Directing FOAM structures with INTruders: self-assembly of architected materials via elasto-capillarity – FOAMINT

Architected materials are attracting a growing interest: structural design results in intriguing features that drastically differ from that of the bulk materials, with a combination of light weight and interesting mechanical, acoustic, electrical or thermal properties. Beyond rapid prototyping and 3D printing of architected materials, polymer foams are mechanically self-assembled cellular materials for which reaching an unprecedented structural control would be highly beneficial: using bottom-up self-assembly is a key advantage in terms of production upscaling. However, the structure of foams is strictly constrained by capillary forces, and more specifically by Plateau’s laws.

The FOAMINT project aims to obtain new types of architectures of solid polymer foams through mechanical self-assembly of bubbles mixed with soft intruders, taking advantage of a competition between elasticity and capillarity in the liquid precursors of solid foams. These structures will be imposed not only by a minimization of interfacial energies (as for usual foams resulting from a liquid precursor for which an equilibrium state is reached before solidification), but by the combination of interfacial and elastic energies. This interdisciplinary strategy is designed to fill the gap between additive manufacturing (allowing to reach customizable structure but hard to upscale) and foam templating (easy to upscale but limited in terms of architectures). For a given foam, the geometry and elasticity of the intruders will be the key control parameters. The project will focus on model polyurethane foam-elastic intruder systems which allow to control all parameters explicitly, to highlight key underlying phenomena and provide a strategy that can then be extended to a larger range of systems.

More specifically, the methodology will be the following: to produce mechanical self-assemblies of bubbles and intruders, we will design millifluidic systems allowing the production of the different building blocks (polyurethane foams and elastic intruders), their mixing, the in-situ visualization of those complex systems, and their solidification. The temporal evolution of those assemblies will be quantified on systems with and without solidification, with and without the presence of intruders, including a careful analysis of all characteristic timescales involved in each system (solidification, ageing). Finally, we will work on mechanics and structural analysis of foam-intruder samples to establish the structure-property relations of those proof-of-concept solid foams. Mechanics will be assessed first in the linear elastic regime, and, in a longer term, for large deformations. Extension of those concepts to biomimetic or biomedical applications will also be explored.

Beyond fundamental understanding of foam-intruder systems, this project is expected to have applications and societal impact by providing a new route towards lightweight and stiff architected materials, promoting sustainability by minimizing raw material use and reducing weight. We also expect applications in the biomimetic and biomedical field, for which a detailed study of opportunities will be performed in this JCJC project. This FOAMINT project will also give a new dimension to the research activities of A. Hourlier-Fargette, allowing her to independently develop her research interests within the Institut Charles Sadron by taking advantage of her background in elastocapillarity (PhD), microfluidics (postdoc) and in foam physics (CR CNRS at ICS). In addition, it will benefit from local, national, and international collaborations.