Hydrogen bonds in camphorsulfonic acid doped polyaniline

We conducted a set of computer simulations to explore in details the way polyaniline (PANI) interacts with its dopant molecules like camphorsulfonic acid (CSA) and with solvent like chloroform, m-cresol or a mixture of m-cresol and water. The simulated system was built of a single layer of polyaniline chains in protonated state with attached camphorsulfonic acid ions as dopants. The system of the size above 50 angstrom was subject to the periodic boundary conditions. All atoms in simulated molecules were assigned to atom types from OPLS-AA force field. However the inter-ring torsion profile for polyaniline in protonated emeraldine state was modified according to the density functional theory simulations. Prepared systems were simulated for 1 ns under the constant temperature (293 K) and constant pressure (1000 hPa) conditions. The results of molecular dynamics simulation exhibit a broad variety of hydrogen bond patterns between PANI-CSA as well as solvent molecules. We observed high probability (36 %) of configurations where single CSA molecule is attached to a PANI chain via a single hydrogen bond. However, the high probability (44 %) of a configuration where single CSA molecule bridges two or more PANT chains via hydrogen bonds was quite unexpected. Our simulations show also that in the presence of solvent, PANI-CSA interaction slightly weakens. Nevertheless, in the case of solvents being able to form hydrogen bonds in which CSA molecule is involved.