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Supramolecular Engineering of Hierarchically Self-Assembled, Bioinspired, Cholesteric Nanocomposites Formed by Cellulose Nanocrystals and Polymers
journal contribution
posted on 2016-04-12, 00:00 authored by Baolei Zhu, Remi Merindol, Alejandro J. Benitez, Baochun Wang, Andreas WaltherNatural
composites are hierarchically structured by combination
of ordered colloidal and molecular length scales. They inspire future,
biomimetic, and lightweight nanocomposites, in which extraordinary
mechanical properties are in reach by understanding and mastering
hierarchical structure formation as tools to engineer multiscale deformation
mechanisms. Here we describe a hierarchically self-assembled, cholesteric
nanocomposite with well-defined colloid-based helical structure and
supramolecular hydrogen bonds engineered on the molecular level in
the polymer matrix. We use reversible addition–fragmentation
transfer polymerization to synthesize well-defined hydrophilic, nonionic
polymers with a varying functionalization density of 4-fold hydrogen-bonding
ureidopyrimidinone (UPy) motifs. We show that these copolymers can
be coassembled with cellulose nanocrystals (CNC), a sustainable, stiff,
rod-like reinforcement, to give ordered cholesteric phases with characteristic
photonic stop bands. The dimensions of the helical pitch are controlled
by the ratio of polymer/CNC, confirming a smooth integration into
the colloidal structure. With respect to the effect of the supramolecular
motifs, we demonstrate that those regulate the swelling when exposing
the biomimetic hybrids to water, and they allow engineering the photonic
response. Moreover, the amount of hydrogen bonds and the polymer fraction
are decisive in defining the mechanical properties. An Ashby plot
comparing previous ordered CNC-based nanocomposites with our new hierarchical
ones reveals that molecular engineering allows us to span an unprecedented
mechanical property range from highest inelastic deformation (strain
up to ∼13%) to highest stiffness (E ∼
15 GPa) and combinations of both. We envisage that further rational
design of the molecular interactions will provide efficient tools
for enhancing the multifunctional property profiles of such bioinspired
nanocomposites.
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Keywords
polymer fractionSupramolecular Engineeringphotonic responsecholesteric nanocompositecombinationbioinspired nanocompositesmultifunctional property profilesproperty rangeAshby plotCholesteric NanocompositesCellulose Nanocrystalssupramolecular motifsstructure formationfunctionalization densitycholesteric phasesengineer multiscale deformation mechanismshierarchicallytoollength scalesinelastic deformationpolymer matrixPolymers Natural compositesbiomimetic hybridshydrogen bondssupramolecular hydrogen bondsCNChelical pitchcellulose nanocrystals
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