A molecular dynamics investigation of chain conformational changes in compressed bilayers

The conformations of the chains constituting the hydrophilic component of a lkyl monolayers and bilayers are investigated by performing molecular dynam ics atomistic simulations on these systems at different temperatures. Sever al monitoring techniques are used to reveal the chain conformations, includ ing atom pair radial distribution functions, evolutions of the torsional an gles over thousands of timesteps, frequency distributions of the torsionl a ngles and 'snapshot' plots of the atomic configurations. These methods cons istently testify to the stability of the trans (fully extended) character o f the strain-free alkyl chains up to room temperature. The chains retain mu ch of this conformation even when the layers are compressed by the applicat ion of pressure, to which the chains respond by 'folding' at the ends attac hing them to the substrate planes while maintaining directions which are ma inly normal to these planes. A non-zero gap between the layers is also main tained. A pressure of about 50 kbar abruptly causes all motion in the chain s to cease, resulting in a highly ordered lattice structure.