Non-surface activity and micellization of ionic amphiphilic diblock copolymers in water. Hydrophobic chain length dependence and salt effect on surface activity and the critical micelle concentration
Non-surface activity and micellization of ionic amphiphilic diblock copolymers in water. Hydrophobic chain length dependence and salt effect on surface activity and the critical micelle concentration
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DOI：
10.1021/la051584r
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发表时间：
2005-10-25
期刊：
影响因子：
3.9
通讯作者：
Matsuoka, H
中科院分区：
文献类型：
--
作者：
Kaewsaiha, P;Matsumoto, K;Matsuoka, H
我们先前报道（Macromolecules 2003，36，5321; Langmuir，2004，20，7412）具有聚电解质作为亲水性链段的两亲性二嵌段共聚物几乎不显示表面活性，但在水中形成胶束。为了进一步研究这一表面和界面科学中的新奇现象，我们采用活性阴离子聚合法合成了另一种水溶性离子型两亲性嵌段共聚物聚（氢化异戊二烯）-b-聚（苯乙烯磺酸）钠PIP-h（2）-b-PSSNa。合成了几种不同疏水链长的嵌段共聚物，并利用表面张力和X射线反射率研究了它们在空气/水界面上的吸附行为。进行染料增溶实验以检测胶束形成。我们发现，在本研究中使用的聚合物也形成胶束超过一定的聚合物浓度（cmc），在无盐条件下，在空气-水界面没有吸附。因此，我们进一步证实了这一现象是普遍的两亲性离子嵌段共聚物，虽然这是很难相信从目前的表面和界面科学。对于具有长疏水链的聚合物（长度为亲水链的三倍以上），并且在高盐浓度下，在空气-水界面处观察到聚合物的轻微吸附。随着盐浓度的增加，长疏水链聚合物表现出低分子量离子表面活性剂的“正常”行为。因此，这种奇怪现象的起源可能是亲水部分的大离子性质。动态光散射分析表明，盐的加入对嵌段共聚物胶束的流体动力学半径影响不大。疏水链长与cmc的关系不寻常，存在某种转变点，而且嵌段共聚物的cmc不随盐浓度的增加而降低，这与通常离子型小分子表面活性剂的cmc随盐浓度的增加而降低（Corrin-Harkins定律）形成鲜明对比。这些行为被认为是特殊的，但普遍的，离子型两亲性嵌段共聚物的特性，和关键因素被认为是从水表面的排斥力之间的平衡的图像电荷效应和疏水吸附。
We reported previously (Macromolecules 2003, 36, 5321; Langmuir, 2004, 20, 7412) that amphiphilic diblock copolymers having polyelectrolytes as a hydrophilic segment show almost no surface activity but form micelles in water. In this study, to further investigate this curious and novel phenomenon in surface and interface science, we synthesized another water-soluble ionic amphiphilic diblock copolymer poly(hydrogenated isoprene)-b-sodium poly(styrenesulfonate) PIp-h(2)-b-PSSNa by living anionic polymerization. Several diblock copolymers with different hydrophobic chain lengths were synthesized and the adsorption behavior at the air/water interface was investigated using surface tension measurement and X-ray reflectivity. A dye-solubilization experiment was carried out to detect the micelle formation. We found that the polymers used in this study also formed micelles above a certain polymer concentration (cmc) without adsorption at the air-water interface under a no-salt condition. Hence, we further confirmed that this phenomenon is universal for amphiphilic ionic block copolymer although it is hard to believe from current surface and interface science. For polymers with long hydrophobic chains (more than three times in length to hydrophilic chain), and at a high salt concentration, a slight adsorption of polymer was observed at the air-water interface. Long hydrophobic chain polymers showed behavior "normal" for low molecular weight ionic surfactants with increasing salt concentration. Hence, the origin of this curious phenomenon might be the macroionic nature of the hydrophilic part. Dynamic light scattering analysis revealed that the hydrodynamic radius of the block copolymer micelle was not largely affected by the addition of salt. The hydrophobic chain length-cmc relationship was found to be unusual; some kind of transition point was found. Furthermore, very interestingly, the cmc of the block copolymer did not decrease with the increase in salt concentration, which is in clear contrast to the fact that cmc of usual ionic small surfactants decreases with increasing salt concentration (Corrin-Harkins law). These behaviors are thought to be the special, but universal, characteristics of ionic amphiphilic diblock copolymers, and the key factor is thought to be a balance between the repulsive force from the water surface by the image charge effect and the hydrophobic adsorption.