Predicting the binding energy for nylon 6,6/clay nanocomposites by molecular modeling

Molecular modeling techniques were applied to predicting binding energies f or nanocomposites comprising exfoliated clay layers treated with ammonium s alts (usually quaternary) and dispersed in nylon 6,6 resin. For each of 12 selected ammonium ions (quats), a molecular dynamics simulation was perform ed at 600 K for 100-300 ps with a time step of 0.001 ps on a computer model built from 20 repeating units of nylon 6,6 polymer, six quat molecules and a montmorillonite platelet. Several conformations were selected from the e quilibrated time region, energy minimization carried out and binding energi es calculated between nylon 6,6 and the clay platelet, between nylon 6,6 an d the quat, and between the quat and the platelet. It was found that the bi nding energy between nylon 6,6 and the clay platelet decreases almost linea rly with the volume of adsorbed quat. Consequently, pristine clay yields th e highest binding strength to the nylon. Clays partially substituted by lon g quats were found to be equivalent to those fully substituted with short q uats. (C) 2001 Elsevier Science Ltd. All rights reserved.