Department of Polymer Chemistry, Kyoto University, Kyoto 615-8510, Japan.
Langmuir. 2009 Dec 15;25(24):13752-62. doi: 10.1021/la901466h.
The nanostructure and its transition of in a poly(acrylic acid) (PAA) brush in the water surface monolayers of poly(hydrogenated isoprene)-b-poly(acrylic acid) with different block lengths and block ratios were investigated by X-ray reflectivity as a function of surface pressure (brush density) and salt concentration in the subphase. The PAA brush showed the same behavior after salt addition as did the poly(methacrylic acid) (PMAA) brush, which was investigated previously. The brush chains expanded and then shrunk after passing the maximum with increasing added salt concentration. This behavior could be explained by the change in electric charges on the PAA brush chains as was observed on the PMAA brush. The PAA brush chains showed a critical brush density, where there was a transition between the carpet layer only and carpet + brush layer structures, as did the PMAA and poly(styrene sulfonic acid) (PSS) brushes. The critical brush density was about 0.4 chains nm(-2), which was higher than that of the PSS brush, a strong acid brush, and was close to that of the PMAA brush, a weak acid brush. However, the critical brush density of the PAA brush was independent of the hydrophilic chain length whereas that of the PMAA brush decreased with increasing PMAA chain length. In addition, the PAA brush had a thicker carpet layer than the PSS and PMAA brushes. Hence, the mechanism of PAA brush formation was predicted to be different from that of not only the PSS brush (strong acid brush) but also the PMAA brush.
在聚异戊二烯-b-聚丙烯酸（PI-b-PAA）的水表面单层中，通过 X 射线反射研究了不同嵌段长度和嵌段比的聚（丙烯酸）（PAA）刷的纳米结构及其转变作为表面压力（刷密度）和亚相盐浓度的函数。PAA 刷在加盐后表现出与之前研究过的聚（甲基丙烯酸）（PMAA）刷相同的行为。随着加盐浓度的增加，刷链先扩张然后收缩，超过最大值。这种行为可以通过观察 PMAA 刷上的 PAA 刷链上的电荷变化来解释。PAA 刷链表现出临界刷密度，在该密度下，仅存在地毯层和地毯+刷层结构之间的转变，PMAA 和聚苯乙烯磺酸（PSS）刷也是如此。临界刷密度约为 0.4 个链 nm(-2)，高于强酸性 PSS 刷，接近于弱酸性 PMAA 刷。然而，PAA 刷的临界刷密度与亲水性链长无关，而 PMAA 刷的临界刷密度随 PMAA 链长的增加而减小。此外，PAA 刷的地毯层比 PSS 和 PMAA 刷厚。因此，PAA 刷的形成机制不仅与 PSS 刷（强酸刷）而且与 PMAA 刷不同。
