Lamellar Salt-Doped Hybrids with Two Reversible Order/Disorder Phase Transitions

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• 作者：S铆lvia C. Nunes ; Rute A. S. Ferreira ; Lu铆s D. Carlos ; Paulo Almeida ; Ver贸nica de Zea Bermudez
• 刊名：Journal of Physical Chemistry B
• 出版年：2013
• 出版时间：November 21, 2013
• 年：2013
• 卷：117
• 期：46
• 页码：14529-14543
• 全文大小：929K
• 年卷期：v.117,no.46(November 21, 2013)
• ISSN：1520-5207

文摘

A lamellar bilayer hierarchically structured amide cross-linked alkyl/siloxane hybrid matrix (mono-amidosil, m-A(14)) was doped with a wide concentration range of potassium triflate (KCF₃SO₃), magnesium triflate (Mg(CF₃SO₃)₂), and europium triflate (Eu(CF₃SO₃)₃). In the K⁺-, Mg²⁺-, and Eu³⁺-based samples with n 鈮?5, 20, and 60 (where n is the molar ratio of amide C鈺怬 groups per cation), respectively, the original lamellar structure of m-A(14) coexists with a new lamellar phase with lower interlamellar distance. The texture of the mono-amidosils doped with K⁺, Mg²⁺, and Eu³⁺ ions mimics cabbage leaves, foliated schist, and sea sponges, respectively. In the three series of materials, the cations bond to the oxygen atoms of the amide carbonyl groups. The amide鈥揳mide hydrogen-bonded array of m-A(14) is less perturbed by the inclusion of KCF₃SO₃ and Mg(CF₃SO₃)₂ than by the incorporation of Eu(CF₃SO₃)₃. The degree of ionic association is low for n 鈮?20. The cations coordinate to the oxygen atoms of the triflate ions, forming contact ion pairs at higher salt content. In the Mg(CF₃SO₃)₂- and Eu(CF₃SO₃)₃-containing materials with n = 5 and 10, respectively, crystalline salt is formed. The structural changes undergone by the alkyl chains of selected mono-amidosils in a heating/cooling cycle are reversible, are time-independent, and exhibit two distinct hysteresis domains, one associated with the order/disorder phase transition of the original lamellar bilayer structure of m-A(14) and the second one associated with the order/disorder phase transition of the new lamellar bilayer structure formed in the presence of the salts.