Polymers in sensor applications

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

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Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

The simultaneous entrapment of biological macromolecules and nanostructured silica-coated magnetite in sol-gel materials using a reverse-micelle technique leads to a bioactive, mechanically stable, nanometer-sized, and magnetically separable particles. These spherical particles have a typical diameter of 53 +/- 4 nm, a large surface area of 330 m(2)/g, an average pore diameter of 1.5 nm, a total pore volume of 1.427 cm(3)/g and a saturated magnetization (M(S)) of 3.2 emu/g. Peroxidase entrapped in these particles shows Michaelis-Mentan kinetics and high activity. The catalytic reaction will take place immediately after adding these particles to the reaction solution. These enzyme entrapping particles catalysts can be easily separated from the reaction mixture by simply using an external magnetic field. Experiments have proved that these catalysts have a long-term stability toward temperature and pH change, as compared to free enzyme molecules. To further prove the application of this novel magnetic biomaterial in analytical chemistry, a magnetic-separation immunoassay system was also developed for the quantitative determination of gentamicin. The calibration for gentamicin has a working range of 200-4000 ng/mL, with a detection limit of 160 ng/mL, which is close to that of the fluorescent polarization immunoassay (FPIA) using the same reactants.

Magnetite-containing spherical silica nanoparticles for biocatalysis and bioseparations （vol 76, pg 1316, 2004）

Polyaniline is a conducting polymer with incredible promise, but it has had limited use due to poor reaction control and processability associated with conventional morphologies. Polyaniline nanofibers, on the other hand, have demonstrated, through manufacturing techniques discovered during the past decade, increased processability, higher surface area, and improved consistency and stability in aqueous dispersions, which are finally allowing for expanded commercial development of this promising polymer. This review explores some intriguing applications of polyaniline nanofibers, as well as the advantages and remaining challenges in developing better products using polyaniline in this new morphology.

Polyaniline nanofibers: broadening applications for conducting polymers

Metal oxide nanoparticles as antimicrobial agents: a promise for the future

Spectroscopic [UV–visible and Fourier transform IR (FTIR)] and thermal properties of chemically synthesized polyanilines are found to be affected by varying the protonation media (acetic, citric, oxalic, and tartaric acid). The optical spectra show the presence of a greater fraction of fully oxidized insulating pernigraniline phase in polyaniline doped with acetic acid. In contrast, the selectivity in the formation of the conducting phase is higher in oxalic acid as a protonic acid media. The FTIR spectra of these polymers reveal a higher ratio of the relative intensities of the quinoid to benzenoid ring modes in acetic acid doped polyaniline. Scanning electron micrographs revealed a sponge-like structure derived from the aggregation of the small granules in acetic acid and oxalic acid doped polyaniline. A three-step decomposition pattern is observed in all the polymers, regardless of the protonic acid used for the doping. The second step loss related to the loss of dopant is found to be higher in the oxalic acid doped polymer. In accordance with these results the conductivity is also found to be higher in oxalic acid doped material. The temperature dependent conductivity measurements show the thermal activated behavior in all the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2043–2049, 2004

Synthesis and characterization of polyaniline doped with organic acids

Comparative studies of chemically synthesized polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid

A conducting polymer, polyaniline, was synthesized by chemical polymerization using different inorganic acids, such as HCl, H2SO4, HClO4, HNO3, and H3PO4, as protonic acid media. The synthesized polymers were characterized using UV-visible and FT-IR spectroscopy. A granular type of morphology was observed under SEM for HCl, HNO3, and H3PO4 doped polyanilines. However, HClO4 doped polyaniline shows the folded lamellar structure derived from the fibers. The thermal stability of these polymers was investigated with the help of thermogravimetric (TG/SDTA) analysis. The formation of a greater fraction of the conducting emeraldine salt phase is observed in HClO4 as a protonic acid media. The thermal stability of H3PO4 doped material is found to be better as compared with other acids. An increase in conductivity with an increase in temperature was observed in all the samples except for HClO4 doped polyaniline. Polym. Eng. Sci. 44:1676–1681, 2004. © 2004 Society of Plastics Engineers.

Spectroscopic, transport, and morphological studies of polyaniline doped with inorganic acids

Thermal degradation properties of solid polymer electrolyte (poly(vinyl alcohol)+phosphoric acid)/methylene blue composites

Poly(o-anisidine), P(o-anis) doped with camphor sulphonic acid (CSA) and p-toluene sulphonic acid (p-TSA) was synthesized by in situ chemical polymerization method using ammonium persulphate as an oxidizing agent This is a single step polymerization process for the direct synthesis of emeraldine salt phase of the polymer The polymers were characterized by using UV–vis and FT-IR spectroscopy, TGA and conductivity measurements Formation of mixed phases of polymer together with conducting emeraldine salt phase are confirmed by spectroscopic techniques Thermal analysis shows that poly(o-anisidine) has three stage decomposition pattern similar to unsubstituted polyaniline The lower conductivity in poly(o-anisidine) compared to polyaniline is due to the cumulative steric as well as electronic effects of the bulky methoxy substituent present on the benzene ring High temperature conductivity measurements show ‘thermal activated behaviour’ The change in resistance with respect to % relative humidity (RH) is observed, when pressed pellets of the polymer were exposed to the broad range of humidity (ranging between 20–100% RH)

Annamraju Kasi Viswanath

Papers

Synthesis and characterization of polyaniline doped with organic acids

Comparative studies of chemically synthesized polyaniline and poly(o-toluidine) doped with p-toluene sulphonic acid

Spectroscopic, transport, and morphological studies of polyaniline doped with inorganic acids

Thermal degradation properties of solid polymer electrolyte (poly(vinyl alcohol)+phosphoric acid)/methylene blue composites

Spectroscopic, thermal and electrical properties of sulphonic acids doped poly(o-anisidine) and their application as humidity sensor