Solid-State NMR, Ionic Conductivity, and Thermal Studies of Lithium-doped Siloxane-Poly(propylene glycol) Organic-Inorganic Nanocomposites Paulo H. de Souza, †,‡ Rodrigo F. Bianchi, † Karim Dahmouche, †,§ Patrick Judeinstein, | Roberto M. Faria, † and Tito J. Bonagamba* ,† Instituto de Fı ´sica de Sa ˜ o Carlos, Universidade de Sa ˜ o Paulo, Caixa Postal 369, CEP 13560-970, Sa ˜ o Carlos-SP, Brazil, and Laboratoire de Chimie Structurale Organique, and UPRESA CNRS 8074, Universite ´ Paris-Sud, 91405 Orsay, France Received February 1, 2001 Hybrid organic-inorganic ionic conductors, also called ormolytes (organically modified electrolytes), were obtained by dissolution of LiClO 4 in siloxane-poly(propylene glycol) matrixes. The dynamic features of these nanocomposites were studied and correlated to their electrical properties. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to probe the effects of the temperature and nanocomposite composition on the dynamic behaviors of both the ionic species ( 7 Li) and the polymer chains ( 13 C). NMR, dc ionic conductivity, and DSC results demonstrate that the Li + mobility is strongly assisted by the segmental motion of the polymer chain above its glass transition temperature. The ac ionic conductivity in such composites is explained by use of the random free energy barrier (RFEB) model, which is in agreement with their disordered and heterogeneous structures. These solid ormolytes are transparent and flexible, and they exhibit good ionic conductivity at room temperature (up to 10 -4 S/cm). Consequently, they are very promising candidates for use in several applications such as batteries, sensors, and electrochromic and photoelectro- chemical devices. Introduction In recent years, the sol-gel method has successfully been used for the production of a significant number of novel organic-inorganic frameworks with tunable de- signs and suitable properties. 1-7 The combination of appropriate processing conditions with adequate choice for the organic and inorganic components dictates the morphology, molecular structure, and features of the resulting materials. The intense activity in this domain of research is due to the extraordinary implications that derive from the possibility of tailoring multifunctional advanced compounds by mixing organic and inorganic components at the nanosize level in a single material. 1-7 The synergy of that combination and the particular role of the inner organic-inorganic interfaces enlarge the scope of application of nanohybrid materials in areas such as electrochemistry, biology, mechanics, ceramics, electronics, and optics. 4-7 The hybrid concept seems to be particularly well-adapted for the production of ad- vanced solid materials presenting ion-conducting prop- erties, with the advantage of replacing viscous liquid systems by solid or rubbery materials. 8,9 These solid polymer electrolytes, so-called ormolytes (organically modified electrolytes), are very promising because of their possible use in various applications such as batteries, data storage, sensors, and electrochromic and photoelectrochemical devices. 9-11 Among the various organic-inorganic hybrids that have been proposed in the past several years, a family of versatile compounds, classified as di-ureasils, in which polyether- [poly- (propylene glycol)- (PPG-) or poly(ethylene glycol)- (PEG-)] based chains of variable length are grafted on both ends to a siliceous backbone through urea func- tionalities, is noteworthy. 8,12-14 When doped with lithium salts, these solid, transparent, and flexible nanocom- posites exhibit good ionic conductivity at room temper- ature (up to 10 -6 S/cm). 15-18 Because of the presence of * Author to whom correspondence should be addressed. Tito J. Bonagamba, Instituto de Fı ´sica de Sa ˜ o Carlos, Universidade de Sa ˜o Paulo, Caixa Postal 369, CEP 13560-970, Sa ˜ o Carlos-SP, Brazil. E-mail: tito@if.sc.usp.br. † Universidade de Sa ˜ o Paulo. ‡ Present address: Centro Federal de Educac ¸ a ˜ o Tecnolo ´gica de Goia ´ s, UNED/Jataı ´, Rua Riachuelo, 2090 - Setor Manuel Graham, CEP: 13580-000, Jataı ´-GO (Brazil). § Present address: Instituto de Quı ´mica de Araraquara-UNESP, Av. Prof. Francisco Degni s/n, CEP 14800-900, Araraquara-SP, Brazil. | Universite ´ Paris-Sud. (1) Brinker, J. C. Sol-Gel Science, The Physics and Chemistry of Sol-Gel Processing; Academic Press: New York, 1989. (2) Uhlmann, D. R.; Ulrich, D. R. Ultrastructure Processing of Advanced Materials; Wiley: New York, 1992. (3) Hench, L. L.; West, J. K. Chemical Processing of Advanced Materials; Wiley: New York, 1992. (4) Mark, J. E., Lee, C. C-Y., Bianconi, P. A., Eds. 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