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The unique frictional behavior of polyethylenimine/molybdenum disulphide (PEI/MoS2)n thin films on steel substrates, deposited via the layer-by-layer (LbL) technique, is explored. The effects of gaseous atmosphere (i.e. air vs. dry nitrogen), and heat treatment of the coatings are investigated. The coefficients of friction (COFs) are reduced by factors of ca. 2 and 11 in air and N2 respectively, compared to an uncoated steel substrate. Ultra-low friction (COF

Highly sensitive fiber-optic ammonia gas sensors were fabricated via layer-by-layer deposition of poly(diallyldimethylammonium chloride) (PDDA) and tetrakis(4-sulfophenyl)porphine (TSPP) onto the surface of the core of a hard-clad multimode fiber that was stripped of its polymer cladding. The effects of film thickness, length of sensing area, and depth of evanescent wave penetration were investigated to clearly understand the sensor performance. The sensitivity of the fiber-optic sensor to ammonia was linear in the concentration range of 0.5–50 ppm and the response and recovery times were less than 3 min, with a limit of detection of 0.5 ppm, when a ten-cycle PDDA/TSPP film was assembled on the surface of the core along a 1 cm-long stripped section of the fiber. The sensor’s response towards ammonia was also checked under different relative humidity conditions and a simple statistical data treatment approach, principal component analysis, demonstrated the feasibility of ammonia sensing in environmental relative humidity ranging from dry 7% to highly saturated 80%. Penetration depths of the evanescent wave for the optimal sensor configuration were estimated to be 30 and 33 nm at wavelengths of 420 and 706 nm, which are in a good agreement with the thickness of the 10-cycle deposited film (ca. 30 nm).

We have prepared new charge-transfer (CT) complex polymer blend membranes (CT membranes), for use as high performance polymer electrolyte membranes (PEMs); with a simple and easy preparation method for application in PEFCs. In this study, electron-accepting sulfonated polyimide (SPI) and electron-donating polyether (PE), were used to develop polymer-polymer type CT membranes. The formation of CT complex in the obtained SPI/PE membranes was confirmed by visible spectroscopy. The use of flexible spacers in the PE and heat treatment of the CT membranes, enhanced the CT complex formation. SPI/PE CT membranes showed 1.9–2.2 times higher mechanical strength than the original SPI, while SPI/PE 0.33 CT membrane with heat treatment at 130 °C for 2 h showed 4.3 times higher mechanical strength than the original SPI. Hydrogen permeability through SPI/PE CT membranes was 4.1–5.4 times lower than Nafion 212 and 1.4–1.9 times lower than the original SPI membrane. We have prepared a thin SPI/PE CT membrane (10 µm thickness), that showed comparable OCV (0.88 V), similar resistance compared to Nafion 212 and demonstrated more than 10 h of durability in a fuel cell test; suggesting that SPI/PE thin CT membrane can be applied for PEFC application.

Graphene oxide (GO) is potentially a useful electrolyte material for polymer electrolyte membrane fuel cells due to its high strength, excellent hydrogen gas barrier properties, hydrophilicity, and proton conducting acidic functional groups. Here, GO paper is prepared from aqueous dispersion by vacuum-filtration, and the hydrogen permeability (2 × 10 −2 barrer) is measured to be 3 orders of magnitude lower than Nafion (30 barrer) at 30 °C. The in-plane and through-plane conductivities are measured to be 49.9 and 0.3 mS cm −1 , respectively. This significant anisotropy is attributed to the lamellar structure of GO, and the physical anisotropy between the thickness and lateral size of the GO nanoplatelets. Interestingly, the in-plane conductivity of GO is comparable to the through-plane conductivity of Nafion. GO membrane fuel cells (GOMFCs) are fabricated. To compensate for the low in-plane conductivity of GO, whilst taking advantage of the excellent hydrogen gas barrier properties, extremely thin electrode-supported GOMFCs are prepared by spray painting GO directly onto the electrocatalyst layer. The effect of membrane thickness on cell performance is investigated. Decreasing membrane thickness by spray painting improves the power density from 3.7 mW cm −2 for a 50 μm-thick membrane-supported GOMFC, to 79 mW cm −2 for a 3 µm-thick, spray-painted membrane, electrode-supported GOMFC.

The efficiency and lifetime of mechanical devices is significantly decreased by friction and wear, significantly contributing to global energy consumption. We previously showed that multilayer polyethyleneimine/graphene oxide thin films, (PEI/GO)15, on steel display superlubricity against a steel counterface ball. Here, the coefficient of friction (COF) and wear of (PEI/GO)15 with six different counterface polymer balls is investigated in air and in nitrogen, with particular focus on the formation of tribological transfer films. The polymers polyoxymethylene (POM), polyetheretherketone (PEEK), polyethylene (PE), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polytetrafluoroethylene (PTFE) are utilized. The COF of (PEI/GO)15 vs steel is 0.35 in both air and nitrogen. In air, the COF ranges from 0.06 to 0.17 for all polymers. Significantly, in nitrogen, four polymers (POM, PEEK, PMMA and PC) display ultra-low friction (COF ∼0.02) whilst two do not (PTFE and PE). The wear tracks and transfer films are investigated using e.g. optical microscopy, electron microscopy, and Raman mapping, and the tribological behavior is correlated to the hydrophilicity and relative hardness of the polymer balls compared to GO.

Membrane thinning is important approach to enhance gas permeation properties of CO 2 capture membranes. We employed cross linkable polymer materials, conventional epoxy resin containing amino groups, for the preparation of free-standing and ultrathin nanomembrane. By simple spincoating, nanometer-thick epoxy membranes were fabricated and detached as a free-standing membrane. The thickness of a membrane was readily controllable by spincoating speed and polymer concentration. Although as-prepared nanomembrane did not show CO 2 selectivity over N 2 , wet membrane shows high CO 2 selectively. Further sophistication of membrane material design and reduction of membrane thickness would be a promising approach to prepare preferential CO 2 separation membrane with high gas flux.

A novel class of alkaline anion exchange membrane (AAEM) is presented, in the form of KOH-modified multilayer graphene oxide paper (GOKOH). Such membranes can be easily fabricated at large scale with varying thickness using conventional filtration techniques, and have high tensile strength (24.5 MPa). However, a large degree of swelling is observed. SEM investigations show that the morphology of GO changes after KOH-treatment, whilst XPS measurements and XRD analysis confirm successful chemical modification. The hydrogen gas permeability is several orders of magnitude lower than conventional polymer-based ionomer membranes. The maximum anion conductivity is 6.1 mS/cm at 70 °C, and the dominant charge carrier is confirmed to be OH− by utilization of anion and proton-conducting blocking layers. The ion exchange capacity is 6.1 mmol/g, measured by titration. A water-mediated reverse Grotthuss-like mechanism is proposed as the main diffusion mode of OH− ions. Finally, a prototype AAEM fuel cell is fabricated using a GOKOH membrane, confirming the applicability to real systems.

In this study, an optical fibre long period grating (LPG) sensor functionalised with a mesoporous thin film was employed for the identification and quality assessment of beverages. The principle of the discrimination of beverages using an LPG sensor is based on the measurement of the change in refractive index of a sensitive film, induced by the binding of the chemical compounds present in the beverage. The sensitive film deposited onto the LPG consisted of poly(allylamine hydrochloride) (PAH) and silica nanospheres (SiO2 NPs) with diameters ranging from 40 nm to 50 nm. PAH imparts selectivity, while the SiO2 NPs endow the film with high porosity and enhanced sensitivity. In this study, five different types of beverages, red and white wines, brandy, nihonshyu (sake, a Japanese rice wine), and shochu (a Japanese distilled beverage), prepared via distillation and fermentation, were used to assess the capability of the sensor to identify the origin of the beverages. In addition, a selection of red wines was used to evaluate the use of the sensor in the assessment of the quality of beverages. The results obtained were benchmarked against those obtained using gas chromatography–mass spectrometry for the determination of volatile compounds contributing to the flavours of a set of red wines. Principal component analysis (PCA) was employed for data analysis. This approach enabled both quality assessment of beverages and identification of the methods and materials used for their preparation. Keywords: Long period grating, Mesoporous thin film, Layer-by-layer, Quality assessment, Beverages

Multilayers of polyethyleneimine and graphene oxide, (PEI/GO)15, were coated onto steel substrates via electrostatic layer-by-layer (LbL) deposition, and their tribological properties were investigated as solid lubricants. The coefficient of friction (COF) and specific wear rate (SWR) were measured against a poly(methyl methacrylate) (PMMA) counterface ball, in various gas environments with different oxygen concentrations. The COF and SWR both significantly decreased with decreasing oxygen content. Detailed surface characterization of the contact area of the counterface ball revealed that continuous transfer films were formed in oxygen-free environments, but not in oxygen-rich environments. This is attributed to an increased proportion of sp3 bonding in the wear debris in the presence of oxygen (as confirmed by Raman spectroscopy), as well as possible suppression of wear debris adhesion on the counterface ball due to oxygen adsorption on the surface.

Alternate TiO2 gel ultrathin films assembled with a macrocyclic carboxylic acids of tetrakis-4-carboxyphenyl porphine (TCPP) or tetra-4-carboxylphthalocyanine cobalt (II) (Co-TCPc) were prepared by the surface sol–gel process. To confirm the film growth and imprinting effect, quartz crystal microbalance (QCM) and UV–vis spectroscopy measurements were employed. The binding of TCPP was 1.2–14.3 times more selective compared to structurally related macrocyclic guest molecules. Among other findings, tetrakis-4-carboxymethyloxyphenyl porphine (TCMOPP) that has a spacer ( O CH2 ) between the phenyl rings and carboxylic acid moieties of TCPP showed a significantly lower binding efficiency equal to 0.07, regardless of its similar molecular structure to the template molecule. Structural difference of porphyrin and phthalocyanine analogs could be also selectively discriminated: the TCPP imprinted film showed ca. 13 times higher selectivity for recognition of TCPP itself from the mixture of TCPP and Co-TCPc. Characterization by AFM demonstrated that the TiO2/TCPP film has highly uniform surface and ultrathin thickness, while both TEM and SEM studies confirmed the immobilized structures of TCPP inside the film.

A fibre optic long period grating (LPG) with an nano-assembled mesoporous coating of alternate layers of poly(diallyldimethylammonium chloride) (PDDA) and SiO 2 nanospheres was used for the development of a highly sensitive fibre-optic chemical sensor. Sensor fabrication involves a 2-stage process: firstly, the deposition of the base mesoporous thin film (PDDA/SiO 2 ) over an LPG written in the optical fibre using a layer-by layer technique, followed by the infusion of a functional material into the porous film. The refractive index of the base mesoporous coating, determined at a wavelength of 633 nm using ellipsometry, was found to be 1.2. The infusion of the functional material into the coating resulted in a significant change in the RI of the coating, producing a dramatic change in the transmission spectrum of the LPG. The sensing mechanism exploited is based upon chemically induced desorption of the functional material from the mesoporous coating. The sensing of ammonia in aqueous solution was chosen as an example to demonstrate the sensing principle of the LPG sensor. The operation of the sensor was characterized using two functional materials, tetrakis-(4-sulfophenyl)porphine (TSPP) and polyacrylic acid (PAA). The device showed high sensitivity to ammonia with a response time less than 100 s and a limit of detection of 140 ppb when the TSPP infused (PDDA/SiO 2 ) film was employed as a sensitive element.

Nano-assembled thin films prepared by a layer-by-layer approach on QCM resonators were used as sensitive elements for monitoring relative humidity. Different types of films, polymer-based (PDDA/PSS)n film and porphyrin-based (PDDA/TSPP)n and (PDDA/MnTSPP)n films (where n = 5, 10, and 15), showed linear responses to relative humidity changes in the range of 4–94%. Increase of the number of bilayers deposited on the QCM electrode enhanced the sensitivity to relative humidity. The porphyrin-based films showed ca. 4.5 times higher sensitivity towards relative humidity than the polymer-based films, owing to presence of the higher number of free sulfonic acid groups. Incorporation of the metal ion into the porphyrin pyrrole ring was not significant in sensitivity. However, all films showed a good reversibility to the stepwise changes of relative humidity and the response and recovery times (t90) were very fast within 15 s.