Hierarchical Architecture and Modeling of Bio-Inspired Mechanically Adaptive Polymer Nanocomposites

This work is concerned with a new class of polymer nanocomposites with tailored mechanical properties. Such materials can reversibly switch their mechanical stiffness by up to three orders of magnitude in response to biomedically relevant chemical stimuli. The architecture of the new synthetic polymer nanocomposites was inspired by the dermis of sea cucumbers and their mechanically adaptivity and exceptional high reinforcement property are potentially suitable for use in biomedicine. According to the current literature, the mechanical morphing of these polymer nanocomposites is a result of changing nanoparticle interactions and it is described in the framework of two mechanical models, viz. the percolation model applies to a stiff (unstimulated) state and the Halpin-Kardos model describes a soft (stimulated) state. In this work, a new model is proposed to describe the reinforcement and adaptivity effects in such nanocomposites within a single theory. The change from the stiff to soft states and back is modulated by a single scalar parameter that describes the extent of stimulus. The essence of the new model lies in physically based modifications of the classical percolation theory applied to the evolution of the network formed by cellulose whisker nanoparticles, which are responsible for the stress-transfer in this class of polymer nanocomposites.