Nakatani Alan I, Mohler Carol E, Hughes Stephanie
The Dow Chemical Company, Core R&D Analytical Sciences, 400 Arcola Rd., Collegeville, PA 19426, USA.
The Dow Chemical Company, Core R&D Formulation, Automation and Materials Science, Midland, MI 48674, USA.
Soft Matter. 2021 Jul 21;17(28):6848-6862. doi: 10.1039/d1sm00674f.
High molecular weight polymers are used in industrially important applications where the polymers adsorb onto surfaces of inorganic particles and facilitate dispersion, stabilization or flocculation of formulations. The surface conformation of these adsorbed polymers is key to their performance, yet an understanding of the effects of polymer charge, concentration and molecular weight on polymer conformation is incomplete. Here the adsorption behavior of high molecular weight, non-ionic, polyethylene oxide (PEO) and anionic partially hydrolyzed polyacrylamide (HPAM) polymers to a model clay, LAPONITE® (a trademark of BYK Additives, Inc.), was studied by small angle neutron scattering over a range of polymer concentrations. The adsorption of PEO was dependent on polymer concentration at all molecular weights, first adsorbing onto the radial edge of the clay particles and then to the clay faces as polymer concentration increased. While similar behavior was observed at low concentrations of HPAM, above a critical concentration, HPAM desorption results in large clay aggregates, which decrease in size at higher polymer loadings. The difference in adsorption properties as a function of polymer charge and concentration is interpreted in terms of conformational differences of adsorbed polymer at the clay surface. Changes in the volume fraction of adsorbed PEO with polymer concentration indicate changes in the relative amounts of adsorbed chain segments in trains, loops and tails, with no clay aggregation. In contrast, a constant volume fraction of adsorbed HPAM at low concentrations gives way to desorption at higher concentration due to charge repulsion, and depletion aggregation of the clay.
高分子量聚合物用于具有重要工业应用的领域，在这些应用中，聚合物吸附到无机颗粒表面，并促进配方的分散、稳定或絮凝。这些吸附聚合物的表面构象是其性能的关键，但对聚合物电荷、浓度和分子量对聚合物构象影响的理解并不完整。在此，通过小角中子散射研究了高分子量非离子聚环氧乙烷（PEO）和阴离子部分水解聚丙烯酰胺（HPAM）聚合物在一系列聚合物浓度下对模型粘土LAPONITE®（毕克添加剂公司的商标）的吸附行为。PEO的吸附在所有分子量下均取决于聚合物浓度，首先吸附到粘土颗粒的径向边缘，然后随着聚合物浓度的增加吸附到粘土表面。虽然在低浓度HPAM下观察到类似行为，但在临界浓度以上，HPAM解吸会导致形成大的粘土聚集体，而在较高聚合物负载量下聚集体尺寸会减小。根据粘土表面吸附聚合物的构象差异来解释吸附特性随聚合物电荷和浓度的变化。随着聚合物浓度的变化，吸附PEO的体积分数发生变化，这表明吸附链段在链段、环和尾中的相对含量发生变化，且没有粘土聚集。相比之下，低浓度下吸附HPAM的恒定体积分数在较高浓度下由于电荷排斥和解吸以及粘土的耗尽聚集而发生变化。
