Molecular Configuration Fitting of Sodium Lignosulfonate in Aqueous Solution
Qiu Xue-qing Qian Yong Guo Yun-qing Deng Yong-hong
School of Chemistry and Chemical Engineering,South China University of Technology,Guangzhou 510640,Guangdong,China
First,sodium lignosulfonate ( NaLS) was purified and fractionated through filtering and gel chromatography. Next,the absolute molecular mass of NaLS was determined by means of the static light scattering,and enough salt was added to eliminate the influence of the slow mode on the determination. Then,the diffusion coefficients of NaLS molecules at different temperatures were measured by means of the dynamic light scattering. Based on the obtained absolute molecular mass and diffusion coefficients,the fitting calculation of the ellipsoid structures of NaLS molecules at different temperatures was carried out by using Perrin formula. The results show that the absolute molecular mass of NaLS obtained through the light scattering methods is larger than that measured via gel permeation chromatography ( GPC) and it is closer to its real molecular mass; and that,with the increase of the temperature,the diffusion coefficient of NaLS molecules increases,indicating that the Brownian motion is accelerated. Fitting results obtained through Perrin formula demonstrate that the structures of NaLS molecules at different temperatures are all disk-like oblate ellipsoids with ratios of the length of longer axis to that of shorter more than 7.5,and they become more oblate when the solution temperature increases. In addition,the ellipsoid models of NaLS molecules at different temperatures were constructed by combining the results in this paper with the existing ones in the literature.
Keywords: sodium lignosulfonate molecular configuration light scattering Perrin formula ellipsoid structure temperature