Laurent Rubatat

Hierarchical structures based on self-assembled diblock copolymers within honeycomb micro-structured porous films

This article details the preparation of hierarchically ordered microporous films using the so-called breath figure approach combined with the self-assembly of well-defined poly(n-butyl acrylate)-block-polystyrene or poly(tert-butyl acrylate)-block-polystyrene copolymers synthesized by nitroxide-mediated polymerization. The first level of organization was the hexagonal pattern of pores at the micrometre length scale leading to iridescence properties and surface hydrophobicity of the honeycomb structured films. Optical microscopy with the corresponding 2-Dimensional Fast Fourier Transform highlighted the ordering of the pores over a large scale (∼1 cm2). The second level of structuring was provided by the diblock copolymers chosen for their ability to self-assemble into ordered nanophases. The nanoscale morphology of both the honeycomb films and the corresponding thermally annealed continuous films was systematically investigated by atomic force microscopy (AFM) and small angle neutron scattering (SANS). The film characterization revealed a nanostructuration of the acrylate-based coil–coil diblock copolymer within the walls of the highly ordered microporous films obtained via a simple solvent evaporation method under humid atmosphere. The four synthesized diblock copolymers exhibited different macromolecular features with respect to the Flory–Huggins interaction parameter, the glass transition temperature of each block and the weight fraction of each monomer that influenced the quality of either the micropores structuration or the nanophase segregation.

pH Sensitive Hierarchically Self-Organized Bioinspired Films

In the present manuscript, we have demonstrated that hierarchically structured smart porous polymer films based on honeycomb-patterned surface can be elaborated from PS-b-P4VP pH-responsive block copolymer using the breath figure process. Despite the fast film formation by a bottom-up process, the copolymer nanostructuration was observed inside the walls of the honeycomb porous film. Atomic force microscopy (AFM), small angle X-ray and neutron scattering (SAXS and SANS) measurements were used to reveal both the hexagonal arrays formed by the pores at the micrometer length scale and the hexagonal copolymer self-assembly at the nanometer length scale. Contact angle (CA) measurements were used to point out the reversible pH-responsive wettability character of the surface. The PS-b-P4VP honeycomb film shows a contact angle variation of 20° between pH 9 and pH 3. An increase of the roughness was obtained with the pincushions hexagonal array enhancing the pH responsiveness of the polymer film with a switching CA gap of 75° when pH tuned from pH 9 to pH 3. This work presents the first report on honeycomb porous and pincushion films exhibiting a reversible pH-responsive character.

Highly structured pH-responsive honeycomb films by a combination of a breath figure process and in situ thermolysis of a polystyrene-block-poly(ethoxy ethyl acrylate) precursor

In the present work, we show that Cu(0)-mediated controlled radical polymerization is a suitable method to synthesize high molar mass polystyrene-b-poly(ethoxy ethyl acrylate) PS-b-PEEA diblock copolymers. This method, applied at room temperature, is mandatory for complete preservation of ethoxy ethyl protecting groups during the course of polymerization. The synthesized PS-b-PEEA diblock copolymers were subsequently used for the elaboration of pH sensitive hierarchically structured honeycomb (HC) films through the Breath Figure (BF) process. The PS-b-PEEA hydrophobic honeycomb films were characterized by optical microscopy and atomic force microscopy (AFM) to reveal the hexagonal array of pores at the micrometer length scale, together with the phase segregation of the diblock copolymer. Similar to highly structured natural materials, the biomimetic honeycomb polymer films displayed intense iridescence. Moreover, the increase of surface roughness by peeling off the top layer of the PS-b-PEEA HC films produced superhydrophobic surfaces exhibiting a water contact angle of 155°. Subsequent deprotection of PEEA into pH-responsive poly(acrylic acid) (PAA) was performed in situ from the PS-b-PEEA honeycomb film by a simple thermolysis step carried out at 90 °C. The resulting PS-b-PAA honeycomb films showed a clear pH-responsive behavior with a water contact angle gap of 65° between a pH of 3 and 10.

Redox-active polyimide–polyether block copolymers as electrode materials for lithium batteries

Redox-active polyimide–polyether multi-block copolymers were synthesized by polycondensation reaction of aromatic dianhydrides with α-ω-diamino poly(ethylene oxide). Polyimide-b-polyether block copolymers showed microphase separation between a hard-polyimide domain and a soft-polyether domain as observed by Atomic Force Microscopy. The block copolymers were investigated as cathodes for polymer/lithium metal batteries. Polymer cathodes were formulated where the block copolymer had a dual role as active material and binder, with a small amount of carbon black (15 wt%). Naphthalene polyimides showed higher discharge voltages, higher specific capacities as well as better cycling performance, compared to pyromellitic polyimides. The longest PEO blocks resulted in a better performance as electrodes. The best performing naphthalene polyimide-b-PEO2000 presented an excellent value of discharge capacity of 170 mA h g−1, stable after 100 cycles at a current density of 1Li+/5 h and considering the polyimide as the active material. The average discharge plateaus were 2.51 V and 2.37 V vs. Li+/Li.

Enhanced thermal stability of organic solar cells by using photolinkable end-capped polythiophenes

The use of poly(3-hexylthiophene) (P3HT) end-capped with anthracene (P3HT-A) in a blend with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is demonstrated to physically stabilize bulk-heterojunction photovoltaic solar cells. Bulk heterojunction-based devices are known to undergo phase separation of donor and acceptor materials during operation resulting in the formation of large (μm scale) PCBM crystals that dramatically decrease the photovoltaic characteristics of the cell. By way of a facile UV-curing step, the P3HT-A chain most likely reacts with PCBM fullerene via a [2+2] cyclo-addition to stabilize the blend. Photovoltaic devices based on P3HT-A and PCBM have been optimised in terms of thermal annealing to obtain initial devices to determine the UV-curing protocols. UV-exposure was found to improve device stability while simultaneously having a minimal effect on device efficiency. Optical microscopy demonstrates that the few reactions of P3HT-A with PCBM are efficient enough to prevent the formation of micro-sized PCBM crystals responsible for the failure of solar cells.

When block copolymer self-assembly in hierarchically ordered honeycomb films depicts the breath figure process

Nowadays, a challenge in the preparation of hierarchically ordered materials is the control of concomitant and interacting self-organization processes occurring in time at different length scales. In the present paper, the breath figure process is combined with block copolymer nano-phase segregation to elaborate hierarchically structured honeycomb porous films. Copolymer ordering, at the nanometer length scale, is observed and described in detail with respect to the array of pores of micrometer dimension, hence pointing out the structural interplays between both length-scales. The study is focused on two diblock copolymers made of polystyrene and poly(tert-butyl acrylate) (PS-b-PtBA) with compositions producing lamellae or hexagonal packing of cylinders at thermodynamical equilibrium. Transmission Electron Microscopy completed with Small and Ultra-Small Angle Scattering are performed to evidence the inner morphologies of the honeycomb. The structural data are discussed in the light of the honeycomb film formation process establishing the interest in using kinetically trapped block copolymer self-organization as an imprint to elucidate the complex breath figure process.

Structure and rheology of di- and triblock copolymers of polystyrene and poly(n-butyl acrylate)

Block copolymers based on acrylate matrices are expected to be good candidates for pressure sensitive adhesives formulations because (i) all-acrylic block copolymers are known to be stable over a wide temperature range and are more resistant to UV radiation than polydiene copolymers and (ii) the soft block exhibits an elasticity that is lower than that of polydiene and closer to the Dalhquist criterion (tacky properties). This last property is due to a higher molar mass between entanglements. The block segregation is the key parameter for these kinds of systems because it induces a solid-like behavior useful for adhesion applications. In this work, we have explored this point by synthesizing styrene/n-butyl acrylate (nBA) and methyl methacrylate/nBA block copolymers by nitroxide-mediated controlled radical polymerization. Atomic force microscopy and small-angle neutron scattering analysis have demonstrated the strong connection between the physico-chemical properties (molar mass, nature of the blocks, χ, ...

Polymeric Ion Gels: Preparation Methods, Characterization, and Applications

In this chapter, we have summarized the preparation methods, properties, and applications of ion gels. Ion gels or ionogels are a new type of gels where the liquid phase, percolating throughout the solid phase, is an ionic liquid. Ion gels are attractive materials especially due to its good ionic conductivity, electrochemical and chemical stability, nonflammability, thermal stability, negligible vapor pressure, solid-like behavior, and tunable flexibility. Inorganic or polymeric materials can be used as gelators in combination with ionic liquids to synthesize ion gels. However, this chapter is mainly focused in the development of ion gels using polymeric materials such as triblock copolymers, fluorinated polymers, or poly(ionic liquids) as gelators.