Chromonic Liquid Crystalline Phases of Pinacyanol Acetate: Characterization and Use as Templates for the Preparation of Mesoporous Silica Nanofibers

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• 作者：Carlos Rodri虂guez-Abreu ; Carolina Aubery Torres ; Gordon J. T. Tiddy
• 刊名：Langmuir
• 出版年：2011
• 出版时间：March 15, 2011
• 年：2011
• 卷：27
• 期：6
• 页码：3067-3073
• 全文大小：987K
• 年卷期：v.27,no.6(March 15, 2011)
• ISSN：1520-5827

文摘

We report on the self-aggregation of the cationic dye pinacyanol acetate and its use for the preparation of nanostructured silica via templated sol鈭抔el reaction. The dye forms nematic and hexagonal chromonic liquid crystals at low concentrations in water (i.e., from 0.75 wt %); the type of counterion appears to play an important role in liquid crystal formation. From analysis of small X-ray scattering (SAXS) curves, it is inferred that dye aggregates have the morphology of hollow long tubes with one-molecule-thick walls; the diameter of the tubes does not to change much with concentration. The dye aggregates can be aligned by shear or by a magnetic field. The high-resolution ¹H NMR spectra show that aggregation takes place over a range of concentrations rather than having a sharp 鈥渃ritical鈥?aggregation. Within the aggregates the conjugated moiety, including the three-carbon link, is in close proximity to the aromatic groups of stack neighbors. On the other hand, dye aggregates direct the formation of silica nanofibers synthesized via sol鈭抔el reaction, mimicking the elongated structures found in aqueous media. The nanofibers show a hierarchical organization; i.e., they contain hexagonal arrays of 3 nm cylindrical mesopores left after calcination of the templating molecules, and the pore walls are 2.7 nm thick. As the nanofibers form entangled networks, the obtained materials also show interparticle porosity. The present findings open new possibilities for the use of commercial cationic dyes in the synthesis of nanostructured materials.