Songmin Shang

Well-Dispersed Chitosan/Graphene Oxide Nanocomposites

Nanocomposites of chitosan and graphene oxide are prepared by simple self-assembly of both components in aqueous media. It is observed that graphene oxide is dispersed on a molecular scale in the chitosan matrix and some interactions occur between chitosan matrix and graphene oxide sheets. These are responsible for efficient load transfer between the nanofiller graphene and chitosan matrix. Compared with the pure chitosan, the tensile strength, and Youngs modulus of the graphene-based materials are significantly improved by about 122 and 64%, respectively, with incorporation of 1 wt % graphene oxide. At the same time, the elongation at the break point increases remarkably. The experimental results indicate that graphene oxide sheets prefer to disperse well within the nanocomposites.

Highly durable all-fiber nanogenerator for mechanical energy harvesting

Future generations of wearable electronic systems and mobile communication place a great demand for harvesting energy from ambient environments or human movements. Soft fiber-based electric power generators are attractive in meeting the requirements of wearable devices because of efficient energy conversion performance, high durability and comfort. In this paper, we present a novel all-fiber wearable electric power nanogenerator, which consists of a PVDF–NaNbO3 nanofiber nonwoven fabric as an active piezoelectric component, and an elastic conducting knitted fabric, made from segmented polyurethane and silver coated polyamide multifilament yarns, as the top and bottom electrodes. The non-uniform deformation distribution in a compressed nanogenerator device determines the complex operating modes in the piezoelectric nanofiber nonwoven fabric. The nanogenerator consistently produces a peak open-circuit voltage of 3.4 V and a peak current of 4.4 μA in cyclic compression tests at 1 Hz and a maximum pressure of 0.2 MPa, which is comparable to normal human walking motion. More importantly, the all-fiber nanogenerator retains its performance after 1 000 000 compression cycles, demonstrating great promise as a wearable energy harvester that converts the mechanical energy of human movement into electricity.

High stretchable MWNTs/polyurethane conductive nanocomposites

Stretchable conductive polymers have aroused extensive interest in research recently due to their hi-tech applications in the fields of novel electronics, particularly for flexible electronic displays, smart textiles, medical electronics, sensors and actuators. In this study, we describe a novel elastic conductive nanocomposite made with multiwall carbon nanotubes (MWNTs) and polyurethane (PU). With the aid of an ionic liquid and under the condition of uniaxial tension, the MWNTs can form well-developed conducting networks in the PU matrix. The developed nanocomposite inherited advantageous properties from its constituents, namely the high conductivity from MWNTs, and the high elastomeric mechanical properties from the PU. Moreover, the stretchable conductive nanocomposite can be uniaxially stretched up to 100% without significant variation in electrical conductivity. The measurement of temperature dependent conductivity indicates that a 3D hopping mechanism dominates the conductivity of MWNTs.

Self-assembly of polypyrrole/chitosan composite hydrogels.

Hydrogels based on the polypyrrole (PPy)/chitosan (CS) composite are self-assembled and characterized for their electrical and swelling properties. The static polymerization of pyrrole monomer in aqueous solution containing CS is accompanied with the formation of PPy/CS composite hydrogel. The feed order in the reaction process plays a key role in the formation of the hydrogels. The participation of one-dimensional PPy blocks in the formation of the hydrogel network avoids a possible migration of PPy from the hydrogel. The effect of pH and ionic strength on the physical properties of PPy/CS composite hydrogels are investigated in detail. The results indicate that the pH-sensitive PPy/CS composite hydrogels show good water absorbencies in distilled water and saline solution. This method may open a new opportunity for the fabrication of composite hydrogels associating the biomacromolecules and conducting polymers, and the improvement of the comprehensive performance of the resulting products.

Controlled growth of polypyrrole hydrogels

Tailoring the morphology and swelling–shrinking behaviors of the conducting polymer hydrogels is vital to realizing enhanced performance. Here, we demonstrate an effective approach for the controlled growth of polypyrrole hydrogels with both electrical properties and hydrogel characteristics. Under the static synthetic conditions, the polypyrrole nanotubes are self-assembled to form mesoscale networks of the hydrogels. The effect of the kind and amount of the oxidants on the morphology and swelling–shrinking behaviors of the polypyrrole hydrogels is investigated in detail. The strength of polypyrrole hydrogel is enhanced with the increase of the amount of the oxidant. In the case of Fe(NO3)3 as the oxidant, the swelling–shrinking properties of the polypyrrole hydrogels are improved due to the more polypyrrole granules as a mesoscale cross-linker on the surface of polypyrrole nanotubes.

Intermolecular interactions between natural polysaccharides and silk fibroin protein

Fabricating novel functional and structural materials from natural renewable and degradable materials has attracted much attention. Natural polysaccharides and proteins are the right natural candidates due to their unique structures and properties. The polysaccharide-protein composites or blends were widely investigated, however, there are few systematical studies on the interactions between natural polysaccharides and silk fibroin protein at the molecular level. Among various interactions, hydrogen bonding, electrostatic interactions and covalent bonding play important roles in the structure and properties of the corresponding materials. Therefore, the focus is placed on the three interactions types in this review. A future challenge is to create polysaccharide and protein composites or blends with tailored structure and properties for the wide applications.

Synthesis and characterization of poly(3-methyl thiophene) nanospheres in magnetic ionic liquid

Poly(3-methyl thiophene) nanospheres with their size ranging around 50-60 nm have been synthesized by simply adding monomers into a magnetic ionic liquid, Bmim[FeCl(4)]. The ionic liquid leads to the formation of uniform nanospheres with a relatively narrow size distribution confined to submicrometer-sized domains. The poly(3-methyl thiophene) nanospheres were characterized by FTIR, Raman and thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) was used to show the morphology of the samples. As compared with the conventional solution polymerization method, the polymerization yield and conductivity of the polymers produced in this magnetic ionic liquid system were improved.

Covalently functionalized graphene with D-glucose and its reinforcement to poly(vinyl alcohol) and poly(methyl methacrylate)

Chemically functionalized graphene has been synthesized by covalently grafting D-glucose on graphene for the first time through an esterification reaction. The D-glucose functionalized graphene was further applied in the preparation of poly(vinyl alcohol) and poly(methyl methacrylate) nanocomposites. The thermal and mechanical properties of the prepared nanocomposites were then investigated. It was demonstrated that the D-glucose was grafted on the surface of the graphene through a covalent attachment. The chemically functionalized graphene had better dispersibility in both water and dimethylformamide than the pristine graphene. The better dispersion of the functionalized graphene in both aqueous and organic solvents simplified the preparation of the polymer nanocomposites. It was found that the D-glucose grafted graphene dispersed homogeneously in both poly(vinyl alcohol) and poly(methyl methacrylate) matrices, increasing the thermal and mechanical properties of the polymers at the same time. The phenomena were ascribed to the introduction of the D-glucose, which induced strong hydrogen bonding interactions between the functionalized graphene and the polymers. The results of this study indicate that this is an effective approach for preparing well-dispersed graphene-based polymer nanocomposites by covalently attaching functional molecules on the surface of graphene.

Highly Stretchable Conductive Polymer Composited with Carbon Nanotubes and Nanospheres

In recent decades, stretchable conductive polymers have gained extensive interest of researchers because of their hi-tech applications in electronics, textiles and medicine devices. In this study, carbon nanotubes and carbon nanospheres, as the chemically stable dopants, were uniformly dispersed in a polyurethane matrix to develop a highly elastic and stretchable conductive polymer composite film. The nanocomposite film inherited the advantageous properties from its constituents, namely the high conductivity from carbon nanotubes and nanospheres, and the elastomeric mechanical properties from the polyurethane. The conductive polymer nanocomposite film can be uniaxially and biaxially stretched up to 50% without clearly mechanical or electrical changes. Stretching beyond 50% would result in the conductivity decreasing gradually. Therefore, the as-prepared stretchable conductive polymer nanocomposites possessed both the high conductivity and the high elasticity, which would have greater application potential in high-performance electronic circuits.

Assembly of Polypyrrole-Graphene Oxide Hydrogel Nanocomposites and Their Swelling Properties

An effective one-step strategy for the static assembly of hydrogels from polypyrrole (PPy) and graphene oxide (GO) is demonstrated. The static polymerization of pyrrole monomer was carried out in the presence of GO nanosheets, leading to the formation of PPy-GO hydrogels. During the static polymerization process, gelation takes place simultaneously by supramolecular interactions. The well-dispersed GO nanosheets in the polymer networks resulted in a significant improvement in water absorbencies. With only a very low loading of GO in the PPy-GO hydrogels, they exhibited significantly larger water uptake compared to a PPy hydrogel. Even in saline solutions, PPy-GO hydrogels also showed obvious water absorbency. Moreover, the PPy-GO hydrogels exhibited a better water retention ability compared with the control under the same conditions. This method is believed to provide possibilities to combine the extraordinary performances of GO with the multifunctional properties of conducting polymers, thus holding great potential for technical applications in the future.