Blanc SIMI 8 - Sciences de l'information, de la matière et de l'ingénierie : Chimie du solide, colloïdes, physicochimie

Supramolecular adhesion – Supradhésion

Supramolecular chemistry and adhesion

Pressure sensitive adhesives (scotch tapes ...) are soft solids that can efficiently bond only if they strongly dissipate energy under strain. Control of weak interactions should enable us to significantly increase this energy dissipation under strain.<br />

Control of the energy dissipation mechanisms in an adhesive

Supramolecular chemistry consists in using non-covalent interactions to organize molecules at the nanometer scale. A careful control of the structure can in turn be expected to yield improved properties. It was shown that it is actually possible to improve the mechanical properties of a polymer network by replacing some covalent cross-links by supramolecular interactions. These low energy interactions are by nature reversible or even dynamic at room temperature. Consequently, they may also bring a self-healing character to the material, and an unusual energy dissipation pathway.<br />The mechanical properties of polymers formed by supramolecular assembly have overwhelmingly been characterized only by rheology in the linear domain or by temperature dependent viscosity measurements. However, the most important contribution of non-covalent interactions can be expected to be in the large deformation regime. <br />Therefore, our aim was to apply supramolecular chemistry concepts to the field of adhesives. Materials specifically designed to function as adhesives must be able to interact strongly with the surfaces being bonded together and to dissipate energy during the debonding process, where large deformations are typically involved. On both counts, supramolecular chemistry with its very polar groups and reversible strong bonds, holds great promise. <br />

We have synthesized low Tg polyacrylates bearing hydrogen bonded stickers. Films were prepared and the structures formed by hydrogen bonding were characterized by X ray scattering (SAXS) and microscopy (AFM). Finally, the influence of hydrogen bonds on the chain dynamics was studied by rheology and adhesion properties were probed.
The synthetic pathway chosen allowed to tune the chain length, the nature and number of stickers and the content of covalent crosslinking. These parameters control the supramolecular structuration in the material. This in turn allowed to tune the relative importance of the main energy dissipation mechanisms.

A large family of polyacrylates was synthesized by ATRP and characterized. The following characteristics were varied: the nature of the monomer, the molar mass, and the nature of the sticker.
The nature of the stickers has a strong influence on both the structure and the viscoelasticity of the samples : some samples are viscous oils at room temperatures whereas others are elastic gels up to 120°C. We showed that if the supramolecular interactions were essential to fine tune the dissipative properties, a small concentration of permanent covalent links was still needed to control large strain elasticity and optimize the adhesive properties.

We are now discussing with a private company to perform tests for a particular application.

3 publications on materials synthesis have been published.
2 publications on structuration and properties of the materials have been submitted.
2 other publications are in preparation.

Pressure-sensitive-adhesives (PSA), or adhesives sticking upon simple contact, are essentially lightly crosslinked polymer networks with a glass transition temperature well below the usage temperature. The design of an optimized PSA requires a good knowledge of polymer synthesis in order to control the polymer architecture (branching, crosslinking, molecular weight distribution). There are currently several routes to achieve such a lightly crosslinked network. However the potential of hydrogen bonding groups to create strong but labile bonds which greatly increase the energy dissipated upon deformation, has not been explored for these soft solids.
Therefore, our objective is to apply the recent concepts of supramolecular chemistry to the field of adhesion.
Soft adhesives are soft solids, which function as efficient adhesives only if they can dissipate a lot of energy when they are mechanically stressed. Rupture and recombination of many hydrogen bonds within the adhesive may be a new mean to dissipate energy, while keeping a reasonable number of permanent bonds; and therefore to avoid macroscopic cohesive failure inside the adhesive.
More specifically, we will synthesize a range of low Tg polymers bearing self-complementary hydrogen bonding moieties; characterize their self-assembled structure in the bulk; and study the influence of hydrogen bonding on the dynamics of these macromolecules.
To test our concept, a model polymer (PIBUT) has been synthesized from readily available building blocks. A soft polyisobutene backbone has been combined with a strongly self-associating bis-urea moiety. Hydrogen bonding has been shown to be responsible for the formation of a dynamic, but long range and hierarchical structure. Moreover, stress strain curves have revealed that the material displays a strong adhesion both on high energy surfaces such as steel, and on low energy surfaces such as crosslinked poly(dimethylsiloxane). Although the detailed molecular mechanisms of interactions are not known, they yield very promising macroscopic effects and clearly deserve further investigation.

Project coordination


The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.



Help of the ANR 420,000 euros
Beginning and duration of the scientific project: - 48 Months

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