Marangoni Flow Manipulated Concentric Assembly of Cellulose Nanocrystals

Abstract

Tunable assembly of cellulose nanocrystals (CNCs) is important for a variety of emerging applications in optics, sensing, and security. Most exploited assembly and optical property of CNCs are cholesteric assembly and corresponding circular dichroism. However, it still remains challenge to obtain homogenous and high‐resolution cholesteric assembly. Distinct assembly and optical property of CNCs are highly demanded for advanced photonic materials with novel functions. Herein, a facile and programmable approach for assembling CNCs into a novel concentric alignment using capillary flow and Marangoni effect, which is in strike contrast to conventional cholesteric assembly, is demonstrated. The concentric assembly, as quantitatively evidenced by polarized synchrotron radiation Fourier transform infrared imaging, demonstrates Maltese cross optical pattern with good uniformity and high resolution. Furthermore, this Maltese cross can be readily regulated to “on/off” states by temperature. By combining with 3D inkjet technology, a functional binary system composed of “on”/“off” CNCs optical patterns with high spatial resolution, fast printing speed, good repeatability, and precisely controllable optical property is established for information encryption and decryption. This concentric assembly of CNCs and corresponding tunable optical property emerge as a promising candidate for information security, anticounterfeiting technology, and advanced optics.

Fast Self‐Assembly of Photonic Crystal Hydrogel for Wearable Strain and Temperature Sensor

“…[12] Benefiting from structure colors, numerous visual devices, such as actuators, [14] flexible electronics, [15,16] strain sensors, [17][18][19] and other sensors [20,21] have been developed to monitor human motions, [15,16,22] temperature, [23,24] pH, [24] chemical sensing, [25][26][27] and cell monitoring. [28] At present, structure colors are obtained mainly via two schemes, including top-down fabrications such as direct laser writing, [29] nanoimprinting, [30] solvent release, [31] and bottom-up methods such as the self-assembly of nanoparticles (NPs), [32][33][34][35] cellulose nanocrystals, [36][37][38] block copolymers, [24,39] under capillary force [40,41] or external forces. [42,43] However, the former methods generally require the assistance of sophisticated and expensive equipment, whereas the latter methods generally take a long period from days [14,44] to weeks [24,45,46] with precise environmental control.…”

Cellulose‐Based Soft Actuators

“…property established for information encryption and decryption, Shao et al introduce the Marangoni effect and capillary flow for controlling assembly of the carboxyl modified CNC(M-CNCs) within evaporating of sessile droplets. [130] Through 3D inkjet printing technology, M-CNCs built a circular shaped micro film array with precisely controlled position, on/off property, and quick fabrication speed. Based on M-CNCs films with on and off Maltese cross optical patterns, a QR code with a 105 × 105 pixels array was constructed by drying at 35 and 25 °C, respectively.…”

“…To precisely control the optical Reproduced with permission. [130] Copyright 2021, John Wiley and Sons; b) Single pattern anticounterfeiting experiment. c) Double patterns anticounterfeiting effect of CNC/PAA10 iridescent coating, respectively.…”

“…Figure 12. a) Encryption and decryption of security QR label created by M-CNCs patterns in a 105 × 105 "pixelated" array fabricated through 3D inkjet printing.Reproduced with permission [130]. Copyright 2021, John Wiley and Sons; b) Single pattern anticounterfeiting experiment.…”

Programmable Birefringent Patterns from Modulating the Localized Orientation of Cellulose Nanocrystals

“…However, most of the current explorations focus on their cholesteric structure and corresponding circular dichroism, which can be spontaneously formed due to the twisting morphology of a single nanocrystal. , Varied approaches have been applied to tune the pitch and tactoid orientation for improving their chiral optical properties, including magnetic and electric alignment, , geometry confinement with a microfluid channel or templates, − co-assembly with inorganic particles or polyols, ,, and mechanical stretching . In contrast, only a few works have reported on cellulose-based birefringent structures, mainly fabricated by mechanical stretching of regenerated cellulose hydrogels or CNC/polymer composition, ,, surface tension directing, and hydrodynamic shearing . The obtained birefringent structures, usually with CNCs ordered in unidirectional or radical orientation, result in tunable interference colors.…”