Molecular dynamics simulations of the characteristics of sodium carboxymethyl cellulose with different degrees of substitution in a salt solution
2017
Li, Wenzhuo | Huang, Shuaiyu | Xu, Dingjia | Zhao, Yingying | Zhang, Yuchao | Zhang, Lin
Sodium carboxymethyl cellulose (SCMC) with different degrees of substitution (DS) possesses structural characteristics and physicochemical properties that are important in broad areas of industrial applications. This reported work investigated the structural characteristics, including the effective length (L ₑf), the radius of gyration (R g), and the hydrodynamic radius (R H), and the physicochemical properties, including intrinsic viscosity ([η]) and salt tolerance, of SCMC with a DS more than 1.0 in NaCl solution using molecular dynamics (MD) simulations. In the MD simulations, the DS of SCMC varied from 1.2 to 2.8, and the NaCl concentration varied from 0 to 1.4 mol/L. MD simulation results showed that with the increment of NaCl concentration, the L ₑf (or R g or R H) of SCMC decreased; with the increment of the DS, the L ₑf of SCMC increased. Also, the variation tendency of [η] in the NaCl solution was consistent with its L ₑf (or R g or R H). It was noted that the salt tolerance (represented by D) of SCMC increased as the DS increased. In addition, the sharp variation of the D value of SCMC occurred in the range of DS of 1.6 to 2.0, which agreed with the reported experimental results. Radial distribution function analyses showed that the Na⁺ cations had a stronger interaction with the carboxyl groups in SCMC with lower DS when it was present in a salt solution of higher concentration, which also reasonably explained the variation of L ₑf, R g, R H, [η], and D of SCMC in NaCl solution.
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