Polyaniline (PANI) films can be prepared on the quartz substrates under high pressure (> 100 MPa). The effect of the applied pressure and the initial molar ratio of ammonium persulphate to aniline (r) on the thickness and the electrical conductivity of the resulting PANI films is reported. It is shown that there is a competition between the surface adsorption and the diffusion of the radical cations in solution in this polymerization. A three-dimensional relationship between film colour (i.e., absorbance at 400 nm), reaction pressure (P), and r is described. The optimum conditions for producing PANI films are established as r = 1.00-1.50 and P = 430-510 MPa. (c) 2006 Published by Elsevier B.V.