Institution: | aDepartamento de Química and CQ-VR, Universidade de Trás-os-Montes e Alto Douro, 5000-911 Vila Real, Portugal bDepartment of Experimental Physics, Chalmers University of Technology, 41296 Göteborg, Sweden cDepartamento de Física and CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal |
Abstract: | The interactions occurring in di-urea ( NHC( O)NH ) cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with zinc triflate (Zn(CF3SO3)2) were investigated by Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies. Bonding of the Zn2+ ions to the urea carbonyl oxygen atoms occurs in the entire range of compositions studied (∞ > n ≥ 1, where n, salt content, is the molar ratio of oxyethylene moieties per Zn2+ ion). At n > 20 the incorporation of the guest cations progressively reduces the number of free C O groups. At n = 20 the saturation of the urea cross-links is attained and the Zn2+ ions start to coordinate to the POE chains giving rise to the formation of a crystalline POE/Zn(CF3SO3)2 complex. The latter process occurs at the expense of the destruction of the hydrogen-bonded POE/urea structures of the host di-ureasil structure. New hydrogen-bonded associations, more ordered than the urea–urea aggregates present in the non-doped matrix and including Zn2+ O C coordination, emerge in parallel. “Free” and weakly coordinated CF3SO3? ions, present in all the xerogels studied, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes located at n = 60 at 30 °C. In materials with n ≤ 20 contact ion pairs, “cross-link separated” ions pairs and higher ionic aggregates appear. The data reported demonstrate that the behaviour of the di-ureasils doped with triflate salts depends on the type of cation. |