Hybrid coarse-grained/atomistic model of "chitosan + carbon nanostructures" composites.

We present a new hybrid molecular dynamics model of chitosan oligomers which is constructed specifically for studying chitosan + carbon nanostructures composites, their structure and mechanical properties. The model is derived for application within the modified molecular mechanics force field AMBER. Method of virtual sites mapping allowed to retain hexagonal rings of chitosan backbone. Mass and structural disposition of virtual atoms has been found as function of joined groups' atoms masses and coordinates. Geometrical parameters (e.g., bond length, valence angles, torsional angles and van der Waals distances) were found using semi-empirical methods. Parameters of interaction within the AMBER force field were estimated according to structural and energy characteristics of chitosan dimers and oligomers. Model has successfully passed multilevel verification based on comparison of its behaviour with atomistic chitosan within the same force field. It appeared that the model reproduces structural and energy characteristics of chitosan and its composites with carbon nanostructures. Moreover, it allows estimation of their mechanical properties. Dynamical characteristics of composite components are also well reproduced.