All-atom molecular simulation study of cellulose acetate: amorphous structure and the dissolution of small molecule

All-atom analysis was conducted for cellulose acetate (CA) using molecular dynamics simulation. The intermolecular interactions were elucidated at the amorphous state with degrees of acetyl substitution (DS) of 2, 2.5, and 3, and the energetics of dissolution was treated for H2O, CO2, and CH4. It was observed for the CA amorphous that DS strongly affects the hydrogen bonding among the hydroxy groups of CA and that the short-range packing of pyranose rings becomes tighter with acetylation. The free energy of dissolution was computed by the energy-representation method of solvation. The dissolution into CA was more favorable in the order of H2O> CO2 > CH4, and the DS dependence of the dissolution free energy was evident only for H2O between DS =2 and 2.5. The roles of the intermolecular interaction components were further addressed. It was seen that the electrostatic component brings the DS dependence of the dissolution free energy for H2O as well as the difference in the affinity to CA between CO2 and CH4. The van der Waals component was still dominant for the nonpolar CO2 and CH4, and the summed contribution to it from the acetyl and main-chain groups of CA was weakly dependent on DS. The connection of the dissolution energetics with the underlying structures is also discussed. [GRAPHICS] .

Automated summary

An all-atom analysis of cellulose acetate was conducted using molecular dynamics simulation, examining the intermolecular interactions, energetics of dissolution, and the underlying structures. The results showed that DS strongly influenced the hydrogen bonding and packing of cellulose acetate, with dissolution being more favorable for H2O compared to CO2 and CH4. The electrostatic component was found to play a crucial role in the DS dependence of dissolution free energy for H2O, as well as the difference in affinity between CO2 and CH4.