Ionization and pH stability of multilayers formed by self-assembly of weak polyelectrolytes
Ionization and pH stability of multilayers formed by self-assembly of weak polyelectrolytes
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DOI：
10.1021/la026546b
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发表时间：
2003-02-18
期刊：
影响因子：
3.9
通讯作者：
Sukhishvili, SA
中科院分区：
文献类型：
--
作者：
Kharlampieva, E;Sukhishvili, SA
研究了弱聚碱和弱聚酸在硅晶体表面逐层自组装形成的聚电解质多层膜及其在酸性条件下的稳定性。该体系为12%、20%、25%、37%、90%或98%的季铵化聚4-乙烯吡啶（Q12、Q20、Q25、Q37、Q90或Q98）作为多碱基（通常缩写为QPVP）和聚甲基丙烯酸（PMAA）作为多酸在缓冲的D2O中。利用傅里叶变换红外光谱在衰减全反射模式下对吡啶环和羧基的吸附和电离进行了量化。在pH = 5时，膜的生长主要受静电相互作用的控制。当QPVP加入到顶层时，羧基的电离值比其在溶液中的值增加。诱导电荷的数量随着多碱总电荷密度（以乙基化吡啶和质子化吡啶的总和计算）的增加而线性增加。这表明形成了两种类型的静电对（COO—NR+和COO—NH+）。薄膜内吡啶基团和羧基的电离度随顶层聚合物的电荷变化而变化，并随层数的变化而变化。在多层膜上加PMAA抑制了多层膜内羧基的平均电离，而在多层膜上加聚碱则增强了多层膜内羧基的平均电离。这种效应的影响范围相当长，持续了三层以上的聚合物层，衰变长度约为100埃。当缓冲溶液的pH值低于pH 2时，由于羧基的质子化和聚合物/聚合物离子接触的破坏，多层膜溶解。QPVP在酸性条件下的多层稳定性与烷基化程度有关。除了烷基化程度最大外，膜的稳定性随QPVP烷基化程度的增加而增加。多层破坏与小分子质子化有关。
The formation of polyelectrolyte multilayers using the layer-by-layer sequential self-assembly of a weak polybase and polyacid onto a surface of Si crystal and their stability under acidic conditions were studied. The system was 12%, 20%, 25%, 37%, 90%, or 98% quaternized poly-4-vinylpyridine (Q12, Q20, Q25, Q37, Q90, or Q98) as polybases (generally abbreviated as QPVP) and poly(methacrylic acid) (PMAA) as a polyacid in buffered D2O. The adsorption and ionization of pyridine rings and carboxylic groups were quantified using Fourier transform infrared spectroscopy in attenuated total reflection mode. At pH = 5, film growth was primarily controlled by electrostatic interactions. When QPVP was included into the top layer, ionization of carboxylic groups was increased compared to its value in solution. The amount of the induced charge increased linearly with the total charge density of the polybase (calculated as a sum of ethylated pyridinium and protonated pyridinium. groups), suggesting the formation of both types of electrostatic pairs (COO--NR+ and COO--NH+). The degree of ionization of both pyridine groups and carboxylic groups within the film responded to the charge of the polymer included in the top layer and oscillated as a function of layer number. The average ionization of the carboxylic groups within the multilayer was suppressed when the multilayer was topped with PMAA, and it was enhanced when the top layer was the polybase. The effect was rather long-ranged and persisted through over three polymer layers with a decay length of about 100 Angstrom. When the pH of the buffer solution was lowered below pH 2, multilayers dissolved due to protonation of carboxylic groups and disruption of polymer/polymer ionic contacts. The multilayer stability under acidic conditions was dependent on the alkylation degree of QPVP. With the exception of the largest alkylation degrees, the stability of the film increased with the alkylation degree of QPVP. The multilayer destruction correlated with the protonation of the small (