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

Abstract

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.

Exploiting Supramolecular Interactions from Polymeric Colloids for Strong Anisotropic Adhesion between Solid Surfaces

“…The process is entirely green as it uses bio‐colloids and water for the formation of the adhesive layer. However, the assembly duration is relatively high (bonding time between 2 and 6 h) compared with some structural adhesives or microfabricated dry adhesives (bonding time of a few seconds), but relatively shorter than more common structural adhesives that cure over 24 h. However, the evaporative flux density distribution across the evaporating interface under confinement having a higher degree of symmetry compared, for instance, with sessile drops32 suggests that increasing evaporation rate with temperature or by adding co‐solvents would still result in highly ordered microstructures. This is further supported by the apparent absence of chiral nematic order even in samples assembled from fully dispersed solutions, suggesting a dominant effect from the drying fluxes.…”

Infiltration of Proteins in Cholesteric Cellulose Structures

“…The films were photographed using the setup described in a previous work. 58 The brightness and contrast of the images were adjusted using Adobe Photoshop software. In addition, low-magnification (8×) and high-resolution (6000 × 4000) microscope images were acquired for some films, using an Olympus SZX10 optical microscope used in the reflection mode.…”

Plant Nanomaterials and Inspiration from Nature: Water Interactions and Hierarchically Structured Hydrogels

“…[ 2,205 ] These two properties are typically exploited in nature to form materials with high fracture resistance and specific nonfading colors. [ 206–208 ] Chiral nematic order occurs due to the lyotropic liquid‐crystal transitions of CNC dispersions above a given threshold, where water interactions are optimized through the phase transitions occurring as water is evaporated or removed. Chiral nematically arranged gels are typically obtained by arresting evaporation at a given concentration, depending on the physicochemical properties of the CNC ( Figure a).…”