Thermal barrier coatings for cellulosic substrates: A statistically designed molecular dynamics study of the coating formulation effects on thermal conductivity

Abstract

A central composite design (CCD) was employed to investigate the effects of cellulose nanocrystal (CNC), cellulose nanofiber (CNF), and relative free volume on the thermal barrier properties of a pigment-based coating for cellulosic substrates, composed of calcium carbonate and poly(styrene-co-methacrylic acid) binder. Average room-temperature thermal conductivity based on three replicates was selected as response and calculated for the different coating formulations using reverse non-equilibrium molecular dynamics (RNEMD) simulation with the Müller-Plathe algorithm. The effects of CNC and relative free volume fractions on the thermal conductivity of the coating were found to be significant, while that of the CNF volume fraction was insignificant. Overall, relative free volume fraction (porosity) had much larger impact on thermal conductivity than CNC volume fraction. Moreover, a weak interaction was observed between these two significant factors. A pore size distribution analysis and average pore size calculation for the coatings (∼5.25 Å for the low and ∼6.50 Å for the high relative free volume fraction) did not reveal any significant effect of CNC on these properties at either the low or high relative free volume fraction. It is speculated that larger CaCO3-CNC interfacial phonon scattering at the low relative free volume fraction leads to the above observations.