Matière Molle
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Matière Molle

Bilayered vesicle formed by PMeOx30-b-POctOx20-C10F21

Sur la base de travaux pionniers établis dans les années 70 au LLB, la physique des polymères et plus largement l’étude de systèmes relevant de la matière molle (tensio-actifs, nanoparticules) continue d'être un domaine très actif de l’équipe matière molle au laboratoire. Parmi les différents sujets abordés, des efforts spécifiques ont été consacrés à la compréhension de l’origine des propriétés mécaniques remarquables dans des nanocomposites à base de polymère en élaborant des systèmes modèles à base de nanoparticules greffées obtenues par des méthodes de synthèse et/ou fonctionnalisées afin de varier la dispersion des nanoparticules et in fine, les propriétés optiques (résonnance plasmon), chirales, catalytiques et de renforcement. Ces nanoparticules peuvent s’auto-organiser en volume dans un liquide ou un fondu de polymère ou un élastomère mais également sous forme de films 2D formés et contrôlés par des liaisons covalentes. On étudie également la structure, l’organisation et les propriétés mécaniques de milieux poreux formés par séchage contrôlé de solutions de particules en volume ou sur une surface. D’autres domaines de physico-chimie étudiés concernent le comportement des poly électrolytes, soit dans des solutions pures ou complexées avec des objets de charges opposées (protéines, nanoparticules inorganique), et d’étudier l’impact du chemin de formulation de ces systèmes hors équilibre comme voie d’ajustement des propriétés macroscopiques. Nous étudions également des systèmes multi-composants d’intérêt industriel tels que les mousses alimentaires, des émulsions et fluides pétroliers ou encore de gels de bio-polymères pour les applications en pharmacie dont l’objectif est de relier la structure locale avec les propriétés macroscopiques (viscosité, stabilité…). Une activité importante est développée autour de vésicules à base de copolymères à blocs pour l’encapsulation de principes actifs et le relargage contrôlé et parfois ciblée par l’application d’un stimulus physico-chimique (changement de pH, de température, application d’un champ magnétique pour l’hyperthermie). On s’intéresse spécifiquement à la conformation de polymères en films minces ainsi qu’à la structure de matériaux pour la catalyse. Pour les applications agro-alimentaires, on étudie la dénaturation des protéines, l’impact de la pression, de la température, des sels, du pH ainsi que des mélanges protéines-polyosides aux interfaces liquide-solide (matériaux nano ou mésoporeux) liquide-liquide (émulsion)/ liquide-air (mousse). Une partie de l’activité s’oriente maintenant vers l’étude de polymères ou copolymères conducteurs et semi-cristallins, ainsi que vers la synthèse de matériaux multifonctionnels à base de charges hybrides, poly-phasiques permettant de combiner plusieurs propriétés macroscopiques telles que la stabilité mécanique et la conduction protonique ou la transparence du matériau. Sur l’ensemble des systèmes abordés par l’équipe matière molle, on bénéficie des possibilités uniques de variation de contraste et de deutération d’un des composants des systèmes de matière molle étudiés mais aussi en diffusion de rayonnement de la complémentarité entre les rayons x et les neutrons pour une gamme de taille caractéristique allant du nm à quelques centaines de nm. Pour certaines études, nous utilisons un nouvel équipement interne de diffusion de rayons x aux petits angles de haute performance, permettant également des mesures par réflectivité et en incidence rasante. Pour des échelles plus grandes (micron), la caractérisation structurale des objets utilise des méthodes complémentaires de microscopie électronique, diffusion de lumière et d’imageries neutronique.

 
#3239 - Màj : 23/06/2020
Faits marquants scientifiques

Marine Le Goas, Tom Roussel, Maria Kalbazova, David Carrière, Elodie Barruet, Valerie Geertsen, Giulia C. Fadda, Fabienne Testard, Geraldine Carrot and Jean-Philippe Renault

Nanomedicines are considered as promising therapeutics for cancer treatment. However, clinical translation is still scarce, partly because their biological behavior is not well understood. Extracting general guidelines from the great variety of nanoparticles and conditions studied is indeed difficult, and relevant techniques are lacking to obtain in situ information. Here, both issues are solved by combining versatile model nanoparticles with in situ tools based on small-angle scattering techniques (SAS). The strategy was to develop a library of nanoparticles and perform systematic study of their interactions with biological systems. Considering the promising properties of gold nanoparticles as cancer therapeutics, polymethacrylate-grafted gold nanoparticles were chosen as models. Modulation of polymer chemistry was shown to change the surface properties while keeping the same structure for all nanoparticles. This unity allowed reliable comparison to extract general principles, while the synthesis versatility enabled to fine-tune the nanoparticles surface properties, especially through copolymerization, and thus to optimize their biological behavior. Two specific aspects were particularly examined: colloidal stability and cell uptake. Positive charges and hydrophobicity were identified as key parameters influencing toxicity and internalization. In situ SAS gave valuable information about nanoparticles evolution in biologically relevant environments. Good colloidal stability was thereby shown in cell culture media, while intracellular transformation and quantity of nanoparticles were monitored, highlighting the potential of these techniques for nanomedicines studies.

https://doi.org/10.1039/d0tb01167c

 

We show by X-ray and neutron small-angle scattering that gold nanoparticles with controlled sizes and morphologies can be obtained by the metallic reduction of AuCl4 ions trapped in 3D organic molds by X-ray radiolysis. The molds are spherical frozen micelles of polystyrene-b-poly(dimethylaminoethyl methacrylate) (PS-b-PDMAEMA) block copolymer in acidic aqueous solution with a PS spherical core surrounded by a corona of PDMAEMA chains in good solvent. The behavior of micelles is controlled by the [AuCl4]/[DMAEMA] ratio RAuCl4/DMAEMA. At low gold concentration, AuCl4 ions condense on the positively charged DMAEMA moieties without changing the behavior of the PDMAEMA chains. At intermediate gold concentration, the ions induce a progressive contraction of the corona’s chains and dehydration of micelles. At large gold concentration, the corona becomes a fully dry phase loaded with gold ions, which induces micelle aggregation. Radiolysis of the solution by an intense X-ray beam produces different types of gold nanoparticles with respect to RAuCl4/DMAEMA and irradiation time. At RAuCl4/DMAEMA = 0.033, irradiation produces in the first step gold clusters in the micelle corona which in the second step merge to form nanoparticles of a similar size to that of the micelle. Conversely, at RAuCl4/DMAEMA = 0.33, micelles do not operate as templates but only as nucleation zones and large nanoparticles grow outside the micelles.

http://doi.org/10.1021/acs.langmuir.0c00554

Andrew M. Jimenez, Dan Zhao, Kyle Misquitta, Jacques Jestin and Sanat K. Kumar

Understanding the structure and dynamics of the bound polymer layer (BL) that forms on favorably interacting nanoparticles (NPs) is critical to revealing the mechanisms responsible for material property enhancements in polymer nanocomposites (PNCs). Here we use small angle neutron scattering to probe the temporal persistence of this BL in the canonical case of poly(2-vinylpyridine) (P2VP) mixed with silica NPs at two representative temperatures. We have observed almost no long-term reorganization at 150 °C (∼Tg,P2VP + 50 °C), but a notable reduction in the BL thickness at 175 °C. We believe that this apparently strong temperature dependence arises from the polyvalency of the binding of a single P2VP chain to a NP. Thus, while the adsorption–desorption process of a single segment is an activated process that occurs over a broad temperature range, the cooperative nature of requiring multiple segments to desorb converts this into a process that occurs over a seemingly narrow temperature range.

https://doi.org/10.1021/acsmacrolett.8b00877

 

Les matériaux composites, dont on peut faire judicieusement varier la composition, permettent de combiner les propriétés de ses constituants. Ainsi, l’ajout de matériaux inorganiques (ou charge) dans une matrice polymère permet d’améliorer les propriétés d’usage de ces matériaux, telles que leurs propriétés mécaniques, électriques ou optiques, et aussi d'alléger le matériau ou d'en diminuer le coût.

Dans l’industrie du pneumatique, et en particulier dans la formulation des bandes de roulement, on utilise ainsi des matrices élastomères que l'on renforce par des particules de silice. L'étude réalisée au LLB, en collaboration avec Michelin, montrent qu'il est possible de jouer sur les effets d'entropie de mélange et la balance des contributions entropique/enthalpique des interactions, pour piloter la dispersion des particules dans la matrice et contrôler les propriétés macroscopiques des matériaux.

 

Des chercheurs de l’I2BC@Saclay et de l’UMR NIMBE, en collaboration avec le Laboratoire Léon Brillouin (LLB), ont analysé la structure de la couronne composée de deux protéines modèles adsorbées sur des nanoparticules de silice, en utilisant la technique de diffusion des neutrons aux petits angles. Ils montrent que les structures formées sont de véritables nanoassemblages contrôlés, dans lesquels les protéines conservent leur forme.

 

D. Russo, A. De Angelis, A. Paciaroni, B. Frick, N. de Sousa, F. R. Wurm, and J. Teixeira

We investigate the relaxation dynamics of proteinpolymer conjugates by neutron scattering spectroscopy to understand to which extent the coating of a protein by a polymer can replace water in promoting thermal structural fluctuations. For this purpose, we compare the dynamics of proteinpolymer mixtures to that of conjugates with a variable number of polymers covalently attached to the protein. Results show that the flexibility of the protein is larger in proteinpolymer mixtures than in native protein or in conjugates, even in the dry state. Upon hydration, both the native protein and the conjugate show equivalent dynamics, suggesting that the polymer grafted on the protein surface adsorbs all water molecules.

http://dx.doi.org/10.1021/acs.langmuir.8b03636

A. Theodoratou, L.-T. Lee, J. Oberdisse and A. Aubert-Pouëssel, Langmuir 35(20) (2019) 6620.

Abstract :

Nanofilms of about 2 nm thickness have been formed at the air–water interface using functionalized castor oil (ICO) with cross-linkable silylated groups. These hybrid films represent excellent candidates for replacing conventional polymeric materials in biomedical applications, but they need to be optimized in terms of biocompatibility, which is highly related to protein adsorption. Neutron reflectivity has been used to study the adsorption of two model proteins, bovine serum albumin and lysozyme, at the silylated oil (ICO)–water interface in the absence and presence of salt at physiologic ionic strength and pH and at different protein concentrations. These measurements are compared to adsorption at the air–water interface. While salt enhances adsorption by a similar degree at the air–water and oil–water interfaces, the impact of the oil film is significant with adsorption at the oil–water interface 3–4-fold higher compared to that at the air–water interface. Under these conditions, the concentration profiles of the adsorbed layers for both proteins indicate multilayer adsorption. The thickness of the outer layer (oil side) is close to the dimension of the minor axis of the protein molecule, ∼30 Å, suggesting a sideway orientation with the long axis parallel to the interface. The inner layer extends to 55–60 Å. Interestingly, in all cases, the composition of the oil film remains intact without significant protein penetration into the film. The optimal adsorption on these nanofilms, 1.7–2.0 mg·m-2, is comparable to the results obtained recently on thick solid cross-linked films using a quartz crystal microbalance and atomic force microscopy, showing in particular that adsorption at these ICO film interfaces under standard physiological conditions is nonspecific. These results furnish useful information toward the elaboration of vegetable oil-based nanofilms in direct nanoscale applications or as precursor films in the fabrication of thicker macroscopic films for biomedical applications.

https://doi.org/10.1021/acs.langmuir.9b00186

Marguerite Léang, Didier Lairez, Fabrice Cousin, Frédérique Giorgiutti-Dauphiné, Ludovic Pauchard, Lay-Theng Lee

During evaporative drying of a colloidal dispersion, the structural behavior at the air-dispersion interface is of particular relevance to the understanding of the consolidation mechanism and the final structural and mechanical properties of the porous media. The drying-interface constitutes the region of initial drying-stress that, when accumulated over a critical thickness, leads to crack formation. This work presents an experimental study of top-down drying of colloidal silica dispersions with three different sizes (radius 5, 8 and 13 nm). Using specular neutron reflectivity, we focus on the structural evolution at the free drying-front of the dispersion with a macroscopic drying surface, and demonstrate the existence of a thick concentrated surface layer induced by heterogeneous evaporation. The reflectivity profile contains a strong structure peak due to scattering from particles in the interfacial region, from which the interparticle distance is deduced. A notable advantage of these measurements is the direct extraction of the corresponding dispersion concentration from the critical total reflection edge, providing a straightforward access to a structure-concentration relation during the drying process. The bulk reservoir of this experimental configuration renders it possible to verify the evaporation-diffusion balance to construct the surface layer and also to check reversibility of particle ordering. We follow the structural evolution of this surface layer from a sol to a soft wet-gel that is the precursor of a fragile skin, and the onset of significant particle aggregation that precedes formation of the wet-crust. Separate complementary measurements on the structural evolution in the bulk dispersion are also carried out by small angle neutron scattering, where the particle concentration is also extracted directly from the experimental curves. The two sets of data reveal similar structural evolution with concentration at the interface and in the bulk, and an increase in the degree of ordering with particle size.

https://pubs.acs.org/doi/pdfplus/10.1021/acs.langmuir.8b03772

 

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