Department of Chemistry and Materials Science, School of Chemical Technology, Aalto University , P.O. Box 16100, FI-00076 Aalto, Finland.
Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences , Niezapominajek 8, PL-30239 Krakow, Poland.
Langmuir. 2018 Jan 23;34(3):999-1009. doi: 10.1021/acs.langmuir.7b02836. Epub 2017 Dec 5.
Polyelectrolyte multilayers and layer-by-layer assemblies are susceptible to structural changes in response to ionic environment. By altering the salt type and ionic strength, structural changes can be induced by disruption of intrinsically bound ion pairs within the multilayer network via electrostatic screening. Notably, high salt concentrations have been used for the purposes of salt-annealing and self-healing of LbL assemblies with KBr, in particular, yielding a remarkably rapid response. However, to date, the structural and swelling effects of various monovalent ion species on the behavior of LbL assemblies remain unclear, including a quantitative view of ion content in the LbL assembly and thickness changes over a wide concentration window. Here, we investigate the effects of various concentrations of KBr (0 to 1.6 M) on the swelling and de-swelling of LbL assemblies formed from poly(diallyldimethylammonium) polycation (PDADMA) and poly(styrene sulfonate) polyanion (PSS) in 0.5 M NaCl using quartz-crystal microbalance with dissipation (QCM-D) monitoring as compared to KCl, NaBr, and NaCl. The ion content after salt exchange is quantified using neutron activation analysis (NAA). Our results demonstrate that Br ions have a much greater effect on the structure of as-prepared thin films than Cl at ionic strengths above assembly conditions, which is possibly caused by the more chaotropic nature of Br. It is also found that the anion in general dominates the swelling response as compared to the cation because of the excess PDADMA in the multilayer. Four response regimes are identified that delineate swelling due to electrostatic repulsion, slight contraction, swelling due to doping, and film destruction as ionic strength increases. This understanding is critical if such materials are to be used in applications requiring submersion in chemically dynamic environments such as sensors, coatings on biomedical implants, and filtration membranes.
聚电解质多层膜和层层组装体易受结构变化的影响，这些结构变化是对离子环境的响应。通过改变盐的类型和离子强度，可以通过静电屏蔽破坏多层网络中内在结合的离子对来诱导结构变化。值得注意的是，高盐浓度已被用于盐退火和 LbL 组装体的自修复，特别是 KBr，这会产生非常迅速的响应。然而，迄今为止，各种单价离子对 LbL 组装体行为的结构和溶胀效应仍不清楚，包括对 LbL 组装体中离子含量的定量观察以及在较宽浓度窗口下的厚度变化。在这里，我们研究了在 0.5 M NaCl 中形成的聚二烯丙基二甲基铵聚阳离子（PDADMA）和聚苯乙烯磺酸钠聚阴离子（PSS）的 LbL 组装体的溶胀和去溶胀，使用石英晶体微天平耗散（QCM-D）监测，与 KCl、KBr 和 NaCl 相比，研究了不同浓度（0 至 1.6 M）的 KBr 的影响。使用中子活化分析（NAA）定量测量盐交换后的离子含量。我们的结果表明，在离子强度高于组装条件时，Br 离子对预制备薄膜的结构的影响比 Cl 离子大得多，这可能是由于 Br 的更混乱性质。还发现，一般来说，与阳离子相比，阴离子主导溶胀响应，因为在多层中存在过量的 PDADMA。确定了四个响应区域，这些区域可以根据静电排斥、轻微收缩、掺杂引起的溶胀以及离子强度增加时的膜破坏来划分溶胀。如果要将此类材料用于需要浸入化学动态环境中的应用，例如传感器、生物医学植入物的涂层和过滤膜，则需要了解这种理解。
