Gradient heating activated ammonium persulfate oxidation for efficient preparation of high-quality chitin nanofibers.

APS is a cheap and eco-friendly oxidant which enables one-step extraction of nanochitin (NCh) from fishery wastes. However, it is challenging to improve the preparation efficiency and NCh quality simultaneously, owing to the uneven or uncontrollable oxidation. Herein, we propose a simple and controllable way to isolate chitin nanofibers (ChNFs) from squid pen by gradient heating activated (GHA)- ammonium persulfate (APS) oxidation. Compared to the isothermal activated (ITA)-APS oxidation, our strategy reduced the mass ratio of squid pen to APS from 1:45 to 1:6 and reaction time from 15 h to 8 h. Meanwhile, the as-prepared ChNFs exhibited high yield (91.5 %), light transmittance (98 % at 500 nm), crystallinity index (96.9 %), and carboxyl content (1.53 mmol/g). GHA-APS oxidation involved multiple continuous heating and isothermal stages. The former stimulates a moderate activation of APS and enhances the oxidation rate, while the latter provides a duration for surface chemistry. This non-isothermal heating facilitates the continuous decomposition of APS at a relatively high and consistent rate, thereby enhances its oxidation efficiency. Furthermore, green assessments indicate this method is simple, time-saving, eco-friendly and cost-effective. Overall, this work introduces a novel perspective for the industrial extraction of high-efficiency and high-quality nanomaterials.

Liquid-crystalline assembly of spherical cellulose nanocrystals.

Rod-shaped cellulose nanocrystals (CNCs), also called cellulose nanorods (CNRs), possess anisotropic properties that allow for their self-organization into chiral nematic liquid crystals. Interestingly, spherical cellulose nanocrystals (cellulose nanospheres, CNSs) have also been shown to form a chiral liquid-crystalline phase in recent years. Herein, to understand how the similar assembly takes places as particle dimension changes, the organization features of CNSs were investigated. Results of this study demonstrate that above a critical concentration in suspension, CNSs organize into a liquid-crystal phase consisting of periodically parallel-aligned layer structures. This structure persists after suspension drying. In comparison with CNRs, the alignment of CNSs exhibits a shorter layer distance, lower order degree, and weaker long-range orientation. To explain the early stages of tactoid formation, a "caterpillar-like" model was proposed, which was captured by freezing the CNS suspension in an intermediate aggregation state. This structure serves as the fundamental unit for further liquid-crystal assembly.

Effects of the surface chemical groups of cellulose nanocrystals on the vulcanization and mechanical properties of natural rubber/cellulose nanocrystals nanocomposites.

Cellulose nanocrystals (CNCs), as the promising reinforcing fillers in the rubber industry, their surface chemical groups have vital effects on the vulcanization kinetics, cross-linking densities, and mechanical properties of rubber composites. Herein, CNCs with acidic carboxyl (CCA) and alkaline amino groups (CCP) were produced by modifying the sulfonic CNCs (CCS) in environment-friendly ways. Studies found the CCS and CCA with acid groups have obvious inhibiting effects on the vulcanization of natural rubber (NR), while CCP with alkaline amino groups accelerates the vulcanization of NR. Differential scanning calorimeter, Fourier transform infrared spectroscopy, and Electron paramagnetic resonance, etc. were performed to clarify the effecting mechanisms of CNCs surface groups on NR vulcanization. It was found that NR/CCS and NR/CCA nanocomposites vulcanize through radical reactions, and the surface acidic groups of CCS and CCA, i.e., hydroxyl, sulfonate, and carboxyl groups inactivate the sulfur radicals generated during vulcanization and depress the vulcanization activity. The amino groups of the polyethyleneimine of CCP promote the ring opening of sulfur (S8) or the breaking of polysulfide bonds connected to NR molecular chains to form sulfur anion with a strong nucleophilic ability, which leads to the cross-linking of NR/CCP reacts via ionic reaction mainly. The vulcanization rate and cross-linking density of NR/CCP are improved by the ionic reaction. And benefiting from the higher cross-linking density and the reinforcement of CCP, NR/CCP had the best physical and mechanical properties. Our work elucidates the mechanism of the surface chemical groups of CNCs affecting NR vulcanization and may provide ideas for the preparation of high-performance rubber composites reinforced by CNCs.

Tuning liquid aggregation of zwitterionic chitin nanocrystals by graphene oxide planar catchers via electrostatic regulation.

As important structural units, biomass nanomaterials have exhibited great potentials to construct high-performance macroscopic materials for broad applications by liquid assembly. However, the liquid aggregation of nanomaterials was less investigated. Here, we demonstrate that the one-dimensional (1D) zwitterionic chitin nanocrystals (ZChNCs) can be reversibly captured and released by two-dimensional (2D) planar catchers of graphene oxide (GO) sheets. The dominant electrostatic regulation strategy by pH variation drives that there are three reversible changes for the liquid aggregation of ZChNCs and GO, which were the isolated dispersion state (pH > 7), homogeneous hybridization state (7 ≥ pH ≥ 5), and partially stacked hybridization state (pH < 5), respectively. We found there are no sedimentation during the change of liquid aggregation with the higher absolute Zeta potentials (almost>30 mV). Moreover, the ZChNCs-GO nanohybrids have reached a maximum Zeta potential up to -80 mV, which can be explained by the ionization of excess carboxyl groups on the surface of ZChNCs. Besides, the electrostatic regulation endows the nanohybrids with rheological behavior, which is beneficial to the macro assembly of liquid nanomaterials. This work provides a new class of hybrid colloidal nanomaterials, opens the structural design dimension of macro assembly and holds great potentials in high-performance biodegradable material.

Electric Field-Induced Assembly and Alignment of Silver-Coated Cellulose for Polymer Composite Films with Enhanced Dielectric Permittivity and Anisotropic Light Transmission.

Multifarious wearable electronics with flexible touch screens have been invented for extensive outdoor activities. One challenge associated with these wearable electronics is the development of materials with both high dielectric permittivity and anisotropic light transmission, which is responsible for high touch sensitivity and screen peep-proof protection, respectively. Herein, we demonstrated a scalable approach for assembling and aligning anisotropic cellulose in a polymer matrix through the thickness direction via the assistance of an electric field to address this challenge. The alignment of silver-coated fibrillated celluloses in the polymer matrix not only significantly increases dielectric permittivity but also effectively enhances optical anisotropy. The impact of alignment degree and filler content on the dielectric and optical properties of polymer composite films has been systematically studied. The kinetics and aligning mechanisms of silver-coated fibrillated celluloses are revealed by in situ optical microscope images while an electric field is applied. We believe that this study provides a facile strategy to enhance both dielectric permittivity and optical anisotropy of polymer composite films by the alignment of embedding nanoparticles via an AC electric field, which is essential for future flexible electronics and display technology.

Modified ammonium persulfate oxidations for efficient preparation of carboxylated cellulose nanocrystals.

Ammonium persulfate (APS) was able to produce carboxylated cellulose nanocrystals (CNCs-COOH) directly from the raw materials of cellulose. However, the industrial production of CNCs-COOH by this method is obstructed by the lower preparation efficiency. Herein, by the activation via N,N,N',N'-tetramethylethylenediamine (TMEDA) and ultrasonic assisted disintegration, modified APS method to extract CNCs-COOH from pulp was presented. A high yield (up to 62.5 %), low usage of APS (8.5 g APS per gram pulp) and less reaction time (6 h) was achieved. The as-prepared CNCs-COOH exhibited high carboxyl group content (1.45 mmol/g) and high crystallinity index of 93 %. The reaction mechanism has been studied, and the results show that with the addition of TMEDA, S2O82-can be converted to free radicals and hydrogen peroxide more quickly. Our studies suggested that modified APS method may be a suitable and economic alternative for the preparation of CNCs-COOH.

Tough, Ultralight, and Water-Adhesive Graphene/Natural Rubber Latex Hybrid Aerogel with Sandwichlike Cell Wall and Biomimetic Rose-Petal-Like Surface.

Graphene aerogel (GA) as a rising multifunctional material has demonstrated great potential for energy storage and conversion, environmental remediation, and high-performance sensors or actuators. However, the commercial use of GA is obstructed by its fragility and high cost. Herein, by a simple stirring-induced foaming of the mixed aqueous solutions of natural rubber latex (NRL) and graphene oxide liquid crystal (GOLC), we obtained tough, ultralight (4.6 mg cm-3), high compressibility (>90%), and water-adhesive graphene/NRL hybrid aerogel (GA/NRL). Of particular note, the NRL particles are conformally wrapped by graphene layers to form a sandwichlike cell wall with a biomimetic rose-petal-like surface. These distinct hierarchical structures endow GA/NRL not only with high toughness to bear impact, torsion (>90°), and even ultrasonication but also with strong adhesion to water. As proof of concept, the utilization of the as-prepared GA/NRL for collecting water droplets suspended in moist air and its improved solar-thermal harvest capacity have been demonstrated. This facile, green, and cost-effective strategy opens a new route for tailoring the microstructure and functionality of GA, which will facilitate its large-scale production and commercial application.

Natural rubber bio-nanocomposites reinforced with self-assembled chitin nanofibers from aqueous KOH/urea solution.

Rigid chitin nanofibers (ChNFs) self-assembled from dilute α-chitin/KOH/urea aqueous solution were utilized as 1D filler to reinforce soft natural rubber (NR). The prepared ChNFs suspension has good compatibility with natural rubber latex (NRL) and thus showing favorable dispersibility in NR matrix at nanoscale. The bio-nanocomposites were fabricated by casting and evaporating the pre-mixed NRL/ChNFs suspensions with different ChNFs loadings. Gratifyingly, the NR/ChNFs bio-nanocomposite with only 0.3 wt% ChNFs content presented distinct improvement in both the strength and toughness due to the large aspect ratio of ChNFs and its homogeneous dispersion in NRL matrix. Moreover, the introduction of ChNFs can promote the proliferation of mBMSCs effectively and endow NR/ChNFs bio-nanocomposites with good biocompatibility, enabling expanded applications of NR in biomedical field, such as artificial blood vessel, cosmetology prosthesis and human diaphragm materials.

Ultrafine and carboxylated ß-chitin nanofibers prepared from squid pen and its transparent hydrogels.

TEMPO-mediated oxidation has been successfully used to prepare carboxylated chitin nanofibers (ChNFs) with purified chitins originating from the outer shells of crab and shrimp (α-form) or tubeworm (ß-form). However, the method for obtaining carboxylated ChNFs with squid pen chitin (hydrated ß-form) has not been developed yet. It might be due to the existence of the small amount of partial deacetylation (DD ≈ 9%) in the squid pen ß-chitins. Herein, ultrafine (2-4 nm in width and several micrometers in length) and carboxylated ß-ChNFs were fabricated directly from the squid pen with simultaneously removing of protein, CaCO3 and other non-chitin components by one-step oxidation procedure using ammonium persulfate (APS) and followed ultrasonic disintegration under acid conditions. When 45 wt% APS was used to react with squid pen, the carboxylate content of ChNFs reaches 0.802 mmol/g. Therefore, the ß-ChNFs with anionically charged groups (COO-) can be dispersed stably in aqueous solution under basic conditions. Meanwhile, thus-obtained ß-ChNFs aqueous solution even with very low concentration (0.8%) can be transformed to transparent, robust and moldable hydrogels by gas coagulation of acetic acid.

Effect of surface chemistry on the dispersion and pH-responsiveness of chitin nanofibers/ natural rubber latex nanocomposites.

Chitin nanofibers (ChNFs) have emerged as a rising nanomaterial due to their excellent mechanical properties, biocompatibility and biodegradability etc. Herein, carbonylated ChNFs (C-ChNFs) and zwitterionic ChNFs (NC-ChNFs) decorated with both amino (-NH2) and carboxyl (-COOH) groups were used to prepare ChNFs/natural rubber (NR) nanocomposite films by dip molding method, respectively. The results showed that C-ChNFs had better dispersion than that of NC-ChNFs in NRL matrix. Moreover, C-ChNFs/NR nanocomposite films demonstrated obvious pH-responsiveness owing to the association and disassociation of the hydrogen bonding between C-ChNFs under various pH conditions. In contrast, NC-ChNFs/NR nanocomposite films showed pH-stable mechanical properties because the protonation of -NH2 at pH < 7 and the ionization of -COOH at pH > 7 resulted in electrostatic repulsive force between NC-ChNFs. This study demonstrates that surface chemistry of ChNFs plays an important role on tailoring the performance of ChNFs/NRL nanocomposites.

Ultralight, Superelastic, and Fatigue-Resistant Graphene Aerogel Templated by Graphene Oxide Liquid Crystal Stabilized Air Bubbles.

Graphene aerogel (GA) has attracted great attention due to its unique properties, such as ultralow density, superelasticity, and multifunctionality. However, it is a great challenge to develop superelastic and fatigue-resistant GA (SFGA) with ultralow density because it is generally contradictory to improve the mechanical properties with reducing density of GA. Herein, we report a simple and efficient approach to prepare ultralight SFGA templated by graphene oxide liquid crystal (GOLC) stabilized air bubbles. The thus-prepared ultralight SFGA (∼2 mg cm-3) exhibits superelasticity (rapid recovery from >99% compression) and unprecedented fatigue-resistant performance (maintaining shape integrity after 106 compressive cycles at 70% strain and 5 Hz). The ultralow density and excellent dynamic mechanical properties of SFGA are mainly associated with the "volume exclusion effect" of the air bubbles as well as the highly ordered, closely packed, and uniform porous structure of the resultant GA, respectively. This study provides a green and facile strategy for preparing high-performance ultralight SFGA, which has great potential in various applications, including ultrafast dynamic pressure sensors, soft robot, and flexible devices.

Influence of Branched Polyester Chains on the Emission Behavior of Dipyridamole Molecule and Its Biosensing Ability.

Toward the development of the smart biosensing drug carrier, integration of dye molecules with polymeric chain has been an emerging method in recent years. In this perspective, dipyridamole (Dip)-based branched poly(l-lactide) (PLLA) and branched polycaprolactone (PCL) have been synthesized by ring-opening polymerization. After polymerization, the influence of the polyester chains on the Dip emission behavior has been studied systematically in this work. Dip-PLLA has undergone C=O···N=C interaction in ground stage, leading to intramolecular charge transfer in the excited state. Limited availability of the C=O in PCL chains resists such interactions with Dip molecule. So, this structural availability of the C=O group in the polymeric chains influences the color change between Dip-PLLA (green fluorescence) and Dip-PCL (blue fluorescence). To visualize the biosensing ability of Dip-PLLA and Dip-PCL, hollow microspheres have been prepared by the double-emulsion solvent evaporation method, and the prepared microspheres cells uptake has been visualized by fluorescence imaging.

Green and facile surface modification of cellulose nanocrystal as the route to produce poly(lactic acid) nanocomposites with improved properties.

In this study, lactic acid monomer or dimer is grafted onto CNC by a simple esterification reaction. The quantitative solid-state 13C NMR spectrum suggests that more than 87% of all the available OH groups on the surface of CNC are substituted by lactic acid. Such modified CNC (CNC-g-LA) exhibits excellent thermostability and nano-sized dispersion in chloroform. Benefit from this character, fully biobased PLLA/CNC-g-LA nanocomposite could be prepared simply by a solution-casting method. The crystallization behavior of obtained nanocomposites has been systematically investigated by differential scanning calorimetry (DSC). The results show that the crystallization rate of PLLA is distinctly enhanced. Moreover, the mechanical properties of nanocomposites are also improved remarkably by the addition of CNC-g-LA because of its excellent dispersion and compatibility with PLLA matrix. This study provides a green and facile way to modify CNC for fabricating bio-nanocomposites with fast crystallization rate and improved mechanical properties.

One-pot synthesis of graphene/chitin nanofibers hybrids and their remarkable reinforcement on Poly(vinyl alcohol).

Novel hybrid nanomaterials composed of graphene and chitin nanofibers (ChNFs) were successfully prepared by one-pot ball milling. Under strong shear and collision force of ball milling, graphite was exfoliated to mono-layer or few-layer graphene with the assistance of chitin nanofibers. Unexpectedly, the hybridization of exfoliated graphene and ChNFs was realized simultaneously. Morphology analysis observed that the ChNFs were adsorbed tightly on the surface of graphene, providing for reduced graphene hydrophobicity and enhanced stability of the hybrid dispersion. In addition, the concentration of exfoliated graphene reaches up to 1.5 mg ml-1. Strong interaction between graphene and ChNFs may benefit from the large amounts of carboxylate groups on the surface of ChNFs, which was prepared by TEMPO-mediated oxidation of chitin. As prepared graphene/ChNFs hybrids can remarkably enhance both the tensile strength and toughness of Poly(vinyl alcohol). This study provides a green, simple and large-scale synthesis method for preparing water-dispersible graphene/ChNFs hybrid nanobuilding blocks, which shows great promise potential in various applications requiring biocompatibility, hydrophilicity, electrical conductivity and strong mechanical properties.

Simultaneous improvement of thermal stability and redispersibility of cellulose nanocrystals by using ionic liquids.

Cellulose nanocrystals (CNCs) are predominantly obtained by the traditional sulfuric acid hydrolysis process. However, as-prepared CNCs powder features low thermal stability and poor redispersibility due to the existence of sulfonate groups and the hydrogen bond interaction among particles. Herein, by mixing the ionic liquid [BMIm][BF4] with freshly prepared CNCs without dialysis through a simple rotary evaporate procedure, the simultaneous improvement of thermal stability and redispersibility of CNCs has been achieved. By combining FTIR, TGA and DLS measurements, the critical role of rotary evaporates process for improving the thermal stability of CNCs has been discussed. Furthermore, the poly(lactic acid) (PLLA)/IL-CNC nanocomposites with enhanced mechanical properties were prepared by the melt-mixing method. This study provides a green and simple strategy for preparing dried CNC powders, which has a great potential in large-scale production of fully bio-based nanocomposites.

Modifying Mechanical, Optical Properties and Thermal Processability of Iridescent Cellulose Nanocrystal Films Using Ionic Liquid.

Iridescent films formed from the self-assembly of cellulose nanocrystals (CNCs) are brittle and difficult to handle or integrate within an industrial process. Here we present a simple approach to prepare iridescent CNC films with tunable pliability and coloration through the addition of ionic liquids (ILs) of 1-allyl-3-methylimidazolium chloride (AmimCl) as plasticizers. By using the undried CNC film as a filter membrane and ILs solution as a leaching liquid, it was found that the filtration process made ILs uniformly interpenetrate into CNC film due to the strong ionic interaction between CNC and AmimCl. Unexpectedly, the filtration process also gave rise to partial desulfurization of CNC film, which is conducive to the improvement of thermal stability. Benefiting from the improved thermal stability and the dissolving capacity of AmimCl for cellulose at high temperature, the incorporated ILs enable the cholesteric CNC film to be further toughened via a hot-pressing treatment. This study demonstrates that ionic liquids have great potential to modify the mechanical, optical properties as well as the thermal stability of iridescent CNC films.

Study on π-π Interaction in H- and J-Aggregates of Poly(3-hexylthiophene) Nanowires by Multiple Techniques.

There has been intense interest in understanding the self-assembled structure of conductive polymer nanowires due to the potential application in photovoltaics area. In the present study, free-standing poly(3-hexylthiophene) (P3HT) thin films consisting of H-aggregated and recently reported J-aggregated nanowires (NWs) were respectively prepared by the vacuum filtration method. The microstructure differences of both samples were studied in detail by combining the multiple techniques, i.e., synchrotron radiation WAXD, solid-state NMR, and IR spectroscopy. It is found that there is stronger π-π interaction ascribed to the slightly closer interchain stacking in J-aggregates than that in H-aggregates, although both aggregates take the same form I crystal modification. The subtle structural difference in the interchain stacking distance (Δd020 = 0.04 Å) is further manifested in the thermal behavior of both aggregates as indicated by the DSC curves, in which J-aggregates exhibit much higher melting point than that of H-aggregates (ΔT = 14 °C). Meanwhile, in situ synchrotron radiation WAXD study suggests that the low-temperature thermal transitions in both aggregates are associated with the shrinkage of the interchain distance. It is expected that this work will be helpful in understanding the structure-properties relationship of varying P3HT aggregate types.

Chemical structure and interlayer distance correlation of graphite oxide in the heating process as revealed by in situ Fourier transform infrared spectroscopy and wide-angle X-ray diffraction techniques.

The thermal reduction behavior of graphite oxide (GO) film in an air atmosphere during a continuous heating process was monitored in situ using temperature-dependent infrared (IR) spectroscopy and synchrotron radiation wide-angle X-ray diffraction (WAXD) techniques. The results show that most of the water adsorbed by the GO sheets is removed by heating them to 130 °C. The dehydration process leads to a slight decrease of the interplane distance of the GO sheets. The IR data suggest that the thermal reduction occurs starting at 160 °C. The synchronous change of the of hydroxyl and carbonyl stretching mode (ν(-OH) and ν(C=C)) bands of GO between 160 and 210 °C suggest that the recovery of conjugated structure is mainly due to the reduction of -OH groups in this temperature region, in which the d spacing has not been affected. When the temperature reaches 210 °C, the rapid reduction of C=O groups together with the removal of the residual -OH and ether (C-O-C) groups leads to the sudden collapse of the GO sheets. Based on these findings, we present a schematic of the thermal stability of GO film in a continuous heating process, in which the thermal-induced chemical and crystallographic structural changes of the GO film have been correlated.

A green and facile approach for the synthesis of water-dispersible reduced graphene oxide based on ionic liquids.

A green and facile route for producing reduced graphene oxide based on ionic liquids has been proposed, in which the as-prepared graphene can be redispersed stably in water (up to 0.6 mg mL(-1)) after being made into a flow-directed solid film.

Physical aging enhanced mesomorphic structure in melt-quenched poly(L-lactic acid).

The structural evolutions and kinetics of melt-quenched poly(L-lactic acid) (PLLA) during the process of isothermal physical aging below the glass transition temperature (T(g)) were investigated by time-resolved infrared spectroscopy. The results show that local ordered structure is developed with aging time. Such local ordered structure shows the same characteristic band at 918 cm(-1) as that of the mesomorphic structure formed during the unaxially drawn process of PLLA from the glassy state. On the basis of spectroscopic evidence, we therefore proposed that the so-called local ordered structure formed by physical aging can be ascribed to a kind of mesophase of PLLA. Of particular note, a very small amount of mesophase already exists in the initial state of melt-quenched PLLA sample, whereas it is totally undetectable in the melt-quenched poly(D,L-lactide) (PDLLA) sample. By temperature-dependent IR spectroscopy, it is found that the local ordered structure formed during the physical aging process will be "partially molten" rather than "totally molten" in the temperature region corresponding to the physical aging peak of aged PLLA. Such an observation can explain the phenomenon of physical aging enhanced cold crystallization rate.