Electrically conductive CuS-poly(acrylic acid) composite coatings

Copper sulfide (CuS) powder precipitated from a chemical bath containing Cu(II) chloride and thiourea and annealed in air at 150 degrees 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 similar to 50 mu m in thickness of a CuS-poly(acrylic acid) composite are formed. Measurement of sheet resistance (R(square)) 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(square) similar to 10(13) Ohm) to conductive state (R(square) similar to 10(2) Ohm). 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 degrees 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.