| Abstract
| - To simulate the processes that take place at the polypyrrole/water interface under different states of oxidationof the polymer, a reliable model of the polymer/water system is necessary. To this end, a model with atomicdetail of the polypyrrole/water system was simulated for first time in both the oxidized (charged) and reduced(uncharged) polymer. The system consists of a single layer of water molecules between two layers ofpolypyrrole film. Each polymer film was formed of 64 polymeric chains of 10 monomeric units each, andafter oxidation of each polypyrrole chain, 128 chloride ions were included to maintain the electroneutralityof the system. In this way, a classical molecular dynamics simulation was carried out for both oxidized andreduced polypyrrole. From the simulated trajectories, macroscopic properties, such as the polypyrrole densityin its reduced state and polymer swelling after oxidation, were simulated. Thus, valuable information relatedto the atom distribution profile and water and counterion permeation across the polymer/water interface wasobtained. In this regard, due to the high hydrophobicity of the reduced polypyrrole, water molecules wererepelled from the core of the polymer matrix and so did not penetrate into the polymer matrix, at least duringour simulations. As a consequence of this hydrophobicity, a sharp polymer/water profile was obtained. In thecase of the oxidized polypyrrole, chloride ions penetrated into the core of the polymer matrix to keep theelectroneutrality of the system. As a result of this ion penetration into the polymer and the strong polymer−polymer repulsions between charged sites inside the oxidized polypyrrole, a swelling of the polymer matrixof 11% was measured, while the thickness of the polypyrrole/water interface increased by 50% comparedwith its reduced state. Finally, charge distribution and electric potential profiles across the polypyrrole/waterinterface were obtained in both oxidized and reduced states. The contribution of water to the electric potentialwhich consists of reorientating its dipoles was measured in both states.
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