Priority Research Centre for Advanced Particle Processing and Transport, University of Newcastle, Callaghan, NSW 2308, Australia.
Phys Chem Chem Phys. 2019 Feb 20;21(8):4650-4662. doi: 10.1039/c8cp06644b.
The temperature induced swelling/collapse transition of poly(oligoethylene glycol methacrylate) (POEGMA) brushes has been investigated in electrolyte solutions comprised of multiple anions. The behaviour of a POEGMA brush in mixed salt environments of potassium acetate (KCH3COO, causes collapse) and thiocyanate (KSCN, causes swelling), two ions at opposite ends of the Hofmeister series, has been monitored with neutron reflectometry (NR) and quartz crystal microbalance with dissipation (QCM-D). These techniques revealed that the balance of the swelling/collapse influence of the two ions on the structure of the brush is temperature dependent. At low temperatures in mixed salt environments, the influence of the acetate and thiocyanate ions appears additive, antagonistic and approximately equal in magnitude, with brush thickness and dissipation similar to the brush in the absence of electrolyte. At higher temperatures, the influence of the acetate ion diminishes, resulting in an increase in the relative influence of the thiocyanate ion on the brush conformation. These temperature dependent specific ion effects are attributed to increased steric crowding in the brush, along with an increased affinity of the thiocyanate ion for the polymer at higher temperatures.
聚（聚乙二醇甲基丙烯酸酯）（POEGMA）刷在包含多种阴离子的电解质溶液中经历了温度诱导的溶胀/坍塌转变。用中子反射测量（NR）和石英晶体微天平耗散（QCM-D）监测了处于霍夫迈斯特序列两端的两种离子（醋酸钾（KCH3COO，引起坍塌）和硫氰酸钾（KSCN，引起溶胀））的混合盐环境中 POEGMA 刷的行为。这些技术表明，两种离子对刷结构的溶胀/坍塌影响的平衡是温度依赖性的。在混合盐环境的低温下，醋酸盐和硫氰酸盐离子的影响似乎是加性的、拮抗的且大小近似相等，刷的厚度和耗散与不存在电解质时的刷相似。在较高的温度下，醋酸盐离子的影响减小，导致硫氰酸盐离子对刷构象的相对影响增加。这些温度依赖性的特定离子效应归因于刷中空间位阻的增加，以及随着温度的升高硫氰酸盐离子与聚合物的亲和力增加。
