Simulation of X-ray diffractograms relevant to the purported polymorphs cellulose IVI and IVII

Abstract

Diffractograms were simulated for model nanocrystals of cellulose I b , using numerical summation of radiation scattered from all carbon and oxygen atoms in the nanocrystal. Diffractogram peaks were sometimes displaced by a few degrees from positions calculated by the Bragg equation, as predicted in a published study based on a different mathematical approach. Simulated diffractograms showed 2 or 3 peaks, depending on the crosssectional size and shape of the model nanocrystal. Some of the 2-peak diffractograms resembled published results for the purported polymorph cellulose IV I , or for cell-wall cellulose, supporting suggestions that cellulose IV I is simply cellulose I fragmented into nanocrystals with relatively small cross-sectional dimensions. A published diffractogram for cellulose IV II could not be simulated with acceptable precision, suggesting that this polymorph might have a crystal structure distinctly different from that of cellulose I b .

Nanostructure of cellulose microfibrils in spruce wood

“…Other primary-wall microfibrils are either similar (74) or smaller (31,71,74) in diameter. C-6 conformations and H-bonding patterns in the disordered fraction of celery cellulose (28) were qualitatively similar to those reported here but primary-wall celluloses show consistent crystallographic differences, particularly the reduced monoclinic angle that has led these celluloses to be described as cellulose IV (48).…”

“…2), but the accuracy of the Scherrer dimensions is likely to be reduced by a number of approximations that are not reflected in the standard deviations quoted. In particular, deviations from the Bragg equation, and apparently also from the Scherrer equation, become significant in lattices with as few crystal planes as those examined here (48). Also the above value for the mean of the dimensions in the directions normal to (1-10) and (110) depends on the assumption that the disorder parameter is the same in all radial directions; and all estimates of radial broadening, even that of the 200 reflection, depend strongly on the function assumed for the noncrystalline background.…”

“…6) if the dimensions parallel and orthogonal to the (200) plane were chosen appropriately. Our diffraction data therefore favored the rectangular shape, but should be viewed with caution because disorder may not be rotationally symmetric and because deviations from the Scherrer equation may be observed in such small crystallites (48). The two model structures shown in Fig.…”

Structure and spacing of cellulose microfibrils in woody cell walls of dicots

“…The influences of dimensions and disorder are difficult to separate, but this can be done by progressively removing the broadening contributions of disorder of different kinds, correcting for instrumental broadening and then using the Scherrer equation to match the remaining broadening to predict lateral dimensions (Fernandes et al 2011;Thomas et al 2013a;Thomas et al 2013b). A more fundamental approach is to predict the radial intensity profile by first-principles calculation from an ensemble of structures simulating the disorder assumed to be present (Newman 2008, Newman et al 2013. These two approaches give comparable results although the first-principles approach shows that in structures containing only a few lattice planes, the Scherrer equation becomes an approximation (Newman 2008).…”

“…A more fundamental approach is to predict the radial intensity profile by first-principles calculation from an ensemble of structures simulating the disorder assumed to be present (Newman 2008, Newman et al 2013. These two approaches give comparable results although the first-principles approach shows that in structures containing only a few lattice planes, the Scherrer equation becomes an approximation (Newman 2008).…”