Lebedeva Olga V, Kim Byoung-Suhk, Vasilev Krasimir, Vinogradova Olga I
Max Planck Institute for Polymer Research, Ackermannweg 10, Mainz 55128, Germany.
J Colloid Interface Sci. 2005 Apr 15;284(2):455-62. doi: 10.1016/j.jcis.2004.10.040.
By using a combination of atomic force and confocal microscopy, we explore the effect of 1:1 electrolyte (NaCl) on the stiffness of polyelectrolyte microcapsules. We study the "hollow" and "filled" (with polystyrene sulfonate) capsules. In both cases the shells are composed of layers of alternating polystyrene sulfonate (PSS) and polyallylamine hydrochloride (PAH). The stiffness of both "hollow" and "filled" capsules was found to be largest in water. It decreases with salt concentration up to approximately 3 mol/L and gets quasi-constant in more concentrated solutions. The "filled" capsules are always stiffer than "hollow." The observed softening correlates with the salt-induced changes in morphology of the multilayer shells detected with the scanning electron microscopy. It is likely that at concentrations below approximately 3 mol/L the multilayer shell is in a "tethered" state, so that the increase in salt concentration leads to a decrease in number of ionic cross-links and, as a result, in the stiffness. In contrast, above the critical concentration of approximately 3 mol/L multilayer shells might be in a new, "melted," state. Here the multilayer structure is still retained, but sufficient amount of ionic cross-links is broken, so that further increase in salt concentration does not change the capsule mechanics. These ideas are consistent with a moderate swelling of multilayers at concentrations below approximately 3 mol/L and significant decrease in their thickness in more concentrated solutions measured with surface plasmon spectroscopy.
通过结合使用原子力显微镜和共聚焦显微镜，我们探究了1:1电解质（氯化钠）对聚电解质微胶囊硬度的影响。我们研究了“空心”和“填充”（填充聚苯乙烯磺酸盐）胶囊。在这两种情况下，壳层均由交替的聚苯乙烯磺酸盐（PSS）和聚烯丙胺盐酸盐（PAH）层组成。发现“空心”和“填充”胶囊在水中的硬度最大。随着盐浓度增加至约3摩尔/升，其硬度降低，而在浓度更高的溶液中趋于恒定。“填充”胶囊总是比“空心”胶囊更硬。观察到的软化现象与扫描电子显微镜检测到的多层壳层形态的盐诱导变化相关。在浓度低于约3摩尔/升时，多层壳层可能处于“束缚”状态，因此盐浓度的增加会导致离子交联数量减少，进而导致硬度降低。相反，在约3摩尔/升的临界浓度以上，多层壳层可能处于一种新的“熔融”状态。此时多层结构仍然保留，但足够数量的离子交联被破坏，因此盐浓度的进一步增加不会改变胶囊的力学性能。这些观点与表面等离子体光谱法测量的结果一致，即在浓度低于约3摩尔/升时多层结构有适度膨胀，而在浓度更高的溶液中其厚度显著减小。
