Vainio Ulla, Lauten Rolf Andreas, Serimaa Ritva
Department of Physical Sciences, P.O. Box 64, FI-00014, University of Helsinki, Helsinki, Finland,
Langmuir. 2008 Aug 5;24(15):7735-43. doi: 10.1021/la800479k. Epub 2008 Jun 27.
Lignosulfonate is a colloidal polyelectrolyte widely used as a dispersant in various industrial applications and produced during chemical pulping of wood chips. Here we present a systematic small-angle X-ray scattering (SAXS) and rheological study of fractionated lignosulfonate (mass weighted molar mass M w 18 000 g/mol) dissolved in water and 0.2 M NaCl. The concentration range varied from semidilute to concentrated regime. SAXS intensity of all solutions followed the Porod law at all concentrations, which is a clear indication of a compact shape of the lignosulfonate particle. In water, below 10 mass % lignosulfonate, the average interparticle distance obtained from SAXS patterns relates to concentration via a power law with exponent -0.28. Deviation of the power law exponent from ideal -0.33 and a linear decrease in volume fraction normalized Porod constant as a function of concentration are taken as indications of self-association of lignosulfonate. In saline solutions at high lignosulfonate mass fractions the average distance between lignosulfonate particles was longer and the average particle size was larger than those in aqueous solutions. The intrinsic viscosity in saline solution also was larger than that in aqueous solution. Lignosulfonate solutions showed Newtonian viscosity, except at very high concentrations. The variation of the relative zero-shear viscosity eta(0),r) with concentration was interpreted with the Krieger-Dougherty equation. An oblate spheroid shape with an axial ratio of 3.5 describes the average shape of the lignosulfonate particles in saline solutions based on SAXS intensities, the size distribution obtained using gel permeation chromatography, and rheological characterization. The largest dimension of the particles was about 8 nm. SAXS and rheology studies as a function of temperature reveal indications of temperature-dependent self-association.
木质素磺酸盐是一种胶体聚电解质，在各种工业应用中广泛用作分散剂，并且是在木片化学制浆过程中产生的。在此，我们展示了对溶解于水和0.2M氯化钠中的分级木质素磺酸盐（质量加权摩尔质量Mw为18000g/mol）进行的系统小角X射线散射（SAXS）和流变学研究。浓度范围从半稀溶液到浓溶液。所有溶液的SAXS强度在所有浓度下均遵循Porod定律，这清楚地表明木质素磺酸盐颗粒呈紧密形状。在水中，木质素磺酸盐含量低于10质量%时，从SAXS图谱获得的平均粒子间距离与浓度通过指数为-0.28的幂律相关。幂律指数偏离理想值-0.33以及体积分数归一化的Porod常数随浓度呈线性下降被视为木质素磺酸盐自缔合的迹象。在高木质素磺酸盐质量分数的盐溶液中，木质素磺酸盐颗粒之间的平均距离比水溶液中的更长，且平均粒径更大。盐溶液中的特性粘度也比水溶液中的大。木质素磺酸盐溶液表现出牛顿粘度，除了在非常高的浓度下。相对零剪切粘度η(0,r)随浓度的变化用Krieger-Dougherty方程进行了解释。基于SAXS强度、使用凝胶渗透色谱法获得的尺寸分布以及流变学表征，轴向比为3.5的扁球体形状描述了盐溶液中木质素磺酸盐颗粒的平均形状。颗粒的最大尺寸约为8nm。作为温度函数的SAXS和流变学研究揭示了温度依赖性自缔合的迹象。
