Zhenghai Tang

Hydrolysable tannin as environmentally friendly reducer and stabilizer for graphene oxide

An environmentally friendly method for preparing reduced graphene oxide (rGO) was established based on the typical hydrolysable tannin, tannic acid (TA). TA is fully competent in reducing GO and stabilizing rGO simultaneously.

Preparation of butadiene–styrene–vinyl pyridine rubber–graphene oxide hybrids through co-coagulation process and in situ interface tailoring

To fully exhibit the potentials of the fascinating characteristics of graphene oxide (GO) in polymer, the achievement of strong interface interactions and fine dispersion of GO in the hybrids is essential. In the present work, the elastomeric hybrids consisting of GO sheets are fabricated by utilizing butadiene–styrene–vinyl pyridine rubber (VPR) as the host through co-coagulation process and in situ formation of an ionic bonding interface. The VPR/GO composites with a normal hydrogen bonding interface are also prepared. The mechanical properties and gas permeability of these hybrids with an ionic bonding interface are obviously superior to those of the composites with a hydrogen bonding interface. With the ionic interfacial bonding, inclusion of 3.6 vol% of GO in VPR generates a 21-fold increase in glassy modulus, 7.5-fold increase in rubbery modulus, and 3.5-fold increase in tensile strength. The very fine dispersion of GO and the strong ionic interface in the hybrids are responsible for such unprecedented reinforcing efficiency of GO towards VPR. This work contributes new insights on the preparation of GO-based polymer hybrids with high performance.

General route to graphene with liquid-like behavior by non-covalent modification

A graphene material with liquid-like behavior has been synthesized by decorating graphene in a generic, non-covalent fashion and subsequently combining the modified material with bulky polymer chains. The independently dispersed graphene core was first prepared through the chemical reduction of graphene oxide using a fluorescent whitening agent, VBL, as a non-covalent modifier. The negative groups of VBL, which are anchored onto the graphene sheets, impart anionic characteristics to graphene. The combination of the modified graphene with bulky Jeffamine M2070 chains through an electrostatic interaction yields a homogeneous graphene fluid, i.e., graphene-based nanoparticle ionic materials (G-NIMs). The microstructures of G-NIMs were characterized. G-NIMs can be stably dispersed in a broad spectrum of solvents with a super-high concentration of 500 mg mL−1. The intriguing properties of the graphene core and fluidity properties of G-NIMs may offer new scientific and technological opportunities for the applications of graphene.

A generic solvent exchange method to disperse MoS2 in organic solvents to ease the solution process

A simple solvent exchange method is presented to suspend monolayers of MoS2 in various organic solvents, which facilitates the phase transformation of MoS2 and preparation of MoS2-filled polymer composites straightforwardly in organic solvents.

Supramolecular ionic liquid based on graphene oxide

For the purpose of preparing liquefied graphene oxide (GO), a process consisting of sulfonation with sodium sulfanilic acid and ionization with bulky amine-terminated Jeffamine® was designed and performed. The obtained hybrid fluid is actually a supramolecular ionic liquid (SIL) with sulfonated GO as the central anions and the terminal ammonium groups of Jeffamine® as the surrounding cations. The successful grafting of the GO sheets with Jeffamine®via an ionic structure was verified and the morphology of the SIL was characterized. The SIL based on GO (GO-SIL) exhibits excellent solubility and amphiphilicity. The rheological measurements confirm the essential viscoelasticity and the liquid-like behavior of GO-SIL. The present GO based SIL suggests promising applications in the fabrication of various GO or graphene based composite materials. In addition, the new functionalization method may guide the future work on acquiring derivatives with tunable properties by simply changing the bulky canopy.

Bioinspired Interface Engineering in Elastomer/Graphene Composites by Constructing Sacrificial Metal-Ligand Bonds.

It remains a huge challenge to create advanced elastomers combining high strength and great toughness. Despite enhanced strength and stiffness, elastomeric nanocomposites suffer notably reduced extensibility and toughness. Here, inspired by the concept of sacrificial bonding associated with many natural materials, a novel interface strategy is proposed to fabricate elastomer/graphene nanocomposites by constructing a strong yet sacrificial interface. This interface is composed of pyridine-Zn(2+) -catechol coordination motifs, which is strong enough to ensure uniform graphene dispersion and efficient stress transfer from matrix to fillers. Moreover, they are sacrificial under external stress, which dissipates much energy and facilitates chain orientation. As a result, the strength, modulus, and toughness of the elastomeric composites are simultaneously strikingly enhanced relative to elastomeric bulk. This work suggests a promising methodology of designing advanced elastomers with exceptional mechanical properties by engineering sacrificial bonds into the interface.

Fluorescent whitening agent stabilized graphene and its composites with chitosan

Individually dispersed graphene colloid is prepared using common and industrially available fluorescent whitening agents (FWAs) as stabilizers. Characterizations by UV-vis, fluorescence and Raman spectra demonstrate that FWAs are successfully anchored onto graphene sheets by π–π interaction. The results from AFM indicate the individual dispersion of graphene sheets in water. FWAs are demonstrated as highly efficient in suspending graphene with high concentration(6.2 mg ml−1). Subsequently, the obtained graphene sheet is incorporated into a chitosan (CS) matrix by solution casting to fabricate CS/graphene composites. Morphological observations substantiate the homogeneous dispersion of graphene in the CS matrix and the strong interfacial adhesion between them. The significant improvements in tensile strength and toughness of the composite films are concurrently observed.

Synthesis and characterization of biobased isosorbide-containing copolyesters as shape memory polymers for biomedical applications

Novel biobased isosorbide-containing copolyesters (PBISI copolyesters) with both biocompatibility and sustainability were synthesized by using commercially available biobased diols and diacids. Due to the presence of itaconate in copolyesters, it can be readily crosslinked by peroxide into a crystallizable network. The structure and thermal properties of PBISI copolyesters were determined by 1H NMR, FTIR, DSC, and WAXD. The chain composition, melting point and crystallinity of the PBISI copolyesters can be tuned continuously by changing the content of isosorbide. The crosslinked copolyester is demonstrated to be a promising shape memory polymer (SMP) with excellent shape memory properties including shape fixity and shape recovery rate close to 100%. The switching temperatures of PBISI-based SMPs can be tuned between 26 °C and 54 °C by altering the composition of PBISI copolyesters and curing extent. Cell adhesion and proliferation were adopted to evaluate the potential biocompatibility of PBISI-based SMPs, and the results indicated that all the PBISI-based SMPs were essentially noncytotoxic, making them suitable for fabricating biomedical devices.

Scalable and Versatile Graphene Functionalized with the Mannich Condensate

The functionalized graphene (JTPG) is fabricated by chemical conversion of graphene oxide (GO), using tea polyphenols (TP) as the reducer and stabilizer, followed by further derivatization through the Mannich reaction between the pyrogallol groups on TP and Jeffamine M-2070. JTPG exhibits solubility in a broad spectrum of solvents, long-term stability and single-layered dispersion in water and organic solvents, which are substantiated by AFM, TEM, and XRD. The paper-like JTPG hybrids prepared by vacuum-assisted filtration exhibits an unusual combination of high toughness (tensile strength of ~275 MPa and break strain of ~8%) and high electrical conductivity (~700 S/m). Still, JTPG is revealed to be very promising in the fabrication of polymer/graphene composites due to the excellent solubility in the solvent with low boiling point and low toxicity. Accordingly, as an example, nitrile rubber/JTPG composites are fabricated by the solution compounding in acetone. The resulted composite shows low threshold percolation at 0.23 vol.% of graphene. The versatilities both in dispersibility and performance, together with the scalable process of JTPG, enable a new way to scale up the fabrication of the graphene-based polymer composites or hybrids with high performance.

New Design Strategy for Reversible Plasticity Shape Memory Polymers with Deformable Glassy Aggregates

Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a phenomenon in which shape memory polymers (SMPs) can undergo a large plastic deformation at room temperature and subsequently recover their original shape upon heating. To date, RPSM behavior has been demonstrated in only a few polymers. In the present study, we implement a new design strategy, in which deformable glassy hindered phenol (AO-80) aggregates are incorporated into an amorphous network of epoxidized natural rubber (ENR) cured with zinc diacrylate (ZDA), in order to achieve RPSM properties. We propose that AO-80 continuously tunes the glass transition temperature (Tg) and improves the chain mobility of the SMP, providing traction and anchoring the ENR chains by intermolecular hydrogen bonding interactions. The RPSM behavior of the amorphous SMPs is characterized, and the results demonstrate good fixity at large deformations (up to 300%) and excellent recovery upon heating. Large energy storage capacities at Td in these RPSM materials are demonstrated compared with those achieved at elevated temperature in traditional SMPs. Interestingly, the further revealed self-healing properties of these materials are closely related to their RPSM behavior.