Polymer thin films are encountered in a variety of different technological applications including adhesives, paint, lubricants, and multiphase composite materials. The overall performance of such materials depends on the polymer properties close to the interface. Nowadays, the design of functional materials used in different applications, such as organic electronics or miniaturized devices, often involves polymer-solid interfaces. Because of this broad spectrum of technological applications, the properties of polymer-solid interfaces are a very intense research field.

 We are using hierarchical multi-scale simulation approaches to study polymer thin films as well as polymer melt/solid and polymer melt/vacuum interfaces [1-6].  The proposed scheme consists of the following stages:

  1. Ab-initio (density functional theory, DFT) calculations of small molecules adsorbed on solid surfaces. These calculations allow us to accurately describe the interaction energy between a small fragment of the polymer (e.g. a monomer) and the solid layer. Furthermore, they can be used in order to construct an accurate classical all-atom force field.[4]
  2. Atomistic molecular dynamics (MD) simulations of short polymer chains/solid systems. Various properties related to density, structure and dynamics of the hybrid materials are predicted. We also develop a methodology to obtain systematically CG models from the atomistic description, for specific polymer/solid systems.[3]
  3. Mesoscopic simulations of polymer/solid (here PS/Au) surfaces. First, the CG model was validated by studying small PS/Au systems, with short (10mer) PS chains, using all-atom and coarse-grained MD simulations. The CG model was then used to study the structural, conformational and dynamical properties of various films and longer polymer chains.

The width of the interphase region of the polymer films found to be property specific. The density profiles reached the bulk value around 1.5 nm from the interface, for all chain lengths. In contrast, an estimate based on the conformation tensor profile, or the chain dynamics, indicates that the interphase width is proportional to the square root of the chain length.[1-2]

References

  1. K. Johnston, V. Harmandaris, “Hierarchical multiscale modeling of polymer?solid interfaces: Atomistic to coarse-grained description and structural and conformational properties of polystyrene/gold systems”, Macromolecules, 2013, 46, 5741?5750.
  2. K. Johnston, V. Harmandaris, “Hierarchical simulations of hybrid polymer/solid materials”, Soft Matter, 2013, 9, 6696-6710 (Review article, Themed Issue on Emerging Investigators).
  3. K. Johnston, V. Harmandaris, “Properties of short polystyrene chains confined between two gold surfaces through a combined density functional theory and classical molecular dynamics approach”, Soft Matter, 2012, 8, 6320-6332.
  4. K. Johnston, V. Harmandaris, “Properties of benzene confined between two Au(111) surfaces using a combined density functional theory and classical molecular dynamics approach.”, J. Phys. Chem. C 2011, 115, 14707-14717.
  5. V. Harmandaris, K. Daoulas, V.G. Mavrantzas, “Molecular dynamics simulation of a polymer melt/solid interface: Local dynamics and chain mobility in a thin film of polyethylene melt adsorbed on graphite”, Macromolecules, 2005, 38, 5796-5809.
  6. K. Daoulas, V. Harmandaris, V.G. Mavrantzas, “Detailed atomistic simulation of a polymer melt / solid interface: Structure, density and conformation of a thin polyethylene melt film adsorbed on graphite”, Macromolecules, 2005, 38, 5780-5795.