title: Lamellar salt-doped hybrids with two reversible order/disorder phase transitions.
abstract: 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(+)-, Mg(2+)-, and Eu(3+)-based samples with n ≥ 5, 20, and 60 (where n is the molar ratio of amide C═O 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(+), Mg(2+), and Eu(3+) 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-amide 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 ≥ 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.
authors.affiliation: Chemistry Department and CICS - Centro de Investigação em Ciências da Saúde, University of Beira Interior , 6200-001 Covilhã, Portugal.
authors.forename: Sílvia C
authors.initials: SC
authors.lastname: Nunes
authors.forename: Rute A S
authors.initials: RA
authors.lastname: Ferreira
authors.forename: Luís D
authors.initials: LD
authors.lastname: Carlos
authors.forename: Paulo
authors.initials: P
authors.lastname: Almeida
authors.forename: Verónica
authors.initials: V
authors.lastname: de Zea Bermudez