Boundary layer analysis for nonlinear singularly perturbed differential equations

This paper focuses on the boundary layer phenomenon arising in the study of singularly perturbed differential equations. Our tools include the method of lower and upper solutions combined with analysis of the integral equation associated with the class of nonlinear equations under consideration

Novel crosslinkers for high performance poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchange membranes (PEM) are one of the main components of PEFCs and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion®, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. 1 Since polyAMPS (PAMPS) excessively swells or even dissolves in water, we investigated several commercial crosslinkers and new multifunctional monomers (Fig. 1) to decrease swelling by crosslinking. AMPS, crosslinker and photoinitiator were dissolved in water and N-methyl-2-pyrrolidone (NMP), respectively. To facilitate conductivity measurements and handling of crosslinked PAMPS formulations after UVinitiated radical polymerization, they were constrained within a porous membrane using a procedure described by Zhou et al. 2 We tested several commercial crosslinkers and according to these results we developed new crosslinkers with enhanced hydrolytical stability and conductivity. In contrast to the commercial crosslinkers, where conductivity increased with increasing amount of crosslinker, our new acrylamide based crosslinkers needed only very low concentrations. They could achieve more than 2.5 times the conductivity of Nafion with only 5 wt% crosslinker. We used this novel crosslinkers to integrate them into asymmetric membranes with interpenetrating proton-conducting morphology for enhanced methanol barrier properties. 3 First results of their performance compared to Nafion will be presented. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. The authors would like to thank 3M for PP membrane samples and Ciba SC, Huntsman, Ivoclar Vivadent and Sartomer for samples of photoinitiator and crosslinker. 1 a) Qiao, J., et al., Journal of Materials Chemistry 2005, 15 (41), 4414-4423. b)Diao, H., et al., Macromolecules 43 (15), 6398-6405. 3 Zhou, J., et al., Journal of Membrane Science 2005, 254 (1-2), 89-99. 4 Radovanovic, P., et al., Journal of Membrane Science 2012, 401-402, 254-261

Photopolymerization of crosslinked proton conducting membranes

Several monomers and crosslinker in a broad range of concentrations in water and 1-Methyl-2-pyrrolidone (NMP) respectively were screened for their mechanical properties, water uptake and conductivity in porous membranes by photo polymerization with a polar photo initiator. As conductive polymer, primarily poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and poly(2-sulfoethyl methacrylate) (PSEM) respectively as well as polymers of phosphonic acid containing monomers or newly synthesized monomers were used. The conductive monomers were crosslinked with varying hydrophobic and hydrophilic multifunctional monomers like N,N'-methylene bisacrylamide (MBA), 2-Propenoic acid, 2-methyl-, 1,1'-(1,10-decanediyl) ester (D3MA) or polyethyleneglycol diacrylates with two varying chainlengths (PEG-DA700, PEG-DA330). The advantage of several different building blocks with known characteristics is the possibility to tune the polymer to special needs of an application. For example, some polymer compositions have good conductivity at lower temperatures whereas other polymers develop better properties at elevated temperatures. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat and with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. We thank 3M for providing us with samples of the PP membrane. 1/ Hamrock, S.J. and M.A. Yandrasits, Proton Exchange Membranes for Fuel Cell Applications. 2006. 46(3): p. 219 - 244. 2/ Hoogers, G., Membranes and Ionomers, in Fuel Cell Technology Handbook G. Hoogers, Editor. 2002, CRC Press. p. 36

Novel crosslinkers for high performance poly-AMPS-based proton exchange membranes for fuel cells

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchange membranes (PEM) are one of the main components of PEFCs and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion®, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. 1 Since polyAMPS (PAMPS) excessively swells or even dissolves in water, we investigated several commercial crosslinkers and new multifunctional monomers (Fig. 1) to decrease swelling by crosslinking. AMPS, crosslinker and photoinitiator were dissolved in water and N-methyl-2-pyrrolidone (NMP), respectively. To facilitate conductivity measurements and handling of crosslinked PAMPS formulations after UVinitiated radical polymerization, they were constrained within a porous membrane using a procedure described by Zhou et al. 2 We tested several commercial crosslinkers and according to these results we developed new crosslinkers with enhanced hydrolytical stability and conductivity. In contrast to the commercial crosslinkers, where conductivity increased with increasing amount of crosslinker, our new acrylamide based crosslinkers needed only very low concentrations. They could achieve more than 2.5 times the conductivity of Nafion with only 5 wt% crosslinker. We used this novel crosslinkers to integrate them into asymmetric membranes with interpenetrating proton-conducting morphology for enhanced methanol barrier properties. 3 First results of their performance compared to Nafion will be presented. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. The authors would like to thank 3M for PP membrane samples and Ciba SC, Huntsman, Ivoclar Vivadent and Sartomer for samples of photoinitiator and crosslinker. 1 a) Qiao, J., et al., Journal of Materials Chemistry 2005, 15 (41), 4414-4423. b)Diao, H., et al., Macromolecules 43 (15), 6398-6405. 3 Zhou, J., et al., Journal of Membrane Science 2005, 254 (1-2), 89-99. 4 Radovanovic, P., et al., Journal of Membrane Science 2012, 401-402, 254-261

High performance proton conducting membranes for fuel cells made by photopolymerization of hydrolytically stable monomers

Proton conducting membranes were prepared by photopolymerization of 2- acrylamido-2-methylpropane sulfonic acid solutions within the pores of polypropylene membranes. Several commercial and novel multifunctional monomers synthesized in IAS lab were investigated as suitable crosslinking agents for this application. Some membranes made with synthesized crosslinkers at low crosslinker concentrations exceeded 2.5 times the conductivity of Nafion® 115 membrane, while exhibiting a good hydrolytical stability, in contrast to the commercial crosslinkers based on multifunctional (meth)acrylates

Asymmetric sol-gel proton-conducting membrane

Proton-conducting membranes with interpenetrating polymer network morphology have gained attention in recent years for potential replacement of standard Nafion membranes in direct methanol fuel cells. These membranes generally consist of fine interpenetrating domains of proton-conducting and mechanically-supporting polymer phases, which often leads to improvements in mechanical strength and methanol barrier properties. Asymmetric sol-gel membranes comprising proton-conducting channels of cross-linked sulfonic acid functionalized ionomers embedded within a matrix of thermally-resistant, glassy polymer were prepared by photopolymerization starting from a polymer solution and evaluated in our laboratories. These membranes have an integral top skin layer with fine biomimetic proton-conducting channels, which provides a barrier against methanol crossover, on top of a coarser proton-conducting support. Conductivity of asymmetric membranes over a range of initial polymer concentrations and ion-exchange capacities (IEC) was just slightly lower than for the corresponding symmetric membranes. Methanol barrier properties of asymmetric sol-gel membranes were better than that of Nafion 115 membrane. The crosslinking agent functionality had a major effect on membrane conductivity. Use of trifunctional crosslinking agents resulted in significantly higher conductivities than those obtained with bifunctional agents, even surpassing the conductivity of Nafion membranes

Proton conducting membranes based on photopolymerizable monomers

The proton exchange barrier or Proton Exchange Membrane (PEM) is the critical part of a fuel cell. The basic function of the membrane is to enable proton transport, while being simultaneously impermeable for electrons and gas. Typically, membranes for the PEM fuel cells (PEMFC) are made of perfluorocarbon-sulfonic acid monomers. The best known material of this class is Nafion which has a unique interpenetrating structure of hydrophobic perfluorocarbon regions providing thermal and chemical resistance, mechanical strength and diffusional resistance combined with hydrophilic regions of water clusters surrounding charged sulfonic acid groups which allow selective proton transport. For these reasons, Nafion is still considered the benchmark against which most of the new materials are compared [1]. At the molecular level, proton transport may follow two principal mechanisms: (a) diffusion mechanism via H3O+ ion as a carrier and (b) proton hopping mechanism (Grotthuss transport) [2]. Contemporary PEMFCs are exclusively based on the vehicle mechanism. PEMFCs produce water as a by-product and H+ ions moving from the anode to the cathode pull water molecules by an electro-osmotic drag force. In addition, membrane suffers from evaporation of water at working temperatures of 60-90ºC. Nafion effectively conducts protons only when imbibed by water within a narrow range, which limits the operating temperature of PEM fuel cells to around 80oC. However an operating temperature above 100ºC is a highly desirable goal. PEM membranes are not dimensionally stable since the material significantly swells upon water absorption. Therefore the aim of our proton conducting membrane is a rigid polymer with perpendicular nano channels which are filled with a conducting sulfonic polymer where conductivity is mainly achieved by the Grotthuss mechanism. Several monomers and crosslinker in a broad range of concentrations in water and 1-Methyl-2-pyrrolidone (NMP) respectively were screened for their mechanical properties, water uptake and conductivity in porous membranes by photo polymerization with a polar photo initiator. As conductive polymer, primarily poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and poly(2-sulfoethyl methacrylate) (PSEM) respectively as well as polymers of phosphonic acid containing monomers or newly synthesized monomers were used. The conductive monomers were crosslinked with varying hydrophobic and hydrophilic multifunctional monomers like N,N'-methylene bisacrylamide (MBA), 2-Propenoic acid, 2-methyl-, 1,1'-(1,10-decanediyl) ester (D3MA) or polyethyleneglycol diacrylates with two varying chainlengths (PEG-DA700, PEG-DA330). The advantage of several different building blocks with known characteristics is the possibility to tune the polymer to special needs of an application. For example, some polymer compositions have good conductivity at lower temperatures whereas other polymers develop better properties at elevated temperatures. The research leading to these results has received funding from the European Community's FP7- NMP Programme, under the Project Acronym MultiPlat and with Grant Agreement: N 228943 and the Austrian Federal Ministry of Science and Research. We thank 3M for providing us with samples of the PP membrane. 1/Hamrock, S.J. and M.A. Yandrasits, Proton Exchange Membranes for Fuel Cell Applications. 2006. 46(3): p. 219 - 244. 2/ Hoogers, G., Membranes and Ionomers, in Fuel Cell Technology Handbook G. Hoogers, Editor. 2002, CRC Press. p

Proton conducting fluorinated polymer nanomembrane for fuel cell applications

Polymer electrolyte fuel cells (PEFC) gained a lot of interest in recent years as a potential solution for an eco-friendly energy. Proton exchage membranes (PEM) are one of the main components of PEFC and require mechanical and chemical stability to ensure high proton conductivity and effective separation of anode and cathode under challenging conditions. Best commercial membranes made from sulfonated fluoropolymers, such as Nafion, are rather expensive. To improve fuel cell performance at a lower cost, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was investigated recently. We investigated crosslinkable polymers consisting of AMPS for proton conductivity, a perfluorinated acrylate to mimic Nafion and glycidyl methacrylate for crosslinking. Since we combine very polar and very apolar monomers in the polymer chain we investigated phase separation and orientation of proton conducting channels in the electric field. First results of conductivity measurements and orientation will be presented

Novel asymmetric interpenetrating proton-conducting membrane

Fuel cells comprising proton-conducting polymer membranes are focus of active research due to their versatile applications as energy sources in the automotive, stationary and portable fields. A fluoro-ionomer membrane, such as Nafion available from Du Pont de Nemours, is commonly used for these applications. High price of these membranes and their limitations, such as high crossover of methanol in Direct Methanol Fuel Cells and performance loss under conditions of low relative humidity, have led to investigations of other proton-conducting membranes from less expensive, nonfluorinated materials. Proton-conducting membranes with interpenetrating polymer network morphology have been a subject of growing interest in recent years [1]. These materials are generally prepared by either in situ polymerization and cross-linking starting from initial reactants, or by sequential synthesis starting from a polymer network swollen with necessary precursors that subsequently react to form the interpenetrating structure within the first network. An interplay of the chemical reaction and liquid-liquid demixing kinetics has a determining effect on the final membrane morphology. Interpenetrating domains of relatively small size are typical, as opposed to macroscopic phase separation observed in most polymer blends. Such fine morphology of interpenetrating proton-conducting membranes often leads to improvement in mechanical strength and reactant barrier properties. Novel asymmetric membranes comprising proton-conducting channels of cross-linked sulfonic acid functionalized ionomers embedded within a matrix of thermally resistant, glassy polymer were prepared and evaluated in our laboratories. These membranes have an integral top skin layer with fine biomimetic proton-conducting channels, which provides a barrier against methanol crossover, on top of a coarser proton-conducting support. Conductivity of asymmetric membranes over a range of initial polymer concentrations and ion-exchange capacities (IEC) was just slightly lower than for the corresponding symmetric membranes. These conductivity measurements were carried out using a 4-point in-plane method. It is expected that the planned measurements in the direction of membrane thickness will result in significantly higher conductivities due to the anisotropic membrane morphology

High temperature vat photopolymerization 3D printing of fully bio-based composites: Green vegetable oil epoxy matrix & bio-derived filler powder

Additive manufacturing (AM) is a well-established process which allows to generate complex and accurate geometry required in several applications, from medical to automotive area. The exploitation of polymer resin into additive manufacturing needs to overcome the problem of viscosity and reactivity which can be improved by high temperature vat photopolymerization (VPP). Moreover, the concern about climate change and depletion of fossil fuels arises the requirement to move toward bio-derived products which can substitute the commercially available resins without compromise the final properties. In order to close this gap, we have studied vegetable epoxy oil polymer resins as main component for new bio-derived formulations which can be used in vat photopolymerization 3D printing. Furthermore, knowing the limits of the vegetable oils in terms of final properties, the investigation explores the possibility to 3D printing bio-derived composites by adding bio-based fillers, such as wall-nut shell. The UV-curing process was investigated by photo-DSC and photorheology to verify the feasibility of AM. Then, the effect of the presence of the filler on the UV-process was assessed and finally we successfully 3D printed composites of different geometries. The thermo-mechanical properties of the thermoset materials were studied by dynamic analysis and tensile testing. The benefit of the addition of the filler was confirmed and explained by investigating the surface modification of the filler which had an incredible impact on the properties of the composite. Finally, we pursuit the possibility to chemically degrade the thermoset joining the proof-of-concept of circular economy