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We report chemiresistive gas sensing characteristics of cobalt phthalocyanine films deposited on flexible bi-axially oriented polyethylene terephthalate substrates. Charge carrier mobility in these films systematically decreases upon bending, which implies that bending reduces π-π interactions among molecules. At room temperature, these films exhibited a reversible change in resistance on exposure to ammonia (5–50 ppm) along with high sensitivity and selectivity as well as fast response and recovery. The chemiresistive sensing properties were found to improve significantly under bend conditions owing to creation of more numbers of interaction sites.

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Pattern materials currently in use are waxes, and plastics, while other pattern materials are used sometimes, and for specific applications. Waxes, blended and developed with different compositions, are more commonly used, while use of plastic patterns, generally polystyrene, may sometimes be required, to produce thin-walled, complex-shaped castings, such as in aerospace integrally cast turbine wheels and nozzles. 2.1. Pattern Waxes Waxes are mostly the preferred material for patterns, and are normally used, modified and blended with additive materials such as plastics, resins, fillers, antioxidants, and dyes, in order to improve their properties, [7]. Paraffins and microcrystalline waxes are the most widely used waxes, and are often used in combination, because their properties tend to be complementary. Paraffin waxes are available in many controlled grades, with melting points ranging from 52 to 68 °C (126 to 156 °F). They are readily available in different grades, have low cost, high lubricity and low melt viscosity. Their usage is, however, limited because of high shrinkage and brittleness. Science and Technology of Casting Processes 26 Microcrystalline waxes tend to be highly plastic and provide toughness to wax blends. Available in both hard, nontacky grades as well as soft, adhesive grades, they have higher melting points, and are often used in combination with paraffin. Other waxes used include: Candelilla, a vegetable wax, which is moderately hard and slightly tacky. Carnauba wax is a vegetable wax with higher melting point, low coefficient of thermal expansion, and is very hard, nontacky and brittle. Beeswax is a natural wax, widely used for modeling, and in pattern blends, provides properties similar to microcrystalline waxes. Fischer-Tropsch waxes are synthetic hydrocarbon waxes resembling paraffins, but are available in harder grades, with higher melting points. Ozocerite is a mineral wax sometimes used in combination with paraffin. Waxes, in general, are moderately priced, and can easily be blended to suit different requirements. Waxes have low melting points and low melt viscosities, which make them easy to blend, inject, assemble into tree-or cluster-assemblies, and melt out with out cracking the thin ceramic shell molds. 2.1.1. Additives to Pattern Waxes Waxes with their many useful properties are, however, deficient in two practically important areas: (a) Strength and rigidity especially required to make fragile patterns; and (b) Dimensional control, especially in limiting surface cavitation due to solidification shrinkage, during and after pattern injection. Additives are made to waxes to cause improvements needed in these two deficient areas. The strength and toughness of waxes are improved by the addition, in required volumes, of plastics such as polyethylene, nylon, ethyl cellulose, ethylene vinyl acetate and ethylene vinyl acrylate. Solidification shrinkage causing surface cavitation in waxes, is reduced to some extent by adding plastics, but is reduced to a greater extent by adding resins ...