All-carbon electrode-based fiber-shaped dye-sensitized solar cells

A novel fiber-shaped dye-sensitized solar cell (DSSC) based on an all-carbon electrode is presented, where low-cost, highly-stable, and biocompatible carbon materials are applied to both the photoanode and the counter electrode. The fibrous carbon-based photoanode has a core-shell structure, with carbon fiber core used as conductive substrate to collect carriers and sensitized porous TiO(2) film as shell to harvest light effectively. The highly catalytic all-carbon counter electrode is made from ink carbon coatings and carbon fiber substrate. Results show that the open circuit voltage can be largely improved through engineering at the carbon fiber/TiO(2) interface. An optimized diameter of the photoanode results in an efficiency of 1.9%. It is the first demonstration of efficient DSSCs based on all-carbon electrodes, and the devices are totally free from TCOs or any other expensive electrode materials. Also, this type of solar cell is significant in obtaining bio-friendly all-carbon photovoltaics suitable for large-scale production.     

The electrochemistry of CVD graphene: progress and prospects

The unique electronic properties of graphene, a one atom thick carbon layer, were reported by scientists in 2004. Since this time graphene has subsequently been found to display several more unique and fascinating electrical, optical and mechanical properties. One particular area in which graphene has reportedly made an impact is in the field of electrochemistry, such as in providing enhancements in energy storage/generation and electrochemical sensing applications. Since 2005, when graphene was shown to be fabricated by the so-called 'Scotch tape technique' where multiple layers of graphene are peeled from a slab of Highly Ordered Pyrolytic Graphite using adhesive tape and transferred onto an appropriate substrate, other fabrication methodologies of graphene have emerged. In the majority of cases, graphene is produced and supplied in solution, such that graphene has to be immobilised onto the desired surface. A fabrication process where graphene is grown upon a substrate and is ready for implementation is the Chemical Vapour Deposition (CVD) of graphene. In this perspective article we overview recent developments in the fabrication of CVD graphene and explore its utilisation in electrochemistry, considering its fundamental understanding through to applications in sensing and energy related devices.     

Field-effect flow control in a polydimethylsiloxane-based microfluidic system.

The application of the field-effect for direct control of electroosmosis in a polydimethylsiloxane (PDMS)-based microfluidic system, constructed on a silicon wafer with a 2.0 microm electrically insulating layer of silicon dioxide, is demonstrated. This microfluidic system consists of a 2.0 cm open microchannel fabricated on a PDMS slab, which can reversibly adhere to the silicon wafer to form a hybrid microfluidic device. Aside from mechanically serving as a robust bottom substrate to seal the channel and support the microfluidic system, the silicon wafer is exploited to achieve field-effect flow control by grounding the semiconductive silicon medium. When an electric field is applied through the channel, a radial electric potential gradient is created across the silicon dioxide layer that allows for direct control of the zeta potential and the resulting electroosmotic flow (EOF). By configuring this microfluidic system with two power supplies at both ends of the microchannel, the applied electric potentials can be varied for manipulating the polarity and the magnitude of the radial electric potential gradient across the silicon dioxide layer. At the same time, the longitudinal potential gradient through the microchannel, which is used to induce EOF, is held constant. The results of EOF control in this hybrid microfluidic system are presented for phosphate buffer at pH 3 and pH 5. It is also demonstrated that EOF control can be performed at higher solution pH of 6 and 7.4 by modifying the silicon wafer surface with cetyltrimethylammonium bromide (CTAB) prior to assembly of the hybrid microfluidic system. Results of EOF control from this study are compared with those reported in the literature involving the use of other microfluidic devices under comparable solution conditions.     

Design of aromatic copolyesters for use in microelectronic devices

The next generation of microelectronic devices will require design of new kinds of polymers which are tailored to display a dielectric constant as low as 2.0, a coefficient of thermal expansion (CTE) which matches the metal circuitry as well as the silicon substrate, moisture and chemical resistance, and dimensional stability at processing temperatures of 300-400°C which are required to form an adhesive bond between laminates. In our program, we have made significant progress in all of these areas through the use of liquid crystalline copolyesters (LCP's) laminated with a newly developed crosslinkable copolyester. In this paper, data are presented which illustrate how films and coatings of either system can be made to adhere in the solid state by interchain transesterification reactions (ITR) at the interface. Ability to foam the crosslinkable copolyester films provides direct control over the dielectric constant. The effect of pore size and distribution on the dielectric constant will be discussed. The potential to dramatically increase the melting point of the LCP's through high temperature annealing is also discussed.     

Room temperature UV adhesive bonding of CE devices

A simple low temperature adhesive 'stamp-and-stick' bonding procedure for lab-on-a-chip glass devices has been tested for capillary electrophoresis applications. This technique involves use of a mask aligner to transfer a UV-curable adhesive selectively onto the top CE substrate which is then aligned with and bonded to the bottom CE wafer. The entire bonding process can be carried out at room temperature in less than 30 minutes, involved only user-friendly laboratory operations, and provided a near 100% success rate. CE microchips made in this manner exhibited similar electroosmotic flow and separation characteristics as ones made via conventional high temperature thermal bonding. Equally important, the devices provided stable long-term performance over weeks of use, encompassing hundreds of individual CE runs without structural failure or any apparent change in operating characteristics. Finally, these devices exhibited excellent chip-to-chip reproducibility. Successful adaptation of the stamp-and-stick approach did require the development and testing of new but easily implemented structural features which were incorporated into the chip design and whose nature is described in detail.     

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/ Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carbon fiber reinforced epoxy resin composite joints,energy dispersive X-ray spectroscopy analysis(EDX)is used to establish the content change of oxygen in the adhesive in adhesive/carbon fiber reinforced epoxy resin composite joints.As water is made up of oxygen and hydrogen,the water diffusion coefficients and dynamics in adhesive/carbon fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging,via EDX analysis.The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of both energy dispersive X-ray spectroscopy and elemental analysis.The determined results with EDX analysis are almost the same as those determined with elemental analysis and the results also show that the durability of the adhesive/carbon fiber reinforced epoxy resin composite joints subjected to silane coupling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treatment.     

Rotaxane‐Like Structures Threaded through the Pores of Hollow Porous Nanocapusles

Nanocapsules with molecules threaded through the porous shells may lead to advanced cell‐mimicking functional devices. Herein, we show the feasibility of synthesizing such hybrid nanostructures by using vesicle‐templated polymer nanocapsules with controlled nanopores. Ship‐in‐a‐bottle assembly inside a nanocapsule created an internal unit. An external unit was then connected to an entrapped internal unit through pre‐attached linker threaded through a nanopore in the shell of the nanocapsule. Both internal and external units are larger than the pore size and cannot cross the shell, producing a rotaxane‐like structure. Successful synthesis was achieved with fairly short linkers (six and ten carbon atoms in a chain), creating an opportunity for facile synthesis of functional devices capable of cross‐shell communication.     

Fibrin Matrices as (Injectable) Biomaterials: Formation,Clinical Use,and Molecular Engineering

This review focuses on fibrin, starting from biological mechanisms (its production from fibrinogen and its enzymatic degradation), through its use as a medical device and as a biomaterial, and finally discussing the techniques used to add biological functions and/or improve its mechanical performance through its molecular engineering. Fibrin is a material of biological (human, and even patient's own) origin, injectable, adhesive, and remodellable by cells; further, it is nature's most common choice for an in situ forming, provisional matrix. Its widespread use in the clinic and in research is therefore completely unsurprising. There are, however, areas where its biomedical performance can be improved, namely achieving a better control over mechanical properties (and possibly higher modulus), slowing down degradation or incorporating cell‐instructive functions (e.g., controlled delivery of growth factors). The authors here specifically review the efforts made in the last 20 years to achieve these aims via biomimetic reactions or self‐assembly, as much via formation of hybrid materials.     

Effect of acetone on mechanical properties of epoxy used for surface treatment before adhesive bonding

A thin layer of un-cured resin over metal substrates applied by using an acetone-diluted resin solution (without hardener) has been found to be beneficial to strong adhesive bonding. The resin pre-coating (RPC) solution can effectively seal sub-surface micro-cavities and increase the substrate wettability. This study examines possible aftermath effects of the acetone dilution on mechanical properties of epoxy through comparison of samples made from as-received resin and resins diluted once and twice by acetone. RPC can be accepted with confidence in substrate pre-treatments for strong adhesive bonding if no detrimental effect on epoxy properties is observed. Fourier transform infrared spectrum (FTIR) was conducted, showing the spectrogram of the resin previously diluted by acetone was the same as that of as-received resin, i.e. no change in epoxy molecular structures after complete evaporation of acetone. Strength and modulus of elasticity measured by flexural and compressive tests were compared using samples made from as-received resin, and resins diluted once and twice by acetone. Variations among results from the three groups were less than 2%, or negligible, affirming the RPC method can be used for substrate pre-treatments and stronger adhesive bonding.     

层层组装构筑聚电解质/碳纳米管导电黏附膜

首先将聚烯丙基胺盐酸盐与碳纳米管制成复合物(PAH-CNT), 再通过层层组装技术构筑了聚丙烯酸和碳纳米管混合物(PAA-CNT)与PAH-CNT多层复合膜(PAH-CNT/PAA-CNT). PAH-CNT/PAA-CNT多层复合膜同时具有导电和黏附性能. 在玻璃和ITO基片上沉积的PAH-CNT/PAA-CNT多层复合膜的最大拉伸剪切强度接近7 MPa, 即1 cm²的黏附膜可以承受约70 kg的重物. 碳纳米管的引入使PAH-CNT/PAA-CNT多层复合膜具有更好的导电性.     

Contact instability of thin elastic films on patterned substrates

The free surface of a soft elastic film becomes unstable and forms an isotropic labyrinth pattern when a rigid flat plate is brought into adhesive contact with the film. These patterns have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. We show that these random structures can be ordered, modulated, and aligned by depositing the elastic film (cross-linked polydimethylsiloxane) on a patterned substrate and by bringing the free surface of the film in increasing adhesive contact with a flat stamp. Interestingly, the influence of the substrate "bleeds" through the film to its free surface. It becomes possible to generate complex two-dimensional ordered structures such as an array of femtoliter beakers even by using a simple one-dimensional stripe patterned substrate when the instability wavelength, lambda approximately 3H, nearly matches the substrate pattern periodicity. The free surface morphology is modulated in situ by merely varying the stamp-surface separation distance. The free surface structures originating from the elastic contact instability can also be made permanent by the UV-ozone induced oxidation and stiffening.     

Electroactive SWNT/PEGDA hybrid hydrogel coating for bio-electrode interface

Electric interface between neural tissue and electrode plays a significant role in the development of implanted devices for continuous monitoring and functional stimulation of central nervous system in terms of electroactivity, biocompatibility and long-term stability. To engineer an interface that possesses these merits, a polymeric hydrogel based on poly(ethylene glycol) diacrylate (PEGDA) and single-walled carbon nanotubes (SWNTs) were employed to fabricate a hybrid hydrogel via covalent anchoring strategy, i.e., self-assembly of cysteamine (Cys) followed by Michael addition between Cys and PEGDA. XPS characterization proves that the Cys molecules are linked to gold surface via the strong S-Au bond and that the PEGDA macromers are covalently bonded to Cys. FTIR spectra indicate the formation of hybrid hydrogel coating during photopolymerization. Electrochemical measurements using cyclic voltammetry (CV) and impedance spectrum clearly show the enhancement of electric properties to the hydrogel by the SWNTs. The charge transfer of the hybrid hydrogel-based electrode is quasi-reversible and charge transfer resistance decreases to the tenth of that of the pure hydrogel due to electron hopping along the SWNTs. Additionally, this hybrid hydrogel provides a favorable biomimetic microenvironment for cell attachment and growth due to its inherent biocompatibility. Combination of these merits yields hybrid hydrogels that can be good candidates for application to biosensors and biomedical devices. More importantly, the hybrid hydrogel coatings fabricated via the current strategy have good adhesion to the electrode substrate which is highly desired for chronically implantable devices.     

二维碳纳米薄膜制备的新途径——由自组装膜到石墨烯

本文描述了芳香族分子作为自组装单分子膜(SAMs)前驱体在电子辐照下引发芳香基团交联,在真空或惰性气氛中转化为具有较高热稳定性的碳纳米薄膜(CNMs)。CNMs具有足够的机械强度,可从其基底表面转移作为独立的薄膜材料,经高温淬火后转化为石墨烯。根据制备条件,如芳香分子前驱体的化学结构、电子辐照和淬火参数等,可以调整所制得的石墨烯的形状、结晶度、厚度、孔径等各种性能。各种芳香族硫醇,如低环及多环芳烃碳氢化合物,获得的CNMs的结构和功能由其单分子膜的结构所决定。本文详细讨论了电子辐射诱导SAMs芳香分子交联反应的机理。CNMs/石墨烯异质结构的非破坏性化学功能化组装为CNMs/石墨烯在电子、光子器件以及生物膜中的应用开辟了一条灵活的途径。     

Forensic isotope ratio mass spectrometry of packaging tapes

Pressure sensitive adhesive tape (brown parcel tape) is employed in a great many criminal activities such as the restraint of individuals during robbery and offences against the person, the enclosure of explosive devices and the packaging and concealment of controlled drugs. Packaging materials are ubiquitous in modern society and are produced in such vast quantities that it is increasingly difficult to distinguish between different products or to link materials to a common source. This study demonstrates the potential of stable isotope ratio mass spectrometry to characterise parcel tapes based on a number of properties. The carbon isotopic signature, derived from the substrate polymer, associated additives and adhesive is highly characteristic of a particular tape and allows samples from different sources to be readily distinguished. Further discrimination may be achieved by the incorporation of deuterium and oxygen isotopic data and by analysis of the isolated backing polymer. Recovery of intact tape from simulated forensic samples proved straightforward and the isotopic signature of the tape did not appear to be affected by adverse storage conditions.     

Preparation of highly monodispersed hybrid silica spheres using a one-step sol-gel reaction in aqueous solution

The successful one-step preparation method of monodisperse hybrid silica particles was studied using organosilane chemicals in aqueous solution. In general, almost all of the hybrid silica materials were made by a complex method where organic materials were coated on the surface of silica substrate via chemical reaction. However, our novel method can be applied to prepare colloidal hybrid particles without using substrate material. This method has three advantages: (i) this simple method gives the opportunity to prepare hybrid particles with high monodispersity through the self-hydrolysis of various organosilane monomers in aqueous solution, (ii) this efficient method can be applied to load lots of organic functional groups on the surface of silica particles through a one-step preparation method using only organosilane, and (iii) this effective method can be used to control the particle size of the product by changing the experimental conditions such as the concentration of the precursor or the reaction temperature. Detailed characterization of the hybrid particles by scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis (TGA) was performed to elucidate the morphologies and properties of the hybrid silica particles.     

Nanostructuring carbon supports for optimal electrode performance in biofuel cells and hybrid fuel cells

The efficiencies of dioxygen reduction on common carbonaceous materials were compared using voltammetry and fuel cell measurements. Carbon paper (CP), carbon fibre (CF) or carbon cloth (CC) conducting supports were covered under water pump pressure with multiwalled carbon nanotubes (MWCNTs) to increase the working surface of the electrode, improve connectivity with enzyme molecules and provide direct electron transfer. Laccase was the biocathode catalyst catalyzing 4-electron reduction of oxygen to water on the nanostructured electrode. CP carbon paper was selected as the favourable electrode substrate, since it provided best durability holding firmly the carbon nanotubes together with the enzyme at the electrode surface. Zinc disc or fructose dehydrogenase was used as anode in the hybrid fuel cell and biofuel cell, respectively. The characteristics under externally applied resistances and potential-time dependencies under flowing solution conditions were evaluated. The hybrid fuel cell based on Zn anode and CP supported laccase cathode gave the best results in terms of power and open circuit potential (OCP). The full biofuel cell based on laccase and fructose dehydrogenase shows lower OCP but the power–time dependencies were similar to those of the hybrid biofuel cell. The nanostructured surfaces show good supercapacitor properties due to the presence of carbon nanotubes at the electrode surface. The fuel cells undergo self-charging/discharging and, therefore, can be conveniently employed in pulsed-work regime to power external devices.     

自偏压作用下纳米碳管的定向生长

以玻璃为基板材料, 在550 ℃的低温条件下利用微波等离子体化学气相沉积法合成了定向纳米碳管.结果表明, 在利用微波等离子体化学气相沉积法合成纳米碳管时, 因等离子体作用存在于基板表面的自偏压对纳米碳管的定向生长起着非常重要的作用.自偏压的作用总是使纳米碳管的生长垂直于基板表面.     

Surfactant-free water-processable photoconductive all-carbon composite

Heterojunctions between different graphitic nanostructures, including fullerenes, carbon nanotubes and graphene-based sheets, have attracted significant interest for light to electrical energy conversion. Because of their poor solubility, fabrication of such all-carbon nanocomposites typically involves covalently linking the individual constituents or the extensive surface functionalization to improve their solvent processability for mixing. However, such strategies often deteriorate or contaminate the functional carbon surfaces. Here we report that fullerenes, pristine single walled carbon nanotubes, and graphene oxide sheets can be conveniently coassembled in water to yield a stable colloidal dispersion for thin film processing. After thermal reduction of graphene oxide, a solvent-resistant photoconductive hybrid of fullerene-nanotube-graphene was obtained with on-off ratio of nearly 6 orders of magnitude. Photovoltaic devices made with the all-carbon hybrid as the active layer and an additional fullerene block layer showed unprecedented photovoltaic responses among all known all-carbon-based materials with an open circuit voltage of 0.59 V and a power conversion efficiency of 0.21%. The ease of making such surfactant-free, water-processed, carbon thin films could lead to their wide applications in organic optoelectronic devices.     

Directed self-assembly of microcomponents enabled by laser-activated bubble latching

This article introduces a method for microscale assembly using laser-activated bubble latching. The technique combines the advantages of directed fluidic assembly and surface tension-driven latching to create arbitrarily complex and irregular structures with unique properties. The bubble latches, generated through the laser degradation of the tile material, are created on the fly, reversibly linking components at user-determined locations. Different phases of latching bubble growth are analyzed, and shear force calculations show that each bubble is able to support a tensile force of approximately 0.33 μN. We demonstrate that by exploiting the compressibility of bubbles, assembled objects can be made to switch between rigid and flexible states, facilitating component assembly and transport. Furthermore, we show reconfiguration capabilities through the use of bubble hinging. This novel hybrid approach to the assembly of microscale components offers significant user control while retaining a simplistic design environment.     

Diffusive Adhesives for Water-Rich Materials: Strong and Tunable Adhesion Beyond the Interface

It is notoriously difficult to adhere water-rich materials, such as hydrogels and biological tissues. Existing adhesives usually suffer from weak and nonadjustable adhesion strength, in part because the contact between the adhesive and substrate is largely restrained to the adhesive/substrate interface. In this study, we have attempted to overcome this shortcoming by developing a class of diffusive adhesives (DAs) that can extend adhesion deep into the substrate to maximize the adhesive/substrate contact. The DAs consist of hydrogel matrices and preloaded water-soluble monomers and crosslinkers that can diffuse extensively into the water-rich substrates after adhesive/substrate contact. Polymerization and crosslinking of the monomers are then triggered leading to a bridging network that interpenetrates the DA and substrate skeletons and topologically binds them together. This kind of adhesion, in the absence of adhesive/substrate covalent bonding, is of high strength and toughness, comparable to those of the best-performing natural and artificial adhesives. More importantly, we can precisely tune the adhesion strength on demand by manipulating the diffusion profile. It is envisioned that the DA family could be extended to include a large pool of hydrogel matrices and monomers, and that they could be particularly useful in biological and medical applications.