Structure Evolution and Drying Dynamics in Sliding Cholesteric Cellulose Nanocrystals

Chu, Guang; Vilensky, Rita; Vasilyev, Gleb; Martin, Patrick; Zhang, Rui‐Yan; Zussman, Eyal

doi:10.1021/acs.jpclett.8b00670

Cited by 32 publications

(34 citation statements)

References 43 publications

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“…A similar approach can be developed to account for additional shear experienced near the edge of the drying suspension. [18,65,92] Besides CNC self-assembly, it will be relevant to other liquid crystalline suspensions that recently triggered interest for their ability to form complex structures upon drying, [17] and can be easily adapted to incompressible liquid crystalline systems subject to a unidirectional mechanical strain. [93] The application of these general ideas can also be relevant to understand alternative self-assembly mechanisms involving unidirectional removal of the solvent such as in vacuum filtration or open ended capillaries.…”

Section: Discussionmentioning

confidence: 99%

Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying

Frka‐Petesic

Kamita

Guidetti

et al. 2019

Phys. Rev. Materials

109

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Cellulose nanocrystals (CNCs) are bio-sourced chiral nanorods that can form stable colloidal suspensions able to spontaneously assemble above a critical concentration into a cholesteric liquid crystal, with a cholesteric pitch usually in the micron range. When these suspensions are dried on a substrate, solid films with a pitch of the order of few hundreds of nanometers can be produced, leading to intense reflection in the visible range. However, the resulting cholesteric nanostructure is usually not homogeneous within a sample and comports important variations of the cholesteric domain orientation and pitch, which affect the photonic properties. In this work, we first propose a model accounting for the formation of the photonic structure from the vertical compression of the cholesteric suspension upon solvent evaporation, starting at the onset of the kinetic arrest of the drying suspension and ending when solvent evaporation is complete. From that assumption, various structural features of the films can be derived, such as the variation of the cholesteric pitch with the domain tilt, the orientation distribution density of the final cholesteric domains and the distortion of the helix from the unperturbed cholesteric case. The angular-resolved optical response of such films is then derived, including the iridescence and the generation of higher order reflection bands, and a simulation of the angular optical response is provided, including its tailoring under external magnetic fields. Second, we conducted an experimental investigation of CNC films covering a structural and optical analysis of the films. The macroscopic appearance of the films is discussed and complemented with angular-resolved optical spectroscopy, optical and electron microscopy, and our quantitative analysis shows an excellent agreement with the proposed model. This allows us to access the precise composition and the pitch of the suspension when it transited into a kinetically arrested phase directly from the optical analysis of the film. This work highlights the key role that the anisotropic compression of the kinetically arrested state plays in the formation of CNC films and is relevant to the broader case of structure formation in cast dispersions and colloidal self-assembly upon solvent evaporation.

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Section: Discussionmentioning

confidence: 99%

Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying

Frka‐Petesic

Kamita

Guidetti

et al. 2019

Phys. Rev. Materials

109

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“…To briefly recapitulate, the phase transitions during EISA and ensuing coffee rings can be described as follows: The chiral nematic liquid crystalline phase forms from a collection of merging spherical CNC assemblies or tactoids (Wang et al 2016). During drying of the CNC suspension, the tactoids follow the capillary flow towards the edge (Chu et al 2018), which is subjected to faster evaporation rates (Hu and Larson 2002). This results in tactoids that are kinetically confined at the air-water and watersubstrate interfaces, with their chiral nematic axes also trapped at random orientations at the coffee ring edge (Hsiao et al 2015).…”

Section: Coffee Ring Development In Square Filmsmentioning

confidence: 99%

“…1a, c, d). As the name indicates, the coffee ring effect refers almost exclusively to sessile drops with circular symmetry (Mu and Gray 2015;Gençer et al 2017Gençer et al , 2018Chu et al 2018). The fitting of asymmetry in the coffee ring development entice fundamental scientific inquiries that, simultaneously, may have far reaching applications in design, visual arts and related industries.…”

Section: Introductionmentioning

confidence: 99%

Asymmetrical coffee rings from cellulose nanocrystals and prospects in art and design

et al. 2018

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The iridescence displayed by films made from cellulose nanocrystals (CNCs) has long been the subject of fundamental research. This has expanded our understanding of colloidal self-assembly towards the development of advanced materials. However, the application of such findings is less reported for visual designs that exploit structural color. Aesthetic outputs are already in reach, but requires input from trend setters in the design and art industries. In this realm, the CNCbased iridescence uniquely offers broadband, multicolored reflections through the ''coffee ring'' effect, which arises upon evaporation-induced self-assembly (EISA). Although this effect has been thoroughly studied in the context of axisymmetric patterns, complex geometries remain to be evaluated for large-scale implementation. This is central to the present efforts, where EISA of CNC suspensions occurred onto noncircular surfaces. We used orientation-dependent contact angle measurements, profilometry and fixed-light source photography to unveil the effect of asymmetric drying fluxes at sharp angles, between 30°and 90°, on CNC particle deposition and resulting color patterns. We also demonstrate the causality between increased capillary fluxes and deposition with the help of modelling via energy minimization of the suspension volume onto a given surface and using the diffusion equation to obtain the local concentration of water vapor during EISA. Lastly, we study the effect of background reflections as well as light and temperature resistance of CNC-based reflectors, both important for any deployment. The results from this multidisciplinary effort, involving applied design, art and colloid chemistry, point to the excellent prospects of CNC films for the development of structured and chromatic patterns.

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“…As an example of such rods with negative surface charges, cellulose nanocrystals (CNCs) have recently attracted great interest due to their environmental friendly and abundant nature, biocompatibility and biodegradability, and their ability to self‐assemble into liquid crystalline order, combined with outstanding mechanical properties that make them attractive candidates as fillers in composites . CNC rods consist of parallel‐packed cellulose molecules held together by hydrogen bonds and hydrophobic interactions and thus can be considered as amphiphilic .…”

Section: Introductionmentioning

confidence: 99%

pH‐Controlled network formation in a mixture of oppositely charged cellulose nanocrystals and poly(allylamine)

Martin

Vasilyev

Chu

et al. 2019

J Polym Sci B Polym Phys

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The behavior of a mixture of negatively charged cellulose nanocrystals (CNCs) and positively charged poly(allylamine) (PAAm) is examined in aqueous media. By modulating the pH, the acting Coulomb forces can be varied that can lead not only to adsorption of PAAm chains on the CNC surface but also to the development of a supermolecular structure by bridging of CNC rods by extended PAAm chains. This bridging can result in the formation of CNC clusters, which was demonstrated experimentally. Light scattering and rheological studies showed that these clusters begin to grow and merge, ultimately forming a global percolated network above a critical degree of PAAm ionization.The adsorption of PEs on oppositely charged nanoparticles (cNPs) influences their net charges; charge neutralization causes van der Waals forces to dominate and consequently leads to aggregation of cNPs, whereas charge reversal stabilizes the colloidal suspension upon sufficient PE adsorption. 28 Under specific conditions, PEs can simultaneously adsorb on two (or maybe more) cNPs, generating "attractive" bridging forces between these particles. 29 The probability of such bridging interactions depends on the interparticle distance, the PE and nanoparticle charge densities, the PE chain length and stiffness, and the ionic strength of the solution. 30 Simulations of interactions between a cNP and an oppositely charged weak PE showed induced ionization and modification of the charge distribution along the charged chain. [31][32][33][34][35] To date, only a few works [36][37][38][39] have experimentally demonstrated bridging of cNPs by PEs. However, the effect of PE charge density on bridging between cNPs to ultimately form a global percolated network consisting of weak PEs and cNPs is so far unknown.Additional Supporting Information may be found in the online version of this article.

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Structure Evolution and Drying Dynamics in Sliding Cholesteric Cellulose Nanocrystals

Cited by 32 publications

References 43 publications

Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying

Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying

Asymmetrical coffee rings from cellulose nanocrystals and prospects in art and design

pH‐Controlled network formation in a mixture of oppositely charged cellulose nanocrystals and poly(allylamine)

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