Ref HAL: hal-03371593_v1
Exporter : BibTex | endNote
Résumé:

Rubber-based nanocomposites prepared by solid-phase mixing with precipitated silica nanoparticles are typically strongly aggregated systems with different levels of spatial organization, as highlighted by our group in the past [1]. The strategy that we developed these past years was to investigate such systems based on the study of simplified industrial samples with ingredients limited to a strict minimum. The analysis of small-angle X-ray scattering data can then be performed on the scale of a micrometric simulation box. Tens of thousands of “model” nanoparticles are embedded in the matrix, and their dispersion strongly affects both the mechanical properties of the material, and the scattered intensity. A statistical method based on a reverse Monte Carlo solution of this many-parameter scattering problem will be presented, showing that some key features like percolation can be described [2].Another key feature of rubber nanocomposites refers to the influence of the filler surfaces on the polymer structure and dynamics, and some recent progress will be discussed [3]. In particular, we have studied blends of short and long chains, where one chain type is deuterated, by small-angle neutron scattering. Different degrees of spatial segregation could be identified recently, including a peculiar, “fish-shaped” interfacial gradient characterized also by reverse Monte Carlo simulations, this time of the interface.References[1] Guilhem P. Baeza, Anne-Caroline Genix, C. Degrandcourt, Laurent Petitjean, Jérémie Gummel, Marc Couty, Julian Oberdisse, Macromolecules 2013, 46, 317−329 (cover article)[2] Musino D, Genix A-C, Chauveau E, Bizien T, Oberdisse J, Nanoscale 2020, 12:3907.[3] A.C. Genix, V. Bocharova, B. Carroll, P. Dieudonné-George, M. Sztucki, R. Schweins, A. P. Sokolov, and Julian Oberdisse, ACS Applied Materials and Interfaces, 2021, in press

Ref HAL: hal-03367183_v1
Ref Arxiv: 2108.09487
DOI: 10.1111/jace.18090
WoS: WOS:000693436300001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote

Ref HAL: hal-03189744_v1
DOI: 10.1021/acs.langmuir.0c03441
Exporter : BibTex | endNote
Résumé:

The adsorption of a sunflower protein extract at two air− water and oil−water interfaces is investigated using tensiometry, dilational viscoelasticity, and ellipsometry. For both interfaces, a three step mechanism was evidenced thanks to master curve representations of the data taken at different aging times and protein concentrations. At short times, a diffusion limited adsorption of proteins at interfaces is demonstrated. First, a two-dimensional protein film is formed with a partition of the polypeptide chains in the two phases that depends strongly on the nature of the hydrophobic phase: most of the film is in the aqueous phase at the air−water interface, while it is mostly in the organic phase at the oil−water interface. Then a three-dimensional saturated monolayer of proteins is formed. At short times, adsorption mechanisms are analogous to those found with typical globular proteins, while strong divergences are observed at longer adsorption times. Following the saturation step, a thick layer expands in the aqueous phase and appears associated with the release of large objects in the bulk. The kinetic evolution of this second layer is compatible with a diffusion limited adsorption of the minor population of polymeric complexes with hydrodynamic radius R H ∼ 80 nm, evidenced in equilibrium with hexameric globulins (R H ∼ 6 nm) in solution. These complexes could result from the presence of residual polyphenols in the extract and raise the question of the role of these compounds in the interfacial properties of plant protein extracts.

Ref HAL: hal-03358931_v1
Exporter : BibTex | endNote

Ref HAL: hal-03358744_v1
Ref Arxiv: 2106.12669
DOI: 10.1021/acs.macromol.1c01394
WoS: 000703552500031
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
21 Citations
Résumé:

Using molecular dynamics simulations, we study the static and dynamic properties of spherical nanoparticles (NPs) embedded in a disordered and polydisperse polymer network. Purely repulsive and weakly attractive polymer–NP interactions are considered. It is found that for both types of particles, the NP dynamics at intermediate and long times is controlled by the confinement parameter C = σN/λ, where σN is the NP diameter and λ is the dynamic localization length of the cross-links. Three dynamical regimes are identified: (i) for weak confinement (C ≲ 1), the NPs can freely diffuse through the mesh; (ii) for strong confinement (1 ≲ C ≲ 3), NPs proceed by means of activated hopping; (iii) for extreme confinement (C ≳ 3), the mean-squared displacement shows on intermediate time scales a quasi-plateau because the NPs are trapped by the mesh for very long times. Escaping from this local cage is a process that depends strongly on the local environment, thus giving rise to an extremely heterogeneous relaxation dynamics. The simulation data are compared with the two main theories for the diffusion process of NPs in gels. Both theories give a very good description of the C dependence of the NP diffusion constant but fail to reproduce the heterogeneous dynamics at intermediate time scales.

Ref HAL: hal-03333988_v1
Exporter : BibTex | endNote
Résumé:

The development of smart nanomaterials has attracted great attention in several fields like nanoscience and nanotechnology due to their unique response to external stimuli. Many of them are based on polymers that can exhibit a shape-changes when submitted to environmental modifications. Poly(N-isopropylacrylamide), PNIPAM, is a thermo-responsive polymer. Linear chains are water soluble at room temperature but undergo a reversible coil-to-globule transition at a lower critical solution temperature (LCST) close to 32°C due to the dehydration and subsequent collapse of its chains into compact globules. [1] This phenomenon results in a volume phase transition (VPT) in PNIPAM based crosslinked microgels and can be used to promote original thermal effects.Hybrid nanocomposite microgels associating PNIPAM and gold nanoparticles (GNP) have thus been designed in order to take advantage of the outstanding plasmonic and photo-thermal properties of GNP to promote the VPT of the microgels through an efficient photo-thermal conversion. [2] With their strong diameter-dependent optical absorption in the near infrared (NIR) and their large surface area favoring photo-thermal transfer, semiconducting single-walled carbon nanotubes (s-SWNT) are also good candidates for photo-thermal conversion in the NIR (Figure 1a). However, to the best of our knowledge, no thorough studies of nanomaterials based on both SWNT and PNIPAM have been reported so far.Here we describe the preparation of SWNT/PNIPAM hybrid microgels through a non-covalent functionalization technique. These nanoparticles are stable in water and show a VPT, which can be promoted either by direct heating or by excitation of the resonant absorption of s-SWNT in the NIR (Figure 1b-c). The photoluminescence (PL) signal can be used to monitor the VPT by a redshift observed when crossing the LCST, while the Raman signatures remain essentially the same.

Ref HAL: hal-03333981_v1
Exporter : BibTex | endNote
Résumé:

Avec la plupart des couches d’alignement classiques des cellules commerciales, il est difficile d’obtenir une texture uniforme des phases nématiques twist bend (NTB) en géométrie planaire, y compris dans des cellules très fines (~1 μm). Même lorsqu’un composé présente une phase nématique N bien alignée, on observe en effet la formation spontanée de bandes lorsque l’on passe en phase NTB [1,2,3] (voir Fig.1-a). Cette texture en rayures est caractérisée par un pas égal à deux fois l’épaisseur de la cellule [1]. Son origine est attribuée à l’amincissement rapide des pseudo-couches NTB en dessous de la température de transition N-NTB qui conduit à une instabilité d’ondulation.Nous avons étudié en détail le rôle de la force d’ancrage des couches d’alignement sur les textures NTB d’un dimère cyanophyphényle, le CB7CB (1,7-bis-4-(4-cyanobiphenyl) heptane). Pour cela nous avons utilisé un polymère dont la force d’ancrage sur les nématiques cyanobiphényles (monomères) était connue pour varier fortement selon les conditions de préparation. Une étude systématique de l’ancrage de ce polymère sur le CB7CB a été faite en phase nématique et nous avons étudié l’influence des énergies d’ancrages zénithale et azimutale sur les textures obtenues en phase NTB. Dans des cellules symétriques, nous avons ainsi montré que la périodicité des instabilités dépendait fortement de l’ancrage et notamment de sa composante azimutale.Par ailleurs, ce travail a permis de montrer qu’avec des conditions d’ancrage adéquates, il était possible d’obtenir un alignement spontané uniforme de la phase NTB (voir Fig.1-b-c). Cet alignement est conservé même en s’éloignant de la température de transition, ouvrant la possibilité future d’utiliser les phases NTB dans des dispositifs électro-optiques.