Chunpeng Wang

From nanocrystal synthesis to functional nanostructure fabrication: laser ablation in liquid

Although nanomaterials investigations have been carried over the recent decades, researchers still face a fundamental challenge: how to control the phase, size and shape of nanocrystals in the synthesis of nanomaterials, i.e., how to achieve the transformation from nanocrytsal synthesis to functional nanostructure fabrication. For this issue, we, in this review, introduce recent developments in laser ablation in liquid (LAL) for the synthesis and fabrication of novel nanostructures with metastable phases and shapes. Laser ablation of solid targets in liquid has actually opened a door toward to synthesize nanocrystals and fabricate nanostructures due to these advantages as follows: (i) LAL is a chemically simple and clean synthesis due to the process with reduced byproduct formation, simpler starting materials, no need for catalyst, etc. (ii) Under ambient conditions, not extreme temperature and pressure, a variety of metastable phases that may not usually be attainable, can be generated by mild preparation methods. (iii) New phase formation involves in both liquid and solid upon LAL, which allows researchers to choose and combine interesting solid target and liquid to synthesize nanocrystals and fabricate nanostructures of new compounds for purpose of fundamental research and potential applications. (iv) The phase, size and shape of the synthesized nanocrystals can be readily controlled by tuning laser parameters and applying assistances such as inorganic salts or electrical field upon LAL. For example, we have synthesized the micro- and nanocubes of carbon with C(8)-like structures by the inorganic salts assisted LAL, and the micro- and nanocubes and spindles of GeO(2) by the electrical field assisted LAL. Additionally, we have developed a new technique to fabricate functional nanopatterns on the basis of the pulsed-laser deposition in liquid. Accordingly, LAL could greatly extend its application in fabrication of functional nanostructures in the future.

Degradable rosin-ester-caprolactone graft copolymers.

We have carried out the synthesis of side-chain rosin-ester-structured poly(ε-caprolactone) (PCL) through a combination of ring-opening polymerization and click chemistry. Rosin structures are shown to be effectively incorporated into each repeat unit of caprolactone. This simple and versatile methodology does not require sophisticated purification of raw renewable biomass from nature. The rosin properties have been successfully imparted to the PCL polymers. The bulky hydrophenanthrene group of rosin increases the glass-transition temperature of PCL by >100 °C, whereas the hydrocarbon nature of rosin structures provides PCL excellent hydrophobicity with contact angle very similar to polystyrene and very low water uptake. The rosin-containing PCL graft copolymers exhibit full degradability and good biocompatibility. This study illustrates a general strategy to prepare a new class of renewable hydrocarbon-rich degradable biopolymers.

Uniformly dispersed self-assembled growth of Sb2O3/Sb@graphene nanocomposites on a 3D carbon sheet network for high Na-storage capacity and excellent stability

Large volume changes cause a series of complicated problems in alloy-type anodes, such as pulverization, exfoliation and the capacity decay which results. Therefore, solutions for the problems caused by large volume changes in sodium ion battery (SIB) anodes are urgently needed. Herein, we report a novel route to encapsulate Sb2O3/Sb nanoparticles (Sb2O3/Sb-NPs) within a graphene shell nanostructure (Sb2O3/Sb@graphene) via microwave plasma irradiation of Sb(CH3COO)3 and a subsequent graphene growth procedure. The designed structure, Sb2O3/Sb@graphene NPs anchored on carbon sheet networks (CSNs), provides an ultra-thin, flexible graphene shell to accommodate the volume changes of Sb2O3/Sb, and thus demonstrates excellent cycling stability (92.7% of the desodiation capacity was retained after 275 cycles), a long cycle life (more than 330 cycles) and a good rate capability (220.8 mA h g−1 even at 5 A g−1). The stability could be compared to that of commercial graphite in lithium ion batteries.

Amphipathic antibacterial agents using cationic methacrylic polymers with natural rosin as pendant group

We prepared a class of novel cationic polymers as antimicrobial agents: quaternary ammonium-containing poly(N,N-dimethylaminoethyl methacrylate) with natural rosin as the pendant group (PDMAEMA-g-rosin). Different from most other amphipathic antimicrobial polymeric systems reported in the literature, our approach sandwiched the hydrophilic cationic group between the polymer backbone and bulky hydrophobic hydrophenanthrene side groups. A simple quaternization reaction was used to link the rosin ester chloride and PDMAEMA homopolymers. Both the Gram-positive bacterium Staphylococcus aureus (S. aureus) and Gram-negative bacterium Escherichia coli (E. coli) were tested against the PDMAEMA-g-rosin copolymers. PDMAEMA-g-rosin copolymers with the amphipathic structure exhibited effective antimicrobial activity against both E. coli and S. aureus. Both the degree of quaternization of rosin group and the molecular weight of PDMAEMA played roles in antimicrobial activities. Our results also indicated that conformation of hydrophobic group (particularly steric hindrance) played a role in dictating antibacterial efficacy. Scanning electron microscopy and confocal laser scanning microscopy were used to characterize morphological changes of bacteria after exposure with PDMAEMA-g-rosin copolymers. Possible mechanisms on a combination of ionic and hydrophobic interactions between bacterial cells and polymers are discussed.

Sustainable thermoplastic elastomers derived from renewable cellulose, rosin and fatty acids

Two series of graft copolymers, cellulose-g-poly(n-butyl acrylate-co-dehydroabietic ethyl methacrylate) (Cell-g-P(BA-co-DAEMA)) and cellulose-g-poly(lauryl methacrylate-co-dehydroabietic ethyl methacrylate) (Cell-g-P(LMA-co-DAEMA)), were prepared by “grafting from” atom transfer radical polymerization (ATRP). In these novel graft copolymers, cellulose, DAEMA (derived from rosin), and LMA (derived from fatty acids) are all sourced from renewable natural resources. The “grafting from” ATRP strategy allows the preparation of high molecular weight graft copolymers consisting of a cellulose main chain with acrylate copolymer side chains. By manipulating the monomer ratios in the P(BA-co-DAEMA) and P(LMA-co-DAEMA) side chains, graft copolymers with varying glass transition temperatures (−50–60 °C) were obtained. Tensile stress–strain and creep compliance testing were employed to characterize mechanical properties. These novel graft copolymers did not exhibit linear elastic properties above about 1% strain, but they did manifest remarkable elasticity at strains of 500% or more. These results suggest that these cellulose-based, acrylate side-chain polymers are potential candidates for service as thermoplastic elastomers materials in applications requiring high elasticity without rupture at high strains.

The synthesis and mechanism investigations of morphology controllable 1-D SiC nanostructures via a novel approach

Single crystalline one-dimensional (1-D) β-SiC nanostructures were synthesized by the CVD (chemical vapor deposition) method using single crystal silicon wafers and detonation soot as the raw materials. The phase, morphology, crystal structure, and defects of the products were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Within a 2 h reaction time, the morphology of the SiC nanostructures can be tuned to nanowires, hexagonal columns and nanopyramids by simply altering the reaction temperature from 1250 °C, 1300 °C to 1350 °C, respectively. Based on the VLS mechanism, we propose a model to explain the novel behavior of the temperature-dependent morphology considering the relationships between catalytic droplets and nucleation.

UV-Absorbent Lignin-Based Multi-Arm Star Thermoplastic Elastomers

Lignin-grafted copolymers, namely lignin-graft-poly(methyl methacrylate-co-butyl acrylate) (lignin-g-P(MMA-co-BA)), are synthesized via grafting from atom transfer radical polymerization (ATRP) with the aid of lignin-based macroinitiators. By manipulating the monomer feed ratios of MMA/BA, grafted copolymers with tunable glass transition temperatures (-10-40 °C) are obtained. These copolymers are evaluated as sustainable thermoplastic elastomers (TPEs). The results suggest that the mechanical properties of these TPEs lignin-g-P(MMA-co-BA) copolymers are improved significantly by comparing with those of linear P(MMA-co-BA) copolymer counterparts, and the elastic strain recovery is nearly 70%. Lignin-g-P(MMA-co-BA) copolymers exhibit high absorption in the range of the UV spectrum, which might allow for applications in UV-blocking coatings.

Integration of renewable cellulose and rosin towards sustainable copolymers by “grafting from” ATRP

A class of sustainable and renewable cellulose–rosin copolymers were prepared by immobilizing rosin-derived polymer chains on the backbone of ethyl cellulose (EC) by “grafting from” atom transfer radical polymerization (ATRP). Four different rosin based polymers derived from dehydroabietic acid (DA), one of the major resin acids in natural rosin, were attached to 2-bromoisobutyryl-functionalized EC. Meanwhile, DA-grafted EC was prepared by the simple esterification reaction between DA and EC. Kinetic studies showed that the polymerization of all monomers was controlled. These grafted copolymers adopt a worm-like or rod-like structure in tetrahydrofuran, verified by light scattering experiments. These copolymers have a tunable glass transition temperature and higher thermal stability in contrast to EC. Surface morphology by AFM analysis indicated good film-forming property when rosin polymers were grafted from EC. Additionally, the introduction of DA and rosin polymers remarkably enhanced the hydrophobicity of EC. The static contact angles of all these modified copolymers are above 90°. XPS analysis revealed that the surface of these rosin-modified EC copolymers was dominated by a hydrocarbon-rich rosin moiety. The UV absorption of modified EC composites is indicative of their potential application in UV-absorbent coating materials.

Eutectic solidification applied to nanofabrication: a strategy to prepare large-scale tungsten carbide nanowalls

Close-packing WC as a kind of metallic carbide, possessing good conductivity, high melting point and superior hardness, has numerous intrinsic properties that deserve to be investigated and then explored for use in micro or nano devices in the photoelectronics field. One of the main reasons why WC has not been considered much is that low-dimensional structures such as nanowires and nanowalls are hard to prepare. Here, we developed a novel method to overcome a series of difficulties in the growth of low-dimensional WC nanostructures and managed to apply eutectic solidification in W–Al–C solution to synthesize a high-quality WC nanowall forest and nanowires on a large scale. The experiment was carried out in a high-vacuum (∼10−4 Pa) chemical vapor deposition system pumped by a turbo molecular pump. We expect that it can be applied as a universal route to prepare low-dimensional nanostructures for refractory metals compound.

Direct synthesis of novel SiC@Al2O3 core-shell epitaxial nanowires and field emission characteristics

SiC@Al2O3 core-shell epitaxial nanowires have been synthesized via one-step process by simply heating evaporating Al source and C source on silicon substrate. Energy dispersive X-ray spectroscopy and transmission electron microscopy analysis of as-fabricated samples indicate that the core-shell nanowires consist of single-crystalline β-SiC core and thin cubic γ-Al2O3 shell. Epitaxial relationship is also observed between SiC core and Al2O3 shell. The corresponding growth model is proposed to describe the growth process of the core-shell epitaxial nanowires. Moreover, field emission measurement reveals the core-shell epitaxial nanowires have the excellent field emission property with low threshold electric field of 13.8 V μm−1.