Janus organic semiconductor nanoparticles prepared by simple nanoprecipitation

Nanoparticles (NPs) of donor–acceptor organic semiconductors are produced by a one-step nanoprecipitation with Janus morphology. Electron donor P3HT was blended with electron acceptor PC61BM in tetrahydrofuran and then precipitated in water, first with surfactant and second without surfactant. Cryogenic transmission electron microscopy reveals an internal Janus structure at high magnification, for NPs which have, in the past, been reported to have a molecularly intermixed morphology. Synchrotron-based scanning transmission X-ray microscopy confirmed the segregation of the organic semiconductors and photoluminescence experiments showed an efficient electron transfer from P3HT to PC61BM. Organic field effect transistors were fabricated with these Janus NPs and showed that the positive charges can be efficiently transported through thin films. This behavior proves that the NPs possess an electron-accepting face (the PC61BM face) able to transport electrons and a hole-accepting face (the P3HT face) for the conduction of holes. Finally, the deposition of silver via the photoreduction of a silver salt (AgNO3(aq)) was demonstrated, as a proof of concept. These experiments show the potential of the Janus NPs for photovoltaics but also photocatalytic reactions in which reduction and oxidation reactions can occur at opposite sides of the nanoreactor (the individual Janus NPs).E2SEncres aqueuses colloïdales de semi-conducteurs organiques pour le photovoltaïqu

RAFT Copolymerization of Vinyl Acetate and N-Vinylcaprolactam: Kinetics, Control, Copolymer Composition, and Thermoresponsive Self-Assembly

International audienceWell-defined thermoresponsive amphiphilic statistical copolymers based on N-vinylcaprolactam (VCL) and vinyl acetate (VAc) were successfully synthesized by RAFT/MADIX polymerization mediated by O-ethyl-S-(1-ethoxycarbonyl)ethyldithiocarbonate chain transfer agent at 65 °C. We achieved the synthesis of a series of copolymers with controlled molar masses and low dispersities over a wide range of monomer feed ratios (0 < fVAc,0 < 1). Both conventional linearization methods and a nonlinear least-squares methods (NLLS) were applied to estimate reliable values of reactivity ratios for VAc and VCL radical polymerization in regards to the disparate values previously reported in the literature. The highest measurement precision was observed for the NLLS method based on the integrated form of the copolymerization equation developed by Skeist. The calculated values of the reactivity ratios (rVAc = 0.33 ± 0.10 and rVCL = 0.29 ± 0.15) perfectly fitted the drift in monomer feed ratio versus conversion. The VCL and VAc monomer units are distributed homogeneously along the copolymer chains. Both the cloud point temperatures and glass transition temperatures evolve linearly with the copolymer composition. Analyses of the aqueous solutions of the amphiphilic copolymers by means of dynamic and static light scattering show that P(VAc-co-VCL) copolymers undergo a reversible temperature-induced conformational change between large aggregates (T > Tcloud point) and either unimers for FVAc inferior to 0.3 (Nagg = 1, Dh7 nm) or small aggregates for FVAc = 0.53 (Nagg = 3, Dh 14 nm). © 2016 American Chemical Society

Cationic Thermoresponsive Poly( N -vinylcaprolactam) Microgels Synthesized by Emulsion Polymerization Using a Reactive Cationic Macro-RAFT Agent

International audienceA series of reactive poly([2-(acryloyloxy)ethyl]trimethylammonium chloride) (P(AETAC)) cationic polymers with varying degrees of polymerization were synthesized by RAFT/MADIX polymerization and investigated as stabilizers for the emulsion polymerization of N-vinylcaprolactam (PVCL) in the presence of a cross-linker. It was demonstrated that the xanthate chain end of the cationic P(AETAC-X) polymers played a crucial role to produce stable cationic PVCL-based microgels at higher initial solids content (5–10 wt %) than usually reported for the synthesis of PVCL microgels. The thermoresponsive PVCL microgels with cationic shell undergo a reversible volume shrinkage upon heating in the absence of any hysteresis in accordance with the narrow particle size distribution. The values of the volume phase transition temperature ranged between 28 and 30 °C for the microgels synthesized using 4 and 8 wt % of P(AETAC-X) based on VCL. The presence of a cationic outer shell onto the microgels was evidenced by the positive values of the electrophoretic mobility. The swelling behavior of the thermoresponsive microgel particles can be tuned by playing on two synthesis variables which are the initial solids content and the content of P(AETAC-X) macro-RAFT stabilizer. Furthermore, the inner structure of the synthesized microgels was probed by transverse relaxation nuclear magnetic resonance (T2 NMR) and small-angle neutron scattering (SANS) measurements. The fit of T2 NMR data confirmed a core–shell morphology with different cross-linking density in PVCL microgels. Through the determination of the network mesh size, SANS was suitable to explain the increase of the values of the PVCL microgel swelling ratios by increasing the initial solids content of their synthesis

Asymmetrical flow field flow fractionation methods to characterize submicron particles: application to carbon-based aggregates and nanoplastics

cited By 0; Article in PressInternational audienceIn the last 10 years, asymmetrical flow field flow fractionation (AF4) has been one of the most promising approaches to characterize colloidal particles. Nevertheless, despite its potentialities, it is still considered a complex technique to set up, and the theory is difficult to apply for the characterization of complex samples containing submicron particles and nanoparticles. In the present work, we developed and propose a simple analytical strategy to rapidly determine the presence of several submicron populations in an unknown sample with one programmed AF4 method. To illustrate this method, we analyzed polystyrene particles and fullerene aggregates of size covering the whole colloidal size distribution. A global and fast AF4 method (method O) allowed us to screen the presence of particles with size ranging from 1 to 800 nm. By examination of the fractionating power Fd, as proposed in the literature, convenient fractionation resolution was obtained for size ranging from 10 to 400 nm. The global Fd values, as well as the steric inversion diameter, for the whole colloidal size distribution correspond to the predicted values obtained by model studies. On the basis of this method and without the channel components or mobile phase composition being changed, four isocratic subfraction methods were performed to achieve further high-resolution separation as a function of different size classes: 10–100 nm, 100–200 nm, 200–450 nm, and 450–800 nm in diameter. Finally, all the methods developed were applied in characterization of nanoplastics, which has received great attention in recent years

Versatile oligo(ethylene glycol)-based biocompatible microgels for loading/release of active bio(macro)molecules

International audienceThe present study aims in the understanding of the effect of oligo(ethylene glycol)-based biocompatible microgels inner structure on the encapsulation/release mechanisms of different types of cosmetic active molecules. For that, multi-responsive microgels were synthesized using three types of cross-linkers: ethylene glycol dimethacrylate (EGDMA), oligo(ethylene glycol) diacrylate (OEGDA) and N,N-methylenebisacrylamide (MBA). The inner morphology of the microgels synthesized was studied by 1H-nuclear magnetic resonance (1H NMR) and small-angle neutron scattering (SANS) techniques and no effect of cross-linker type on microgel microstructure was observed in the case of analysing purified microgel dispersions. Moreover, all the microgels synthesized presented conventional swelling/de-swelling behavior as a function of temperature and pH. Two hydrophobic, one hydrophilic, and one macromolecule as cosmetic active molecules were effectively loaded into different microgel particles via hydrophobic interactions and hydrogen-bonding interactions between −OH groups of active molecules and ether oxygens of different microgel particles. Their release profiles as a function of cross-linker type used and encapsulated amounts were studied by Peppas-Sahlin model. No effect of the cross-linker type was observed due to the similar inner structure of all the microgels synthesized

Amphiphilic diblock copolymers with a moderately hydrophobic block: Toward dynamic micelles

cited By 40International audienceA study was conducted to propose a way of transforming a frozen system into a dynamic one by acting on the chemical structure of the amphiphilic block copolymer. The approach consisted of introduction of some hydrophilic units in the hydrophobic block to reduce the interfacial tension between the moderately hydrophobic block the hydrophilic block and the aqueous medium, promoting unimer exchange. The investigation on a P(nBA-stat-AA)-b-PAA block copolymer, which was a pure poly(acrylic acid) (PAA) hydrophilic block connected to a statistical copolymer of nBA and AA units forming the moderately hydrophobic block. The investigation also focused on controlled synthesis of the P(nBA50%-stat-AA50%)99-b-PAA98 block copolymer using atom transfer radical polymerization (ATRP). This emphasized the statistical distribution of the hydrophobic (nBA) and hydrophilic (AA) units in the P(nBA50%-stat-AA50%)99 first block

Dual stimuli-responsive oligo(ethylene glycol)-based microgels: insight into the role of internal structure in volume phase transitions and loading of magnetic nanoparticles to design stable thermoresponsive hybrid microgels

International audienceMulti-responsive biocompatible microgels with long term stability were synthesized by precipitation copolymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA), di(ethylene glycol) methyl ether methacrylate (MEO2MA), methacrylic acid (MAA) and crosslinkers in aqueous dispersed media. Different crosslinkers, i.e. ethylene glycol dimethacrylate (EGDMA), oligo(ethylene glycol) diacrylate (OEGDA) or N,N-methylenebisacrylamide (MBA) were used for the synthesis of the microgels. The present work investigates for the first time how the inner structure of the biocompatible P(MEO2MA-co-OEGMA-co-MAA) microgels impacts their swelling-to-collapse transition in response to both temperature and pH. The EGDMA-crosslinked microgels obviously differ from the OEGDA- and MBA-crosslinked microgels. The OEGDA-crosslinked P(MEO2MA-co-OEGMA-co-MAA) microgels are ideal candidates to prepare robust thermoresponsive hybrid magnetic microgels by a straightforward method involving simple loading of pre-formed magnetic nanoparticles (NP) in the absence of NP release. The crosslinker distribution is at the origin of differences in the distribution of iron oxide nanoparticles. The homogeneous distribution of both MAA units and the OEGDA crosslinker in the P(MEO2MA-co-OEGMA-co-MAA) microgels ensured a sharp VPTT of microgels over a wide range of pH values (from pH 4 to 9) and the retention of the thermoresponsiveness of the corresponding hybrid microgels for the different contents of magnetic nanoparticles (from 7 to 33 wt% of γ-Fe2O3versus polymer). Turbidimetry measurements highlighted the unique stability of the hybrid microgels over several hours even for the highest content of iron oxide nanoparticles

Synthesis and Viscosimetric Behavior of Poly(acrylamide- co -2-acrylamido-2-methylpropanesulfonate) Obtained by Conventional and Adiabatic Gel Process via RAFT/MADIX Polymerization

International audienceHigh molar masses homopolymers of both acrylamide (AM) and 2-acrylamido-2-methylpropanesulfonate (AMPS) as well as poly(AM-stat-AMPS) exhibiting a large range copolymer composition has been obtained via the optimization of a purely adiabatic gel process. Monomer concentrations ranging from 2.0 to 3.47 M have been successfully tested while keeping the control of the molar masses up to 5 × 106 g mol–1. The products have been characterized in terms of molecular mass and viscosimetric propertie

Interplay of Thermosensitivity and pH Sensitivity of Amphiphilic Block–Gradient Copolymers of Dimethylaminoethyl Acrylate and Styrene

International audienceovel pH- and thermoresponsive amphiphilic diblock copolymer, comprising hydrophilic poly(2-dimethylaminoethyl acrylate) (PDMAEA) and amphiphilic poly(styrene-grad-2-dimethylaminoethyl acrylate) (P(S-grad-DMAEA)) blocks, was synthesized by nitroxide-mediated radical polymerization. A series of copolymers (PS-grad-PDMAEA) with controlled molar masses and low dispersities over a wide range of monomer feed ratios (0 < fS,0 < 1) were synthesized. Both conventional linearization and nonlinear least-squares methods were applied to estimate reliable values of the reactivity ratios for S and DMAEA radical polymerization. The calculated values of the reactivity ratios (rDMAEA = 0.25 and rS = 1.15) perfectly fitted the drift in monomer feed ratio versus conversion, showing a gradient distribution along the copolymer chains. The self-assembling behavior of the copolymers in the aqueous medium was investigated by dynamic light scattering and small-angle neutron scattering over a wide range of pH, temperature, and salt concentration. These block-gradient copolymers show reversible self-association into micelle-like structure (Dh ∼ 20 nm) in aqueous solutions triggered by both pH and temperatur

Biosourced Polymeric Emulsifiers for Miniemulsion Copolymerization of Myrcene and Styrene: towards biobased Waterborne Latex as Pickering Emulsion Stabilizer

Biobased waterborne latexes were synthesized by miniemulsion radical copolymerization of biosourced -myrcene (My) terpenic monomer and styrene (S). Biobased amphiphilic copolymers were designed to act as stabilizers of the initial monomer droplets and the polymer colloids dispersed in the water phase. Two types of hydrophilic polymer backbones were hydrophobically modified by terpene molecules to synthesize two series of amphiphilic copolymers with various degrees of substitution. The first series consists of poly(acrylic acid) modified with tetrahydrogeraniol moieties (PAA-g-THG) and the second series is based on the polysaccharide carboxymethylpullulan amino-functionalized with dihydromyrcenol moieties (CMP-g-(NH-DHM)). The produced waterborne latexes with diameters between 160 and 300 nm and were composed of polymers with varying glass transition temperatures (Tg, PMy =-60°C, Tg, P(My-coS) =-14°C, Tg, PS = 105 °C) depending on the molar fraction of biobased -myrcene (fMy,0 = 0, 0.43 or 1). The latexes successfully stabilized dodecane-inwater and water-in-dodecane emulsions for months at all compositions. The waterborne latexes composed of low Tg poly(-myrcene) caused interesting different behavior during drying of the emulsions compared to polystyrene latexes