Facile preparation and thermoelectric properties of Bi₂Te₃ based alloy nanosheet/PEDOT:PSS composite films

Bi2Te3 based alloy nanosheet (NS)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) composite films were prepared separately by spin coating and drop casting techniques. The drop cast composite film containing 4.10 wt % Bi2Te3 based alloy NSs showed electrical conductivity as high as 1295.21 S/cm, which is higher than that (753.8 S/cm) of a dimethyl sulfoxide doped PEDOT:PSS film prepared under the same condition and that (850-1250 S/cm) of the Bi2Te3 based alloy bulk material. The composite film also showed a very high power factor value, ∼32.26 μWm(-1) K(-2). With the content of Bi2Te3 based alloy NSs increasing from 0 to 4.10 wt %, the electrical conductivity and Seebeck coefficient of the composite films increase simultaneously.

ZnO flower/PEDOT:PSS thermoelectric composite films

ZnO flower/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) composite films were prepared by spin-coating dimethyl sulfoxide doped PEDOT:PSS on the ZnO flowers grown on glass substrate. The thermoelectric properties of the ZnO flower/PEDOT:PSS composite films were measured at room temperature. As the number of spin coated PEDOT:PSS layer increased, the electrical conductivity of the ZnO flower/PEDOT:PSS composite films increases dramatically from 1-layer (177.3 S/m) to 4-layer (910.4 S/m), however, all the composite films have almost the same Seebeck coefficient (~20–22 μV/K). A maximum power factor of ~0.4 μWm−1 K−2 at room temperature was obtained from the composite film with 4-layer PEDOT:PSS.

Transparent uv-shielding films from organic small molecule-intercalated layered double hydroxide nanoplatelets/polymer composite

In this study, layered double hydroxide (LDH) with nitrate as the interlayer anion has been partially exfoliated in dimethyl sulfoxide (DMSO). Atomic force microscopy (AFM) images showed that both the lateral size and the thickness of the LDH nanoplatelets were decreased after DMSO treatment. Formation of transparent LDH suspension in DMSO was observed. Taking this advantage, we have prepared transparent LDH/ethylene-vinyl alcohol copolymer (EVOH) nanocomposite films using DMSO as the processing solvent. Organic small molecules, UV absorbers, were intercalated into the LDH interlayers to incorporate the UV-shielding property into the transparent composite films. The thermal stability of UV absorbers was considerably improved after intercalation, which was attributed to the electrostatic interaction between the guest UV absorbers and the host LDH layers. The prepared composite films were flexible and exhibited excellent UV-shielding capability, but had transmittance as high as 90% in the visible region. The effect of LDH filler on thermal and mechanical properties of the composite films was also examined.

Mechanical properties of graphene films enhanced by homo-telechelic functionalized polymer fillers via π-π Stacking interactions

© 2015 Elsevier Ltd. All rights reserved. Most researches on graphene/polymer composites are focusing on improving the mechanical and electrical properties of polymers at low graphene content instead of paying attention to constructing graphene's macroscopic structures. In current study the homo-telechelic functionalized polyethylene glycols (FPEGs) were tailored with π-orbital-rich groups (namely phenyl, pyrene and di-pyrene) via esterification reactions, which enhanced the interaction between polyethylene glycol (PEG) molecules and chemical reduced graphene oxide (RGO) sheets. The π-π stacking interactions between graphene sheets and π-orbital-rich groups endowed the composite films with enhanced tensile strength and tunable electrical conductivity. The formation of graphene network structure mediated by the FPEGs fillers via π-π stacking non-covalent interactions should account for the experimental results. The experimental investigations were also complemented with theoretical calculation using a density functional theory. Atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), UV-vis and fluorescence spectroscopy were used to monitor the step-wise preparation of graphene composite films.

High-performance flexible all-solid-state supercapacitor from large free-standing graphene-PEDOT/PSS films

Although great attention has been paid to wearable electronic devices in recent years, flexible lightweight batteries or supercapacitors with high performance are still not readily available due to the limitations of the flexible electrode inventory. In this work, highly flexible, bendable and conductive rGO-PEDOT/PSS films were prepared using a simple bar-coating method. The assembled device using rGO-PEDOT/PSS electrode could be bent and rolled up without any decrease in electrochemical performance. A relatively high areal capacitance of 448 mF cm(-2) was achieved at a scan rate of 10 mV s(-1) using the composite electrode with a high mass loading (8.49 mg cm(-2)), indicating the potential to be used in practical applications. To demonstrate this applicability, a roll-up supercapacitor device was constructed, which illustrated the operation of a green LED light for 20 seconds when fully charged.

Artificial Muscles Based on Polypyrrole/Carbon Nanotube Laminates

A novel method for the periodical assembly of laminates of forest-drawn carbon nanotube (CNT) sheets and polypyrrole (PPy) is described. The method produces composite films in which the volume fraction and orientation of CNTs can be controlled. Actuator stroke and strength is increased and work capacity per cycle doubled when nanotube orientation is perpendicular to the actuation direction. Most importantly, these PPy/CNT laminates have dramatically decreased creep during actuation, which has been a major barrier for the application of PPy actuators.

Cellulose-based biodegradable blends and composites regenerated from ionic liquids

This thesis presents the fabrication of biodegradable polymer blends and composites with the assistance of ionic liquids. The work included preparation and characterization of cellulose/PCL blend films, cellulose/ PCL-PDMS-PCL blend films, cellulose/ PVAL blend films and cellulose/clay composite films. An efficient and feasible approach of reducing plastic pollution was developed.

Graphene and graphitic derivative filled polymer composites as potential sensors

Graphite and numerous graphitic-derived micro- and nano-particles have gained importance in current materials science research. These two-dimensional sheets of sp(2)-hybridized carbon atoms remarkably influence the properties of polymers. Graphene mono-layers, graphene oxides, graphite oxides, exfoliated graphite, and other related materials are derived from a parental graphite structure. In this review, we focus primarily on the role of these fillers in regulating the electrical and sensing properties of polymer composites. It has been demonstrated that the addition of an optimized mixture of graphene and or its derivatives to various polymers produces a record-high enhancement of the electrical conductivity and achieved semiconducting characteristics at small filler loading, making it suitable for sensor manufacture. Promising sensing characteristics are observed in graphite-derived composite films compared with those of micro-sized composites and the properties are explained mainly based on the filler volume fraction, nature and rate of dispersion and the filler polymer interactions at the interface. In short, this critical review aims to provide a thorough understanding of the recent advances in the area of graphitic-based polymer composites in advanced electronics. Future perspectives in this rapidly developing field are also discussed.

Superhydrophobic and superoleophilic micro-wrinkled reduced graphene oxide as a highly portable and recyclable oil sorbent.

The potential of superhydrophobic and superoleophilic microwrinkled reduced graphene oxide (MWrGO) structures is here demonstrated for oil spill cleanup. The impact of the thickness of MWrGO films on the sorption performance of three different oils was investigated. Water contact angles across the MWrGO surfaces were found to exceed 150°, while oil could be easily absorbed by the microwrinkled structures of MWrGO within seconds after contact. Although the oil surface diffusion rate was not found to be dependent on the thickness of the graphene oxide films, the oil sorption capacity was the largest with the thinner MWrGO films due to the high surface area resulting from their fine surface texture. Furthermore, the composite films can be repeatedly used for at least 20 oil sorption-removal cycles without any notable loss in selectivity and uptake capacity. These MWrGO/elastomer composite films could be applied as a potential candidate material for future oil spill cleanup.

Study on the oriented recrystallization of carbon-coated polyethylene oriented ultrathin films

It is confirmed that a layer of vacuum-evaporated carbon on the surface of a preoriented ultrathin polymer film can lead to an oriented recrystallization of the polymer film. This has been attributed to a strong fixing effect of vacuum-evaporated carbon layer on the film surface of the polymer. To study the origin of the strong fixing effect of vacuum-evaporated carbon layer on the polymer films, the melting and recrystallization behaviors of the preoriented ultrathin PE film with a vacuum-evaporated carbon layer were studied by using atomic force microscopy, electron diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. We found that there exists some extent of chain orientation of carbon-coated polyethylene (PE) preoriented ultrathin film above its melting temperature. These oriented PE chain sequences act as nucleation sites and induce the oriented recrystallization of preoriented PE film from melt. Raman spectroscopy results suggest that new carbon-carbon bonds between the carbon layer and the oriented PE film are created during the process of vacuum carbon evaporation. As a result, some of the PE chain stems are fixed to the coated carbon substrate via covalent bond. Such a bonding has retarded the relaxation of the PE chains at the spot and, therefore, preserves the original orientation of the PE stems at high temperature, which in turn derives the recrystallization of the PE chains in an oriented structure.

Crosslinking neat ultrathin films and nanofibres of pH-responsive poly(acrylic acid) by UV radiation

Electrospun polyelectrolyte hydrogel nanofibres are being developed for many applications including artificial muscles, scaffolds for tissue engineering, wound dressings and controlled drug release. For electrospun polyelectrolytes, a post-spinning crosslinking process is necessary for producing a hydrogel. Typically, radiation or thermal crosslinking routines are employed that require multifunctional crosslinking molecules and crosslink reaction initiators (free radical producers). Here, ultraviolet subtype-C (UVC) radiation was employed to crosslink neat poly(acrylic acid) (PAA) nanofibres and films to different crosslink densities. Specific crosslink initiators or crosslinking molecules are not necessary in this fast and simple process providing an advantage for biological applications. Scanning probe microscopy was used for the first time to measure the dry and wet dimensions of hydrogel nanofibres. The diameters of the swollen fibres decrease monotonically with increasing UVC radiation time. The fibres could be reversibly swollen/contracted by treatment with solutions of varying pH, demonstrating their potential as artificial muscles. The surprising success of UVC radiation exposure to achieve chemical crosslinks without a specific initiator molecule exploits the ultrathin dimensions of the PAA samples and will not work with relatively thick samples.

Ag/AgCl composite nanoparticles/polyacrylonitrile nanofiber films for visible-light photocatalysis

Ag/AgCl composite nanoparticles/polyacrylonitrile nanofiber films were prepared by electrospinning and subsequent in-situ reduction combining in-situ oxidation strategy. Electrospinning was firstly used to fabricate PAN/AgNO3 composite nanofibers; then the AgNO3 was reduced by in-situ reduction with glycol; finally, an in-situ oxidation between Ag nanoparticles and FeCl3 solution was carried on to prepare the compo-site nanofiber films. The as-prepared materials can be used as high-performance photocatalysts, taking the advantage of the visible-light activity, flexibility, and high photocatalytic kinetics. The present method is helpful for the development of the high-performance membrane based photocatalysts.

Moisture uptake by some uncured adhesive films

The uptake of moisture by epoxy-based adhesives and fibre reinforced composites after cure has been the topic of many studies. The extent of moisture uptake by uncured adhesive films and composite prepregs, and the effect which this has on the performance of such systems after cure, has received much less attention. It is, nonetheless, recognised as an important consideration and most aerospace lay up facilities include controlled humidity conditions.

Tri-component bio-composite materials prepared using an eco-friendly processing route

We report on the blending of three natural polymers, raw cotton, silk and wool, using ionic liquids as the dissolving media. We find that with increased content of wool and silk the thermal degradation temperature of the new bio films increases. This is due to an increase in the hydrogen bond network between the blended polymers. We also investigated the role of the coagulating solvent by coagulating the bio films using water, methanol or isopropanol. Again, we find the coagulating solvent impacts the final properties of the bio films with water shown to coagulated films with the best material properties.

Promoted water transport across graphene oxide-poly(amide) thin film composite membranes and their antibacterial activity

Hybrid composite membranes have great potential for desalination applications since water transport can be favorably promoted by selective diffusion at the interface between matrix and reinforcement materials. In this paper, graphene oxide nano-sheets were successfully incorporated across 200nm thick poly(amide) films by interfacial polymerization to form novel thin-film composite membranes. The impact of the graphene oxide on the morphology, chemistry, and surface charge of the ultra-thin poly(amide) layer, and the ability to desalinate seawater was investigated. The graphene oxide nano-sheets were found to be well dispersed across the composite membranes, leading to a lower membrane surface energy and an enhanced hydrophilicity. The iso-electric point of the samples, key to surface charge repulsion during desalination, was found to be consistently shifted to higher pH values with an increasing graphene oxide content. Compared to a pristine poly(amide) membrane, the pure water flux across the composite membranes with 0.12wt.% of graphene oxide was also found to increase by up to 80% from 0.122 to 0.219L·μm·m-2·h-1·bar-1 without significantly affecting salt selectivity. Furthermore, the inhibitory effects of the composite membrane on microbial growth were evaluated and the novel composite membranes exhibited superior anti-microbial activity and may act as a potential anti-fouling membrane material.