Charge and Pressure-TunedSurface Patterning of Surfactant-EncapsulatedPolyoxometalate Complexes at the Air–Water Interface.

In this paper, four organic–inorganic hybrid complexeswereprepared using a cationic surfactant dimethyldioctadecylammonium (DODA)to replace the counter cations of four Keggin-type polyoxometalate(POM) clusters with gradually increased negative charges, PW12O403–, SiW12O404–, BW12O405–, and CoW12O406–. The formedsurfactant-encapsulated POM (SEP) complexes showed typical amphiphilicproperties and can be spread onto the air–water interface toform Langmuir monolayers. The interfacial behavior of the SEP monolayerfilms was systemically studied by multiple in situand ex situcharacterization methods includingBrewster angle microscopy (BAM), atomic force microscopy (AFM), reflection–absorptioninfrared (RAIR), and X-ray photoelectron spectroscopy (XPS). We foundthat the increasing alkyl chain density of SEPs leads to an enhancedstability and a higher collapse pressure of SEP Langmuir monolayers.Moreover, a second layer evolved as patterns from the initial monolayersof all the SEPs, when the surface pressures approached the collapsevalues. The rational combination of alkyl chain density and surfacepressure can precisely control the size and the morphology of SEPpatterns transforming from disk-like to leaf-like structures on amicrometer scale. The pattern formation was demonstrated to be drivenby the self-optimized surface energy of SEP monolayers. This findingcan direct a new strategy for the fabrication of POM-hybrid filmswith controllable patterns, which should be instructive for designingPOM-based thin film devices. [ABSTRACT FROM AUTHOR]