Nicolas Jouault

Muscle‐like Supramolecular Polymers: Integrated Motion from Thousands of Molecular Machines

Pumping iron: Double-threaded rotaxanes can be linked to coordination units and polymerized in the presence of iron or zinc ions. pH modulation triggers cooperative contractions (or extensions) of the individual rotaxanes, thus resulting in an amplified motion of the muscle-like supramolecular chains with changes of their contour lengths of several micrometers (see picture).

Tuning the mechanical properties in model nanocomposites: Influence of the polymer‐filler interfacial interactions

This paper presents a study of the polymer-filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS) / silica nanocomposites by direct comparison of two model systems: un-grafted and PS-grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining Small Angle Neutron Scattering (SANS) measurements and Transmission Electronic Microscopic (TEM) images. The mechanical properties were studied over a wide range of deformation by plate/plate rheology and uni-axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size non-connected aggregates and the materials exhibit a solid-like behavior independent of the local polymer/fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle/particle interactions and lower with grafting likely due to deformation of grafted polymer.

SANS, SAXS, and light scattering investigations of pH-responsive dynamic combinatorial mesophases

The structural variations of dynamic combinatorial mesophases are investigated in dilute aqueous solutions by a combination of small-angle-neutron, X-ray, and light scattering. The supramolecular structures are composed of self-assembled dynamic covalent hydrophobic and hydrophilic blocks (Dynablocks), linked together by reversible and pH-dependent imine bonds. When several Dynablocks compete from a set of constituents, it is possible to tune their molecular associations by pH modulation, which results in structuring variations of the supramolecular self-assemblies. We here demonstrate that even complex supramolecular mixtures of micellar and vesicular Dynablocks libraries can be quantitatively characterized by the complementarity of these three scattering techniques. It becomes thus envisageable for chemists to design very elaborated stimuli-responsive mesophases based on these objects which represent a new class of “smart” soft materials.

Light-triggered self-assembly of triarylamine-based nanospheres

Tailored triarylamine units modified with terpyridine ligands were coordinated to Zn(2+) ions and characterized as discrete dimeric entities. Interestingly, when these complexes were subsequently irradiated with simple visible light in chloroform, they readily self-assembled into monodisperse spheres with a mean diameter of 160 nm.

Enhanced Glassy State Mechanical Properties of Polymer Nanocomposites via Supramolecular Interactions

It is now well accepted that the addition of nanoparticles (NPs) can strongly affect the thermomechanical properties of the polymers into which they are incorporated. In the solid (glassy) state, previous work has implied that optimal mechanical properties are achieved when the NPs are well dispersed in the matrix and when there is strong interfacial binding between the grafted NPs and the polymer matrix. Here we provide strong evidence supporting the importance of intermolecular interactions through the use of NPs grafted with polymers that can hydrogen bond with the matrix, yielding to significant improvements in the measured mechanical properties. Our finding thus supports the previously implied central role of strong interfacial binding in optimizing the mechanical properties of polymer nanocomposites.

Hierarchical supramolecular structuring and dynamical properties of water soluble polyethylene glycol-perylene self-assemblies.

The structural and dynamical properties of dilute aqueous solutions of poly(ethylene glycol)-perylene diimides (PEG(n)-PDI) have been investigated by means of static and dynamic light scattering, TEM microscopy, and small-angle X-ray scattering experiments. The amphiphilic PEG(n)-PDI molecules first self-assemble into stable and compact primary stacks of a few units of planar PDI through hydrophobic and π-π interactions. These primary stacks subsequently arrange in large and globular aggregates of typically 100-250 nm via weak PEG chain interpenetration. Surprisingly, the scattered electric field autocorrelation function g((1))(q,t) measured by dynamic light scattering evolves over very long periods of times (several months) and up to a bimodal distribution. The fast relaxation mechanism is associated to the diffusion of free primary stacks, whereas the slower relaxation still indicates the presence of large self-assemblies. Kinetic experiments show that the large supramolecular aggregates slowly release the free primary stacks whose proportion increases with time. This dissociation depends on several parameters such as PEG side chain length, total concentration, and shaking.

Autopoietic Behavior of Dynamic Covalent Amphiphiles

The condensation of aldehydes and amines in water to give amphiphilic imines can lead to a particular autocatalytic behavior known as autopoiesis, in which the closed micellar structure made by the amphiphile at the mesoscale can accelerate the condensation of its constituents. Herein, through a combination of analytical tools, including diffusion ordered spectroscopy (DOSY) as well as light, neutron, and X-ray scattering techniques, the thermodynamic and kinetic parameters were probed at both the level of dynamic covalent imine bond formation and the level of the resulting micellar self-assemblies. It was found that the autopoietic behavior was the result of a combination of several parameters, including solubilization of hydrophobic building blocks, template effect at the core-shell interface, and growth/division cycles of the micellar objects.