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.

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.

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.

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.

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.