Elaboration and rheological characterization of nanocomposite hydrogels containing C60 fullerene nanoplatelets.

Nanocomposite hydrogels were elaborated that consisted of a physical network formed by an amphiphilic polymer in which C60 fullerene nanoplatelets were embedded. Characterization showed that the nanoplatelets within the polymer network were aggregated. The presence of these nanoplatelets led to an increase of the shear modulus of the hydrogels, that cannot be explained by a filler effect alone. The nanocomposite gels displayed similar rheological behavior, both in linear and non-linear domains, as neat hydrogels at higher polymer concentrations. We suggest that the particles reinforced the gels by forming additional connections between the polymer chains.

Self-Assembly in water of C60 fullerene into isotropic nanoparticles or nanoplatelets mediated by a cationic amphiphilic polymer.

HYPOTHESIS: To disperse high concentration of C60 fullerene in water, we propose to use an emulsification-evaporation process in the presence of an amphiphilic polymer whose chemical structure has been chosen for inducing specific interaction with fullerene The viscosity enhancement provided by self-assembly of the amphiphilic polymers in water should result in high stability of the suspensions. The organic solvent has also to been chosen so as to maximize the initial fullerene concentration. EXPERIMENTS: The concentrations of polymer and fullerene, the solvent type and the volume fraction of the organic phase have been varied. Their influence on the concentration of the fullerene dispersions and on the size and shape of the resulting nanoparticles have been investigated by UV-Visible spectroscopy, light scattering and cryo-transmission electron microscopy experiments. FINDINGS: The resulting nanoparticles consist of aggregates of C60 fullerene stabilized by the cationic polymer with morphologies/sizes tunable through fullerene and polymer concentration. At high fullerene concentration, nanoplatelets are obtained that consist in thin 2D nanocrystals. Their suspensions are very stable with time due to the viscosity of the dispersing aqueous medium. The concentration of fullerene nanoparticles dispersed in water is as high as 8 g/L which corresponds to an upper limit that has never been reached so far.

Thermo-induced inversion of water-in-water emulsion stability by bis-hydrophilic microgels.

HYPOTHESIS: Stabilization of water-in-water (W/W) emulsions resulting from the separation of polymeric phases such as dextran (DEX) and poly(ethyleneoxide) (PEO) is highly challenging, because of the very low interfacial tensions between the two phases and because of the interface thickness extending over several nanometers. In the present work, we present a new type of stabilizers, based on bis-hydrophilic, thermoresponsive microgels, incorporating in the same structure poly(N-isopropylacrylamide) (pNIPAM) chains having an affinity for the PEO phase and dextran moieties. We hypothesize that these particles allow better control of the stability of the W/W emulsions. EXPERIMENTS: The microgels were synthesized by copolymerizing the NIPAM monomer with a multifunctional methacrylated dextran. They were characterized by dynamic light scattering, zeta potential measurements and nuclear magnetic resonance as a function of temperature. Microgels with different compositions were tested as stabilizers of droplets of the PEO phase dispersed in the DEX phase (P/D) or vice-versa (D/P), at different concentrations and temperatures. FINDINGS: Only microgels with the highest DEX content revealed excellent stabilizing properties for the emulsions by adsorbing at the droplet surface, thus demonstrating the fundamental role of bis-hydrophilicity. At room temperature, both pNIPAM and DEX chains were swollen by water and stabilized better D/P emulsions. However, above the volume phase transition temperature (VPTT ≈ 32 °C) of pNIPAM the microgels shrunk and stabilized better P/D emulsions. At all temperatures, excess microgels partitioned more to the PEO phase. The change in structure and interparticle interaction induced by heating can be exploited to control the W/W emulsion stability.

Synthesis and self-assembly of a penta[60]fullerene bearing benzo[ghi]perylenetriimide units.

A benzo[ghi]perylenetriimide (BPTI) derivative bearing a terminal azido group on the expanded π-conjugated backbone has been synthesized and characterized. This promising photo- and electroactive BPTI motif has been used to obtain an original penta(organo)fullerene as a promising multi-electron acceptor system. Our studies show its self-assembly resulting from aggregation via π-π stacking interaction in solution and in the solid state.