Identification of interphase properties in nanocomposites

• Applicant: Dr.-Ing. Sebastian Pfaller
• Subject Area: Mechanics ; Polymeric and Biogenic Materials and Derived Composites ; Polymer Materials
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 396414850

In engineering applications, plastics play an important role and offer new possibilities to achieve and to adjust a specific material behaviour. They consist of long-chained polymers and possess, together with additives, an enormous potential for tailored properties.Recently, techniques have been established to produce and to disperse filler particles with typical dimensions in the range of nanometers. Even for low volume contents of filler particles, these so-called nanofillers may have significant impact on the properties of plastics. This can be most likely traced back to their very large volume-to-surface ratio. In this context, the polymer-particle interphase is of vital importance: as revealed by experiments, certain nanofillers may e.g. increase the fatigue lifetime of plastics by a factor of 15.The effective design of such nanocomposites quite frequently requires elaborated mechanical testing, which might - if available - be substituted or supplemented by simulations. For this purpose, however, continuum mechanics together with the Finite Element Method (FE) as the usual tool for engineering applications is not well-suited since it is not able to capture processes at the molecular level. Therefore, particle-based techniques such as molecular dynamics (MD) have to be employed. However, these typically allow only for extremely small system sizes and simulation times. Thus, a multiscale technique that couples both approaches is required to enable the simulation of so-called representative volume elements (RVE) under consideration of atomistic effects.The goal of this 4-year project is the development of a methodology which yields a continuum-based description of the material behaviour of the polymer-particle interphase of nanocomposites, whereby the required constitutive laws are derived from particle-based simulations. Due to their very small dimensions of some nanometers, the interphases cannot be accessed directly by experiments and particle-based simulations must substitute mechanical testing. The recently developed Capriccio method, designed as a simulation tool to couple MD and FE descriptions for amorphous systems, will be employed and refined accordingly in the course of the project.In the first step, the mechanical properties of the polymer-particle interphase shall be determined by means of inverse parameter identification for small systems with one and two nanoparticles. In the second step, these properties shall be transferred to large RVEs. With this methodology at hand, various properties as e.g. the particles’ size and shape as well as grafting densities shall be mapped from pure particle-based considerations to continuum-based descriptions. Further consideration will then offer prospects to transfer the material description to applications relevant in engineering and eventually suited for the simulation of parts.

• DFG Programme: Research Grants