Date of Award
M.S. in Engineering Science
A statistical central composite design (CCD) was employed to investigate the effects of cellulose nanocrystal (CNC) and cellulose nanofiber (CNF) volume fractions, as well as relative free volume fraction, on the thermal barrier properties of a pigment-based coating for cellulosic substrates composed of calcium carbonate (CaCO3) and a copolymer binder, poly(styrene-co-methacrylic acid). Average room-temperature thermal conductivity (based on three replicates) was selected as a response and calculated for the different coating formulations using reverse non-equilibrium molecular dynamics (RNEMD) simulation with the MÃ¼ller-Plathe algorithm. A reduced quadratic response surface model was fitted to the response data and analysis of variance (ANOVA) was performed. The effects of CNC and relative free volume fractions on the average thermal conductivity of the coatings were found to be significant, while the CNF volume fraction was insignificant. Overall, relative free volume fraction, which is representative of the porosity in the coating, showed a much larger impact on the average thermal conductivity than that of CNC volume fraction. Moreover, a weak interaction was observed between the two significant factors. Specifically, at low relative free volume fractions, addition of CNC to the formulation lowered the average thermal conductivity more than that of high relative free volume fractions. The pore size distribution analysis and average pore size calculation for the coatings (~5.25 Ã… for low and ~6.50 Ã… for high relative free volume fractions) did not reveal any significant effect of CNC on these properties at either low or high relative free volume fractions. However, the larger average pore size in the coatings associated with larger relative free volume fractions correlated well between the increase in pore size and reduced thermal conductivity in these coatings. IV Consequently, a larger CaCO3-CNC interfacial phonon scattering at low relative free volume fractions is believed to be the reason behind the above observations. The lowest thermal conductivity (0.075 W m-1 K-1), corresponding to highest thermal barrier property, was obtained for the coating with 2.50 vol.% CNC at a relative free volume fraction of 30%. Since CNF volume fraction was not a significant factor, its level was set at 0 vol.%. The results of this study provide a framework for a systematic design and optimization of pigment-based thermal barrier coatings for cellulosic substrates.
MANSOURIANTABAEI, MOHAMMAD, "SYSTEMATIC COMPUTATIONAL INVESTIGATION OF THERMAL BARRIER COATINGS FOR CELLULOSE SUBSTRATES" (2021). Electronic Theses and Dissertations. 2162.