Department of Inorganic and Analytical Chemistry, University of Geneva, Sciences II, 30 Quai Ernest-Ansermet, 1205 Geneva, Switzerland.
Nanoscale. 2016 Jul 21;8(27):13498-506. doi: 10.1039/c6nr02665f. Epub 2016 Jun 29.
The persistence length of cationic dendronized polymers adsorbed onto oppositely charged substrates was studied by atomic force microscopy (AFM) and quantitative image analysis. One can find that a decrease in the ionic strength leads to an increase of the persistence length, but the nature of the substrate and of the generation of the side dendrons influence the persistence length substantially. The strongest effects as the ionic strength is being changed are observed for the fourth generation polymer adsorbed on mica, which is a hydrophilic and highly charged substrate. However, the observed dependence on the ionic strength is much weaker than the one predicted by the Odijk, Skolnik, and Fixman (OSF) theory for semi-flexible chains. Low-generation polymers show a variation with the ionic strength that resembles the one observed for simple and flexible polyelectrolytes in solution. For high-generation polymers, this dependence is weaker. Similar dependencies are found for silica and gold substrates. The observed behavior is probably caused by different extents of screening of the charged groups, which is modified by the polymer generation, and to a lesser extent, the nature of the substrate. For highly ordered pyrolytic graphite (HOPG), which is a hydrophobic and weakly charged substrate, the electrostatic contribution to the persistence length is much smaller. In the latter case, we suspect that specific interactions between the polymer and the substrate also play an important role.
通过原子力显微镜（AFM）和定量图像分析研究了带正电荷的树枝状聚合物在带相反电荷的基底上的固有长度。可以发现，离子强度的降低会导致固有长度的增加，但基底的性质和侧枝的生成会对固有长度产生很大的影响。在离子强度发生变化时，第四代聚合物在云母上的吸附表现出最强的影响，云母是一种亲水且带高电荷的基底。然而，观察到的对离子强度的依赖比 Odijk、Skolnik 和 Fixman（OSF）理论对半柔性链预测的要强得多。低代聚合物的变化与离子强度的变化与溶液中简单和柔性聚电解质的变化相似。对于高代聚合物，这种依赖性较弱。在二氧化硅和金基底上也发现了类似的依赖性。观察到的行为可能是由不同程度的带电基团屏蔽引起的，这种屏蔽程度受聚合物代次的影响，在较小程度上受基底性质的影响。对于高度有序的热解石墨（HOPG），这是一种疏水且带弱电荷的基底，静电对固有长度的贡献要小得多。在后一种情况下，我们怀疑聚合物和基底之间的特定相互作用也起着重要作用。
