Charge and mass balance in polyelectrolyte multilayers
Charge and mass balance in polyelectrolyte multilayers
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DOI：
10.1021/ja980350
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发表时间：
1998-08-05
影响因子：
15
通讯作者：
Li, M
中科院分区：
文献类型：
--
作者：
Schlenoff, JB;Ly, H;Li, M
通过逐层沉积构建的聚电解质多层的离子和聚合物含量已使用放射分析方法直接探测。使用含盐或无盐溶液制造多层。聚离子上的电荷在数量上相互平衡。沉积态多层膜不含盐离子，检测限为几 ppm。所有多余的电荷（在每个沉积步骤中都会反转）都驻留在表面。表面电荷控制聚合物沉积的量，平均代表单个分子层内电荷的一半。如果所使用的聚电解质之一具有氧化还原活性，例如聚紫精，则可以在沉积后调节内部电荷。在电化学还原下，聚紫罗碱/聚（苯乙烯磺酸盐）多层中的体电荷补偿主要通过阳离子流入得以保留。在重复的电化学循环过程中，随着构象变化的发生，残留的盐离子会积累。当聚(对亚苯基亚乙烯基)的热不稳定前体作为聚阳离子掺入时，当正电荷从多层热消除时观察到盐阳离子吸收。当其中一种成分的电荷密度接近零时，可以观察到这种结构被破坏的证据。对于典型的沉积时间（通常长达 1 小时）来说，聚合物沉积在动力学上是不可逆的，并且顶层在暴露于带相反电荷的对应物时不会从表面剥离。这些结果进一步证实了聚电解质多层内广泛的互穿和无序以及有限的迁移率。
The ion and polymer content of polyelectrolyte multilayers constructed via layer-by-layer deposition have been directly probed using radioanalytical methods. Multilayers were fabricated using salt-containing or salt-free solutions. Charges on polyions quantitatively balance each other. As-deposited multilayers contain no salt ions within a limit of detection of a few ppm. All excess charge, which is reversed on each deposition step, resides at the surface. Surface charge controls the amount of polymer deposited and represents, on average, one-half of the charge within a single molecular layer. Internal charge can be regulated following deposition if one of the polyelectrolytes employed is redox-active, such as a polyviologen. Under electrochemical reduction, bulk charge compensation in a polyviologen/poly(styrene sulfonate) multilayer is preserved mainly by cation influx. Residual salt ions accumulate as conformational changes occur during repeated electrochemical cycling. When a thermally labile precursor to poly(p-phenylene vinylene) is incorporated as polycation, salt cation uptake is observed when positive charge is thermally eliminated from the multilayer. Evidence for disruption of this structure is observed when the charge density on one of the constituents approaches zero. For typical deposition times, usually up to 1 h, polymer deposition is kinetically irreversible, and the top layer is not stripped from the surface on exposure to its oppositely charged counterpart. These results provide further confirmation of extensive interpenetration and disorder as well as limited mobility within polyelectrolyte multilayers.