Highly conductive, methanol resistant fuel cell membranes fabricated by layer-by-layer self-assembly of inorganic heteropolyacid

Layer-by-layer (LBL) self-assembly is a simple and elegant method of constructing organic-inorganic composite thin films from environmentally benign aqueous solutions. In this paper, we utilize this method to develop proton-exchange membranes for fuel cells. The multilayer film is constructed onto the surface of sulfonated poly(arylene ether ketone) (SPAEK-COOH) membrane by LBL self-assembly of polycation chitosan (CTS) and negatively charged inorganic particle phosphotungstic acid (VIA). The highly conductive inorganic nanoparticles ensure SPAEK-COOH-(CTS/PTA)(n) membranes to maintain high proton conductivity values up to 0.086 S cm(-1) at 25 degrees C and 0.24S cm(-1) at 80 degrees C, which are superior than previous LBL assembled electrolyte systems.

Self-Assembly of Hyperbranched Multiarmed PEG-PEI-PLys(Z) Copolymer into Micelles, Rings, and Vesicles

Self-assembling of synthesized novel biodegradable hyperbranched amphiphilic poly(ethylene glycol)-polyethylenimine-poly(epsilon-benzyloxycarbonyl-L-lysine) (PEG-PEI-PLys(Z)) in aqueous media is studied. In aqueous media. PLys(Z) is the hydrophobic segment, with PEG and PEI as the hydrophilic segments. It will self-assemble into spherical shape when the selected solvent water is dropped into the common solvent tetrahydrofuran (THF). And when PEG-PEI-PLYS in common solvent is dropped into mixed solvent water and THF, rings will come into King. The spherical and rings are observed by environmental scanning electron microscopy (ESEM) and transmission electron microscopy ITEM). It shows that the size of the sphere is about 100 nm, and the diameter of ring distributes from 400 nm to 10 mu m and bigger with the time roll around.

Synthesis and self-assembly of poly(ethylene oxide)-b-poly(2-hydroxyethyl methacrylate)

Poly(ethylene oxide)-b-poly(2-hydroxyethyl methacrylate) (PEO-b-PHEMA) was synthesized by successive atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate(HEMA) monomer using PEO-Br macroinitiator as initiator, CuBr/CuBr2 and 2,2.-bipyridyl (bpy) as catalyst and ligand. IR, H-1 NMR, and GPC analysis indicate that PEO-b-PHEMA block copolymer with low polydispersity index (M-w/M-n approximate to 1.1) has been formed. Self-assembly of this double hydrophilic block copolymer in the selective solvent and water was also studied. Owing to the high hydrophilic nature of the PEO and PHEMA blocks, this double hydrophilic block copolymer cannot disperse well in water. So block copolymer was modified by part esterification of PEO-b-PHEMA with acetic anhydride, which increased the hydrophobic group of the PHEMA block. The TEM results show that this block copolymer spontaneously form well-defined micelles in water.

Synthesis and self-assembly of a novel Y-shaped copolymer with a helical polypeptide arm

novel biodegradable Y-shaped copolymer, poly(L-lactide)(2)-b-poly(gamma-benzyl-L-glutamic acid) (PLLA(2)-b-PBLG), was synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with centrally amino-functionalized poly(L-lactide), PLLA(2)-NH2, as a macroinitiator in a convenient way. The Y-shaped copolymer and its precursors were characterized by H-1 NMR, FT-IR, GPC, WAXD and DSC measurements. The self-assembly of the PLLA(2)-b-PBLG copolymer in toluene and benzyl alcohol was examined. It was found that the self-assembly of the copolymer was dependent on solvent and on relative length of the PBLG block. For a copolymer with PLLA blocks of 26 in total degree of polymerization (DP), if the PBLG block was long enough (e.g., DP = 54 or more), the copolymer/toluene solution became a transparent gel at room temperature. In benzyl alcohol Solution, only PLLA(2)-b-PBLG containing ca. 190 BLG residues could form a gel: those with shorter PBLG blocks (e.g., DP = 54) became nano-scale fibrous aggregates and these aggregates were dispersed in benzyl alcohol homogeneously.

Electrochemiluminescence-based DNA detection using guanine oxidation at electrostatic self-assembly of Ru(bpy)(3)(2+)-doped silica nanoparticles on indium tin oxide electrode

A Ru(bpy)(3)(2+)-doped silica nanoparticle-[Ru@Silica] modified indium tin oxide electrode was prepared by simple electrostatic self-assembly technique, and one-electron catalytic oxidation of guanine bases in double-strand and denatured DNA was realized using the electrochemiluminescence detection means.

Study of self-assembly of symmetric coil-rod-coil ABA-type triblock copolymers by self-consistent field lattice method

The self-assembly of symmetric coil-rod-coil ABA-type triblock copolymer melts is studied by applying self-consistent field lattice techniques in a three-dimensional space. The self-assembled ordered structures differ significantly with the variation of the volume fraction of the rod component, which include lamellar, wave lamellar, gyroid, perforated lamellar, cylindrical, and spherical-like phases. To understand the physical essence of these phases and the regimes of occurrence, we construct the phase diagram, which matches qualitatively with the existing experimental results. Compared with the coil-rod AB diblock copolymer, our results revealed that the interfacial grafting density of the separating rod and coil segments shows important influence on the self-assembly behaviors of symmetric coil-rod-coil ABA triblock copolymer melts. We found that the order-disorder transition point changes from f(rod)=0.5 for AB diblock copolymers to f(rod)=0.6 for ABA triblock copolymers. Our results also show that the spherical-like and cylindrical phases occupy most of the region in the phase diagram, and the lamellar phase is found stable only at the high volume fraction of the rod.

Self-assembly of ionic liquids-stabilized Pt nanoparticles into two-dimensional patterned nanostructures at the air-water interface

In this paper, we demonstrate the self-assembly of ionic liquids (ILs)-stabilized Pt nanoparticles into two-dimensional (2D) patterned nanostructures at the air-water interface under ambient conditions. Here, ILs are not used as solvents but as mediators by virtue of their pronounced self-organization ability in synthesis of self-assembled, highly organized hybrid Pt nanostructures. It is also found that the morphologies of the 2D patterned nanostructures are directly connected with the quantities of ILs. Due to the special structures of ILs-stabilized Pt nanoparticles, 2D patterned Pt nanostructures can be formed through the pi-pi stack interactions and hydrogen bonds. The resulting 2D patterned Pt nanostructures exhibit good electrocatalytic activity toward oxygen reduction.

Self-assembly of diblock copolymer mixtures in confined states: A Monte Carlo study

The self-assembly of diblock copolymer mixtures (A-b-B/A-b-C or A-b-B/B-b-C mixtures) subjected to cylindrical confinement (two-dimensional confinement) was investigated using a Monte Carlo method. In this study, the boundary surfaces were configured to attract blocks A but repel blocks B and C. Relative to the structures of the individual components, the self-assembled structures of mixtures of the diblock copolymers were more complex and interesting. Under cylindrical confinement, with varying cylinder diameters and interaction energies between the boundary surfaces and the blocks, we observed a variety of interesting morphologies. Upon decreasing the cylinder's diameter, the self-assembled structures of the A(15)B(15)/A(15)C(15) mixtures changed from double-helix/cylinder structures (blocks B and C formed double helices, whereas blocks A formed the outer barrel and inner core) to stacked disk/cylinder structures (blocks B and C formed the stacked disk core, blocks A formed the outer cylindrical barrel), whereas the self-assembled structures of the A(15)B(7)/B7C15 mixtures changed from concentric cylindrical barrel structures to screw/cylinder structures (blocks C formed an inside core winding with helical stripes, whereas blocks A and B formed the outer cylindrical barrels) and then finally to the stacked disk/cylinder structures.

Self-assembly of a polymer pair through poly(lactide) stereocomplexation

A polymer pair composed of poly( N-isopropylacrylamide-co-2-hydroxyethyl methacrylate terminated oligo( L-lactide)) ( poly( NIPAAm-co-HEMAOLLA)) graft random copolymer and poly( D-lactide) ( PDLA) homopolymer was self-assembled into micelles with a diameter around 100 nm through the stereocomplexation between the OLLA branches of the graft copolymer and the PDLA homopolymer. The specific intermolecular stereocomplexation was considered as the powerful ordered aggregation force in the micelle cores. The shell's component of poly( NIPAAm-co-HEMA) and its thermosensitivity were proved by H-1 nuclear magnetic resonance ( NMR) and dynamic light scattering ( DLS), respectively. The incorporation of PDLA homopolymer into the graft copolymer affected the micelle size and the critical micelle concentration ( CMC). The incorporation of even a small quantity ( 11 wt%) of PDLA into the graft copolymer micelles resulted in a great decrease of the micelle size. For the graft copolymer with low per cent grafting of 18%, the size of the corresponding micelles decreased slightly even if the PDLA content increased up to 33 wt%. For the graft copolymer with high per cent grafting of 58%, with the further increase of PDLA content, the size of the corresponding micelles at first decreased further and then began to increase. The molecular weight of the PDLA did not significantly affect the micelle size.

Self-assembly of polypeptide-containing ABC-type triblock copolymers in aqueous solution and its pH dependence

Self-assembling of novel biodegradable ABC-type triblock copolymer poly(ethylene glycol)-poly(L-lactide)-poly(L-glutamic acid) (PEG-PLLA-PLGA) is studied. In aqueous media, it self-assembles into a spherical micelle with the hydrophobic PLLA segment in the core and the two hydrophilic segments PEG and PLGA in the shell. With the lengths of PEG and PLLA blocks fixed, the diameter of the micelles depends on the length of the PLGA block and on the volume ratio of H2O/dimethylformamide (DMF) in the media. When the PLGA block is long enough, morphology of the self-assembly is pH-dependent. It assembles into the spherical micelle in aqueous media at pH 4.5 and into the connected rod at or below pH 3.2. The critical micelle concentration (cmc) of the copolymer changes accordingly with decreasing solution pH. Both aggregation states can convert to each other at the proper pH value. This reversibility is ascribed to the dissociation and neutralization of the COOH groups in the LGA residues. When the PLGA block is short compared to the PEG or PLLA block, it assembles only into the spherical micelle at various pH values.

Synthesis, characterization, and self-assembly of protein lysozyme monolayer-stabilized gold nanoparticles

Lysozyme monolayer-protected gold nanoparticles (Au NPs) which are hydrophilic and biocompatible and show excellent colloidal stability at low temperature, ca. 4 degrees C, were synthesized in aqueous medium by chemical reduction of HAuCl4 with NaBH4 in the presence of a familiar small enzyme, lysozyme. UV-vis spectra, transmission electron microscopy (TEM), atomic force microscopy, and X-ray photoelectron spectroscopy characterization of the as prepared nanoparticles revealed the formation of well-dispersed An NPs of ca. 2 nm diameter. Moreover, the color change of the An NP solution as well as UV-vis spectroscopy and TEM measurements have also demonstrated the occurrence of Ostwald ripening of the nanoparticles at low temperature. Further characterization with Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering indicated the formation of a monolayer of lysozyme molecules on the particle surface. FTIR data also indicated the intactness of the protein molecules coated on An NPs. All the characterization results showed that the monodisperse An NPs are well-coated directly with lysozyme. Driven by the dipole-dipole attraction, the protein-stabilized Au NPs self-assembled into network structures and nanowires upon aging under ambient temperature.

Self-assembly of a water chain with tetrameric and decameric clusters in the channel of a mixed-valence (CuCuII)-Cu-I complex

The reaction of Cu(BF4)(2) with pyridine-2,6-dicarboxylic acid (H(2)pydc) and trans-1,2-bis(4-pyridyl)ethylene (bpe) under hydrothermal conditions afforded a porous mixed-valence (CuCuII)-Cu-I coordination polymer. Coexistence of tetrameric and decameric water clusters within the channels of the complex leads to a novel water chain. The metal-organic framework provides both hydrophilic and hydrophobic environments for stabilizing the clusters and retains its integrity upon dehydration and rehydration.

Self-assembly of crystalline-coil diblock copolymer in solvents with varying selectivity: From spinodal-like aggregates to spheres, cylinders, and lamellae

We have investigated systematically the morphology of thin films spin-coated from solutions of a semicrystalline diblock copolymer, poly(L-lactic acid)-block-polystyrene (PLLA-b-PS), in solvents with varying selectivity. In neutral solvents (chloroform and tetrahydrofuran (THF)), a spinodal-like pattern was obtained and the pattern boundary was sharpened by diluting the solution. Meanwhile, loose spherical associates, together with larger aggregates composed of these associates by unimer bridges, formed partly due to crystallization of the PLLA blocks in relatively concentrated solutions. In slightly PS-selective solvent (e.g., benzene), both loose and compact spherical micelles were obtained, depending on the polymer concentration, coexisting with unimers. When enhancing the selectivity with mixed solvents, for example, mixing the neutral solvent and the slightly selective solvent with a highly PS-selective solvent, CS2, loose assemblies (nanorods in CS2/THF mixtures and polydisperse aggregates in CS2/benzene mixtures) and well-developed lamellar micelles were obtained.

Ordered macroporous films from self-assembly of two-armed polymer with a crown ether core

Highly ordered honeycomb-like macroporous films were obtained via self-assembly of a two-armed polymer with a crown ether core under controlled conditions. A possible mechanism is speculated, primarily based on the strong affinity between the crown ether cores. The pore size and arrangement are sensitive to the solvent evaporation rate and the solution concentration. Upon spontaneous drying, the pore diameter (D) depends on the concentration (c) by a relation of D=518c(-0.610).