A Classical Density Functional Theory for Predicting Energy and Orientation Properties of Chain-Like Molecules on Structured Interfaces

The orientation of chain-like molecules is an important issue in many fields, but the theoretical understanding remains limited. In this work, we introduce a classical density functional theory (CDFT) to investigate the orientation and energy properties of chain-like molecules on structured interfaces. The interface is represented by a face of a body-centered cubic (BCC) crystal, and the theory is implemented by a 3-dimensional algorithm. The predictions for potential mean force (PMF), density profile and orientation order parameter are consistent with molecular simulations. The orientation distribution function suggests a bimodal orientation distribution and a vertical-horizontal transition governed by surface separation. The interfacial structure exerts a significant influence on PMF, density profile and orientation. The (111) face generates a repulsive PMF and a flat density profile, which is in contrast to the (100) and (110) faces. We also examine the roles of molecular interaction, surface attraction, chain length and packing fractions, which may provide an insight into the design of nanoparticles and porous adsorbents.