Orientation Of Cellulose Nanocrystals Research Articles

Plasmonic metasurfaces of cellulose nanocrystal matrices with quadrants of aligned gold nanorods for photothermal anti-icing

Cellulose nanocrystals (CNCs) are intriguing as a matrix for plasmonic metasurfaces made of gold nanorods (GNRs) because of their distinctive properties, including renewability, biodegradability, non-toxicity, and low cost. Nevertheless, it is very difficult to precisely regulate the positioning and orientation of CNCs on the substrate in a consistent pattern. In this study, CNCs and GNRs, which exhibit tunable optical and anti-icing capabilities, are employed to manufacture a uniform plasmonic metasurface using a drop-casting technique. Two physical phenomena—(i) spontaneous and rapid self-dewetting and (ii) evaporation-induced self-assembly—are used to accomplish this. Additionally, we improve the CNC-GNR ink composition and determine the crucial coating parameters necessary to balance the two physical mechanisms in order to produce thin films without coffee rings. The final homogeneous CNC-GNR film has consistent annular ring patterns with plasmonic quadrant hues that are properly aligned, which enhances plasmonic photothermal effects. The CNC-GNR multi-array platform offers above-zero temperatures on a substrate that is subcooled below the freezing point. The current study presents a physicochemical approach for functional nanomaterial-based CNC control.

Mechanical responsive visible structural colors based on chiral-nematic cellulose nanocrystals photonic hydrogels

It has been extensively reported that cellulose nanocrystals (CNCs) are capable of exhibiting structural colors due to their unique chiral nematic self-assembly. However, further investigation is required to effectively utilize these remarkable properties for addressing real-world challenges, such as development of advanced materials like mechanical sensors and smart wearable devices. One particular challenge has been maintaining the refractive properties of structural colors resulting from the CNCs structure within the visible spectrum. In this study, we introduce a one-step hydrogel fabrication method involving chiral nematic CNC films embedded within poly(acrylic acid). These hydrogels exhibit naked-eye-visible structural colors and exhibit responsiveness to mechanical stresses. The resulting photonic hydrogels exhibit a blue shift in response to mechanical stretching. The hydrogels demonstrated self-recovery capabilities, as observed through cyclic loading–unloading stress tests. The color of the materials was characterized using UV–Vis spectroscopy to determine the wavelength of the reflected light. Additionally, we investigated the mechanism of CNCs orientation change using 2D-X-ray diffraction. Demonstrated by our simulation study, the morphology of the CNC bundles significantly influenced the characteristics of the chiral nematic structure as they orient due to the force application. Notably, the color change of the photonic hydrogels was reversible within the optimal range of applied force and can be repeated numerous times. This work presents a new strategy for fabricating optically functional photonic hydrogels with stimuli-responsive properties, enabling their potential applications in biomedical engineering and wearable responsive sensor technologies.

Uniaxial orientation of cellulose nanocrystals by zone-casting technique

Cellulose nanocrystals (CNCs) are biomass-based nanoparticles with attractive properties. Using a zone-casting technique, transparent films 2 cm wide and 4 cm long, and 2 µm thick, with uniaxially oriented CNCs were prepared from aqueous suspension of CNCs. The nanocrystals were aligned within the entire film perpendicular to the zone-casting direction. The orientation of the CNCs was confirmed by polarized light microscopy, X-ray diffraction and atomic force microscopy. The intensity of the light transmitted through the films depended on its polarization direction and was the strongest for the light polarized perpendicularly to the crystal orientation direction. The orientation of CNCs in the films resulting in optical anisotropy makes them promising materials for applications in optoelectronics.

Cellulose nanocrystals lime mortar based on biomimetic mineralization

Sticky rice-lime mortar has been widely used in the construction of traditional buildings. It has been known as the best available material for restoring ancient buildings. However, it is unbenevolent to use edible sticky rice for a large scale restoration considering hunger crises. In addition, the component of sticky rice is complex, the mechanism of how sticky rice mediates the properties of lime mortar is still unclear. In this work, as a kind of abundant, inedible and single-component polysaccharide, nematic cellulose nanocrystals (CNCs) were used to prepare lime mortars. The characteristics, such as compressive strength, molar percent of calcium carbonate, microscopic morphology, of lime mortars were characterized to explore the function of CNCs in lime mortars. Compressive strength is related to molar percent of calcium carbonate and the organization of CNCs. The main polymorph of calcium carbonate is calcite. Rod-like CNCs orient themselves in one direction and control calcium carbonate to grow along the particular direction of CNCs orientation based on biomimetic mineralization. External force field further organizes CNCs and the growth of calcium carbonate. It is promising to restore ancient building with lime mortar containing CNCs since the properties, such as compressive strength and polymorph of calcium carbonate, of lime mortar added CNCs are similar to that of traditional sticky rice-lime mortar. Additionally, the mechanism of biomimetic mineralization process of CNCs is clear. Our work opens a way to develop traditional material with new technology and new materials.

Microscale 3D Printing and Tuning of Cellulose Nanocrystals Reinforced Polymer Nanocomposites.

The increasing demand for functional materials and an efficient use of sustainable resources makes the search for new material systems an ever growing endeavor. With this respect, architected (meta-)materials attract considerable interest. Their fabrication at the micro- and nanoscale, however, remains a challenge, especially for composites with highly different phases and unmodified reinforcement fillers. This study demonstrates that it is possible to create a non-cytotoxic nanocomposite ink reinforced by a sustainable phase, cellulose nanocrystals (CNCs), to print and tune complex 3D architectures using two-photon polymerization, thus, advancing the state of knowledge toward the microscale. Micro-compression, high-res scanning electron microscopy, (polarised) Raman spectroscopy, and composite modeling are used to study the structure-property relationships. A 100% stiffness increase is observed already at 4.5 wt% CNC while reaching a high photo-polymerization degree of ≈80% for both neat polymers and CNC-composites. Polarized Raman and the Halpin-Tsai composite-model suggest a random CNC orientation within the polymer matrix. The microscale approach can be used to tune arbitrary small scale CNC-reinforced polymer-composites with comparable feature sizes. The new insights pave the way for future applications where the 3D printing of small structures is essential to improve performances of tissue-scaffolds, extend bio-electronics applications or tailor microscale energy-absorptiondevices.

Programmable Birefringent Patterns from Modulating the Localized Orientation of Cellulose Nanocrystals.

Birefringence has been attracting broad attention due to its strong potential for applications in biomedicine and optics, such as biomedical diagnosis, colorimetric sensing, retardant, and polarization encoding. However, engineering architectures with precisely controllable birefringence remains a challenge due to the lack of effective modulation of the localized orientation. Here, by taking advantage of the inherently one-dimensional (1D) anisotropic structure of cellulose nanocrystals (CNCs), we demonstrate an approach to tune the alignment of CNCs with a well-controllable orientation at localized preciseness, which is in contrast to the previously reported unidirectional/radical orientation of CNC-based birefringent structures. The localized modulation of CNC orientation is facilitated by directing the 1D nanocrystals to align along the template periphery and the migrated three-phase contact line during the evaporation. The resultant CNC films exhibit birefringent extinction patterns under polarized light, in which versatile pattern designs can be obtained by employing templates with different shapes and template arrays with varied layouts. Due to the locally modulated orientation of CNCs, the films indicate "kaleidoscope-like" dynamically transformable designs of the birefringent patterns depending on the polarized angle, which has barely been observed previously. Furthermore, an N-nary encoding system for abundant information storage is demonstrated based on the sunlight-transparent CNC films, but with visible extinction patterns under polarized light, which is promising for encryptions, anticounterfeiting, and imaging, enriching the attractive research area of bio-based photonics.

Microstructure and dynamics of nanocellulose films: Insights into the deformational behavior

Cellulose nanocrystals (CNCs) thin films draw considerable interest in engineering and technological applications due to their excellent mechanical and physical properties associated with dynamic and microstructural features. Here, we employ coarse-grained molecular dynamics (CG-MD) simulations to investigate how the dynamics and microstructure change in the CNC films under tensile deformation. Our results show that the Young’s modulus can be quantitatively predicted by the power-law scaling relationship with initial packing density, where higher density leads to an increase in both modulus and strength. By evaluating the molecular local stiffness during the tensile process, our findings show that CNC film with a higher density exhibits a higher degree of dynamic heterogeneity, which is greatly reduced under deformation. Our results further demonstrate that randomly oriented CNCs tend to be more aligned with the tensile direction associated with higher free volume and porosity during the deformation; however, the dynamics of CNC is more associated with the degree of local packing and density rather than the CNC orientation. Our study provides fundamental insights into deformational mechanisms associated with the microstructure and dynamics of CNC films at a molecular level, aiding in the tailored design of cellulose-based materials for their mechanical performance.

Orientation of Cellulose Nanocrystals Controlled in Perpendicular Directions by Combined Shear Flow and Ultrasound Waves Studied by Small-Angle X-ray Scattering

The combined effect of shear flow and ultrasound (US) waves on the dynamical structural orientations of cellulosic cholesteric liquid crystals was investigated by time-resolved, in situ small-angle X-ray scattering (SAXS). A dedicated channel-type shear flow/ultrasound cell for SAXS characterization was developed to simultaneously generate a shear flow-induced horizontal stress force and a US-induced vertical acoustic radiation force. The control of the alignment of anisometric cellulose nanocrystals (CNCs), with their director parallel to the ultrasonic wave direction of propagation, was revealed at an unprecedented nanometer scale. Concurrently, the application of shear flow induced a horizontal orientation of CNCs with their directors aligned along the velocity direction. By adjusting the level of simultaneously applied shear flow and US intensity to the CNC suspensions, it was possible to tune the direction and the level of orientation of the CNCs during a period of time. For a specific ratio of the applied shear rate to acoustic power, some transient orientation of the CNCs at an intermediate angle between horizontal and vertical directions was evidenced. Relaxation of these orientations’ phenomena upon cessation of flow and/or US was also highlighted.

Multi-axis alignment of Rod-like cellulose nanocrystals in drying droplets

HypothesisRadial capillary flow in evaporating droplets carry suspended nanoparticles to its periphery where they are deposited and form a coffee-ring. Rod-like nanoparticles seeking to minimize their capillary energy will align with their long-axis parallel to the contact line. Particles exhibiting electrostatic repulsion, such as cellulose nanocrystals (CNCs), establish a competition between capillary flow-induced impingement against a growing coffee-ring and entropic minimization leading to enhanced particle mobility. Therefore, balancing these effects by manipulating the local particle concentration in drying droplets should result in deposition with a controlled orientation of CNCs. ExperimentsThe dynamic local order in aqueous suspensions of CNCs in evaporating sessile droplets was investigated through time-resolved polarized light microscopy. The spatial distribution of alignment in deposited CNCs was explored as a function of nanoparticle concentration, droplet volume, initial degree of anisotropy, and substrate hydrophobicity. Computational analysis of the rotational Péclet number during evaporation was also investigated to evaluate any effects of shear-induced alignment. FindingsMultiple modes of orientation were identified suggesting local control over CNC orientation and subsequent properties can be attained via droplet-based patterning methods. Specifically, high local particle concentrations led to tangential alignment and lower local particle concentrations resulted in new evidence for radial alignment near the center of dried droplets.

A Combined Theoretical and Experimental Study of the Polymer Matrix-Mediated Stress Transfer in a Cellulose Nanocomposite

We study composites of cellulose nanocrystals (CNCs) in an ionomer matrix of poly(ethylene-stat-sodium acrylate) and find that direct cellulose/cellulose interactions in the composite are not a requirement for achieving reinforcement. While isotropic composites only show a slightly enhanced stiffness compared to the neat ionomer, a more substantial increase in Young’s modulus by a factor of up to 5 is achieved by uniaxial alignment of the composites through melt spinning. The orientation of CNC in melt-spun composites reduces the probability of cellulose/cellulose interactions, which suggests that cellulose/polymer interactions must be present that lead to the observed reinforcement. Molecular dynamics simulations confirm strong cellulose/polymer interactions in the form of ionic interactions as well as hydrogen bonding. These cellulose/polymer interactions facilitate efficient stress transfer, leading to the high reinforcing effect of CNC, while cellulose/cellulose interactions play a minor role in the mechanical response of the composite.

Actuation of Three‐Dimensional‐Printed Nanocolloidal Hydrogel with Structural Anisotropy

AbstractPolymer hydrogels exhibit actuation properties that result in reversible shape transformations and have promising applications in soft robotics, drug delivery systems, sensors, and microfluidic devices. Actuation occurs due to differential hydrogel swelling and is generally achieved by modulating hydrogel composition. Here a different approach to hydrogel actuation that originates solely from its structural anisotropy is reported. For 3D‐printed single‐layer hydrogels formed by cellulose nanocrystals (CNCs) and gelatin methacryloyl it is shown that shear‐induced orientation of CNCs results in anisotropic mechanical and swelling properties of the hydrogel. Upon swelling in water, planar hydrogels acquire multiple complex 3D shapes that are achieved by i) varying CNC orientation with respect to the shape on the hydrogel sheet and ii) patterning the hydrogel with the regions of shear‐mediated and random CNC orientation. This study shows the capability to generate multiple shapes from the same hydrogel actuator based on the degree of its structural anisotropy. In addition, it introduces a biocompatible nanocolloidal ink with shear‐thinning and self‐healing properties for additive manufacturing of hydrogel actuators.

Magnetic field effects on cellulose nanocrystal ordering in a non-aqueous solvent

Cellulose nanocrystals (CNCs) are rod-shaped particles that can self-assemble into a chiral nematic phase at certain contents. Due to their negative diamagnetic susceptibility and high aspect ratio, the structure of the chiral nematic phase of CNC suspensions can be manipulated using a magnetic field, which is a promising path to extending local order to a larger scale. The ability to manipulate CNCs in non-aqueous solvents is critically needed to incorporate them in a wide range of polymers. So far, magnetic field-induced manipulation of CNCs in suspension was reported for aqueous suspensions only, whereas a much-needed similar study for non-aqueous solvents has not been reported to the best of our knowledge. In this paper, we investigate the CNC ordering in n-methylformamide (NMF) under a 0.7 T magnetic field and compare it to the order achieved in H2O. The formation of a well-defined chiral nematic phase and its viscosity have a significant influence on the rate and extent of the field-induced orientation of CNCs. A clearly formed chiral nematic phase has a high potential for increased levels of field-induced ordering. And the chiral nematic phase with the lowest viscosity showed the largest increase in ordering when the magnetic field is applied before reaching equilibrium and plateauing. In contrast, the higher viscosity suspensions exhibited limited temporal changes after the initial field effect. These findings will facilitate the fabrication of globally ordered CNCs in a variety of polymers under a magnetic field, which is a necessary step to expanding the engineering applications of large-scale cellulose-based composites with anisotropic properties.

Plant cell wall inspired xyloglucan/cellulose nanocrystals aerogels produced by freeze-casting

Cellulose nanocrystals (CNC) and xyloglucan (XG) were used to construct new aerogels inspired by the hierarchical organization of wood tissue, i.e., anisotropic porous cellular solid with pore walls containing oriented and stiff cellulose nanorods embedded in hemicellulose matrix. Aerogels with oriented or disordered pores were prepared by directional and non-directional freeze-casting from colloidal dispersions of XG and CNC at different ratios. XG addition induced a clear improvement of the mechanical properties compared to the CNC aerogel, as indicated by the Young modulus increase from 138 kPa to 610 kPa. The addition of XG changed the pore morphology from lamellar to alveolar and it also decreased the CNC orientation (the Hermans’ orientation factor was 0.52 for CNC vs 0.36−0.40 for CNC-XG). The aerogels that contained the highest proportion of XG also retained their structural integrity in water without any chemical modification. These results open the route to biobased water-resistant materials by an easy and green strategy based on polymer adsorption rather than chemical crosslinking.

Effects of aspect ratio and crystal orientation of cellulose nanocrystals on properties of poly(vinyl alcohol) composite fibers

This work reports a study on the effects of different types and aspect ratios of cellulose nanocrystals (CNCs) on properties of poly (vinyl alcohol) (PVA) composite fibers. CNCs were extracted from wood pulp and cotton and reinforced into PVA to produce fibers by dry-jet-wet spinning. The fibers were collected as-spun and with the first stage drawing up to draw ratio 2. The elastic modulus and tensile strength of the fibers improved with increasing CNC content (5–15 wt. %) at the expense of their strain-to-failure. It was also observed that the mechanical properties of fibers reinforced with cotton CNC were higher than the fibers with wood CNC at the same amount of CNCs due to their higher aspect ratio. The degree of orientation along the spun fiber axis was quantified by 2D X-ray diffraction. As expected, the CNC orientation correlates to the mechanical properties of the fibers. Micromechanical models were used to predict the fiber performance and compare with experimental results. Finally, surface and cross-sectional morphologies of fibers were analyzed by scanning electron microscopy and optical microscopy.

Dynamics of Cellulose Nanocrystal Alignment during 3D Printing.

The alignment of anisotropic particles during ink deposition directly affects the microstructure and properties of materials manufactured by extrusion-based 3D printing. Although particle alignment in diluted suspensions is well described by analytical and numerical models, the dynamics of particle orientation in the highly concentrated inks typically used for printing via direct ink writing (DIW) remains poorly understood. Using cellulose nanocrystals (CNCs) as model building blocks of increasing technological relevance, we study the dynamics of particle alignment under the shear stresses applied to concentrated inks during DIW. With the help of in situ polarization rheology, we find that the time period needed for particle alignment scales inversely with the applied shear rate and directly with the particle concentration. Such dependences can be quantitatively described by a simple scaling relation and qualitatively interpreted in terms of steric and hydrodynamic interactions between particles at high shear rates and particle concentrations. Our understanding of the alignment dynamics is then utilized to estimate the effect of shear stresses on the orientation of particles during the printing process. Finally, proof-of-concept experiments show that the combination of shear and extensional flow in 3D printing nozzles of different geometries provides an effective means to tune the orientation of CNCs from fully aligned to core-shell architectures. These findings offer powerful quantitative guidelines for the digital manufacturing of composite materials with programmed particle orientations and properties.

Rheological behavior of cellulose nanocrystal suspensions in polyethylene glycol

The rheological behavior of cellulose nanocrystals (CNCs) in polar media based on polyethylene glycol (PEG) was investigated from aqueous suspensions to nanocomposites. The aim of this work is to improve our knowledge on the CNC behavior in polymer media and develop rheological indices to characterize the dispersion of nanoparticles in polymer matrices. CNCs were obtained from sulfuric acid hydrolysis of wood pulp and supplied after a spray- or freeze-drying process. Ultrasonication was used to break agglomerates and disperse CNCs in aqueous suspensions before mixing with an aqueous PEG solution at room temperature. The samples were subsequently dried and compression molded. From capillary and oscillatory shear rheology, no adsorption of PEG chains on CNCs could be detected, as many had previously hypothesized. The increase of PEG concentration in aqueous suspension favored the gelation by depletion effect and suggested CNC orientation. Viscoelastic properties and transmission electronic images of PEG/CNC nanocomposites highlighted the formation of a percolated network of CNCs for low concentrations ≥ 0.15 vol. %. From the model of Shih et al., a fractal dimension of 2 was obtained for these percolated nanocomposites, suggesting a 2D network of CNCs in the PEG matrix.

Order and gelation of cellulose nanocrystal suspensions: an overview of some issues.

Cellulose nanocrystals (CNCs) are polydisperse rod-shaped particles of crystalline cellulose I, typically prepared by sulfuric acid hydrolysis of natural cellulose fibres to give aqueous colloidal suspensions stabilized by sulfate half-ester groups. Sufficiently dilute suspensions are isotropic fluids, but as the concentration of CNC in water is increased, a critical concentration is reached where a spontaneously ordered phase is observed. The (equilibrium) phase separation of the ordered chiral nematic phase is in competition with a tendency of the CNC suspension to form a gel. Qualitatively, factors that reduce the stability of the CNC suspension favour the onset of gelation. The chiral nematic structure is preserved, at least partially, when the suspension dries. Solid chiral nematic films of cellulose are of interest for their optical and templating properties, but the preparation of the films requires improvement. The processes that govern the formation of solid chiral nematic films from CNC suspensions include phase separation, gelation and also the effects of shear on CNC orientation during evaporation. Some insight into these processes is provided by polarized light microscopy, which indicates that the relaxation of shear-induced orientation to give a chiral nematic structure may occur via an intermediate twist-bend state.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

Injectable Anisotropic Nanocomposite Hydrogels Direct in Situ Growth and Alignment of Myotubes.

While injectable in situ cross-linking hydrogels have attracted increasing attention as minimally invasive tissue scaffolds and controlled delivery systems, their inherently disorganized and isotropic network structure limits their utility in engineering oriented biological tissues. Traditional methods to prepare anisotropic hydrogels are not easily translatable to injectable systems given the need for external equipment to direct anisotropic gel fabrication and/or the required use of temperatures or solvents incompatible with biological systems. Herein, we report a new class of injectable nanocomposite hydrogels based on hydrazone cross-linked poly(oligoethylene glycol methacrylate) and magnetically aligned cellulose nanocrystals (CNCs) capable of encapsulating skeletal muscle myoblasts and promoting their differentiation into highly oriented myotubes in situ. CNC alignment occurs on the same time scale as network gelation and remains fixed after the removal of the magnetic field, enabling concurrent CNC orientation and hydrogel injection. The aligned hydrogels show mechanical and swelling profiles that can be rationally modulated by the degree of CNC alignment and can direct myotube alignment both in two- and three-dimensions following coinjection of the myoblasts with the gel precursor components. As such, these hydrogels represent a critical advancement in anisotropic biomimetic scaffolds that can be generated noninvasively in vivo following simple injection.

Orientation and interfacial stress transfer of cellulose nanocrystal nanocomposite fibers

Orientation and interfacial stress transfer in cellulose nanocrystals (CNC) reinforced polyacrylonitrile (PAN) nanocomposite fibers were determined by Raman spectroscopy. The 1095 cm−1 Raman band was used to quantify the orientation of CNC in composite fiber. Under VV (vertical/vertical) mode, polar plots of all composite fibers showed a two-fold symmetry. Under VH (vertical/horizontal) mode, it showed a four-fold symmetry. The CNCs are highly oriented in the composite fiber, which is confirmed by second and fourth order orientation parameters:〈P2(cosθ)〉 and〈P4(cosθ)〉. The 1095 cm−1 Raman band shift under uniaxial deformation was used to characterize the interfacial shear stress transfer between PAN matrix and CNCs.

Morphological investigation of cellulose acetate/cellulose nanocrystal composites obtained by melt extrusion

ABSTRACTComposites were prepared from cellulose acetate (CA) and cellulose nanocrystals (CNC) by melt extrusion using two methods for the introduction of CNC: direct mixing and predispersion in CA solution. CNC were isolated using hydrochloric acid to increase thermal stability allowing the composites to be processed above 150 °C. The effect of CNC dispersion on the composites morphology, thermal, and mechanical properties was investigated. Field emission scanning electron microscopy and transmission electron microscopy results indicated that the predispersion method allows better CNC dispersion and distribution when compared to the direct mixture method. In addition, predispersion promotes preferential CNC orientation in relation to the injection flow. The predispersion method also showed a 14% Young's modulus increase in composites containing 15 wt % CNC while no significant change was observed when using the direct mixing. The results obtained in this work show that, to achieve the percolation threshold, nanoparticle distribution is as important as their content. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44201.