From Stimuli-Responsive to Renewable Materials
Responsive materials, which change their properties in response to an external stimulus (e.g. temperature, light, chemical changes) in a predictable manner, allow accomplishing complex tasks such as actuation, switchable wettability, and sensing. The incorporation of dynamic bonds, which can rely on either non-covalent or covalent interactions, into polymers have been widely exploited to impart these new material functionalities. Due to their tunable interaction strength and reversibility, dynamic interactions can enhance the mechanical properties and processability of functional materials, thus making them an attractive alternative to classical covalent linkages. In this presentation, several approaches that exploit supramolecular interactions to prepare polymer materials exhibiting a macroscopic optical response upon mechanical activation are introduced. These so-called mechanochromic systems play an important role for the detection of excessive stress experienced by a material and can thus prevent catastrophic failure. As another example, dynamic covalent chemistry was employed to functionalize the surface of cellulose nanocrystals (CNCs) under melt processing conditions as a sustainable route for the preparation of homogeneous and mechanically enhanced bio-based polymer composites. While CNCs have shown outstanding reinforcement capabilities when used as a filler in a range of polymer matrices, their dispersion remains one of the biggest obstacles for the technological exploitation of such composites. It is shown that the thermal dissociation of dynamic covalent motifs under melt processing conditions and reaction of the resulting products with the hydroxyl groups present on the surface of CNCs can be used to functionalize such nanoparticles in situ with molecules of choice. This process was used to modify the surface of the CNCs with small molecules and polymeric species, leading to a significant mechanical reinforcement of composites materials thus produced. This concept potentially opens the door to an industrially scalable sustainable approach towards the development of nanocellulose bio-composites.
Bio: Céline was born and grew up in La Chaux-De-Fonds, Switzerland. She received her MS degree from the department of Chemistry at the University of Fribourg, Switzerland, with a focus in organic synthesis, polymer chemistry, and materials science. She completed her master’s thesis at Asulab, a division of The Swatch Group R&D Ltd, investigating the formation of homogeneous and resistant anchor layers on the surface of watch components, and on the introduction of the epilam (anti-spreading agent) effect using controlled polymerization processes via “grafting from” and “grafting to” methods. Céline stayed in Fribourg to pursue her PhD in polymer chemistry and materials at Adolphe Merkle Institute under the supervision of Prof. Christoph Weder. Her thesis focused on the design of chromogenic systems relying on supramolecular interactions and on their incorporation into polymeric materials to create new functional mechanoresponsive materials. Céline joined the group of Stuart Rowan at Pritzker School of Molecular Engineering, at the University of Chicago, as a postdoctoral fellow with a SNFS Mobility Fellowship seeking to enhance her knowledge on the preparation and the use of cellulose nanocrystals, dynamic covalent bonds and materials engineering. Her ongoing research focuses on the use of dynamic covalent chemistry to functionalize cellulose nanocrystals and on the development of appropriate engineering melt processes for the preparation of mechanically reinforced and sustainable nanocomposite materials.