These films can be operated and regenerated at mild temperatures.

Films made of certain polymer/carbon composites have been found to be potentially useful as sensing films for detecting airborne elemental mercury at concentrations on the order of tens of parts per billion or more. That is to say, when the polymer/carbon composite films are exposed to air containing mercury vapor, their electrical resistances decrease by measurable amounts. Because airborne mercury is a health hazard, it is desirable to detect it with great sensitivity, especially in enclosed environments in which there is a risk of a mercury leak from lamps or other equipment.

Figure 1. These Polymers were selected as components of mercury- detecting polymer/carbon sensor films based on quantummechanical computations of energies of binding between mercury atoms and polymer chemical functionalities, like these, containing amine functional group.
The present effort to develop polymer-based mercury- vapor sensors complements the work reported in NASA Tech Briefs “Detecting Airborne Mercury by Use of Palladium Chloride” (NPO- 44955), Vol. 33, No. 7 (July 2009), page 48 and “De - tecting Airborne Mer cury by Use of Gold Nanowires” (NPO-44787), Vol. 33, No. 7 (July 2009), page 49. Like those previously reported efforts, the present effort is motivated partly by a need to enable operation and/or regeneration of sensors under relatively mild conditions — more specifically, at temperatures closer to room temperature than to the elevated temperatures (>100°C ) needed for regeneration of sensors based on noble-metal films.

Figure 2. Small Changes in Electrical Resistances of four polymer/carbon composite films to airborne mercury vapor were observed at concentrations as low as tens of parts per billion.
The present polymer/carbon films are made from two polymers, denoted EYN1 and EYN2 (see Figure 1), both of which are derivatives of poly-4-vinyl pyridine with amine functional groups. Composites of these polymers with 10 to 15 weight percent of carbon were prepared and solution-deposited onto the JPL ElectronicNose sensor substrates for testing. Preliminary test results showed that the resulting sensor films gave measurable indications of airborne mercury at concentrations on the order of tens of parts per billion (ppb) or more. The operating temperature range for the sensing films was 28 to 40°C and that the sensor films regenerated spontaneously, without heating above operating temperature (see Figure 2).

This work was done by Abhijit Shevade, Margaret Ryan, Margie Homer, Adam Kisor, April Jewell, Shiao- Pin Yen, Kenneth Manatt, Mario Blanco, and William Goddard of Caltech for NASA’s Jet Propulsion Laboratory.

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