Bio-inspired non-iridescent structural coloration enabled by self-assembled cellulose nanocrystal composite films with balanced ordered/disordered arrays

https://doi.org/10.1016/j.compositesb.2021.109456Get rights and content

Highlights

  • Low-/non-angle-dependent structural-color CNC composite films are fabricated.

  • Balanced ordered/disordered arrays are manipulated by co-assembly with PDDA.

  • The composite films can be used as colorimetric sensor.

Abstract

Cellulose nanocrystal (CNC) is an interesting polysaccharide nanomaterial that can self-assemble into a chiral nematic liquid crystalline structure in aqueous solution, producing brightly structural color upon selectively reflection of visible light. However, till now, only iridescent structural colors can be created by such colloidal array, making it impossible to be used as colorimetric sensors. Here, inspired by longhorn beetle having short-range ordered but long-range disordered microstructures, it is demonstrated to develop low-/non-angle-dependent structural-color CNC composite films through interference against the long-range orders as a result of introducing positively charged poly (dimethyl diallyl ammonium chloride) (PDDA). By exploring balanced ordered/disordered structures, vivid angle-independent structural colors are realized, enabling accurate cognition for environmental signals, which is crucial to promising applications in sensing, anti-counterfeit, and decoration technology.

Introduction

Brilliant structural colors existing widely in nature and living organisms, like butterfly wings, pearls, and peacock feathers, have attracted particular interest in wide applications of decoration, anti-counterfeiting and colorimetric sensing [[1], [2], [3], [4], [5], [6], [7], [8]]. Unlike pigment color and luminescence, structural coloration originates from diffraction, scattering and interference of light with periodic nanostructures. During past decades, a variety of nanoarrays with tunable size and spacing have been developed to generate iridescent structural colors in terms of the principle of Bragg reflection [[9], [10], [11], [12]]. For example, Duempelmann et al. presented a plasmonic color filter, capable of changing the output color by simple rotation of a polarizer [9]; Wang et al. prepared reversible full-color plasmonic cells/display by electrochemically controlling the structure of an Au/Ag core-shell nano-array [11]. Due to the long-range ordered arrangement of the materials, the anisotropic photonic band gap (PBG) appears, allowing light reflection at certain wavelengths [13]. With respect to such mechanism, these materials show changeable structural colors at different viewing angles, namely, iridescent colors.

Unlike the iridescent structural colors, vivid angle-independent structural colors are formed on the basis of amorphous arrays with merely short-range orders, which are found from blue integumentary of dragonfly as well as back contour feather barbs of bluebird [[14], [15], [16]]. Inspired by these creatures, Zhao et al. used barbs of blue parrot as a template to prepare three-dimensional macroporous SiO2 and TiO2 structures with a short-range order displaying blue colors [17]; Takeoka et al. prepared amorphous arrays of submicrometer-sized fine spherical silica colloidal particles [19]; Zhu et al. used two-step calcination to prepare noniridescent Air@C@TiO2 sphere [21]; Song's group fabricated brilliant noniridescent poly (styrene-methyl-methacrylate-acrylic acid) nanospheres doping with graphene nanosheets containing GQDs [22]. However, these low angle-dependent materials are prepared from regular nanoparticles based on either inorganic substances (e.g., SiO2, TiO2, and Cu2O) or non-renewable petroleum-based polymers (e.g., polydopamine, poly (methylmethacrylate) and polystyrene) [[17], [18], [19], [20], [21], [22], [23], [24]].

Featuring with renewability and sustainability, cellulose nanocrystal (CNC) has naturally occurring needle-like nanostructures with chirality [[25], [26], [27], [28], [29]]. Upon solvent evaporation at controlled conditions, interestingly, CNC tends to spontaneously assemble into a helical chiral nematic structure that enables brilliant iridescent structural coloration of resulting solid composite films [[30], [31], [32], [33], [34], [35], [36], [37], [38], [39]]. Until now, the iridescent CNC composite films have been explored as chemical, physical, and mechanical sensors. For example, MacLachlan's group introduced urea-formaldehyde and amino-formaldehyde resins into the CNC matrix, constructing mesoporous photonic CNC composite films sensitive to humidity and pressure [30]; Zhou et al. prepared humidity-responsive chiral nematic cellulose nanocrystal/poly (ethylene glycol) composite films [32]; He et al. introduced glycerol into CNC as a plasticizer to fabricate an environmental humidity-responsive composite film [33]; very recently, Tsukruk and co-workers reported a self-assembled carbon quantum dot-decorated CNC composite film with obviously enhanced fluorescence [35]. Wang et al. fabricated mechano-thermo-chromic hydrogels with uniform iridescent interference colors by locking of aligned CNC into poly(N-isopropylacrylamide) networks [38]. Unfortunately, the state of art of CNC composite films is still limited at iridescent structural colors, giving rise to serious judgment errors if using for optical sensing. Development of low-/non-angle-dependent structural-color materials from CNC is therefore urgently required but has not been reported yet.

Here, inspired by longhorn beetle, an insect with non-iridescent colors relying on an internal short-range ordered structure that generates isotropic PBG to allow multiple photon scattering (Fig. 1a), we propose a simple and effective strategy to construct non-iridescent structural-color CNC composite films by incorporating poly (dimethyl diallyl ammonium chloride) (PDDA) into the CNC array. Through electrostatic co-assembly of CNC and PDDA, the long-range ordered structure of CNC is destroyed, enabling the angle-independent colors. Due to the intercalation of PDDA into the interlayer of CNC as well as tunable nanostructures, the structural coloration is adjusted. Furthermore, the potential application of the resulting non-iridescent CNC composite film as a chromatic sensing material is investigated.

Section snippets

Materials

Cotton wool (product No. YZB/Chuan 0177-2013) was provided by Kangda Health Materials Co. (Sichuan, China). Sulfuric acid (CAS No. 7664-93-9) was purchased from Kelong Co. (Sichuan, China). Poly (dimethyl diallyl ammonium) chloride (PDDA, CAS No. 26062-79-3, Mw 100,000-200,000, 20 wt%) was purchased from Sigma-Aldrich. Acetic acid (CAS No. 64-19-7) was purchased from Chengdu Kelong Co. (Sichuan, China). These reagents were used without any further purification. Deionized (DI) water was obtained

Preparation of non-iridescent structural-color CNC films

Iridescent structural colors are formed by selective reflection of incident light with unique photonic nanostructures [40]. However, in the case of sensing applications, the strong angle-dependent coloration is highly unwanted because of inaccurate detection. A long-range disordered but short-range ordered structure is the key point for fabricating low angle-dependent structural-color materials [[17], [18], [19], [20], [21], [22], [23], [24],41]. In this work, therefore, the long-range ordered

Conclusion

In summary, a low-/non-angle-dependent structural-color CNC composite film is developed through co-assembly with PDDA. The introduction of PDDA induces structural transition of CNC from long-range order to long-range disorder but causes no changes of short-range order, thus non-iridescent structural colors are realized for the CNC/PDDA composite films in case of the PDDA amount over 1.13%. Due to the water sensitivity of CNC, such composite films can perceive water molecules in mixing solutions

Credit authorship contribution statement

Xiu Dong: Conceptualization, Methodology, Investigation, Writing-original draft. Ze-Lian Zhang: Development or design of methodology.Yu-Yao Zhao: Software, Investigation.Dong Li: Software, Investigation. Zi-Li Wang: Investigation.Chen Wang: Investigation.Fei Song: Conceptualization, Methodology, Investigation, Writing-editing, Funding acquisition. Xiu-Li Wang: Conceptualization, Supervision, Funding acquisition. Yu-Zhong Wang: Conceptualization, Supervision, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Key R & D Program of China (2020YFD1100702), the National Natural Science Foundation of China (Grants 52073189), Science and Technology Fund for Distinguish Young Scholars of Sichuan Province (2019JDJQ0025), State Key Laboratory of Polymer Materials Engineering (sklpme2020-3-09), and the Fundamental Research Funds for the Central Universities.

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