We report a theoretical investigation of hydrated clay-polymer nanocomposites exchanged with Li+, Na+ and K+. This work is the result of the implementation of Teppen's force field within a highly scalable molecular dynamics (MD) program called Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) with which, we performed large-scale MD simulations. The results show that, in contradiction to the situation pertaining in the absence of polymer, the behaviour of Li+ and Na+ based nanocomposites is quite distinct. Unlike K+ and Na+, the Li+ cations are observed to diffuse within the tetrahedral pockets of the clay sheets as well as the centre of the galleries. (C) 2004 Elsevier B.V. All rights reserved.