Department of Chemistry and Biochemistry , The Florida State University , Tallahassee , Florida 32306-4390 , United States.
Langmuir. 2018 Apr 3;34(13):3874-3883. doi: 10.1021/acs.langmuir.8b00336. Epub 2018 Mar 21.
Polyelectrolyte multilayers (PEMUs) are ultrathin membranes made by alternating adsorption of oppositely charged polyelectrolytes on substrates. Although PEMUs have shown exceptional selectivity for certain ion-filtering applications, they usually contain an excess of one of the polyelectrolytes due to the history- and condition-dependent mode of PEMU assembly. This excess charge provides fixed sites for ion exchange, enhancing the concentration of oppositely charged ions. Thus, the ion-permselective properties of PEMUs cannot be compared unless they are assembled under identical conditions. This work demonstrates the enhanced permeability of PEMUs as-made from poly(diallyldimethylammonium) (PDADMA), and poly(styrene sulfonate) (PSS) to ferricyanide as an example of an anion. Annealing by NaCl followed by pairing of excess PDADMA with additional PSS produces an almost stoichiometric film that better reflects the intrinsic transport properties of PEMUs. This pairing, observed in real time using electrochemical methods, occurs at the PEMU/solution interface under countercurrent transport of PSS from solution and excess PDADMA paired with a counterion, termed PDADMA*, from the PEMU bulk. A quantitative comparison of PSS and PDADMA* diffusion reveals the conditions under which PEMU assembly depends on PSS molecular weight and concentration.
聚电解质多层（PEMUs）是通过在基底上交替吸附带相反电荷的聚电解质而制成的超薄膜。尽管 PEMUs 已经在某些离子过滤应用中表现出了非凡的选择性，但由于 PEMU 组装的历史和条件依赖性模式，它们通常含有过量的一种聚电解质。这种过剩电荷为离子交换提供了固定的位点，增强了相反电荷离子的浓度。因此，除非在相同的条件下组装，否则不能比较 PEMUs 的离子选择性性能。这项工作以铁氰化物为例，展示了由聚二烯丙基二甲基氯化铵（PDADMA）和聚苯乙烯磺酸盐（PSS）制成的 PEMUs 的增强渗透性。用 NaCl 退火，然后将过量的 PDADMA 与额外的 PSS 配对，会产生一种几乎化学计量的膜，更好地反映了 PEMUs 的固有传输特性。这种配对是通过电化学方法实时观察到的，在 PSS 从溶液中逆流运输和过量 PDADMA 与从 PEMU 本体中配对的反离子 PDADMA配对的情况下，在 PEMU/溶液界面发生。对 PSS 和 PDADMA扩散的定量比较揭示了 PEMU 组装取决于 PSS 分子量和浓度的条件。
