We demonstrate a "universal solvent sensor" constructed from a small array of carbon/polymer composite chemiresistors that respond to solvents spanning a wide range of Hildebrand volubility parameters. Conductive carbon particles provide electrical continuity in these composite films. When the polymer matrix absorbs solvent vapors, the composite film swells, the average separation between carbon particles increases, and an increase in fihn resistance results, as some of the conduction pathways are broken. The adverse effects of contact resistance at high solvent concentrations are reported. Solvent vapors including isooctane, ethanol, dlisopropyhnethylphosphonate (DIMP), and water are correctly identified ("classified") using three chemiresistors, their composite coatings chosen to span the full range of volubility parameters. With the same three sensors, binary mixtures of solvent vapor and water vapor are correctly classified, following classification, two sensors suffice to determine the concentrations of both vapor components. Polyethylene vinylacetate and polyvinyl alcohol (PVA) are two such polymers that are used to classifj binary mixtures of DIMP with water vapor; the PVA/carbon-particle-composite films are sensitive to less than 0.25°A relative humidity. The Sandia-developed VERI (Visual-Empirical Region of Influence) technique is used as a method of pattern recognition to classi~the solvents and mixtures and to distinguish them from water vapor. In many cases, the response of a given composite sensing film to a binary mixture deviates significantly from the sum of the responses to the isolated vapor components at the same concentrations. While these nonlinearities pose significant difficulty for (primarily) linear methods such as principal components analysis, VERI handles both linear and nonlinear data with equal ease. In the present study the maximum speciation accuracy is achieved by an array containing three or four sensor elements, with the addition of more sensors resulting in a measurable accuracy decrease.

Arrays of unheated chemically sensitive resistors (chemiresistors) can serve as extremely small, low-power-consumption sensors with simple read-out electronics. We report here results on carbon-loaded polymer composites, as well as polymeric ionic conductors, as chemiresistor sensors. We use the solubility parameter concept to understand and categorize the chemiresistor responses and, in particular, we compare chemiresistors fabricated from polyisobutylene (PIB) to results from PIB-coated acoustic wave sensors. One goal is to examine the possibility that a small number of diverse chemiresistors can sense all possible solvents-the "Universal Solvent Sensor Array".

We have demonstrated a sensor based on an interdigitated electrode platform coated with a conductive viologen polymer that has excellent moisture sensitivity, response time, and low power consumption. Work has been done to explain the limits of sensitivity and characterize the response of the sensor in low‐humidity environments and also characterize the response of the device to various organic interferents such as alcohols and organophosphonates. Using lumped‐circuit models, the nature of the response is explained and design parameters are isolated that will allow future performance improvements. In addition, the temperature dependence of moisture sensitivity is presented. © 1999 The Electrochemical Society. All rights reserved.

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In this paper, fusing of a metallic conductor is studied by judiciously using the solution of the one-dimensional heat equation, resulting in an approximate method for determining the threshold fusing current. The action is defined as an integration of the square of the wire current over time. The burst action (the action required to completely vaporize the material) for an exploding wire is then used to estimate the typical wire gapping action (involving wire fusing), from which gapping time can be estimated for a gapping current greater than a factor of two over the fusing current. The test data are used to determine the gapped length as a function of gapping current and to show, for a limited range, that the gapped length is inversely proportional to gapping time. The gapping length can be used as a signature of the fault current level in microelectronic circuits.