Fares Hadi M, Ghoussoub Yara E, Surmaitis Richard L, Schlenoff Joseph B
Department of Chemistry and Biochemistry, The Florida State University, Tallahassee, Florida 32306-4390, United States.
Langmuir. 2015 Jun 2;31(21):5787-95. doi: 10.1021/la504910y. Epub 2015 Feb 22.
Polyelectrolyte multilayers (PEMUs) are made from various combinations of polyanions and polycations. It is now understood that these ultrathin films of polyelectrolyte complex may also incorporate counterions derived from the solutions from which the PEMU was deposited or exchanged into the film postassembly. If these ions are required to compensate nonstoichiometric ratios of polycation and polyanion they cannot leave the film and exert considerable influence on film properties, such as modulus and permeability. These "extrinsic" charges also complicate fundamental studies on PEMUs. We report a method to remove almost all ionic content from a PEMU made of poly(diallyldimethylammonium chloride), PDADMAC, and poly(styrenesulfonate), PSS. In this method, a high salt concentration plasticizes the multilayer past its glass transition, dispersing all the buried excess PDADMA throughout the film. Exposure to a solution of PSS in a lower salt concentration consumes excess PDADMA near the surface without overcompensating with PSS. The process is repeated in a cyclic fashion, removing >95% of the ions charge present in the as-made PEMU.
聚电解质多层膜（PEMUs）由聚阴离子和聚阳离子的各种组合制成。现在人们认识到，这些聚电解质复合物的超薄膜也可能包含源自PEMU沉积或组装后交换到膜中的溶液中的抗衡离子。如果这些离子需要补偿聚阳离子和聚阴离子的非化学计量比，它们就不能离开膜，并对膜的性能，如模量和渗透性产生相当大的影响。这些“外在”电荷也使对PEMUs的基础研究变得复杂。我们报告了一种从由聚二烯丙基二甲基氯化铵（PDADMAC）和聚苯乙烯磺酸盐（PSS）制成的PEMU中去除几乎所有离子成分的方法。在这种方法中，高盐浓度使多层膜在其玻璃化转变温度以上发生塑化，将所有埋藏的过量PDADMA分散在整个膜中。暴露于较低盐浓度的PSS溶液中会消耗表面附近的过量PDADMA，而不会被PSS过度补偿。该过程以循环方式重复进行，去除了制成的PEMU中>95%的离子电荷。
