Elongated Rodlike Particle Formation of Methyl Cellulose in Aqueous Solution.

Abstract

The conformation and structure of methyl cellulose (MC) ether samples dissolved in pure water under dilute conditions were carefully reconsidered based on the results obtained using small-to-wide-angle neutron scattering (S-WANS), static light scattering (SLS), dynamic light scattering (DLS), and viscometric techniques. The examined MC samples possessed an average degree of substitution by methyl groups per glucose unit of ca 1.8 and weight average molar masses (Mw), ranging from 23 to 790 kg mol–1. S-WANS experiments clearly demonstrated that the samples possess highly elongated rigid rodlike local structures in deuterium oxide solutions with weak periodicities of ca 0.4 and 1.0 nm on a length scale, which correspond to the average intermolecular distance between molecular chain portions facing each other in the formed rodlike structure and the repeating length of the monomeric cellobiose unit of molecular chains, respectively. Ratios of the particle length (L) to the radius of gyration (Rg) determined by SLS techniques approximately showed the relationship LRg–1 = holding in rigid rods over the entire Mw range examined in this study. However, the folding number, defined as the ratio of the average molecular contour length (l) to L, remained at the value of lL–1 ∼ 2, representing an elongated one-folded hairpin structure, until Mw ∼ 300 kg mol–1 and increased substantially up to ca 4.9 at the highest Mw of 790 kg mol–1. The observed increase in the lL–1 value corresponded well with an increase in the diameter of the formed rod with increasing Mw observed in the S-WANS data. The Mw dependencies of the translational diffusion coefficient determined via DLS measurements and that of the intrinsic viscosity detected via viscometric techniques also distinctly demonstrated that particles formed by the MC samples dissolved in aqueous solution behave as elongated rigid rods irrespective of Mw.