New organic–inorganic hybrid membranes based on sulfonated polyimide/aminopropyltriethoxysilane doping with sulfonated mesoporous silica for direct methanol fuel cells

A series of novel composite methanol‐blocking polymer electrolyte membranes based on sulfonated polyimide (SPI) and aminopropyltriethoxysilane (APTES) doping with sulfonated mesoporous silica (S‐mSiO₂) were prepared by the casting procedure. The microstructure and properties of the resulting hybrid membranes were extensively characterized. The crosslinking networks of amino silica phase together with sulfonated mesoporous silica improved the thermal stability of the hybrid membranes to a certain extent in the second decomposition temperature (250–400°C). The composite membranes doping with sulfonated mesoporous silica (SPI/APTES/S‐mSiO₂) displayed superior comprehensive performance to the SPI and SPI/APTES membranes, in which the homogeneously embedded S‐mSiO₂ provided new pathways for proton conduction, rendered more tortuous pathways as well as greater resistance for methanol crossover. The hybrid membrane with 3 wt % S‐mSiO₂ into SPI/APTES‐4 (SPI/A‐4) exhibited the methanol permeability of 4.68 × 10^?6 cm² s^?1at 25°C and proton conductivity of 0.184 S cm^?1 at 80°C and 100%RH, while SPI/A‐4 membrane had the methanol permeability of 5.16 × 10^?6 cm² s^?1 at 25°C and proton conductivity of 0.172 S cm^?1 at 80°C and 100%RH and Nafion 117 exhibited the values of 8.80 × 10^?6 cm² s^?1 and 0.176 S cm^?1 in the same test conditions, respectively. The hybrid membranes were stable up to about 80°C and demonstrated a higher ratio of proton conductivity to methanol permeability than that of Nafion117. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Phthalonitrile end-capped sulfonated polyarylene ether nitriles for low-swelling proton exchange membranes

A series of phthalonitrile end-capped sulfonated polyarylene ether nitriles are synthesized via K₂CO₃ mediated nucleophilic aromatic substitution reaction at various molar ratios. The as-prepared polymer structures are confirmed by ¹H NMR and FTIR spectroscopy. The properties of membranes cast from the corresponding polymers are investigated with respect to their structures. The membranes exhibit good thermal and mechanical properties, low methanol permeability (0.01?×?10^?6–0.58?×?10^?6 cm²·s^?1 at 20 °C), and high proton conductivity (0.021–0.088 S·cm^?1 at 20 °C). The introduction of phthalonitrile is proved to increase intermolecular interaction, mainly contributing to the reduction in water uptake, swelling ratio, and methanol permeability. More importantly, its introduction does not decrease the proton conductivity, but there is a slight increase. Furthermore, the selectivity of SPEN-CN-50 can reach 4.11?×?10⁵ S·s·cm^?3, which is about nine times higher than that of Nafion 117. All the data show that the as-prepared membranes may be potential proton exchange membrane for DMFCs applications.     

A novel heteropolyacid-doped carbon nanotubes/Nafion nanocomposite membrane for high performance proton-exchange methanol fuel cell applications

A novel proton-exchange polymer composite membrane was synthesized using Nafion^®, tetraethoxysilane-modified carbon nanotubes (CNTs) and phosphotungstic acid-modified carbon nanotubes with the aim of using direct methanol fuel cells (DMFCs). Physicochemical properties of the modified CNTs and fabricated composite membranes were investigated by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, water uptake, thermogravimetric analysis, ion exchange capacity, proton conductivity and methanol permeability tests. It was demonstrated that chemical surface modification of CNTs and introduction of the phosphotungstic acid (PWA) groups effectively improved the performance of DMFC. It was found that the presence of PWA groups on the surface of CNTs led to the formation of strong electrostatic interactions between the PWA groups and clusters of sulfonic acid in Nafion^® macromolecules. Hence, the incorporation of inorganic phosphotungstic super-acid-doped silicon oxide-covered carbon nanotubes (CNT@SiO₂-PWA) into Nafion^® matrices enhanced the proton conductivity of the prepared membranes. Moreover, the methanol permeability was reduced to 2.63 × 10^?7 cm² s^?1 in comparison with the recast Nafion^® membrane (2.25 × 10^?6 cm² s^?1). Enhancing the proton conductivity and reducing the methanol permeability, the selectivity of the prepared nanocomposite membranes was enhanced to a greater value of 330,700 S s cm^?3 as compared to the value of 38,222 S s cm^?3 for recast Nafion^®.     

Performance evaluation of sodium alginate–Pebax polyion complex membranes for application in direct methanol fuel cells

A novel polyion complex membrane was synthesized for direct methanol fuel cell application through the blending of the natural biopolymer sodium alginate (SA) with the synthetic polymer Pebax [poly(ether‐block ‐amide)]. The blend was covalently crosslinked with glutaraldehyde (GA) and sulfonated with sulfuric acid (H₂SO₄), after which characterization by Fourier transform infrared spectroscopy, scanning electron microscopy, X‐ray diffractometry, thermogravimetric analysis, and universal testing machine techniques was carried out. The SA–Pebax–GA–H₂SO₄ membrane exhibited a high ion‐exchange capacity of 2.1 mequiv/g, an optimum water sorption of 17.3%, and a low methanol sorption of 9.5%. A desirably low methanol permeability of 9.25 × 10^?8 cm²/s and a high proton conductivity of 0.067 S/cm were obtained as against corresponding values of 1.82 × 10^?6 cm²/s and 0.077 S/cm reported for a commercial Nafion 117 membrane. Moreover, a high selectivity of 6.5 × 10⁵ Ss/cm³ with a power density of 0.17 W/cm² was achieved with the indigenous blend membrane at a potential of 0.34 V. Molecular dynamics simulation was performed along with the estimation of fractional free volume to explain the transport behavior of water and methanol molecules through the membrane. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44485.     

Influence of Sulfonated Graphene Oxide on Sulfonated Polysulfone Membrane for Direct Methanol Fuel Cell

Novel proton exchange membranes consisting of an inorganic filler, namely sulfonated graphene oxide, embedded in sulfonated polysulfone were fabricated. The membrane performance depended on the sulfonated graphene oxide content possessed the functional groups to provide the interfacial interaction with sulfonated polysulfone through ionic channels and blocking effect. The membrane with 3% v/v sulfonated graphene oxide content embedded in the matrix was shown to be suitable for direct methanol fuel cell applications. The membrane exhibited the highest proton conductivity of 4.27?×?10^?3 S cm^?1 which was higher than that of Nafion117. Moreover, the membrane provided the lowest methanol permeability of 3.48?×?10^?7?cm²/s which was lower than that of Nafion117.     

Methanol permeability and proton conductivity of polybenzimidazole and sulfonated polybenzimidazole

The preparation of sulfonated polybenzimidazole (sPBI) by the grafting of (4‐bromomethyl) benzenesulfonate onto polybenzimidazole (PBI) has been investigated. The methanol permeability and proton conductivity of PBI and sPBI have been studied, and the effects of methanol concentration and temperature on the methanol permeability of PBI and sPBI membranes are discussed. The results showed that the PBI membrane is a good methanol barrier. Methanol permeability in this membrane decreases with increasing methanol concentration and increases with increasing temperature. The temperature‐dependence of methanol permeability of PBI and sPBI membranes is of the ‘Arrhenius type’. Methanol permeation of sPBI is less sensitive to temperature than that of PBI. However, sPBI is a poorer methanol barrier when compared to PBI. Methanol permeability in sPBI membranes increases with increasing methanol concentration and temperature. The proton conductivity of sPBI is 4.69 × 10^?4 S cm^?1 at room temperature in the hydrated state. The DC conductivity of sPBI–H₃PO₄ increases with increasing temperature. Proton transport in sPBI–H₃PO₄ is less sensitive to temperature than that in PBI–H₃PO₄. Copyright © 2004 Society of Chemical Industry     

Montmorillonite‐reinforced sulfonated poly(phthalazinone ether sulfone ketone) nanocomposite proton exchange membranes for direct methanol fuel cells

To produce a composite membrane with high conductivity and low permeability, SPPESK with a degree of sulfonation of 101% was carefully selected for the preparation of montmorillonite (MMT)‐reinforced SPPESK using solution intercalation. The fundamental characteristics such as water uptake, swelling ratio, proton conductivity, methanol permeability, and mechanical properties of the composite membranes were studied. Water uptake is improved when organic MMT (OMMT) loading increase. The composite membranes with CTAB‐MMT loading of 4–0.5% show 0.143–0.150 S cm^?1 proton conductivity at 80°C, which approaches the value of Nafion112. In addition, methanol permeability was decreased to 6.29 × 10^?8 cm² s^?1 by the addition of 6 wt % OMMT. As a result, the SPPESK‐MMT composite membrane is a good candidate for use in direct methanol fuel cells. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39852.     

Synthesis of Low Methanol Permeation Polymer Electrolyte Membrane from Polystyrene-Butadiene Rubber

In order to find a low cost polymer electrolyte membrane with low methanol cross-over, the development of novel polymer electrolytes have been actively carried out in recent time as alternatives to Nafion®, which is the state-of-the art membrane. The problems associated with these alternative membranes are higher permeability to the fuel, lower proton attraction and thermal stability. This work therefore was focused on synthesizing low methanol permeable membrane with good proton conductvity and thermal stability from locally available polymer (Polystyrene-butadiene rubber). Results obtained revealed that the synthesized membrane exhibited methanol permeation in the ranges of 2.13 × 10^?7 to 7.58 × 10^?7 mol/cm²s which was lower than that of Nafion® (3.15 × 10^?6 cm²/s). The proton conductivity of the synthesized membrane is in the order of 10^?2 S/cm. The results also show that water and solvent uptake of the synthesized membrane are moderate as compared to that of Nafion®. These results are influenced by the degree of sulphonation and membrane thickness ranging from 0.112 mm?0.420 mm.     

Sulfonated (graphene oxide/poly(ether ketone ether sulfone) (S-GO/S-PEKES) composite proton exchange membrane with high proton conductivity for direct methanol fuel cell

ABSTRACT

Sulfonated poly(ether ketone ether sulfone) (S-PEKES) was successfully prepared to obtain the currently highest degree of sulfonation of 0.744. Sulfonated graphene oxide (S-GO) was incorporated into the S-PEKES matrix to increase sulfonic groups (SO₃H) which significantly improved the proton conductivity, methanol blocking, and mechanical stability. The proton conductivity of the S-GO/S-PEKES composite membrane was enhanced up to 5.93 × 10^?2 S.cm^?1, which was 7 times higher than the commercial Nafion 117. S-GO exhibited additional positive effects namely the blocking of methanol passing through the membrane, leading to lower methanol crossover than Nafion 117 by two orders of magnitude and high mechanical stability.     

Preparation of phosphorylated nata‐de‐coco for polymer electrolyte membrane applications

Fuel cells are being developed to overcome the global energy crisis. The objective of this research is to prepare an environmental‐friendly and cheap material as the polymer electrolyte membrane. Coconut water was fermented by Acetobacter xylinum to produce nata‐de‐coco and the phosphorylation was carried out by microwave‐assisted reaction. The resulting membranes are characterized by ion exchange capacity, contact angle, proton conductivity, swelling index, methanol permeability, mechanical properties measurement and morphological analysis. At the optimum phosphorylation condition using 17.35 mmol of phosphoric acid, membrane showed a proton conductivity of 1.2 × 10^?2 S/cm and a methanol permeability of 2.3 × 10^?6 cm²/s. The tensile strength of the produced membranes increases significantly and the arrangement of the cellulosic fibers are kept well‐aligned. It is concluded that a green and sustainable natural resources can be used for preparing electrolyte membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Sulfonated poly(ether ether ketone)/epoxy/phenol novolac blend proton‐exchange membranes with low methanol permeability

A crosslinked epoxy [4,4′‐diglycidyl‐(3,3′,5,5′‐tetramethylbiphenyl) epoxy resin (TMBP)], cured by phenol novolac (PN), was introduced into a sulfonated poly(ether ether ketone) (SPEEK) membrane (ion‐exchange capacity = 2.0 mequiv/g) with a casting‐solution, evaporation, and heating crosslinking method to improve the mechanical properties, dimensional stability, water retention, and methanol resistance. By Fourier transform infrared analysis, the interactions between the sulfonic acid groups and hydroxyl groups in the blend membranes were confirmed. The microstructure and morphology of the blend membranes were investigated with atomic force microscopy. As expected, the blend membranes showed excellent mechanical properties, good thermal properties (thermal stability above 200°C), lower swelling ratios (1.4% at 25°C and 7.0% at 80°C), higher water retention (water diffusion coefficient = 9.8 × 10^?6 cm²/s), and a lower methanol permeability coefficient (3.6 × 10^?8 cm²/s) than the pristine SPEEK membrane. Although the proton conductivity of the blend membranes decreased, a higher selectivity (ratio of the proton conductivity to the methanol permeability) was obtained than that of the pristine SPEEK membrane. The results showed that the SPEEK/TMBP/PN blend membranes could have potential use as proton‐exchange membranes in direct methanol fuel cells. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hybrid nanocomposite membranes of sulfonated poly(ethersulfone)/1,1-carbonyl diimidazole/1-(3-aminopropyl)-silane/silica for direct methanol fuel cells

Composite membranes of sulfonated poly(ethersulfone)/1,1-carbonyl diimidazole/1-(3-aminopropyl)-silane/silica (SPES/CDI/AS/SiO₂) with silica of various contents (3, 5 and 8 wt%) were prepared as electrolytes for direct methanol fuel cells (DMFCs). Comparison was made with pure SPES and SPES/SiO₂. The properties of the composite membranes were studied by FTIR, TGA, XRD, water and methanol uptake, proton conductivity. SPES/CDI/AS/SiO₂ membranes were also characterized by scanning electron microscopy (SEM), which showed good adhesion between the modified sulfonic acid (-SO3H) groups of SPES and silica because of cross-linking with covalent bond formation and reduced cavities in the composites. This effect played an important role in reducing water uptake, methanol uptake and methanol permeability of the SPES/CDI/AS/SiO₂ composites. The water and methanol uptake and also methanol permeability of the SPES/CDI/AS/SiO₂ composite membrane with 8% SiO₂ were found in the order 3.58%, 2.48% and 1.91×10^?7 (cm²s^?1), lower than those of SPES and Nafion 117. In SPES membrane of 16.94% level of sulfonation, the proton conductivity was 0.0135 s/cm at 25 °C, which approached that of Nafion 117 under the same conditions. Also, the proton conductivity of the SPES/CDI/AS/SiO₂ 8% membrane was 0.0186 s/cm, which was higher than that of SPES at room temperature. The preparation of SPES/SiO₂ composites in the presence of AS and CDI, led to 63%, 56% and 64% reduction of water uptake, methanol uptake and methanol permeability, respectively without a sharp drop in proton conductivity of the composite membranes which featured a good balance between high proton conductivity, water and methanol uptake of SPES/CDI/AS/SiO₂ membranes.     

Preparation and characterization of sulfonated block‐graft copolyimide/sulfonated polybenzimidazole blend membranes for fuel cell application

Polymer electrolyte blend membranes composed of sulfonated block‐graft polyimide (S‐bg‐PI) and sulfonated polybenzimidazole (sPBI) were prepared and characterized. The proton conductivity and oxygen permeability coefficient of the novel blend membrane S‐bg‐PI/sPBI (7 wt%) were 0.38 S cm^?1 at 90 °C and 98% relative humidity and 7.2 × 10^?13 cm³(STP) cm (cm² s cmHg)^?1 at 35 °C and 76 cmHg, respectively, while those of Nafion^® were 0.15 S cm^?1 and 1.1 × 10^?10 cm³(STP) cm (cm² s cmHg)^?1 under the same conditions. The apparent (proton/oxygen transport) selectivity calculated from the proton conductivity and the oxygen permeability coefficient in the S‐bg‐PI/sPBI (7 wt%) membrane was 300 times larger than that determined in the Nafion membrane. Besides, the excellent gas barrier properties based on an acid ? base interaction in the blend membranes are expected to suppress the generation of hydrogen peroxide and reactive oxygen species, which will degrade fuel cells during operation. The excellent proton conductivity and gas barrier properties of the novel membranes promise their application for future fuel cell membranes. © 2015 Society of Chemical Industry     

Synthesis and characterization of acid–base polyimides bearing pendant sulfoalkoxy groups for direct methanol fuel cell applications

A series of acid–base polyimides with sulfonic acid groups in the side chains have been prepared, based on a new synthesized sulfonated diamine monomer containing pyridine functional group. The effect of the introduction of pyridine groups into copolymer backbone on the properties of membrane were evaluated through the investigation of membrane parameters. The copolymers produced flexible, tough, and transparent membranes by solvent casting method. All the prepared membranes displayed high thermal stability, great oxidative stability and good mechanical properties. They exhibited appropriate water uptake (15.8–30.2 wt % at 80°C) and remarkable dimensional stability (2.5–6.9% at 80°C). The proton conductivity of SPI‐80 was 1.01 × 10^?2 S cm^?1 at room temperature. Moreover, the methanol permeability of SPI‐80 membrane was 1.22 × 10^?7 cm² s^?1, which was lower than 23.8 × 10^?7 cm² s^?1 of Nafion 117. Therefore, these acid‐base polyimides materials have a promising prospect for direct methanol fuel cell applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42238.     

Vinyl‐addition type norbornene copolymer containing sulfonated biphenyl pendant groups for proton exchange membranes

The vinyl addition type copolymer poly(butoxymethylene norbornene‐co‐biphenyl oxyhexamethyleneoxymethylene norbornene) (P(BN/BphN)) was synthesized by using bis‐(β‐ketonaphthylimino)nickel(II)/B(C₆F₅)₃ catalytic system. P(BN/BphN) was sulfonated to give sulfonated P(BN/BphN) (SP(BN/BphN)) with concentrated sulfuric acid (98%) as sulfonating agent in a component solvent. The ion exchange capacity (IEC), degree of sulfonation (DS), water uptake, and methanol permeability of the SP(BN/BphN)s were increased with the sulfonated time. The methanol permeability of the SP(BN/BphN) membranes was in the range of 1.8 × 10^?7 to 7.5 × 10^?7 cm²/s, which were lower than the value 1.3 × 10^?6 cm²/s of Nafion®115. The proton conductivity of SP(BN/BphN) membranes increased with the increase of IEC values, temperature, and water uptake. Water uptake of the SP(BN/BphN) membranes was lower than that of Nafion® 115 and leads to low proton conduction. Microscopic phase separation occurred in SP(BN/BphN) membrane and domains containing sulfonic acid groups were investigated by SEM and TEM. SP(BN/BphN) membranes had good mechanical properties, high thermal stability, and excellent oxidative stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

CHITOSAN-BASED FUEL CELL MEMBRANES

Chitosan complex membranes are prepared and characterized at room temperature. They are expected to be used as proton exchange membranes. The studied membranes are cross-linked membranes with sulfuric acid; salt-complexed membranes with lithium nitrate; cross-linked and salt-complexed membranes; plasticized and salt-complexed membranes; cross-linked, plasticized, and salt-complexed membranes; and doped membranes with sulfuric acid. A fixed amount of ethylene carbonate is used as plasticizer. It is found that the ion exchange capacity and hydrogen gas permeability of all membranes is better than that of Nafion membranes. However, their proton conductivities are worse than Nafion membranes. It can be stated that ethylene carbonate does not improve conductivity. An optimum amount of lithium nitrate salt can enhance conductivity. The formation of a sulfate group in cross-linked membranes is necessary for proton conduction. The proton conductivities of 4%cross-linked and 50%LiNO₃ membrane before and after acid doping are (3.11±0.40) × 10^?2 and (6.64±0.11) × 10^?2 S cm^?1, respectively. That of Nafion is (8.02±1.19) × 10^?2 S cm^?1.     

Sulfonated poly(ether sulfone)/silica composite membranes for direct methanol fuel cells

A series of sulfonated poly(ether sulfone) (SPES)/silica composite membranes were prepared by sol–gel method using tetraethylorthosilicate (TEOS) hydrolysis. Physico–chemical properties of the composite membranes were characterized by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscope–energy dispersive X‐ray (SEM–EDX), and water uptake. Compared to a pure SPES membrane, SiO₂ doping in the membranes led to a higher thermal stability and water uptake. SEM–EDX indicated that SiO₂ particles were uniformly embedded throughout the SPES matrix. Proper silica loadings (below 5 wt %) in the composite membranes helped to inhibit methanol permeation. The permeability coefficient of the composite membrane with 5 wt % SiO₂ was 1.06 × 10^?7 cm²/s, which was lower than that of the SPES and just one tenth of that of Nafion® 112. Although proton conductivity of the composite membranes decreased with increasing silica content, the selectivity (the ratio of proton conductivity and methanol permeability) of the composite membrane with 5 wt % silica loading was higher than that of the SPES and Nafion® 112 membrane. This excellent selectivity of SPES/SiO₂ composite membranes could indicate a potential feasibility as a promising electrolyte for direct methanol fuel cell. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of proton exchange membrane based on polyphosphoric acid modified by PVDF‐HFP

A polyphosphoric acid functionalized proton exchange membrane (PEM) was prepared by a ring opening reaction using the epoxycyclohexylethyltrimethoxysilane (EHTMS) and amino trimethylene phosphonic acid (ATMP) as raw materials and was modified by poly(vinylidene fluoride)–hexafluoro propylene (PVDF‐HFP). The structure of the membranes was characterized by Fourier transform infrared and scanning electron microscopy. The X‐ray photoelectron spectroscopy explores the content of the elements in the membrane related to the ion exchange capacity value. The membranes’ properties including water uptake, swelling ratio, proton conductivity, and hydrolysis stability were studied. Performance tests show that when ATMP/EHTMS = 1/5, conductivity of the PVDF‐HFP modified PEMs increased from 0.83 × 10^?4 S cm^?1 at 20 °C to 9.53 × 10^?3 S cm^?1 at 160 °C, the swelling ratio of membranes decreased from 2.71% to 2.13%. The results indicate that the introduction of F atoms is beneficial to increase the proton conductivity and the dimensional stability. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46737.     

New composite membrane poly(vinyl alcohol)/graphene oxide for direct ethanol–proton exchange membrane fuel cell

This study investigated a simple synthesis of a crosslinked poly(vinyl alcohol)/ graphene oxide composite membrane with lower ethanol permeability membrane for passive direct ethanol–proton exchange membrane fuel cells (DE-PEMFCs). The chemical and physical structure, morphologies, ethanol uptake and permeability, ion exchange capacities, water uptake, and proton conductivities were determined and found that transport properties of the membrane were affected by the GO loading. The composite membrane with optimum GO content (15 wt %) exhibited the highest proton conductivity of 9.5 × 10⁻³ Scm⁻¹ at 30°C, 3.24 × 10⁻² Scm⁻¹ at 60°C, respectively and reduced ethanol permeability until 1.75 × 10⁻⁷ cm² s⁻¹. In the passive DE-PEMFC, the power density at 60°C were obtained as 5.84 mW cm⁻² higher than those by commercial Nafion 117 is 4.52 mW cm⁻². © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46928.     

Alkaline polymer electrolyte membranes from quaternized poly(phthalazinone ether ketone) for direct methanol fuel cell

Quaternized poly(phthalazinone ether ketone)s (QPPEK)s were synthesized by the chloromethylation and quaternization of poly(phthalazinone ether ketone) (PPEK) with chloromethyl methyl ether in 98% concentrated sulfuric acid and following trimethylamine. The presence of ? CH₂Cl groups in chloromethylated PPEK was confirmed by ¹H‐NMR. An alkaline QPPEK membrane was prepared and its thermal and mechanical properties were tested. The alkaline QPPEK membrane had a methanol permeability 6.57 × 10^?7 cm²/s and the highest anion conductivity 1.14 × 10^?2 S/cm. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008