MAGNETIC-SUSCEPTIBILITY OF POLYANILINE IN SOLUTION IN NONPOLAR ORGANIC-SOLVENTS AND IN POLYBLENDS IN POLY(METHYL METHACRYLATE)

We report electron spin resonance measurements of the magnetic susceptibility (chi) of the protonated conducting form of polyaniline (PANI) in solution in non-polar or weakly polar organic solvents and as thin films cast from such solutions. At room temperature, chi = 3 X 10(-5) e.m.u./mol (two rings) for PANI films with camphor sulfonic acid (CSA) and dodecylsulfonic acid (DBSA) as counter-ions. In both cases, the concentration of localized Curie-Law spins is about 1 % (per two rings of PANI). In solution, chi = 2.8 X 10(-5) e.m.u./mol (two rings) for PANI-CSA in m-cresol and chi = 3.8 X 10(-5) e.m.u./mol (two rings) for PANI-DBSA in xylene, and they are found to be temperature independent. In polyblends with PMMA, chi = 3 X 10(-5) e.m.u. /mol (two rings) at room temperature, independent of the volume fraction of PANI-CSA. The temperature independence implies a metallic state with Pauli spin susceptibility, chi(P), resulting from a density of states at the Fermi level of about 1 state per eV per two rings. The small Curie-law contribution demonstrates that the DBSA and CSA surfactant counter-ions (S-1) lead to higher quality material with reduced disorder. The concentration independence of chi(P) in blends implies that the PANI complex is phase separated in the PMMA matrix, consistent with a network-like microstructure. Since the Pauli susceptibility indicates the existence of a true metallic state, the PANI-S- complexes are the first examples of metallic polymers in solution, i.e. stable 'liquid metals'.