Two-dimensional molecular clusters of a few tens nanometer size were found in spread monolayers of a series of partially fluorinated long-chain acids. Atomic force microscopy images have revealed that the size of the clusters is sharply monodisperse. The size changes systematically with changing structure of the hydrophobic chain of the amphiphiles. The smallest cluster has a circular shape of 17 nm diameter. One cluster is composed of about 700 film molecules. These clusters gather to form macroscopic domains of millimeter size without compression. A formation mechanism of these molecular clusters is discussed. Clusters are formed during the spreading process due to the instability of the film materials at the spreading process. It was made clear that cluster formation during the spreading is rather general for amphiphiles under the conditions where condensed monolayers are formed.
A concept is shown to fabricate mesoporous ceria thin films with a crystalline framework and a bimodal pore size distribution by evaporation-induced self-assembly followed by a suitable temperature treatment and template removal strategy. The use of a suitable block copolymer ((CH 2 CH 2 CH 2 (CH)CH 2 CH 3 ) 79 (OCH 2 -CH 2 ) 89 OH), "KLE") and an ionic liquid template (leading to pores 3 nm in diameter) generated a bimodal pore system of deformed spherical mesopores of ca. 6 nm × 16 nm with the smaller pores being located in the matrix between the larger ones. The porosity was studied by a combination of quantitative SAXS analysis, physisorption, AFM, and TEM, introducing a general methodology for a quantitative structural characterization of such films.
Crack‐free, mesoporous SnO2 films with highly crystalline pore walls are obtained by evaporation‐induced self‐assembly using a novel amphiphilic block‐copolymer template (“KLE” type, poly(ethylene‐co‐butylene)‐block‐poly(ethylene oxide)), which leads to well‐defined arrays of contracted spherical mesopores by suitable heat‐treatment procedures. Because of the improved templating properties of these polymers, a facile heat‐treatment procedure can be applied whilst keeping the mesoscopic order intact up to 600–650 °C. The formation mechanism and the mesostructural evolution are investigated by various state‐of‐the‐art techniques, particularly by a specially constructed 2D small‐angle X‐ray scattering setup. It is found that the main benefit from the polymers is the formation of an ordered mesostructure under the drastic conditions of using molecular Sn precursors (SnCl4), taking advantage of the large segregation strength of these amphiphiles. Furthermore, it is found that the crystallization mechanism is different from other mesostructured metal oxides such as TiO2. In the case of SnO2, a significant degree of crystallization (induced by heat treatment) already starts at quite low temperatures, 250–300 °C. Therefore, this study provides a better understanding of the general parameters governing the preparation of mesoporous metal oxides films with crystalline pore walls.
Micro-phase separation in binary mixed Langmuir monolayers of cadmium salts of n-alkyl fatty acids (CH3(CH2)n-2COOH; Cn (n ) 18, 20, 22, 24)) and a perfluoropolyether surfactant (F(CF(CF3)CH2O)3CF-(CF3)COOH, PFPE) is studied by film balance measurement and atomic force microscopy (AFM). At different temperatures, mixtures of Cn/PFPE in chloroform were spread onto the aqueous Cd 2+ subphase and deposited on silicon wafers. AFM images showed that Cn and PFPE separate into microscopic domains of condensed phase and a surrounding matrix of expanded phase, respectively, in their mixed monolayers. The morphological feature of phase-separated structures was characterized by characteristic length (λ) expressing the periodicity of two-phase distribution and fractal dimension (D) of Cn domains reflecting the complexity of domain shape, which were determined through AFM image analyses. It was found that the monolayer morphologies systematically vary with alkyl chain length of Cn and temperature of the water surface; circular-shaped condensed phase microdomains with D of about 1.1 are formed at λ of 7-9 µm when the mixed monolayers are prepared using a shorter alkyl chain fatty acid and/or at a higher temperature, whereas branched narrow domains with D close to 2 are formed at λ of approximately 4 µm when a longer chain fatty acid is used at a lower temperature.
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