High molecular weight polyaniline (PANI) was synthesized by a combined procedure incorporating various synthesis methods. Temperature and open circuit potential of the reaction mixture were collected to monitor the reaction progress. The polymer is characterized by various techniques including gel permeation chromatography, dynamic light scattering, infrared spectroscopy, solid‐state nuclear magnetic resonance, and differential scanning calorimetry for elucidating the molecular architecture obtained by this method. As‐synthesized PANI was found to possess high molecular weight, reduced branching, reduced cross‐linking, and to predominantly consist of linear polymer chains. This polymer was also found to be more stable in solution form. J–V characteristics of as‐synthesized PANI films indicate a high current density which is due to increased free pathways and less traps for the charge transport to occur in PANI films. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

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An organic molecule--o-phenylene diamine (OPD)--is selected as an aldehyde sensing material. It is studied for selectivity to aldehyde vapours both by experiment and simulation. A chemiresistor based sensor for detection of aldehyde vapours is fabricated. An o-phenylene diamine-carbon black composite is used as the sensing element. The amine groups in the OPD would interact with the carbonyl groups of the aldehydes. The selectivity and cross-sensitivity of the OPD-CB sensor to VOCs--aldehyde, ketone and alcohol--are studied. The sensor shows good response to aldehydes compared to other VOCs. The higher response for aldehydes is attributed to the interaction of the carbonyl oxygen of aldehydes with -NH2 groups of OPD. The surface morphology of the sensing element is studied by scanning electron microscopy. The OPD-CB sensor is responsive to 10 ppm of formaldehyde. The interaction of the VOCs with the OPD-CB nanocomposite is investigated by molecular dynamics studies. The interaction energies of the analyte with the OPD-CB nanocomposite were calculated. It is observed that the interaction energies for aldehydes are higher than those for other analytes. Thus the OPD-CB sensor shows selectivity to aldehydes. The simulated radial distribution function is calculated for the O-H pair of analyte and OPD which further supports the finding that the amine groups are involved in the interaction. These results suggest that it is important and easy to identify appropriate sensing materials based on the understanding of analyte interaction properties.

Agricultural and industrial wastes cause contamination of groundwater by the accumulation of various organic, inorganic and metallic pollutants including nitrate ions. In this work, a conducting polymer is designed and synthesized to interact specifically with nitrate ions in water. This designed molecule has conjugation in the backbone, also thiourea moiety which interacts and complexes with the analyte nitrate ions by hydrogen bonding. This binding with nitrate ion perturbs the electron distribution along conjugated polymer backbone which translates to change in conductivity of the polymer. This response of the change in conductivity is used as chemosensing. The sensor exhibited stability, repeatability and reproducibility for more than 20 months. The sensor performance is further compared with a nitrate ion selective electrode for real-world sample applications. The electronic property of the polymer and complex and interaction mechanism is elucidated using UV-Visible spectroscopy, dynamic light-scattering analysis and density functional theory calculations. A practically useful lower limit of detection by the present method is ∼14 ppm NO 3 − -N in pH 7 water.

Abstract. Aldehydes are used in food and beverage industries, production of resins, soap and perfume industries. When used in excess quantity or found in products in undesired quantity this is a threat to humans. Hence it becomes very important to detect these VOCs even at lower concentration. The other sources of aldehyde are polluted air and water. Exposure to aldehyde can cause gene mutation and cancer. Conductometric sensors with metal oxide semiconductors as sensing films, cataluminesence based sensors, quartz crystal microbalance sensors, analytical methods such as HPLC have been used for the detection of aldehydes. These are sophisticated techniques require skilled staff to perform the tests. Chemiresistor is a simple method of fabrication of conductometric sensor. In this method the sensing layer is a film cast between two electrodes deposited on an insulating substrate. The response of the sensor to various analytes is monitored by recording the changes taking place in the sensing element. Organic molecule based sensors are low cost and operate at room temperature. Selectivity of the sensors to a particular analyte is an issue in sensors. An analyte molecule can interact with the various binding sites on a molecule. A molecule has to be designed and synthesized to be selective to a particular analyte of interest. This can be achieved by selecting a molecule which has a functional group that interacts with the analyte molecule. The mechanism of interaction of the analyte with the sensing molecule can be understood by doing molecular simulations. Molecular modelling allows monitoring the interaction of the analyte and sensing molecule. Here an example of organic molecule based sensor for selective interaction with aldehydes is illustrated.The organic molecule ophenylenediamine blended with carbon black as sensing element of the chemiresistor to decrease the resistance. Molecular modelling can be used to understand the interaction between aldehyde and o-phenylenediamine molecule.