Electrically conductive CuS–poly(acrylic acid) composite coatings

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Abstract
Copper sulfide (CuS) powder precipitated from a chemical bath containing Cu(II) chloride and thiourea and annealed in air at 150 °C for 1 h was dispersed in a poly(acrylic acid) aqueous solution (with additional water or propylene glycol as a dispersive agent) and cast on glass slides. Upon evaporation of the solvent, coatings of ∼50 μm in thickness of a CuS-poly(acrylic acid) composite are formed. Measurement of sheet resistance (R□) indicates a percolation threshold of electrical conduction at a weight fraction [wf is wt. % of CuS to poly(acrylic acid) + CuS] of about 40%; the composite undergoes a transition from insulator (R□ ∼ 1013 Ω) to conductive state (R□ ∼ 102 Ω). The morphology and thermal stability of the composite depend on the choice of the dispersive agent for the CuS powder; smoother and thermally stable (up to a temperature of 250 °C) coatings are obtained when propylene glycol is used. The results on x-ray diffraction, thermogravimetric analysis, and Fourier transform infrared spectroscopy studies are given to indicate the structure and bonding mechanisms and their dependence on temperature and dispersive agents.