Coarse-grained model of the native cellulose $$\hbox {I}\alpha$$ and the transformation pathways to the $$\hbox {I}\beta$$ allomorph

Abstract

Abstract All-atom simulations are used to derive effective parameters for a coarse-grained description of the crystalline cellulose $$\hbox {I}\alpha$$ I α . In this description, glucose monomers are represented by the C4 atoms and non-bonded interactions within the cellulose sheets and between the sheets by effective Lennard-Jones interactions. The parameters are determined by two methods: the Boltzmann inversion and through monitoring of the energies associated with changes of the coarse-grained degrees of freedom. We find that the stiffness-related parameters for cellulose $$\hbox {I}\alpha$$ I α are nearly the same as for $$\hbox {I}\beta$$ I β allomorph. However, the non-bonded terms are placed differently and are weaker leading to an overall lower energy, and free energy, of $$\hbox {I}\beta$$ I β compared to $$\hbox {I}\alpha$$ I α . We apply the coarse-grained description to determine amorphous transition states for the room-temperature conversion process between the $$\hbox {I}\alpha$$ I α and $$\hbox {I}\beta$$ I β allomorphs and to characterize the interface between the crystalline forms of the allomorphs.