Towards an atomistic model for ORMOCER®-I: application of forcefield methods

ORMOCER®s are an outstanding class of hybrid materials due to their tuneable properties, e.g. hardness, resistivity and refractive index. These materials are well-characterized with regard to their macroscopic properties, but understanding the system at the atomistic level still remains challenging. Understanding the material formation process at this level becomes especially important when three-dimensional nanoscale patterns are generated employing processes as laser-based multi-photon polymerization. We have developed an atomistic model based on the COMPASS forcefield to simulate the reference system ORMOCER®-I. We chose representative compositions for the condensation reaction product as well as for the organically cross-linked polymerized product. In the first part of the study, the results of forcefield validation experiments and the development of the atomistic model for ORMOCER®s are presented. The second part contains the results from molecular dynamics simulations at room temperature and under periodic boundary conditions, performed in order to test the feasibility of our model. The densities of the simulated materials are in very good agreement with experimentally determined densities for the unpolymerized as well as for the polymerized state, respectively.