Precipitation effects in polyelectrolytes on addition of salts
Precipitation effects in polyelectrolytes on addition of salts
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聚电解质中的沉淀对盐添加的影响
DOI：
10.1002/polb.1993.090310213
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
A. Keller
中科院分区：
文献类型：
--
作者：
K. A. Narh;A. Keller
我们在这里报告的沉淀现象，在聚电解质添加某些盐。可以说，在一个更广泛的聚电解质计划过程中，观察到了“侧面”的影响。由于我们认为它们对大分子的行为具有重要意义，而且据我们所知，它们在文献中没有出现，因此我们将它们记录在案。具体如下。作为我们对长链分子在拉伸流动中的行为进行更广泛研究的一部分，我们还研究了聚电解质，特别是聚苯乙烯磺酸盐（PSS），一种分子量分布较窄的聚合物。正如之前几次报道的那样，使用我们的设计方法，我们可以几乎完全延伸长链分子，记录这种链延伸，并通过单个参数r（构象弛豫时间）表征链的可延伸性。反过来，r取决于初始分子构象，较小的T反映了无规卷曲的更紧凑的初始构象。在使用完全磺化的PSS的Na+盐的前述工作中发现，随着过量盐浓度的增加，延展性（因此I）降低，反映了增加的线圈收缩。根据聚电解质的基本理论，通过在溶液中自由移动的Na+阳离子增加对连接到链上的磺酸根阴离子的屏蔽，预期这种效果。然而，更新颖的是在添加CaCl 2形式的Ca+离子的情况下观察到的效果。在这里，与Na+相比，r的下降要大得多，平均下降两个数量级，并且进一步地，对于给定的Ca '+浓度，随着聚合物浓度的增加，发现r增加。然而，Ca+的整个效应类别被解释为通过二价Ca+离子在统计学上形成离子桥的结果。在低聚合物浓度下，当链被隔离时，这些桥将主要是分子内的，导致增强的卷曲收缩。可以预期的是，在增加聚合物浓度时，当链开始重叠时，一些桥将是分子间的，导致表观分子量增加，从而导致r增加，这是前面的工作结束的注意事项。正是这条线，即多价性的counterparents和由此产生的竞争之间的假设分子内和分子间的离子桥，这一直是我们目前更新的计划的出发点。在此过程中，上述不同-
We report here on precipitation phenomena in polyelectrolytes on addition of certain salts. The effects in question were observed “on the side” so to speak, in the course of a wider program on polyelectrolytes. As we consider them of significance for the behavior of macromolecules and, as to our knowledge, they do not feature in the literature, we are placing them here on record. The preliminaries are as follows. As part of our wider ranging investigations on the behavior of long-chain molecules in elongational flow we have also been examining polyelectrolytes, polystyrene sulfonate in particular (PSS), a polymer available in narrow molecular weight distribution. As reported on several occasions previously’using a method of our design, we can extend long-chain molecules practically fully, register this chain extension, and characterize chain extensibility through a single parameter r, the conformational relaxation time. In turn, r depends, among other things, on the initial molecular conformation, smaller T reflecting more compact initial conformation of the random coil. It was found in the preceding work ‘using the Na+ salt of the fully sulfonated PSS that with increasing excess salt concentration extensibility, hence I, decreased, reflecting increasing coil contraction. This effect was expected from basic theory of polyelectrolytes on the basis of the increasing screening of the sulfonate anions attached to the chain by the Na+ cations freely moving in the solution. More novel, however, was the effect observed with the addition of Ca” ions in the form of CaC12. Here, the decrease in r was much larger, on average by two orders of magnitudes, compared to Na+, and further, on increasing polymer concentration for a given Ca’+ concentration, r was found to increase. Tentatively, the whole class of effects with Ca’+ was interpreted as the consequence of statistically forming ionic bridges through the bivalent Ca” ions. At low polymer concentration, when the chains are isolated, these bridges will be largely intramolecular leading to enhanced coil contraction. It could be expected that on increasing the polymer concentration, when chains start to overlap, some of the bridges will be intermolecular leading to an increase in apparent molecular weight with a consequent increase in r a note on which the preceding work’ends. It is this line, namely the effect of multivalency of the counterion and the resulting competition between assumed intramolecular and intermolecular ionic bridging, which has been the starting point of our presently renewed program. In the course of it, the above mentioned differ-