Self-assembly of polypeptide/pi-conjugated polymer/polypeptide triblock copolymers in rod-rod-rod and coll-rod-coil conformations

Self-assembly in the bulk of a series of hybrid triblock copolymers formed by a poly(9,9-dihexylfluorene-2,7-diyl) (PHF) middle block and two poly(gamma-benzyl-L-glutamate) (PBLG) end blocks has been studied. Since the alpha-helical secondary structure of the PBLG block may be either maintained or suppressed depending on the solvent casting history, the PBLG-PHF-PBLG copolymers exhibit two different conformations: a rod-rod-rod or coil-rod-coil configuration, respectively. In order to provide insight into the influence of conformation on self-aggregation of these systems, three copolymers with different block ratio were investigated in both conformations using small- and wide-angle scattering techniques and transmission electron microscopy. Time-resolved photoluminescence measurements were performed on the same samples to explore the effect of morphology on photophysical properties. The observed photoluminescence spectra and dominant excited lifetimes of the poly(9,9-dihexylfluorene-2,7-diyl) block were found to differ markedly in rod-rod-rod and coil-rodcoil configurations and were correlated to the morphology of the self-assembled triblock copolymers

Synthesis and characterization of novel functional electrosterically stabilized colloidal particles prepared by emulsion polymerization using a strongly ionized amphiphilic diblock copolymer

Amphiphilic diblock copolymers such as poly(styrene)-block-poly(styrene sulfonate) (PS-b-PSS) (Matsuoka, H.; Maeda, S.; Kaewsaiha, P.; Matsumoto, K. Langmuir 2004, 20, 7412), belong to a class of new polymeric surfactants that ionize strongly in aqueous media. We investigated their self-assembly behavior in aqueous solutions and used them as an emulsifier to prepare electrosterically stabilized colloidal particles of different diameters between 70 to 400 nm. We determined the size, size polydispersity, effective charge, total dissociable charge, structural ordering, and phase behavior using light scattering, transmission electron microscopy (TEM), small-angle neutron scattering (SANS), and potentiometric titration. These experiments clearly demonstrated that all of the synthesized particles were nearly monodisperse (polydispersity index ≤ 6%). The results of DLS and TEM clearly suggested the existence of hairy particles. The form factors obtained by SANS were well described by a polydisperse sphere model. The estimated total number of dissociable charges per particle was found to be larger than 10⁴e, whereas the effective charges per particle were found to be around 1000e. This significant difference suggested the confinement of charges inside the corona regions of the polyelectrolyte brush shell. Finally, these monodisperse particles were found to self-assemble into 3D ordered colloidal crystalline arrays at a low volume fraction (= 0.00074) that diffract light in the visible region

Block copolymer electrolytes for fuel cells and secondary batteries, the small angle neutron scattering inputs

This paper aims at giving an overview on the importance of scattering, and more specifically neutron scattering, for probing the nanomorphology of polymer electrolytes made of block copolymers. Two types of self-assembled polymer electrolyte materials will be discussed: (i) the ionomer membranes used in fuel cell and (ii) the solid polyelectrolytes used in secondary batteries. Both are used to physically separate the electrodes in the respective electrochemical devices and are expected to have a high ion transport capacity so as good chemical and mechanical stabilities. Unfortunately, in most cases improving one property leads to the degradation of the others. Nonetheless, through block copolymers selfassembly it is possible to tackle this issue; indeed, antagonist properties can be decoupled and associated within controlled nano-morphologies. This aspect will be discussed and supported by examples based on published studies; in parallel useful scattering analytical tools and models will be presented along the paper and detailed in annex

Block copolymer electrolytes for fuel cells and secondary batteries, the small angle neutron scattering inputs

International audienceThis paper aims at giving an overview on the importance of scattering, and more specifically neutron scattering, for probing the nanomorphology of polymer electrolytes made of block copolymers. Two types of self-assembled polymer electrolyte materials will be discussed: (i) the ionomer membranes used in fuel cell and (ii) the solid polyelectrolytes used in secondary batteries. Both are used to physically separate the electrodes in the respective electrochemical devices and are expected to have a high ion transport capacity so as good chemical and mechanical stabilities. Unfortunately, in most cases improving one property leads to the degradation of the others. Nonetheless, through block copolymers selfassembly it is possible to tackle this issue; indeed, antagonist properties can be decoupled and associated within controlled nano-morphologies. This aspect will be discussed and supported by examples based on published studies; in parallel useful scattering analytical tools and models will be presented along the paper and detailed in anne

Nouveau modèle structural des membranes Nafion ®, polymère de référence pour l'application pile à combustible basse température

au micromètre en relation avec les propriétés de transport, est primordiales pour l'optimisation des systèmes pile à combustible H2/O2. Nous Une compréhension globale de la structure des membranes ionomères Nafion® de l'Ångström proposons un nouveau modèle structural de type fibrillaire, basé sur l'agrégation des chaînes polymères, permettant d'expliquer de façon continue le processus d'hydratation de la membrane sèche à la suspension colloïdale. Par le biais de techniques de diffusion de rayonnement aux petits angles (RX & neutrons) et de microscopie (AFM & TEM) nous avons étudié l'organisation du polymère sur une large gamme d'échelle et de teneur en eau. Les corrélations entre les propriétés de transport et la structure ont été discutées. L'analyse des expériences de membranes sous contraintes a permis de conforter notre modèle et a mis en évidence l'effet de l'orientation sur la conduction protonique.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Self-assembly of rod-coil block copolymers for photovoltaic applications

Two different approaches to obtain electron donor-acceptor interfaces via self-assembly of block copolymer systems are discussed, where the donor domains are formed by a π-conjugated rod-like polymer and the acceptor domains result from a coiled polymer modified by C₆₀ fullerenes. In the first strategy, C₆₀ is chemically grafted onto the coil polymer, typically a statistical copolymer of styrene and chloromethyl styrene. This has as major effect the increase in molecular weight and volume fraction of the coil block, which can markedly perturb the self-assembled block copolymer final morphologies and eventually suppress any microseparated nanostructure in favour of fully isotropic homogeneous phases. We discuss how the presence of free homopolymer rods in the system can help recovering a microphase separated morphology suitable for photovoltaic applications. In the second approach we discuss the poly(diethylhexyl-p-phenylenevinylene-b-4-vinylpyridine) (PPV-P4VP) rod-coil block copolymer system and we argue how supramolecular interactions among P4VP and free C₆₀ can be exploited to blend rod-coil block copolymers and C₆₀ preserving the original lamellar phase

Self-assembly of poly(diethylhexyloxy-p-phenylenevinylene)-b-poly(4-vinylpyridine) rod-coil block copolymer systems

We describe the synthesis, the morphology, and self-assembly behavior of semiconducting poly(4-vinylpyridine-b-diethylhexyloxy-p-phenylenevinylene) (P4VP-b-PPV) rod-coil block copolymer systems. Three different block copolymers with 55%, 80%, and 88% coil volume fraction were synthesized by convergent anionic polymerization in THF using lithium α-methylstyrene as initiator. The morphology of the block copolymers was studied by transmission electron microscopy, small-angle X-ray scattering, and small-angle neutron scattering as a function of the volume fraction of the rod block as well as different annealing conditions. The microphase-separated morphologies in these block copolymers vary from lamellar, to hexagonal, and spherical, when the volume fraction of the rod is progressively reduced. By combining the lattice parameter measured by scattering techniques with the volume fraction of rod domains obtained by nuclear magnetic resonance, it was shown that the block copolymers in the lamellar structure are organized in a smectic C double layer, while in the hexagonal phase they self-organize in a homeotropic arrangement, with the rod blocks forming the dispersed phase. Furthermore, while self-assembly of rod-coil block copolymers in columnar hexagonal phase prevents close rod packing, for the lamellar phase evidence of this configuration among rods is shown by wide-angle X-ray scattering. As a consequence, the morphology and long-range order in the lamellar phase are the result of simultaneous inter-rods liquid crystalline interactions and the tendency to microphase segregation of rod and coil. As a result, depending on temperature, the lamellar phase can exist both with rods oriented in a smectic configuration and with randomly packed rods. We show that annealing the lamellar phase below its order-disorder transition temperature, TODT, but above the maximum affordable temperature for inter-rods liquid crystalline interactions, called smectic-in-lamellar to lamellar order-disorder transition temperature, TSL (with TSLTODT), leads to highly improved long-range lamellar order, which is then preserved when the system is cooled below TSL, at which temperature rod close packing is fully recovered

Poly(benzyl methacrylate)-Poly[(oligo ethylene glycol) methyl ether methacrylate] Triblock-Copolymers as Solid Electrolyte for Lithium Batteries

A triblock copolymer of benzyl methacrylate and oligo(ethylene glycol) methyl ether methacrylate was polymerized to form the general structure PBnMA-POEGMA-PBnMA, using atom transfer radical polymerization (ATRP). The block copolymer (BCP) was blended with lithium bis(trifluoro methylsulfonate) (LiTFSI) to form solid polymer electrolytes (SPEs). AC impedance spectroscopy was used to study the ionic conductivity of the SPE series in the temperature interval 30 °C to 90 °C. Small-angle X-ray scattering (SAXS) was used to study the morphology of the electrolytes in the temperature interval 30 °C to 150 °C. By using benzyl methacrylate as a mechanical block it was possible to tune the microphase separation by the addition of LiTFSI, as proven by SAXS. By doing so the ionic conductivity increased to values higher than ones measured on a methyl methacrylate triblock copolymer-based electrolyte in the mixed state, which was investigated in an earlier paper by our group. A Li|SPE|LiFePO4 half-cell was constructed and cycled at 60 °C. The cell produced a discharge capacity of about 100 mAh g−1 of LiFePO4 at C/10, and the half-cell cycled for more than 140 cycles