Internal Structure of Methylcellulose Fibrils

Abstract

Methylcellulose (MC) is a water-soluble cellulose derivative with a wide range of commercial applications. Upon heating, MC solutions reversibly form ∼15–20 nm diameter fibrils, which percolate into a fibrillar network, resulting in macroscopic gelation. Using mid-angle X-ray scattering (MAXS) and wide-angle X-ray scattering (WAXS), we have analyzed MC chain organization within fibrils aligned in dried films that have been stretched by over 300%. MAXS and WAXS show distinct anisotropic scattering features, which we interpret as reflecting crystalline domains within the fibrils. The scattering peaks are consistent with a body-centered monoclinic unit cell, with similar dimensions as other cellulosic crystals, a = 11.4 Å, b = 8.9 Å, and c = 10.2 Å, and γ in the range of 90–100°, with MC chains oriented along the long axis of the fibril. Phase-plate cryogenic transmission electron microscopy images of MC fibrils contribute to a more comprehensive picture. Along the long axis of MC fibrils, there is evidence of dense twisted domains, which are interpreted as regions containing semicrystalline MC, interspersed with looser, less organized amorphous domains. Together, these two techniques provide the most complete interpretation of MC subfibril structure currently available.

Salt-Dependent Structure in Methylcellulose Fibrillar Gels

“…The relation between the length of the polymer chains and the fibril suggests that the macromolecules are aligned parallel to the fibril axis. Another study by Schmidt et al 30 has confirmed that the subfibril structure is semicrystalline in nature. The crystalline structure that has been proposed is a two-chain monoclinic unit cell, with dimensions consistent with other cellulosic crystalline structures.…”

Methylcellulose–Cellulose Nanocrystal Composites for Optomechanically Tunable Hydrogels and Fibers

“…Additionally, fibril formation may be induced by the addition of salt [ 64 , 65 ]. Rather recently, the tightly packed core region of the fibers has been suggested to comprise semicrystalline twisted MC chain domains aligned along the fibril long axis and surrounded by amorphous and less-ordered regions [ 66 ]. The percolation of the semi-stiff fibril network contributes to the increased macroscopic gel stiffness and turbidity at elevated temperatures.…”

Gelation under stress: impact of shear flow on the formation and mechanical properties of methylcellulose hydrogels

“…A fibrillar gel network structure has been reported for MC polymers of molecular weights 150 kg mol À1 and higher, 36,56 but currently the precise microstructure of the material used in our study here (M w approximately 50 kg mol À1 , details given below) is still unknown. The material used in this study becomes optically turbid (Fig.…”