrylate polymer is compared to that reported in the literature for other polymer types. This substitution causes a larger increase in permeability the smaller the repeat unit of the base polymer since this results in a greater modification in structure and subsequent greater decrease in efficiency of chain packing.

Mechanical and Transport Properties of Poly(ethyleneterephthalate) Films with Reference to Sulphur Mustard

Influence of sulphur mustard (SM), a chemical warfare agent, on mechanical and transport properties of poly(ethyleneterephthalate) (PET) films was investigated. The objective of the study was to assess the agent–substrate interaction. SM induces changes in PET in that the elongation as well as strength of SM-exposed films decreases considerably. The reduction in percentage elongation at break is very significant, perhaps because of the antiplasticizing effect of SM on PET. The breakthrough time (BTT) of SM is higher for the film, which showed greater resistance to amine etching. The critical dissolution time measurement substantiates the data on mechanical behaviour of SM-exposed films. © of SCI.

Transport Properties of Poly(ethylene terephthalate) Crystallized from the Glassy State

Poly(ethylene terephthalate) was crystallized from the glassy state at 120 and 200°C. The structural organization of samples, after the primary and secondary crystallizations, was analyzed by density, X-rays, infrared and transport properties of dichloromethane vapor. The values of crystallinity derived with different methods do not agree, indicating that the crystallized samples cannot be considered simply biphasic. Since the fraction of the impermeable phase is much higher than the fraction of the crystalline phase, it suggested that the presence of mesomorphic form, impermeable to the vapors at low activity. With this hypothesis, the complete composition of the crystalline samples, in terms of fraction of crystalline, amorphous and mesomorphic form was derived. A value of density of the mesomorphic form of 1.39 g/cm3 was also derived.

Transport Properties of Poly(ethylene terephthalate) Crystallized from the Glassy State

Poly(ethylene terephthalate) was crystallized from the glassy state at 120 and 200°C. The structural organization of samples, after the primary and secondary crystallizations, was analyzed by density, X-rays, infrared and transport properties of dichloromethane vapor. The values of crystallinity derived with different methods do not agree, indicating that the crystallized samples cannot be considered simply biphasic. Since the fraction of the impermeable phase is much higher than the fraction of the crystalline phase, it suggested that the presence of mesomorphic form, impermeable to the vapors at low activity. With this hypothesis, the complete composition of the crystalline samples, in terms of fraction of crystalline, amorphous and mesomorphic form was derived. A value of density of the mesomorphic form of 1.39 g/cm3 was also derived.

The influence of chain configuration and, in turn, chain packing on the sorption and transport properties of poly(tert‐butyl acetylene)

AbstractA series of poly(tert‐butyl acetylene) (PTBA) polymers was prepared with cis contents, as characterized by 13C NMR spectroscopy, ranging from 44% to 100%. The sorption and transport properties of propane in this systematically varied series were determined by a sensitive gravimetric sorption technique. As the cis content of the polymer increased, propane solubility and diffusivity decreased markedly and the d‐spacing, determined by wide angle x‐ray diffraction spectroscopy, decreased monotonically with increasing cis content, suggesting that higher order molecular structure, related explicitly to configurational variations, may strongly influence chain packing in these rigid, glassy materials and, in turn, sorption and transport properties of small molecules in this polymer series. © 1993 John Wiley & Sons, Inc.

Transport properties of poly(vinyl alcohol) membranes of different degrees of crystallinity. I. Pervaporation results

AbstractDense poly (vinyl alcohol) (PVA) membranes of different crystallinities were prepared and studied in pervaporation of water‐ethanol mixtures. High selectivities to water were obtained with all types of membranes. Permeation fluxes increase exponentially with the water content in the liquid mixture. At a given water content, the membrane permeability decreases drastically when its crystallinity increases. When the pervaporation temperature increases, the permeation flux increases according to the Arrheniuslike law, with a permeation acti‐vation energy that depends strongly on the crystallinity of the membrane. A permeation model, in which the volume fraction of amorphous polymer intervenes in both the sorption and the diffusion laws, was proposed and validated by the experimental data. With the obtained values of the parameters, the permeation Olux can be calculated for membranes of a given crystallinity at any temperature and composition of the water‐alcohol mixture. © 1993 John Wiley & Sons, Inc.