Nos tutelles



Accueil > Équipes > Soft Matter: Organization, Dynamics and Interfaces > Thèmes de Recherche

Complex soft matter assemblies

publié le , mis à jour le

Structure, dynamics and mechanical properties of filled elastomers

(Françoise EHRBURGER-DOLLE and Isabelle MORFIN in coll. with F. Livet and F. Bley (SiMAP-Grenoble-INP), M. Sutton (Univ. McGill, Montreal), Y. Chushkin (ESRF, Grenoble) and G. Heinrich (Polymer Institute, Dresden)))

The research work performed in the field of polymer nanocomposites was aiming at relating the dynamics of the filler particles with the mechanical stress relaxation in strained materials.
To this end, a first series of X-ray Photon Correlation Spectroscopy (XPCS) experiments has been performed at the Advance Photon Source (APS, Argonne, USA) on strained samples. Experiments were performed alternately in the classical homodyne regime (XPCS) and in our new heterodyne regime (HD-XPCS) (Livet et al. 2006 (1)). The latter allows us to determine the real velocity of the nanoparticles in the strained nanocomposites during aging. The stress relaxation was measured simultaneously. The mechanical protocol was established in order to compare UP and DOWN jumps as well as first and second tensile stress relaxation. The matrix was an ethylene propylene diene monomer (EPDM) cross-linked rubber. The parameters involved were the matrix-filler and the filler-filler interaction, the filler volume fraction (close to or above the percolation threshold), the strain intensity and the mechanical history of the sample. At a given strain, the velocity of the filler particles deduced from XPCS performed with heterodyne detection (HD-XPCS) was shown to become smaller and its decrease with time faster as the filler-matrix interaction became stronger (2). For all materials, the tensile relaxation modulus was shown to vary as a power law of time for strains above a given threshold. Pertinence of the soft glassy rheology (SGR) models to the description of the stress relaxation modulus was discussed (3). In particular, the noise temperature x defined in the SGR model could be related to the mobility of the polymer chains influenced by the interaction with the surface of the filler and the strain. The dynamical behavior of the filler particles deduced from HD-XPCS experiments appears to be consistent with this interpretation.
In a series of XPCS experiments performed on the beamline ID10 at ESRF (Grenoble), we have investigated strained elastomer samples containing a small volume fraction (about 0.005) of solid particles. In this situation, the particles are isolated and cannot form a network throughout the elastomer matrix, as it was the case in the former experiments. The goal was to investigate the long time relaxation process at different azimuthal angles in order to check for anisotropic dynamics. It is shown that, at the same azimuthal direction, the relaxation process depends on the filler-matrix interaction. Particularly, anisotropic dynamics is observed only if the particle-matrix interactions are strong. In this case, the solid particles may act as probe for investigating the dynamics of the strained elastomer chains.

(1) X-ray intensity fluctuation spectroscopy by heterodyne detection, F. Livet, F. Bley, F. Ehrburger-Dolle, I. Morfin, E. Geissler, M. Sutton J. Synchrotron Rad. 13, 453-458 (2006)

(2) Tensile stress relaxation and recovery behavior of a cross-linked EPDM rubber matrix loaded with different fillers, F. Ehrburger-Dolle, I. Morfin, F. Bley, F. Livet, G/ Heinrich, L. Piché, M. Sutton, Macromolecules, 45, 8691−8701(2012)

(3) Experimental clues of soft glassy rheology in strained filled elastomers, F. Ehrburger-Dolle, I. Morfin, F. Bley, Frédéric Livet, G. Heinrich, L. Piché, M. Sutton, Journal of Polymer Science Part B : Polymer Physics, 52, pp.647-656, (2014).

Physical molecular gels

(Marie PLAZANET, Isabelle MORFIN and Sylvie SPAGNOLI)

Physicals gels formed by small organic gelators find applications in diverse domains, although the understanding of their formation and stability severely limits their practical use. We therefore undertook the study of a small amphiphilic gelator in various solvents as model system, we the aim of characterising both structural and dynamical aspects involved in the gel phase stability. Using quasielastic neutron scattering, we have been able to quantify the number of solvent molecules that are immobilised with the solid network, as well as the fraction of slow-down molecules on the picosecond timescale. These results show a direct correlation with the stability of the gel.

Structure and reactivity in polydiacetylenes

(Sylvie SPAGNOLI, in coll with INSP and ITODYS labs in Paris)

Diacetylenes (DA) R-C-C-C-C-R’ can be polymerized by UV or gamma irradiation of self assembled DA (crystal, Langmuir-Blodgett film) through a topochemical reaction. Microcrystalline films of the DA 4BCMU (R=R’=(CH2)4-OCONH-CH2-COOC4H9) were polymerized by UV irradiation. A method for determining the absolute polymer content X in films has been developed. In this DA the reaction rate is strongly decreased beyond X 0.3. Existing models fail to fit the kinetics. A model based on quenching of the monomer excited state precursor to initiation by energy transfer to a nearby existing chain is developed and quantitatively fits the kinetics. Such quenching may occur in any diacetylene film. One should not assume that an apparent saturation of the absorbance of a film coresponds to complete polymerization. Most often the polymerization leads to long conjugated blue PDA which can undergo a transition to red PDA under various stimuli (temperature, pressure...). In 4BCMU the amide bands associated to the urethanes in the side groups, which form one-dimensional H-bond linear chains are quite similar to those found in peptides and proteins. The positions and strengths of these absorptions, studied by FTIR, are practically unchanged by polymerization or blue to red color transition. This suggests that the H-bond linear chains are the main constitutive interactions in these crystals, and that the conjugated parts must and do “adapt” to the unchanged H-bond lines. No evidence of side group disordering was observed at the irreversible blue to red transition in polymer crystal as often stated.

Polyelectrolyte complexes

(Isabelle MORFIN in coll. with I. Grillo (ILL, Grenoble), J. Combet (ICS, Strasbourg) and LLB (Saclay))

Hyaluronan complexes have been studied for a few years at the LIPhy. The hyaluronan, HA, is a negatively charged polysaccharide which has many biological functions that can even be opposite depending on the chain length. In spite of a large use for pharmaceutical applications, almost no research investigates the multiscale HA structure in complex, possibly in relation with these biological processes. Our goal is a precise knowledge of the full structures and dynamics of HA complex systems in aqueous solutions, the effect of the surrounding medium (salt for example), the role played by the chain stiffness or the HA chain length. Large instrument facilities, in particular small angle neutron or X-ray scattering (SANS and SAXS), are essential for such studies involving HA/protein, HA/ionic micellar or HA/non ionic micellar systems. A first study on HA/lysozyme (a globular protein mainly positively charged) has shown a particular rod like structure revealed by SANS.
Such structure has not been observed with other polyelectrolytes/proteins mixtures (HA/Human Serum Albumin or sulphonated polystyrene (PSS)/lyso) for which the polymer chains seem to wrap more closely the proteins. In addition, in contrast with the PSS/lyso complexes, no experimental condition leading to protein unfolding has been obtained with HA/Lyso. The effect of the chain stiffness is also considered in other systems, HA/Dotab, a positively charged surfactant forming micelles and the PSS/Dotab are investigated in parallel.