Mesomorphic Structures of Protonated Surfactant-Encapsulated Polyoxometalate Complexes

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• 作者：Shengyan Yin ; Wen Li ; Jinfeng Wang ; Lixin Wu
• 刊名：Journal of Physical Chemistry B
• 出版年：2008
• 出版时间：April 3, 2008
• 年：2008
• 卷：112
• 期：13
• 页码：3983 - 3988
• 全文大小：590K
• 年卷期：v.112,no.13(April 3, 2008)
• ISSN：1520-5207

文摘

Keggin-type heteropolyanions, H₃PW₁₂O₄₀ (HPW), Na₃PW₁₂O₄₀ (NaPW), H₄SiW₁₂O₄₀ (HSiW) and K₄SiW₁₂O₄₀(KSiW), were encapsulated by a cationic surfactant, di[12-(4'-octyloxy-4-azophenyl)dodecyloxy]dimethylammonium bromide (L), through the replacement of counterions. The resulting surfactant-encapsulatedpolyoxometalate complexes were characterized by UV-vis, Raman, and NMR spectra in detail. Themeasurement results indicated that some azobenzene groups of the surfactant were protonated in the complexesHL/HPW (HL is the abbreviation of the protonated surfactant), HL/NaPW, and HL/HSiW during the processof encapsulation, whereas the protonation was not observed in L/KSiW. The thermotropic liquid crystalproperties of these complexes were investigated by differential scanning calorimetry, polarized opticalmicroscopy and variable-temperature X-ray diffraction. Interestingly, different smectic mesophases wereobserved between the protonated HL/HSiW and the non-protonated L/KSiW, which suggests that theprotonation of azobenzene groups in HL/HSiW plays a key role in the liquid crystalline organization. However,protonated HL/HPW and HL/NaPW exhibit a similar smectic B phase to that of the de-protonated one, L/HPW.A competitive balance between the phase separation and the volume minimization of surfactants was proposedto explain the self-organized liquid crystal structures of these protonated and non-protonated complexes. Tothe best of our knowledge, the present investigation provides a specific example for protonated hybrid materialswith stable liquid crystal properties.