Abstract
AbstractControlled self‐assembly of bio‐sourced nanocolloids is of high importance for the development of sustainable and low‐cost functional materials but controlling nanocomposite fabrication with both satisfactory optical properties and composition remains challenging. Silk fibroin (SF) and cellulose nanocrystals (CNCs) have independently demonstrated their ability to produce high‐quality photonic materials, in part due to their low absorbance and their transparency in the visible range. While SF is able to replicate inverse structures by high‐resolution nano‐templating, CNCs can spontaneously assemble into cholesteric liquid crystalline structures that are retained upon solvent evaporation, yielding photonic films. In this work, the conditions of successful co‐assembly of regenerated SF, extracted from silkworm silk, with CNCs extracted from cotton, are investigated. Their co‐assembly is investigated for various relative concentration ratios and pH, combining polarized optical microscopy and spectroscopy, SEM, and other characterization techniques (XRD, ATR‐FTIR, TGA). The appearance of photonic properties is observed when CNC and SF are assembled at pH ≥ 4.15, highlighting the importance of suppressing attractive electrostatic interactions between the two species for an organized structure to emerge. Beyond its fundamental motivations for colloidal co‐assembly with structural proteins, this work is relevant to design sustainable optical materials compatible with food packaging coatings and edible coloring pigments.
Highlights
The MIT Faculty has made this article openly available
The earlier report we found combining Silk fibroin (SF) and cellulose I into composite films for mechanical reinforcement is from Noishiki et al using cellulose nanocrystals (CNCs),[53] later followed by other groups, using either CNCs,[47,54,55,56,57] or cellulose nanofibrils (CNFs).[57,58,59,60,61]
SF presents an optical index (1.54) similar to the average optical index of CNCs films (1.555), which should benefit the optical properties of the composite.[62,63]. All these results indicate that SF and CNCs can bind strongly to one another, which suggests this could benefit the cohesion of composites in which the CNCs are self-assembled into a cholesteric order
Summary
The MIT Faculty has made this article openly available. Please share how this access benefits you. The conditions of successful co-assembly of regenerated SF, extracted from silkworm silk, with CNCs extracted from patibility for a successful one-pot co-assembly are not met, either no underlying order is preserved,[2,3] or the proposed preparation strategies have to circumvent the problem by introducing several additional steps relying cotton, are investigated. Their co-assembly is investigated for various relative on various post-treatments (e.g., swelling, concentration ratios and pH, combining polarized optical microscopy and spectroscopy, SEM, and other characterization techniques (XRD, ATR-FTIR, TGA). Introduction splinter-like nanoparticles, isolated from cotton or wood pulp and recently at an industrial scale,[10,11,12] can spontaneously organize
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