Ulama Jeanette, Oskolkova Malin Zackrisson, Bergenholtz Johan
Department of Chemistry and Molecular Biology, University of Gothenburg , SE-41296 Göteborg, Sweden.
Division of Physical Chemistry, Center of Chemistry and Chemical Engineering, Lund University , SE-22100 Lund, Sweden.
Langmuir. 2016 Mar 29;32(12):2882-90. doi: 10.1021/acs.langmuir.5b04739. Epub 2016 Mar 14.
Aqueous dispersions of fluorinated colloidal spheres bearing grafted poly(ethylene glycol) (PEG) are studied as a function of salt and particle concentration with the aim of improving the understanding of interactions among polymer-grafted particles. These dispersions can sustain large concentrations of salt, but crystals nucleate in dilute dispersions when a sufficient Na2CO3 concentration is reached, which is attributed to the presence of attractions between particles. On further increasing the Na2CO3 concentration, the solvent is rapidly cleared of particles. Small-angle X-ray scattering and cryogenic transmission electron microscopy are employed in order to quantify the attractions. The former is used to extract a second virial coefficient, and the latter shows that the PEG-graft contracts as a function of increasing salt concentration. The contraction not only leads to a reduction in excluded volume but also is accompanied by attractions of moderate magnitude. In contrast, dispersion of the particles in ethanol, in which bulk PEG solutions crystallize, lead to fractal structures caused by strong attractions.
研究了接枝聚乙二醇（PEG）的氟化胶体球的水分散体，考察了盐浓度和颗粒浓度对其的影响，目的是增进对聚合物接枝颗粒间相互作用的理解。这些分散体能够承受高浓度的盐，但当达到足够的碳酸钠浓度时，在稀分散体中会形成晶体，这归因于颗粒间存在吸引力。进一步增加碳酸钠浓度时，溶剂中的颗粒会迅速消失。采用小角X射线散射和低温透射电子显微镜来量化吸引力。前者用于提取第二维里系数，后者表明PEG接枝链会随着盐浓度的增加而收缩。这种收缩不仅导致排斥体积减小，还伴随着中等强度的吸引力。相比之下，颗粒在乙醇中的分散（本体PEG溶液在乙醇中会结晶）会由于强吸引力而导致分形结构的形成。
