Reprogrammable and Light-Adaptive Mechanical Gradients in Waterborne High-Performance Nanocellulose Materials

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Mechanical gradients are ubiquitous in nature (attachment of ligaments to bones) and serve stress delocalization and optimize mechanical properties with regard to toughness, stiffness and abrasion resistance. They are inspiring for future synthetic materials in both structural as well as functional applications, where they can provide tougher joints between stiff and elastic materials, allow morphing procedures in structured, responsive hydrogels, or instruct cell fate and migration. Conceptually, gradient materials can be divided into (i) lateral and sandwich type gradients, (ii) 2D versus 3D patterned materials, and (iii) in terms of complexity from a one-time, irreversibly written gradient to a reprogrammable/rewritable gradient to an adaptive gradient. The central aim of this proposal is to implement, understand and exploit one-way and reversible photochemical conjugations to structure permanent, reprogrammable and light adaptive lateral gradients in mechanical properties to engineer mechanically superior and transparent hybrid nanopapers composed of highly defined complementary cellulose nanofibrils and polymers. We focus on three generations of CNF/polymer hybrid nanopapers with evolving complexity and property levels: (i) One-way gradients with self-reporting and irreversible photo-conjugations, (ii) Rewritable gradients using reversible photo-conjugations, (iii) Light-adaptive mechanical gradients exploiting the dynamics of reversible photo-conjugations. To address these interdisciplinar and multiscale challenges, we forge a coherent consortium of two complementary research groups to merge the required expertise in highly efficient photochemistry, precision macromolecular synthesis and surface engineering (Barner-Kowollik, KIT) with nanocellulose, colloid science, biomimetic nanocomposites and advanced mechanical testing (Walther, DWI). Jointly we aim at an integral understanding from the fundamental kinetics of the photochemical reactions via nano-/meso-/top-down structuring to molecularly controlled complex macroscale mechanical properties.