MS25-P01 Structure of the conducting PANI/CSA polymer system as seen by XRD, neutron diffraction and advanced computer modeling Wojciech Łużny (AGH UST, Fac. of Physics and Applied Computer Science, Krakow, Poland) Maciej Śniechowski (AGH UST, Fac. of Physics and Applied Computer Science, Krakow, Poland) Tomasz Kozik (AGH UST, Fac. of Physics and Applied Computer Science, Krakow, Poland)email: luzny@agh.edu.plThe structure of the conducting polymer system of polyaniline (PANI) protonated with camphorsulfonic acid (CSA) remained unclear for several years and resisted attempts at solving by use of typical methods. This case may serve as an example of how different experimental and computational methods may impact each other and develop a successful, combined approach to structural study aimed at determining a reliable model and verifying its properties.
            Molecular dynamics simulations may provide useful information concerning the studied system, even if the accuracy of such simulations is finite. These were performed for PANI/CSA [1] and allowed  drawing important conclusions regarding the type of structure – alternating double layers of polymer chains and counterions. Additionally, they suggested the indexing of principle peaks observed in the X-ray powder diffraction pattern obtained for samples of this polymer. Finally, they were the basis for formulating a hypothesis regarding the preferred orientation of crystallites in thin film samples of this system cast from different solvents in agreement with grazing incident beam X-ray diffraction data.
            The above described simulations were the foundation for the scope a crystallographic unit cell model. After taking advantage of artificial intelligence based methods aimed at optimizing the layout of the structural units of PANI/CSA within such a cell with respect to the powder diffraction pattern, a new model was found [2]. Apart from satisfying the optimization criteria, is allows explaining the differences observed in neutron diffraction patterns recorded for regular and partially deuterated samples of the studied system. It also has all the previously reported advantages of the principal structure obtained from molecular dynamics simulations and allows verifying the hypothesis regarding preferred orientation in thin films cast from different solvents.
            Taking a generalized look at the process of obtaining this new structural model of PANI/CSA, it could be described as an example of a systematic approach in which various experimental (XRD, grazing incident beam X-ray scattering, neutron diffraction) and computational (molecular dynamics, artificial intelligence) techniques mutually inspire one another and allow developing and verifying a structural model of a polymer system. Each of the contributing pieces listed above by themselves are not enough to develop a good structural model, while combining insight into the studied problem provided by each of them leads to one which is reliable.
 
References:

[1] Śniechowski M., Borek R., Piwowarczyk K., Łużny W. (2015) Macromolecular Theory and Simulations 24, 284–290.

[2] Kozik T., Śniechowski M., Łużny W., Proń A., Djurado D. (2017) Polymer 111, 148–155.

Keywords: polyaniline, crystalline structure, simulations