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Novel impedance-type humidity sensors were fabricated by coating 2,5-dimethyl-1-phenyl-1 H -pyrrole ( 1 ), 1-(4-aminophenyl)-2,5-dimethyl-1 H -pyrrole ( 2 ), 1-(4-nitrophenyl)-2,5-dimethyl-1 H -pyrrole ( 3 ) and gold nanoparticles/compound 3 (AuNPs/compound 3 ) composite films on alumina and plastic substrates. Compound 1 , compound 2 , compound 3 and AuNPs/compound 3 composite films were analyzed using atomic force microscopy (AFM) and UV–vis spectroscopy. The effects of the substituents on the benzene ring of compound 1 on the electrical and humidity-sensing properties of the compound 1 film were studied. The humidity sensor that was fabricated with the compound 3 exhibited high sensitivity but a higher resistance at low humidity than that which was made of the compound 1 . The effects of the AuNPs on the electrical and humidity sensing properties of the AuNPs/compound 3 composite film on a PET substrate were investigated. The sensor that was made of the AuNPs/compound 3 composite film exhibited high sensitivity, good linearity, small hysteresis, high flexibility, a short response/recovery time, a weak dependence on temperature and high long-term stability. The linearity of the humidity sensor depended on the applied frequency. The sensing mechanism of the AuNPs/compound 3 composite film was elucidated with reference to impedance plots. [ABSTRACT FROM AUTHOR]

Novel room-temperature NH 3 gas sensors based on Pd, tin oxide (SnO 2 ) and reduced graphene oxide (RGO) ternary nanocomposite (Pd/SnO 2 /RGO) film were fabricated by the one-pot route. The Pd/SnO 2 /RGO ternary nanocomposite films were characterized by Fourier transform infrared spectroscopy (FTIR), Raman, X-ray diffractometry (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Microstructural observations revealed that the Pd and SnO 2 nanoparticles easily and homogeneously attached to the surface of RGO. The sensor that was based on a Pd/SnO 2 /RGO ternary nanocomposite film responded strongly to low concentrations of NH 3 gas at room-temperature. Its better sensor sensitivity than that of the pristine of SnO 2 and SnO 2 /RGO nanocomposite film was related to the higher conductivity and catalytic activity of the Pd/SnO 2 /RGO ternary nanocomposite film. [ABSTRACT FROM AUTHOR]

Novel impedance-type humidity sensors were made by coating diamine-functionalized graphene oxide (GO) films on alumina or plastic substrates. Ethylenediamine (EA) and 1,6-hexanediamine (HA) were used to functionalize GO using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) (EDC/NHS) as the coupling reagent. The effects of the chain length of diamine on the electrical and humidity-sensing properties of the diamine-functionalized GO film were investigated. The diamine-functionalized GO film was characterized by atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR). The impedance-type humidity sensor that was made of the EA-GO film exhibited a wide range of working humidities, a high sensitivity, satisfactory linearity, a small hysteresis, high flexibility, a short response/recovery time, a weak dependence on temperature and high long-term stability. The linearity of the humidity sensor depended on the applied frequency. The ions (H 3 O + ) dominate the conductance of the diamine-functionalized GO film. [ABSTRACT FROM AUTHOR]

Abstract: Humidity sensors were made by coating 25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene (TBHC) and 5-(4′-nitrophenyl)azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene (NTBHC) thin films on a gold electrode of a quartz crystal microbalance (QCM). The thin films were analyzed by atomic force microscopy (AFM). The humidity sensing properties, including sensitivity, sensing linearity, hysteresis, cross-sensitivity effects and long-term stability were also investigated. Water vapor molecules that were adsorbed onto the NTBHC thin film exhibited a larger frequency shift than those adsorbed onto TBHC thin films. Adsorption dynamic analysis and a molecular mechanical calculation (of the association constant) were made to elucidate the way in which a substituent on the upper and lower rims of calix[4]arene increases the sensitivity to humidity. [Copyright &y& Elsevier]

Abstract: Low-humidity sensing performance of generation 1 amine terminated polyamidoamine (PAMAM) dendrimer (G1-NH2), generation 5 amine terminated PAMAM dendrimer (G5-NH2) and G5-NH2–Au nanoparticles (G5-NH2–AuNPs) thin films were investigated by using a quartz crystal microbalance (QCM). The formation of AuNPs was characterized by UV–vis spectrophotometer. The characterizations of the thin films were analyzed by atomic force microscopy (AFM). Water vapor molecules adsorbed onto the G5-NH2–AuNPs thin film had a larger frequency shift than the G1-NH2 and G5-NH2 thin films. Adsorption dynamic analysis, molecular mechanics calculation (association constant), was applied to elucidate how number of amine surface functional groups of PAMAM dendrimer and doped AuNPS in PAMAM dendrimer increase the sensitivity to low-humidity. [Copyright &y& Elsevier]

Abstract: Novel flexible NH3 gas sensors were formed by the in situ self-assembly of polypyrrole (PPy) on plastic substrates. A negatively charged substrate was prepared by the formation of an organic monolayer (3-mercapto-1-propanesulfonic acid sodium salt—MPS) on a polyester (PET) substrate using a pair of comb-like Au electrodes. Two-cycle poly(4-styrenesulfonic acid) sodium salt/poly(allylamine hydrochloride) (PSS/PAH) bilayers (precursor layer) were then layer-by-layer (LBL) deposited on an MPS-modified substrate. Finally, a monolayer of PPy self-assembled in situ and PPy multilayer thin films self-assembled LBL in situ on a (PSS/PAH)2/MPS/Au/Cr/PET substrate. The thin films were analyzed by atomic force microscopy (AFM). The effects of the precursor layer (PSS), the deposition time of the monolayer of PPy and the number of PPy multilayers on the gas sensing properties (response) and the flexibility of the sensors were investigated to optimize the fabrication of the film. Additionally, other sensing properties such as sensing linearity, reproducibility, response and recovery times, as well as cross-sensitivity effects were studied. The flexible NH3 gas sensor exhibited a strong response that was comparable to or even greater than that of sensors that were fabricated on rigid substrate at room temperature. [Copyright &y& Elsevier]

Abstract: Low-humidity sensors were made by layer-by-layer (LBL) self-assembly of poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA) or poly(styrenesulfonic acid) sodium salt (PSS) and poly(allylamine hydrochloride) (PAH) into multilayer thin films on a gold electrode of quartz crystal microbalance (QCM). The thin films were characterized by QCM and atomic force microscopy (AFM). The effects of maleic acid (MA) in PSSMA, the number of layers and the ionic strength on the low-humidity sensing properties (sensitivity) were compared with those of PSS. The sensitivity of the PSSMA/PAH multilayer thin film exceeded that of the PSS/PAH multilayer thin film when the multilayered thin films of polyelectrolytes were prepared from solutions without NaCl. The sensitivity of both PSSMA/PAH and PSS/PAH multilayered thin films was increased by increasing the number of layers and by adding salt to the deposition solution. The PSS/PAH multilayered thin film that was prepared from the solutions with NaCl had the highest sensitivity (1.923 −ΔHz/Δppmv at 27.5ppmv) and a short response time. Spin-coating was also adopted to fabricate PSS-based low-humidity sensors for comparison. [Copyright &y& Elsevier]

Abstract: Mica multilayer thin films were assembled layer-by-layer (LBL) from mica that was modified with carboxylic groups ( cationic polyelectrolyte (poly(allylamine hydrochloride)) (PAH) on a quartz-crystal microbalance (QCM) for low-humidity sensing applications. The surface characteristics of the thin films were studied for various assembly conditions of pH and ionic strength of modified mica solutions. The thin films were characterized using QCM and by atomic force microscopy (AFM). The thickness of mica-COOH/PAH multilayer thin films increased with assembly pH of modified mica solution. When salt was added, the multilayer films became thicker, smoother and grew more regularly. The mica-COOH/PAH multilayer films that were deposited from the mica-COOH solution with salt at pH 3 was coated on the gold electrode of the QCM exhibited excellent sensitivity (0.524 −ΔHz/Δppmv at 36.1ppmv) and linearity and a short response time (13s at 60.4ppmv). [Copyright &y& Elsevier]

Abstract: This study investigated the low-humidity sensing performance of raw multi-walled nanotubes (MWCNTs), oxidized MWCNTs (MWCNT–COOH) and Pd-modified MWCNT–COOH (Pd–MWCNT–COOH) thin films by using a quartz crystal microbalance (QCM). The characteristics of the thin films were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Water vapor molecules adsorbed onto the Pd–MWCNT–COOH thin film had a larger frequency shift than raw MWCNTs and MWCNT–COOH thin films. Adsorption dynamic analysis, molecular mechanics calculation (association constant), was applied to elucidate how surface modification and functionalization of MWCNTs increase the sensitivity to low-humidity. [Copyright &y& Elsevier]

• Flexible humidity sensor basedon Pt/polythiophene/RGO filmwas fabricated. • 2-TPM is polymerizedandsimultaneouslyto reduce GOand PtCl 4 2– to RGO and Pt, respectively. • The sensitivity of the flexible humidity sensor was enhanced by theRGO and Pt. • The flexibility of the humidity sensor was enhanced by the added RGO. A novel, flexible humidity sensor based on ternary nanocomposite films of Pt nanoparticles, polythiophene, and reduced graphene oxide (Pt/polythiophene/RGO) was fabricated using a simple one-pot redox synthesis. First, 2-thiophene methanol (2-TPM) was allowed to react with PtCl 4 2– ions via an oxidative polymerization process, which released electrons that simultaneously reduce the PtCl 4 2– ions and GO to Pt nanoparticles and RGO, respectively. The effects of the amounts of added PtCl 4 2– ions and RGO on the electrical, flexibility, and humidity-sensing properties of the Pt/polythiophene/RGO ternary nanocomposite films were investigated. The Pt/polythiophene/RGO ternary nanocomposite films were characterized by using the Fourier transform infrared spectroscopy (FTIR), Raman, atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A Pt/polythiophene/RGO ternary nanocomposite film containing 30 mg of Pt and 0.1 g of RGO exhibited the greatest flexibility, sensitivity, and long-term stability. This flexible humidity sensor also demonstrated a wide range of working humidities, an acceptable linearity, a small hysteresis, a short response/recovery time, and a weak temperature dependence. We used complex impedance spectra to explain the humidity-sensing mechanism of the flexible sensor based on Pt/polythiophene/RGO ternary nanocomposite films and thus found that the ions (H 3 O+) in this system dominate the conductance process of the sensor. [ABSTRACT FROM AUTHOR]

In the present investigation, we have studied the influence of oxygen (O 2 ) flow rate in the atmospheric pressure argon (Ar) plasma zone for improvement of the surface and cell compatible properties of LDPE film. Various characterization techniques such as contact angle (CA), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), etc were used to investigate the hydrophilicity, surface chemistry and morphology of LDPE films respectively. Fowke's approximation method was used to evaluate the polar and dispersion components of the total surface energy of LDPE films using contact angle values of three testing liquids. Moreover T-peel and lap shear tests were used to analyze the adhesive strength of the surface modified LDPE films. Finally cyto-compatibility of the surface modified LDPE film was analyzed by in vitro cell compatibility analysis which includes the cell viability and adhesion using NIH-3T3 fibroblast cells. The results obtained from various characterization techniques evidently revealed that cold atmospheric pressure (CAP) plasma treatment enhanced the surface properties (hydrophilicity, surface morphology and surface chemistry) of LDPE film. Owing to tailored physico-chemical changes induced by the CAP plasma treatment facilitates improvement in adhesive strength as well as adhesion and proliferation of cells on the surface of LDPE films. [ABSTRACT FROM AUTHOR]