Cationic and anionic environments in LiTFSI-doped di-ureasils with application in solid-state electrochromic devices

Fourier Transform mid-infrared and Raman spectroscopies were used to investigate the cation/polymer, cation/urea bridge, cation/anion and hydrogen bonding interactions in poly(oxyethylene) (POE)/siloxane di-ureasil networks prepared by the sol–gel route and doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Materials with compositions 200 ?n ? 5 (where n expresses the molar ratio OCH₂CH₂/Li⁺) were studied. The Li⁺ ions coordinate to the urea carbonyl oxygen atoms over the whole range of salt concentration considered. Bonding to the ether oxygen atoms of the POE chains occurs at n ? 40, although a significant fraction of the POE chains remain non-coordinated. In these high salt content samples, the cations interact with the anions forming contact ion pairs. “Free” ions are probably the main charge carriers at the room temperature conductivity maximum of these ormolytes.     

Study of sol–gel derived di-ureasils doped with zinc triflate

Zinc triflate (Zn(CF₃SO₃)₂)-doped sol–gel derived di-urea cross-linked POE/siloxane ormolytes (designated as di-ureasils) with ∞>n1 (where the salt content is expressed as n, the molar ratio of oxyethylene moieties to Zn²⁺ ions) were investigated. The hybrids with n5 are entirely amorphous; those with n>10 are thermally stable up to approximately 305 °C. The siliceous network of representative samples (n=200 and 10) is essentially composed of (SiO)₃Si(CH₂)-environments and is thus highly branched. The distance between the structural units in samples with 200n10 and n7 is 4.2 and 4.3 Å, respectively. The estimated interdomain distance is 11 and 13 Å for xerogels with 200n20 and n10, respectively. At n=1 a crystalline POE/Zn(CF₃SO₃)₂ complex of unknown stoichiometry is formed. The conductivity maxima are located at n=60 () and n=20 () at 30 and 100 °C, respectively.     

FT-IR and Raman spectroscopic study of di-urea cross-linked poly(oxyethylene)/siloxane ormolytes doped with Zn ions

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 CO 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⁺OC 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.