Department of Radiochemistry, Faculty of Nuclear Sciences and Technology, Higher Institute of Applied Sciences and Technologies, Salvador Allende y Luaces, Quinta de los Molinos, Plaza, Ciudad de La Habana, Cuba.
J Colloid Interface Sci. 2009 Nov 15;339(2):495-501. doi: 10.1016/j.jcis.2009.07.067. Epub 2009 Aug 4.
Dilute mixtures of the water soluble polymer polyethyleneimine (PEI) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) form mesostructured thin films at the air/solution interface. In this paper we show that these films form spontaneously, reaching an equilibrium composition. When the film is removed, a new solid film rapidly reforms, with a similar morphology when inspected by Brewster angle microscopy (BAM). Successive removal of films lead to a series of structurally similar films, until the amount of surfactant in solution approaches the lower limit of film forming concentration. The results obtained using surfactant-selective potentiometry suggest that the incipient polymer:surfactant aggregates are in a position to migrate to the surface rapidly after film removal, prior to mesostructure formation. X-ray reflectivity indicates that films formed at different PEI:CTAB compositions retain mesophase regular structures with the same d-spacing feature, equal to 52.2A. Grazing incidence diffraction measurements indicate that films are composed of small crystallites arranged in a random powder fashion, developing a rough surface morphology evidenced by BAM. The central finding is that PEI:CTAB films form when the amount of CTAB in solution is higher than a critical film formation concentration, very close to the critical aggregation concentration (CAC), allowing the formation of several equilibrated films from the same growing solution.
水溶性聚合物聚乙烯亚胺（PEI）和阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）的稀混合物在空气/溶液界面形成介孔薄膜。在本文中，我们表明这些薄膜自发形成，达到平衡组成。当薄膜被去除时，新的固体薄膜会迅速重新形成，用布鲁斯特角显微镜（BAM）检查时具有相似的形态。连续去除薄膜会导致一系列结构相似的薄膜，直到溶液中的表面活性剂量接近形成薄膜的浓度下限。使用表面活性剂选择性电位法得到的结果表明，在薄膜去除后，初生聚合物：表面活性剂聚集体迅速迁移到表面，然后再形成介孔结构。X 射线反射率表明，在不同的 PEI：CTAB 组成下形成的薄膜保留了具有相同 d 间距特征的介相规则结构，等于 52.2A。掠入射衍射测量表明，薄膜由小的结晶颗粒以随机粉末的方式排列而成，形成了由 BAM 证明的粗糙表面形貌。中心发现是，当溶液中的 CTAB 量高于临界成膜浓度时，PEI：CTAB 薄膜会形成，非常接近临界聚集浓度（CAC），允许从同一生长溶液形成几个平衡的薄膜。
