Self-assembly of rod-coil block copolymers from weakly to moderately segregated regimes

We report on the self-assembly behaviour of two homologue series of rod-coil block copolymers in which, the rod, a π -conjugated polymer, is maintained fixed in size and chemical structure, while the coil is allowed to vary both in molecular weight and chemical nature. This allows maintaining constant the liquid crystalline interactions, expressed by Maier-Saupe interactions, ω , while varying the tendency towards microphase separation, expressed by the product between the Flory-Huggins parameter and the total polymerization degree, χN . Therefore, the systems presented here allow testing directly some of the theoretical predictions for the self- assembly of rod-coil block copolymers in a weakly segregated regime. The two rod- coil block copolymer systems investigated were poly(DEH-p-phenylenevinylene-b- styrene), whose self-assembly takes place in the very weakly segregated regime, and poly(DEH-p-phenylenevinylene-b-4vinylpyridine), for which the self-assembly behaviour occurs under increased tendency towards microphase separation, hereby referred to as moderately segregated regime. Experimental results for both systems are compared with predictions based on Landau expansion theories

Synthèse et caractérisation d'encres électrophorétiques pour la réalisation de papier électronique couleur

Cette thèse s intéresse principalement à la réalisation de nouvelles encres électrophorétiques pour les applications de type papier électronique couleur. Une méthode simple et peu contraignante basée sur la polymérisation en dispersion a été développée, permettant de réaliser de manière contrôlée et en milieu peu polaire des particules de polymère chargeables positivement ou négativement. Puis, grâce à ce nouvel outil, des particules électrophorétiques hybrides ont été synthétisées à partir de pigments inorganiques et caractérisées sous champ électrique. Enfin une nouvelle solution pour aller vers des dispositifs couleur a été proposée et la fabrication d un démonstrateur test a été abordée.The effective sharing of information is a key parameter in our actual society. Electronic paper based on the controlled motion of electrophoretic particles appears thus promising since it combines the advantages of the usual paper (flexibility, reflective display) and the capacity to refresh information on the same support like the more common LCD or OLED technologies. Electrophoretic inks are composed of coloured charged particles which migrate under an electrical field between two electrodes. Depending of the position of the particles on the front plane, the colour on the screen can be tuned. The design of electrophoretic particles based on pigment or dyed polymer and their integration in electronic devices were successfully achieved during the last decade but are still limited to a two colour-electrophoretic system. Up to date the majority of these particles were synthesized in aqueous media and the electrophoretic mobility was achieved by a ionic stabilizer or by a polyelectrolyte surfactant. Moreover the final electrophoretic particles incorporated in the electronic devices have to be dispersed in an organic media (paraffin oil) in order to achieve the desired stability of the display and thus leads to a large variety of problems during the phase exchange process.In this work our goals were to rationalize and improve the ink synthesis as well as to design electrophoretic inks with the full colour panel in order to realize the next generation of electrophoretic displays. We performed the particle synthesis by using an organic dispersion technique in aliphatic hydrocarbon solvents leading to chargeable electrophoretic particles with a good size control over a large range (from 75nm to 20 m) and a good stability. In order to obtain the full color panel, the encapsulation of several inorganic pigments was achieved by using the same technique and the electrophoretic behaviour of the resulting inks was characterized in a cell specially designed for electrophoretic measurements in organic media.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Chitosan-Modified Polyethyleneimine Nanoparticles for Enhancing the Carboxylation Reaction and Plants' CO2 Uptake

Increasing plants' photosynthetic efficienc y is a major challenge that must be addressed in order to cover the food demands of the growing population in the changing climate. Photosynthes i s is greatly limited at the initial carboxylation reaction, where CO2 is converted to the organic acid 3-PGA, catalyzed by the RuBisCO enzyme. RuBisCO has poor affinity for CO2, but also the CO2 concentration at the RuBisCO site is limited by the diffusion of atmospheric CO2 through the various leaf compartments to the reaction site. Beyond genetic engineer-ing, nanotechnology can offer a materials-based approach for enhancing photosynthesis, and yet, it has mostly been explored for the light-dependent reactions. In this work, we developed polyethyleneimine-based nanoparticl e s for enhancing the carbox-ylation reaction. We demonstrate that the nanoparticles can capture CO2 in the form of bicarbonate and increase the CO2 that reacts with the RuBisCO enzyme, enhancing the 3-PGA production in in vitro assays by 20%. The nanoparticles can be introduced to the plant via leaf infiltration and, because of the functionalization with chitosan oligomers, they do not induce any toxic effect to the plant. In the leaves, the nanoparticles localize in the apoplastic space but also spontaneously reach the chloroplasts where photosynthetic activity takes place. Their CO2 loading-dependent fluorescence verifies that, in vivo, they maintain their abi l i t y to capture CO2 and can be therefore reloaded with atmospheric CO2 while in planta. Our results contribute to the development of a nanomaterials-based CO2-concentrating mechanism in plants t h a t can potentially increase photosynthetic efficiency and overall plants' CO2 storage

CASPワークショップ参加記

The nanostructure of the active layer in polymer/fullerene bulk heterojunction solar cells is known to have a strong impact on the device performances. Controlling the polymer/fullerene blend morphology is therefore particularly important. In this work, a rod-coil block copolymer, based on a regioregular poly(3-hexylthiophene) electron-donor rod block and a C-60-grafted coil block, is used as compatibilizer and its influences on the thin film morphology as well as the photovoltaic performances are investigated. It is shown that a small fraction of compatibilizer can enhance the device performances in an otherwise non-optimized process. At higher fractions or long annealing times however, the fullerene-grafted copolymer is found to behave as a nucleation center and triggers the formation of fullerene crystals

Enhanced Electrocaloric Response of Vinylidene Fluoride–Based Polymers via One‐Step Molecular Engineering

Electrocaloric refrigeration is one of the most promising environmentally-friendly technologies to replace current cooling platforms—if a notable electrocaloric effect (ECE) is realized around room temperature where the highest need is. Here, a straight-forward, one-pot chemical modification of P(VDF-ter-TrFE-ter-CTFE) is reported through the controlled introduction of small fractions of double bonds within the backbone that, very uniquely, decreases the lamellar crystalline thickness while, simultaneously, enlarging the crystalline coherence along the a-b plane. This increases the polarizability and polarization without affecting the degree of crystallinity or amending the crystal unit cell—undesirable effects observed with other approaches. Specifically, the permittivity increases by >35%, from 52 to 71 at 1 kHz, and ECE improves by >60% at moderate electric fields. At 40 °C, an adiabatic temperature change >2 K is realized at 60 MV m−1 (>5.5 K at 192 MV m−1), compared to ≈1.3 K for pristine P(VDF-ter-TrFE-ter-CTFE), highlighting the promise of a simple, versatile approach that allows direct film deposition without requiring any post-treatment such as mechanical stretching or high-temperature annealing for achieving the desired performance

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

Weakly segregated smectic C lamellar clusters in blends of rods and rod-coil block copolymers

The morphology arising from the self-assembly of π-conjugated poly(diethylhexyloxy-p-phenylenevinylene) rod homopolymers (PPV) and poly(diethylhexyloxy-p-phenylenevinylene)-polystyrene (PPV-PS) rod-coil block copolymers is described. Two PPV-PS block copolymers, one with low rod volume fraction (~17%) and the other with high volume fraction (~50%), were synthesized by convergent anionic polymerization and atom transfer radical polymerization, respectively. In the first case, given the low volume fraction of the rod block, the pure asymmetrical rod-coil block copolymer formed an isotropic homogeneous phase. However, ordered clusters of alternating PS and PPV domains with characteristic length of the order of several micrometers appeared when PPV rod homopolymers were blended to the PS-PPV diblock. Furthermore, the long-range order of the clusters as well as their volume fraction could be greatly increased when the symmetric rod-coil PPV-PS was blended to PPV homopolymer. Tomographic reconstruction from transmission electron micrographs allowed demonstrating that the clusters were organized in lamellar phase with well-defined width for both the intercalated PS and PPV domains, while wide-angle X-ray scattering showed that within the PPV domains the PPV blocks and PPV homopolymer rods were closely packed. The study of the spacing widths of the PPV and PS domains showed that clusters are organized in a smectic C configuration with large tilt angles of the rods (54°) and stretching of the coil blocks which is typical of weakly segregated block copolymers organized in a lamellar phase. The stability of the rod-to-rod interaction peak at high temperatures (190 °C), well beyond the order-disorder transition temperature of the clusters (130 °C), suggests that the (i) aggregation of the rods is mediated by π-π interactions and (ii) the clusters are thermodynamically stable structures. The energetic driving force toward the formation of these clusters is discussed in the last part of this work

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

Copolymères semi-conducteurs à architectures variées (de l'ingénierie macromoléculaire à l'électronique organique)

A une époque où les technologies nouvelles fleurissent chaque jour, un domaine particulier se détache : l électronique organique. Par son utilité et sa facilité de mise en œuvre, l électronique organique affiche de grandes promesses pour l avenir. Dans le but d améliorer le procédé de fabrication et la durée de vie de ces dispositifs, le travail de cette thèse s'est focalisé sur la synthèse de copolymères à architectures variées à base de poly(3-hexylthiophène) (P3HT). Après avoir exposé les problématiques et objectifs de la thèse dans une première partie, la synthèse de différents précurseurs P3HT est décrite. Ces matériaux représentent la base des travaux présentés dans cet ouvrage. Dans un premier temps, l'optimisation de la synthèse des copolymères à blocs rigide-flexible a été réalisée en suivant une stratégie adaptée pour une application en électronique organique. La conception de nouveaux matériaux semi-conducteurs à architectures ramifiées est traitée par la suite. Enfin, le dernier chapitre porte sur l'intégration d un copolymère, le P3HT-b-Poly(4vinylpyridine), en cellule photovoltaïque organique en tant qu'additif de la couche active. Cette approche s avère être particulièrement puissante, permettant notamment de diminuer le temps et le coût énergétique de la mise en œuvre de ces cellules en s affranchissant d une étape clé de la fabrication, le recuit.At a time when new technologies emerge every day, a specific domain stands out: the organic electronic. Through its low cost processing or even its utility, the organic electronic constitutes a very promising future.In order to improve the fabrication process and the lifetime of the devices, the work of this thesis was focused on the synthesis of copolymers with various architectures based on poly(3-hexylthiophene) (P3HT). After a first part where main issues and objectives are presented, the synthesis of different P3HT-based precursors is described in a part which could be considered as the heart of these works. Starting with appropriated precursors, the optimization of rod-coil diblock copolymer synthesis was performed following a strategy designed specifically for organic electronic application. Moreover, the precursors were used for the conception of new semi-conducting materials with a variety of architectures, such as graft and star copolymers. Finally, the last part deals with the integration of the P3HT-b-Poly(4-vinylpyridine) copolymer into organic solar cell as an additive of the active layer. This approach turns out to be powerful, especially allowing decreasing the time and the energy cost by avoiding the key step of the fabrication process of those devices, the annealing step.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF