Effect of Ionic Strength and Surface Charge Density on the Kinetics of Cellulose Nanocrystal Thin Film Swelling

Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation

A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high-aspect-ratio 1D flexible nanocellulose fibrils, and 2D Ti3 C2 Tx MXene is presented. The self-assembly process results in a stratified structure with the nanoparticles aligned in-plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm-1 and the in-plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano- and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out-of-plane swelling, reaching 85% strain.

Hornification of cellulose-rich materials - A kinetically trapped state

The fundamental understanding concerning cellulose-cellulose interactions under wet and dry conditions remains unclear. This is especially true regarding the drying-induced association of cellulose, commonly described as an irreversible phenomenon called hornification. A fundamental understanding of the mechanisms behind hornification would contribute to new drying techniques for cellulose-based materials in the pulp and paper industry while at the same time enhancing material properties and facilitating the recyclability of cellulose-rich materials. In the present work, the irreversible joining of cellulose-rich surfaces has been studied by subjecting cellulose nanofibril (CNF) films to different heat treatments to establish a link between reswelling properties, structural characteristics as well as chemical and mechanical analyses. A heating time/temperature dependence was observed for the reswelling of the CNF films, which is related to the extent of hornification and is different for different chemical compositions of the fibrils. Further, the results indicate that hornification is related to a diffusion process and that the reswellability increases very slowly over long time, indicating that equilibrium is not reached. Hence, hornification is suggested to be a kinetically limited phenomenon governed by non-covalent reversible interactions and a time/temperature dependence on their forming and breaking.

Understanding Nanocellulose-Water Interactions: Turning a Detriment into an Asset

Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose-water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Cellulose Nanocrystals' Assembly under Ionic Strength Variation: From High Orientation Ordering to a Random Orientation

We discuss the effect of the ionic strength and effective charge density on the final structural organization of cellulose nanocrystals (CNCs) after drying suspensions with different ionic strengths in terms of quantitative characteristics of the orientation order, rarely considered to date. We observed that increasing the ionic strength in the initial suspension results in continuous shrinking of the helical pitch length that shifts the photonic band gap to a far UV region from the visible range (from 400 to 250 nm) because of the increase in the helical twisting power from 4 to 6 μm^-1 and doubling of the twisting angle between neighboring monolayers from 5.5 to 9°. As our estimation of the Coulombic interactions demonstrates, the reduction of the Debye charge screening length below a critical value of 3 nm results in the loss of the long-range helicoidal order and the transition to a disordered morphology with random packing of nanocrystals. Subsequently, very high orientation ordering with the 2D orientation factor, S, within the range 0.8-0.9, close to the theoretical limit of 1, gradually decreased to a very low value of S = 0.1-0.2, a characteristic of random organization at high ionic strength. We suggest that the loss of the chiral ordering is a result of the reduction of repulsive forces, promoting direct physical contact with the reduced contact area during Brownian motion, combined with increased repulsive Coulombic interactions of nanocrystals at nonparallel local packing. Notably, electrolyte addition enhances chiral interactions to the point where the helical twisting power is too large and the resulting nanocrystal bundles can no longer compactly pack without creating unfavorably large free volume. We propose that the Debye charge screening length in suspensions can be used as a universal parameter for CNCs under different conditions and can be used to assess expected ordering characteristics in the solid films.

Modulating the chiral nanoarchitecture of cellulose nanocrystals through interaction with salts and polymer

HYPOTHESIS

The conditions to allow self-assembly of cellulose nanocrystal (CNC) suspensions into chiral nematic structures are based on aspect ratio, surface charge density and a balance between repulsive and attractive forces between CNC particles.

EXPERIMENTS

Three types of systems were characterized in suspensions and subsequently in their solid dried films: 1) neat water dialyzed CNC, 2) CNC combined with polyethylene glycol(PEG) (CNC/PEG), and 3) CNC with added salt (CNC/Salt). All suspensions were characterized by polarized optical microscope (POM) and small angle X-ray scattering (SAXS), while the resultant dried films were analyzed by reflectance spectrometer, scanning electron microscope (SEM) and SAXS.

FINDINGS

The presence of chiral nematic (CN*) structures was not observed in dialyzed aqueous suspensions of CNC during water evaporation. By introducing salts or a non-adsorbing polymer, chirality was apparent in both suspensions and films. The interaxial angle between CNC rods increased when the suspensions of CNC/PEG and CNC/salt were dried to solid films. The angle was found to be dependent on both species of ions and ionic strength, while the inter-particle distance was only related to the salt concentration, as explained in terms of interaction energies. The CNC suspensions/film chirality can be modulated by controlling the colloidal forces.

Polymerizable Choline- and Imidazolium-Based Ionic Liquids Reinforced with Bacterial Cellulose for 3D-Printing

In this work, a novel approach is demonstrated for 3D-printing of bacterial cellulose (BC) reinforced UV-curable ion gels using two-component solvents based on 1-butyl-3-methylimidazolium chloride or choline chloride combined with acrylic acid. Preservation of cellulose's crystalline and nanofibrous structure is demonstrated using wide-angle X-ray diffraction (WAXD) and atomic force microscopy (AFM). Rheological measurements reveal that cholinium-based systems, in comparison with imidazolium-based ones, are characterised with lower viscosity at low shear rates and improved stability against phase separation at high shear rates. Grafting of poly(acrylic acid) onto the surfaces of cellulose nanofibers during UV-induced polymerization of acrylic acid results in higher elongation at break for choline chloride-based compositions: 175% in comparison with 94% for imidazolium-based systems as well as enhanced mechanical properties in compression mode. As a result, cholinium-based BC ion gels containing acrylic acid can be considered as more suitable for 3D-printing of objects with improved mechanical properties due to increased dispersion stability and filler/matrix interaction.

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

Recent developments in the area of plant-based hydrogels are introduced, especially those derived from wood as a widely available, multiscale, and hierarchical source of nanomaterials, as well as other cell wall elements. With water being fundamental in a hydrogel, water interactions, hydration, and swelling, all critically important in designing, processing, and achieving the desired properties of sustainable and functional hydrogels, are highlighted. A plant, by itself, is a form of a hydrogel, at least at given states of development, and for this reason phenomena such as fluid transport, diffusion, capillarity, and ionic effects are examined. These aspects are highly relevant not only to plants, especially lignified tissues, but also to the porous structures produced after removal of water (foams, sponges, cryogels, xerogels, and aerogels). Thus, a useful source of critical and comprehensive information is provided regarding the synthesis of hydrogels from plant materials (and especially wood nanostructures), and about the role of water, not only for processing but for developing hydrogel properties and uses.

Mesophase characteristics of cellulose nanocrystal films prepared from electrolyte suspensions

Cellulose nanocrystals (CNCs) exhibit a cholesteric mesophase above a critical concentration in aqueous suspensions. Above this concentration, CNCs self-organize into left-handed helicoidal structures that can be preserved in dried, stratified films. In this systematic study, we have prepared optically-active CNC films cast from different electrolyte suspensions and investigated, via circular dichroism and other techniques, the effects of counterion type (six mono/divalent salts, including those responsible for promoting "salting-out" and "salting-in" in the Hofmeister series) and ionic strength on mesomorphic behavior and cholesteric arrangement. The presence of electrolytes influences CNC colloidal stability by compressing the electric double layer and altering interactions among neighboring CNCs and water, thereby affecting the extent to which the CNCs form a mesophase. Interestingly, mesomorphic behavior and CNC alignment appear to be sensitive to cationic radius and charge valence, in which case the optical properties of CNC films can be adjusted for targeted sustainable applications. Such heuristic rules can be valuable for predicting the stability and characteristics of CNC microstructure in designer coatings and thin films prepared by introducing suitable cations prior to film formation.

A facile one-pot synthesis of microgels and nanogels of laminarin for biomedical applications

HYPOTHESIS

Laminarin (LAM) as a nontoxic, biodegradable, and biocompatible marine polysaccharide, has been reported for its ingenious bioactivities such as antioxidant, antitumor antiapoptotic anti-inflammatory, immunomodulatory and dietary fiber activities, and distinct physicochemical structure possess a remarkably promising potential in biomaterial science. Synthesis of LAM-based microgels and bulk hydrogels have been reported in two stages: modification of LAM polysaccharide with polymerizable functional groups and subsequent crosslinking reaction. Therefore, here an easier and more effortless methods to prepare poly(laminarin) (p(LAM)) particles were tackled.

EXPERIMENTAL

A direct and facile single step fabrication of micro/nanogels of p(LAM) for the first time by means of reverse micelle microemulsion system were illustrated. Preparation of p(LAM) particles were achieved by the well-known Oxa-Michael addition reaction mechanism using divinyl sulfone as the crosslinker.

FINDINGS

P(LAM) particles in 0.3-10 µm size range in spherical morphologies were prepared with 93 ± 7% yield and functionalized with chlorosulfonic acid (CSA) demonstrating their chemical modifiability for variety of agents e.g., targeting ligands. The bare and modified p(LAM) particles showed excellent blood compatibility with hemolytic indices of <1% and blood clotting indices higher than 90%. The reported p(LAM) particles hold great promise as natural alternative surrogates in biomedical applications including drug delivery.

Isolation of cellulose nanocrystals from different waste bio-mass collating their liquid crystal ordering with morphological exploration

Cellulose nanocrystals (CNCs) have been recognized as one of the most promising nanofillers in modern science and technology owing to their outstanding characteristics of renewability, biodegradability, excellent mechanical strength, and liquid crystalline behavior. Interestingly, these properties are dependent on their genetic and also on the isolation process. Therefore, this research aimed to unveil how the biological variations of cellulose can influence on the physical properties of the extracted CNCs. A standard optimized extraction process was adopted to isolate the CNCs from different sources. Extracted CNCs were compared through characterization tools, including Fourier Transformation Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Thermogravimetry Analysis (TGA), Dynamic Light Scattering (DLS), Field Emission Scanning Electron Microscopy (FE-SEM), Atomic Force Microscopy (AFM), and Polarized Optical Microscopy (POM). Different self-assembly patterns were observed for different CNCs, owing to their biological variations. The resultant nanocrystals displayed variable morphologies such as spherical, rod, and needle shape. The hydrodynamic diameter, crystallinity index, decomposition temperature, liquid crystallinity, and storage modulus were varied. Nanocrystals isolated from non-wood feedstock have shown a higher degree of polymerization of 108.2 and a high Crystllinity Index (C·I.) of 55.1%. The rod-like morphology with the liquid crystalline pattern was obtained at 3 wt% concentration for SCNC.

Injectable Biocompatible Hydrogels from Cellulose Nanocrystals for Locally Targeted Sustained Drug Release

Injectable hydrogels from biocompatible materials are in demand for tissue engineering and drug delivery systems. Here, we produce hydrogels from mere cellulose nanocrystals (CNCs) by salt-induced charge screening. The injectability of CNC hydrogels was assessed by a combination of shear and capillary rheology, revealing that CNC hydrogels are conveyed via plug flow in capillaries allowing injection with minimal impact on mechanical properties. The potential of CNC hydrogels as drug carriers was elaborated by the in vitro release of the model protein bovine serum albumin (BSA), poorly water soluble tetracycline (TC), and readily soluble doxorubicin (DOX) into physiological saline and simulated gastric juice. For TC, a burst release was observed within 2 days, whereas BSA and DOX both showed a sustained release for 2 weeks. Only DOX was released fully from the hydrogels. The different release patterns were attributed to drug size, solubility, and specific drug-CNC interactions. The biocompatibility of CNC hydrogels and maintained bioactivity of released DOX were confirmed in a HeLa cell assay. The drug release was modulated by the incorporation of sucrose or xanthan gum in CNC hydrogels, whereas altering CNC concentration showed minor effects. The release into simulated gastric juice at pH 2 ceased for BSA due to charge inversion and electrostatic complexation, but not for smaller TC. Thus, CNC hydrogels may act as pH-responsive delivery systems that preserve drugs under gastric conditions followed by pH-triggered release in the duodenum.

Alkali Hydrolysis of Sulfated Cellulose Nanocrystals: Optimization of Reaction Conditions and Tailored Surface Charge

Cellulose nanocrystals (CNCs) are a biorenewable resource, which may be chemically modified to impart specific properties. Modified CNCs have found use in imaging applications, as rheology modifiers, polymer reinforcements, barrier and/or optical films, and nanocomposites. Nanoparticle dimensions of CNCs are typically 5-10 nm in width, with lengths of <100-300 nm. However, the physical properties are dependent upon the number and nature of the surface charge groups imparted during preparation. In the case of CNCs produced from sulfuric acid hydrolysis, the sulfated surface groups may be partially removed prior to further functionalization. This gives more available hydroxyls yet renders the CNCs less colloidally stable. Furthermore, conditions vary significantly and there is no consensus about the optimal conditions for partial removal of sulfate functionality or conditions developed to give specific surface charge. In the following, alkali hydrolysis of sulfate half-esters was quantified by conductometric titration of the strong acid groups, and using a design of experiments (DOE), optimal conditions were determined to produce CNCs with tailored surface charge.

An insight into nanocellulose as soft condensed matter: Challenge and future prospective toward environmental sustainability

Nanocellulose, a structural polysaccharide that has caught tremendous interests nowadays due to its renewability, inherent biocompatibility and biodegradability, abundance in resource, and environmental friendly nature. They are promising green nanomaterials derived from cellulosic biomass that can be disintegrated into cellulose nanofibrils (CNF) or cellulose nanocrystals (CNC), relying on their sensitivity to hydrolysis at the axial spacing of disordered domains. Owing to their unique mesoscopic characteristics at nanoscale, nanocellulose has been widely researched and incorporated as a reinforcement material in composite materials. The world has been consuming the natural resources at a much higher speed than the environment could regenerate. Today, as an uprising candidate in soft condensed matter physics, a growing interest was received owing to its unique self-assembly behaviour and quantum size effect in the formation of three-dimensional nanostructured material, could be utilised to address an increasing concern over global warming and environmental conservation. In spite of an emerging pool of knowledge on the nanocellulose downstream application, that was lacking of cross-disciplinary study of its role as a soft condensed matter for food, water and energy applications toward environmental sustainability. Here we aim to provide an insight for the latest development of cellulose nanotechnology arises from its fascinating physical and chemical characteristic for the interest of different technology holders.

The Phases of WS2 Nanosheets Influence Uptake, Oxidative Stress, Lipid Peroxidation, Membrane Damage, and Metabolism in Algae

Application of transition metal dichalcogenide (TMDC) nanosheets with different phases have attracted much attention in various fields. However, the effects of TMDC phases on environmental biology remain largely unknown. In this study, chemically exfoliated WS₂ nanosheets (Ce-WS₂, mainly the 1T phase) and annealed exfoliated WS₂ nanosheets (Ae-WS₂, 2H phase) were fabricated to serve as representative TMDC nanomaterials. Ce-WS₂ showed higher levels of cellular uptake, oxidative stress, lipid peroxidation, membrane damage, and inhibition of photosynthesis than Ae-WS₂ in Chlorella vulgaris. These differences were attributed to the higher electron conductivity and higher separation efficiency of electrons and holes in the 1T phase, a typical feature of Ce-WS₂. Correspondingly, 2H-phase Ae-WS₂ exhibited lower photooxidation/reduction activity and a lower ability to generate reactive oxygen species (mainly •OH) under visible-light irradiation. 1T-phase Ce-WS₂ dissolved more readily than Ae-WS₂ and released more W ions into aqueous environments, but the W ions exhibited negligible toxicity. Metabolomic analysis revealed that Ce-WS₂ induced more obvious alterations in metabolites (e.g., amino acids and fatty acids) and metabolic pathways (e.g., starch and sucrose metabolism) than Ae-WS₂. These alterations correlated with cell membrane damage, oxidative stress and photosynthesis inhibition. The present work provides insights into the environmentally friendly design of two-dimensional TMDCs.

Adsorption of Xyloglucan onto Thin Films of Cellulose Nanocrystals and Amorphous Cellulose: Film Thickness Effects

The interaction between cellulose and hemicelluloses is of fundamental importance for understanding the molecular architecture of plant cell walls. Adsorption of xyloglucan (XG) onto regenerated cellulose (RC), sulfated cellulose nanocrystal (s-CNC), and desulfated cellulose nanocrystal (d-CNC) films was studied by quartz crystal microbalance with dissipation monitoring, surface plasmon resonance, and atomic force microscopy. The amount of XG adsorbed onto different cellulose substrates increased in the order RC < s-CNC < d-CNC. The adsorption of XG onto RC films was independent of film thickness (d), whereas XG adsorption was weakly dependent on d for s-CNC films and strongly dependent on d for d-CNC films. However, approximately the same amount of XG adsorbed onto "monolayer-thin" films of RC, s-CNC, and d-CNC. These results suggest that the morphology and surface charge of the cellulose substrate played a limited role in XG adsorption and highlight the importance of film thickness of cellulose nanocrystalline films to XG adsorption.

The Self-Assembly of Cellulose Nanocrystals: Hierarchical Design of Visual Appearance

By controlling the interaction of biological building blocks at the nanoscale, natural photonic nanostructures have been optimized to produce intense coloration. Inspired by such biological nanostructures, the possibility to design the visual appearance of a material by guiding the hierarchical self-assembly of its constituent components, ideally using natural materials, is an attractive route for rationally designed, sustainable manufacturing. Within the large variety of biological building blocks, cellulose nanocrystals are one of the most promising biosourced materials, primarily for their abundance, biocompatibility, and ability to readily organize into photonic structures. Here, the mechanisms underlying the formation of iridescent, vividly colored materials from colloidal liquid crystal suspensions of cellulose nanocrystals are reviewed and recent advances in structural control over the hierarchical assembly process are reported as a toolbox for the design of sophisticated optical materials.

Surface Charge Influence on the Phase Separation and Viscosity of Cellulose Nanocrystals

A series of four cellulose nanocrystal (CNC) suspensions were prepared from bleached softwood kraft pulp using different conditions of sulfuric acid hydrolysis. The CNCs were identical in size (95 nm in length × 5 nm in width) but had different surface charges corresponding to the harshness of the hydrolysis conditions. Consequently, it was possible to isolate the effects of surface charge on the self-assembly and viscosity of the CNC suspensions across surface charges ranging from 0.27%S to 0.89%S. The four suspensions (never-dried, free of added electrolyte) all underwent liquid crystalline phase separation, but the concentration onset for the emergence of the chiral nematic phase shifted to higher values with increasing surface charge. Similarly, suspension viscosity was also influenced by surface charge, with suspensions of lower surface charge CNCs more viscous and tending to gel at lower concentrations. The properties of the suspensions were interpreted in terms of the increase in effective diameter of the nanocrystals due to the surface electrostatic repulsion of the negative sulfate half-esters, as modified by the screening effects of the H⁺ counterions in the suspensions. The results suggest that there is a threshold surface charge density (∼0.3%S) above which effective volume considerations are dominant across the concentration range relevant to liquid crystalline phase formation. Above this threshold value, phase separation occurs at the same effective volume fraction of CNCs (∼10 vol %), with a corresponding increase in critical concentration due to the decrease in effective diameter that occurs with increasing surface charge. Below or near this threshold value, the formation of end-to-end aggregates may favor gelation and interfere with ordered phase formation.