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Self-assembled nanostructures of block copolymer : the impact of macromolecular architecture

Oleg Borisov Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Matériaux, Pau

Jeudi 25 janvier -14h00- Amphi Boreau

 

Applications of block copolymer nanostructures in soft nanotechnology and in medicine impose, as general requirements, precise control over dimensions and morphology of the nanostructures in combination with pronounced stimuli-responsive properties.
The statistical thermodynamic theory enables us to predict how the morphologies of the self-assembled structures can be on purpose tuned by varying not only the intra-molecular solvophilic/solvophobic balance, but also by changing macromolecular architecture, i.e., replacing conventional linear block copolymers by miktoarm starlike, linear-cyclic and linear-dendritic block copolymers. In particular, we focus on structural properties of micelles formed upon self-assembly of linear-dendritic block copolymers. We demonstrate that both hydrodynamic dimensions and aggregation number in such micelles decrease as a function of degree of branching of the dendron blocks whereas the number of potentially functionalizable exposed to the solution terminal groups of the corona-forming dendron blocks increases. This result may have important implication for design of linear-dendritic block copolymer micelles with smart functionalities for targeted drug delivery. Furthermore, the theory predicts that copolymers with dendronized coronal block demonstrate weaker tendency to form wormlike micelles or polymersomes as compared to homologous linear diblock copolymers. Dendronization of the associating block leads to the opposite effect.
Polymeric nanoparticles with non-conventional multicompartment structure, including asymmetric Janus particles, patchy spherical or wormlike micelles or polymersomes can be obtained upon assembly of triblock terpolymers comprising three chemically different blocks in selective solvent. These particles may serve as building blocks for hierarchically assembled materials. Our theoretical model enables us to predict morphology of the assemblies (number and shape of different nano-domains) as a function of the terpolymer composition and interaction parameters. The theoretical predictions are supported by experimental data.

Adhesion for ‘‘soft’’ bodies shows instabilities...

Michele Ciavarella Polyetchnico di Bari, Italie

Mardi 6 février 2016 - 14h00 - Amphi Urbain

 

Adhesion for ‘‘soft’’ bodies shows instabilities like in the simple case of a single sinusoid even in the so called JKR regime (Johnson 1995) which leads to hysteretic behavior. Hence, for very soft and large bodies, and special types of roughness, this could be maximized (Guduru, 2007) with possible enhancement of adhesion.
However, at nanoscales and for hard solids, very simple equations like Rumpf-Rabinowicz (Rumpf, 1990,
Rabinovich et al., 2000) work very well for the spherical geometry, and show large reduction with roughness. These show only dependence on rms heights of roughness and not slopes or curvatures, as confirmed by extensive AFM experiments by Jacobs et al (2013) where from atomic corrugation up to a few nm, the measured work of adhesion was found to decrease by more than an order of magnitude. This naturally also raise the very delicate issue of what is “work of adhesion” in experimental measurements of adhesion forces.
In a recent note BAM (Bearing Area Model) was introduced by Ciavarella (2017b), a single-line equation estimate for adhesion between elastic (hard) rough solids with Gaussian multiple scales of roughness. It was successfully validated with high quality numerical data from the literature from Pastewka and Robbins (2014) for pull-off. The reason why the area-slope relationship seems to depend on rms slopes and curvature in Pastewka and Robbins (2014), while pull-off primarily on rms heights, has been the subject of a few efforts (Ciavarella, 2016, 2017a,b, Ciavarella and Papangelo, 2017a,b,c, Ciavarella, Papangelo and Afferrante, 2017), yet calls for more investigations. BAM starts from the observation that the entire DMT solution for ‘‘hard’’ spheres (Tabor parameter tending to zero) assuming the Maugis law of attraction, is very easily obtained using the Hertzian load-indentation law and estimating the area of attraction as the increase of the bearing area geometrical intersection when the indentation is increased by the Maugis range of attraction. BAM is therefore an equation similar to Rumpf-Rabinowicz for the sphere, but as applied to elastic nominally flat surfaces. BAM shows that adhesion, as already well known, for hard solids at macroscopic scale is destroyed quite easily and the problem remains that contact area is a ill-defined “magnification” dependent quantity (Ciavarella and Papangelo, 2017b). When elastic modulus decreases sufficiently, observable adhesion may be possible, although then the assumptions of BAM may become questionable. In 1969 Carl Dahlquist at 3M suggested a "Criterion" bearing his name : "For measurable quick tack, the elastic modulus must be below a certain fixed value (0.3MPa) which is fairly independent of the nature of the adhesive, the adherend and the applied pressure". While this is clearly a rule-of-thumb, it has been a useful rough guide for more than 40 years. Some comparisons with BAM follow.

References

Ciavarella, M. (2016). On a recent stickiness criterion using a very simple generalization of DMT theory of adhesion. Journal of adhesion science and Technology, 30(24), 2725-2735.
Ciavarella, M. (2017a). On Pastewka and Robbins’ Criterion for Macroscopic Adhesion of Rough Surfaces.
Journal of Tribology, 139(3), 031404.
Ciavarella, M. (2017b) A very simple estimate of adhesion of hard solids with rough surfaces based on a bearing area model. Meccanica, 1-10. DOI 10.1007/s11012-017-0701-6
Ciavarella, M., & Papangelo, A. (2017a). A modified form of Pastewka–Robbins criterion for adhesion. The Journal of Adhesion, 1-11.
Ciavarella, M., & Papangelo, A. (2017b). Discussion of “Measuring and Understanding Contact Area at the Nanoscale : A Review” by Tevis DB Jacobs and Ashlie Martini. Applied Mechanics Reviews. http://appliedmechanicsreviews.asmedigitalcollection.asme.org/article.aspx?articleid=2658189
Ciavarella, M., & Papangelo, A. (2017c). A generalized Johnson parameter for pull-off decay in the adhesion of rough surfaces, Physical Mesomechanics · December 2017
Ciavarella, M., Papangelo, A., & Afferrante, L. (2017). Adhesion between self-affine rough surfaces : Possible large effects in small deviations from the nominally Gaussian case. Tribology International, 109, 435-440. Guduru PR (2007) Detachment of a rigid solid from an elastic wavy surface : theory. J Mech Phys Solids 55:473–
Jacobs, T. D., Ryan, K. E., Keating, P. L., Grierson, D. S., Lefever, J. A., Turner, K. T., ... & Carpick, R. W. (2013). The effect of atomic-scale roughness on the adhesion of nanoscale asperities : a combined simulation and experimental investigation. Tribology Letters, 50(1), 81-93.
Johnson KL (1995) The adhesion of two elastic bodies with slightly wavy surfaces. Int J Solids Struct 32(3/4):423–430
Pastewka L, Robbins MO (2014) Contact between rough surfaces and a criterion for macroscopic adhesion.
Proc Nat Acad Sci 111(9):3298–3303
Rabinovich YI, Adler JJ, Ata A, et al. (2000) Adhesion between nanoscale rough surfaces : I. Role of asperity geometry. J Colloid Interface Sci 232(1) : 10–16.
Rumpf H. Particle Technology. London/New York : Chapman and Hall, 1990.

Technologie Additives : une nouvelle façon de penser la fabrication de pièces céramiques

Thierry Chartier Science des Procédés Céramiques et des Traitements de Surface, European Ceramic Center, Limoges

Jeudi 22 février 2018 - 14h00 - Amphi à définir

 

Les technologies additives font actuellement l’objet d’un fort engouement au niveau international. Ces procédés conduisent à de nouvelles façons de penser le design et la fabrication de pièces fonctionnelles organiques, métalliques, céramiques ou hybrides et constituent une vraie révolution industrielle. Dans le domaine de la céramique, ces méthodes ouvrent la voie à la conception et à la fabrication de composants innovants pour diverses applications qui nécessitent des propriétés spécifiques (espace, télécommunications, biomédical, ingénierie, bijoux ...).

Parmi les procédés additifs céramiques, la stéréolithographie est basée sur la photopolymérisation d’un système réactif consistant en une dispersion de particules céramiques dans un monomère/oligomère associé à un photoinitiateur. La polymérisation est assurée sélectivement sur chaque couche par un laser UV défléchi à partir des informations du fichier CAO de la pièce. Le challenge de la formulation est de répondre à plusieurs contraintes. La première est une concentration élevée en céramique (>50vol%) tout en maintenant une rhéologie adaptée au dépôt de couches de faible épaisseur (10 µm). La seconde est de maintenir une réactivité suffisante aux UV de la suspension chargée. Enfin, il faut limiter la diffusion de la lumière afin de contrôler la résolution dimensionnelle.

L’obtention de pièces céramiques d’architectures complexes, avec une haute résolution dimensionnelle et des propriétés similaires à celles obtenues par des procédés conventionnels, nécessite la compréhension des principaux paramètres qui influencent la polymérisation (conversion and cinétique) ainsi que la profondeur et la largeur de polymérisation.


Microbial glycolipid biosurfactants : from self-assembly to hydrogel formation

Niki Baccile Laboratoire de Chimie de la Matière Condensée de Paris, Université Pierre et Marie Curie

Jeudi 11 janvier 2018

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Nanoparticules d’or sous irradiation laser pulsée : spécificités et applications de la plasmonique ultrarapide

Bruno Palpant Laboratoire de Photonique Quantique et Moléculaire, CentraleSupélec – Ecole Normale Supérieure Paris-Saclay – CNRS

Jeudi 30 novembre 2017

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Strain stiffening in self-assembled biomimetic hydrogels

Rint P. Sijbesma Department of Chemical Engineering and Chemistry and Institute for Complex Molecular Systems, Eindhoven University of Technology, The Netherlands

Jeudi 23 novembre 2017

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