Thermal Response in Crystalline Iβ Cellulose: A Molecular Dynamics Study
2007 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 111, no 30, 9138-9145 p.Article in journal (Refereed) Published
The influence of temperature on structure and properties of the cellulose Iβ crystal was studied by molecular dynamics simulations with the GROMOS 45a4 force-field. At 300 K, the modeled crystal agreed reasonably with several sets of experimental data, including crystal density, corresponding packing and crystal unit cell dimensions, chain conformation parameters, hydrogen bonds, Young's modulus, and thermal expansion coefficient at room temperature. At high-temperature (500 K), the cellulose chains remained in sheets, despite differences in the fine details compared to the room-temperature structure. The density decreased while the a and b cell parameters expanded by 7.4% and 6%, respectively, and the c parameter (chain axis) slightly contracted by 0.5%. Cell angles α and β divided into two populations. The hydroxymethyl groups mainly adopted the gt orientation, and the hydrogen-bonding pattern thereby changed. One intrachain hydrogen bond, O2'H2'···O6, disappeared and consequently the Young's modulus decreased by 25%. A transition pathway between the low- and high-temperature structures has been proposed, with an initial step being an increased intersheet separation, which allowed every second cellulose chain to rotate around its helix axis by about 30°. Second, all hydroxymethyl groups changed their orientations, from tg to gg (rotated chains) and from tg to gt (non-rotated chains). When temperature was further increased, the rotated chains returned to their original orientation and their hydroxymethyl groups again changed their conformation, from gg to gt. A transition temperature of about 450 K was suggested; however, the transition seems to be more gradual than sudden. The simulated data on temperature-induced changes in crystal unit cell dimensions and the hydrogen-bonding pattern also compared well with experimental results.
Place, publisher, year, edition, pages
Washington: ACS Publications , 2007. Vol. 111, no 30, 9138-9145 p.
cellulose, molecular dynamics, thermal expansion
Physical Chemistry Polymer Chemistry
IdentifiersURN: urn:nbn:se:kth:diva-9474DOI: 10.1021/jp072258iISI: 000248315700062ScopusID: 2-s2.0-34548219478OAI: oai:DiVA.org:kth-9474DiVA: diva2:114133
QC 201006182008-11-172008-11-062010-07-05Bibliographically approved