Charge and Pressure-Tuned Surface Patterning of Surfactant-Encapsulated Polyoxometalate Complexes at the Air鈥揥ater Interface

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• 作者：Miao Xu ; Haolong Li ; Liying Zhang ; Yizhan Wang ; Yuan Yuan ; Jianming Zhang ; Lixin Wu
• 刊名：Langmuir
• 出版年：2012
• 出版时间：October 16, 2012
• 年：2012
• 卷：28
• 期：41
• 页码：14624-14632
• 全文大小：589K
• 年卷期：v.28,no.41(October 16, 2012)
• ISSN：1520-5827

文摘

In this paper, four organic鈥搃norganic hybrid complexes were prepared using a cationic surfactant dimethyldioctadecylammonium (DODA) to replace the counter cations of four Keggin-type polyoxometalate (POM) clusters with gradually increased negative charges, PW₁₂O₄₀^{3鈥?/sup>, SiW₁₂O₄₀4鈥?/sup>, BW₁₂O₄₀5鈥?/sup>, and CoW₁₂O₄₀6鈥?/sup>. The formed surfactant-encapsulated POM (SEP) complexes showed typical amphiphilic properties and can be spread onto the air鈥搘ater interface to form Langmuir monolayers. The interfacial behavior of the SEP monolayer films was systemically studied by multiple in situ and ex situ characterization methods including Brewster angle microscopy (BAM), atomic force microscopy (AFM), reflection鈥揳bsorption infrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We found that the increasing alkyl chain density of SEPs leads to an enhanced stability and a higher collapse pressure of SEP Langmuir monolayers. Moreover, a second layer evolved as patterns from the initial monolayers of all the SEPs, when the surface pressures approached the collapse values. The rational combination of alkyl chain density and surface pressure can precisely control the size and the morphology of SEP patterns transforming from disk-like to leaf-like structures on a micrometer scale. The pattern formation was demonstrated to be driven by the self-optimized surface energy of SEP monolayers. This finding can direct a new strategy for the fabrication of POM-hybrid films with controllable patterns, which should be instructive for designing POM-based thin film devices.}