| 11. |
- Nunes, S. C., et al.
(författare)
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Cationic and anionic environments in LiTFSI-doped di-ureasils with application in solid-state electrochromic devices
- 2008
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 345:1, s. 32-40
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 12. |
- Nunes, S. C., et al.
(författare)
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Di-ureasil ormolytes doped with Mg2+ ions: Part 2. Cationic and anionic environments
- 2005
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Ingår i: Solid State Ionics. - : Elsevier BV. - 0167-2738. ; 176:17-18, s. 1601-1611
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Tidskriftsartikel (refereegranskat)abstract
- Fourier Transform mid-infrared and Raman (FT-IR and FT-Raman, respectively) spectroscopies were used to investigate the cation/polymer, cation/cross-link, cation/anion and hydrogen bonding interactions in sol-gel derived ormolytes doped with magnesium triflate (Mg(CF3SO3)2). The framework of these xerogels (di-ureasils) contains poly(oxyethylene) (POE) segments with about 40.5 repeat units bonded at both ends to a siliceous backbone through urea cross-links. Materials with compositions ∞ > n ≥ 1 (where n is the ratio of oxyethylene moieties per Mg2+ ion) were studied. FT-IR data revealed that, while the urea carbonyl oxygen atoms bond to the cations in all the compounds analyzed, the POE chains complex the Mg2+ ions only at high salt content. Although the beginning of the POE/Mg2+ interaction was detected spectroscopically at n = 10, thermal data obtained in Part 1 of this series of papers suggest that this threshold composition is probably located at lower salt content. Bonding of the Mg2+ ions to the ether oxygen atoms of the POE chains is accompanied by the destruction of the urea/POE hydrogen-bonded aggregates formed in the d-U(2000) medium. Proofs of the existence of a crystalline POE/Mg(CF 3SO3)2 complex in samples with n ≤ 10 were found. "Free" and weakly coordinated CF3SO3- ions, present in all the samples examined, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes (i.e., d-U(2000)20Mg(CF3SO3)2). At n ≤ 40, along with those anionic species, another anionic configuration, attributed to contact ion pairs, emerges. Higher ionic aggregates are formed in di-ureasils with n ≤ 5.
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| 13. |
- Nunes, S. C., et al.
(författare)
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Diurea cross-linked poly(oxyethylene)/siloxane ormolytes for lithium batteries
- 2005
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 152:2
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Tidskriftsartikel (refereegranskat)abstract
- Poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with a wide concentration range of lithium triflate (LiCF3SO3) were investigated. The host matrix of these materials [d-U(2000)] is a sol-gel-derived siliceous framework to which POE chains with about 40.3 repeat units are bonded through urea linkages. Xerogels with ∞ ≥ n ≥ 5 (n is the molar ratio OCH2CH2/Li+) were obtained as amorphous monoliths thermally stable up to at least 340°C. A crystalline POE/LiCF3SO3 complex was detected spectroscopically in samples with n ≤ 10. Below 90°C the ormolyte with n = 20 exhibits the highest conductivity (5.8 × 10-6 n-l cm-1 at 26°C). The redox stability domain of this material spans 4.1 V. Although Fourier transform infrared spectroscopy data suggest that the Li+ ions are complexed by the POE ether oxygen atoms at n ≤10, this threshold composition is probably located at slightly lower salt content "Free" triflate ions and weakly coordinated anions, present in all the samples examined, must be the main charge carriers of the d-U(2000) 20LiCF3SO3 xerogel. Ion pairs (Li +CF3SO3-) or negatively charged triplets ([Li(CF3SO3)2]-) are formed at n ≤ 40. At n ≤ 5 positively charged triplets [Li2(CF 3SO3)]+ also appear. Divalent positively charged multiplets [Li3(CF3SO3)]2+ occur at n = 1.
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| 14. |
- Nunes, S. C., et al.
(författare)
-
FT-IR and Raman spectroscopic study of di-urea cross-linked poly(oxyethylene)/siloxane ormolytes doped with Zn2+ ions
- 2006
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Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031. ; 40:2, s. 278-288
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Tidskriftsartikel (refereegranskat)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 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 CF 3SO3- 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.
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| 15. |
- Nunes, S. C., et al.
(författare)
-
Sol-gel-derived potassium-based di-ureasils for "smart windows''
- 2007
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 17:40, s. 4239-4248
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Tidskriftsartikel (refereegranskat)abstract
- Sol-gel-derived KCF3SO3-doped di-urea cross-linked poly(oxyethylene) (POE)/siloxane (di-ureasil) ormolytes with infinity > n >= 1 (n is the number of oxyethylene units per K+ ion) have been analysed. Samples with n. 40 are thermally stable up to 310 degrees C. At n >= 100, POE crystallites are present. At n = 5, a crystalline POE-KCF3SO3 complex with stoichiometry 1 : 1 is formed. In the xerogel with n = 1 this complex coexists with free salt. The highest ionic conductivity is reached at n = 20. The redox stability domain of this material spans 5.0 V. "Free'' anions and weakly coordinated CF3SO3- ions appear to be the main charge carriers at n = 20. The K+ ions interact with the urea carbonyl oxygen atoms at all salt concentrations. Complexation of the cations by POE occurs at n
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| 16. |
- Nunes, S. C., et al.
(författare)
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Spectroscopic and structural studies of di-ureasils doped with lithium perchlorate
- 2007
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Ingår i: Electrochimica Acta. - : Elsevier BV. - 0013-4686. ; 53:4, s. 1466-1475
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Tidskriftsartikel (refereegranskat)abstract
- Di-urea cross-linked POE/siloxane hybrid ormolytes (di-ureasils) doped with a wide concentration range of lithium perchlorate trihydrate (LiClO4 center dot 3H(2)O) (200 >= n >= 0.5, where n expresses the salt content in terms of the number of ether oxygen atoms per Li+ ion) have been analysed by Fourier transform infrared and Raman (FT-IR and FT-Raman, respectively) spectroscopies and X-ray diffraction (XRD). The results obtained lead us to conclude that the xerogels with n >= 5 are totally amorphous. At n
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| 17. |
- Nunes, S. C., et al.
(författare)
-
Structure and photoluminescence of di-amidosil nanohybrids incorporating europium triflate
- 2006
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 451:1-2, s. 510-515
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Konferensbidrag (refereegranskat)abstract
- The sol-gel process was used to prepare amorphous di-amide cross-linked alkyl/siloxane hybrid materials (di-amidosils) incorporating europium triflate (Eu(CF3SO3)(3)). Samples with 200 F-7(0-4) transitions. Photoluminescence data suggest that in the dilute di-amidosil with n = 100 the Eu3+ ions occupy the same type of chemical local environment. (C) 2007 Elsevier B.V. All rights reserved.
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| 18. |
- Nunes, S. C., et al.
(författare)
-
Structure and photoluminescent features of di-amide cross-linked alkylene-siloxane hybrids
- 2005
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501 .- 0959-9428. ; 15:35-36, s. 3876-3886
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Tidskriftsartikel (refereegranskat)abstract
- Novel amide cross-linked alkylene-siloxane hybrid materials (di-amidosils) synthesized by the sol-gel process have been investigated. Two samples identified by the notation d-A(x) with x = 4 and 8 (where x is the number of methylene groups of the alkylene chain) have been produced as transparent, amorphous, rigid monoliths. The d-A(8) material is thermally stable up to approximately 245°C. In this hybrid the siliceous framework is mainly composed of [-(CH2)Si(OSi)3)] and [-(CH 2)Si(OSi)2(OH)] substructures. Structural unit distances of 4.1 and 4.2 Å and average interparticle distances of 12 and 17 A have been determined for d-A(4) and d-A(8), respectively. In these compounds the alkylene chains are disordered and adopt gauche conformations. While a negligible proportion of the amide linkages remain non-bonded, the great majority of these groups belong to highly disordered strong hydrogen-bonded amide-amide associations. The hybrids introduced are room temperature white light emitters, presenting an intense, broad emission band in the blue/purplish-blue spectral region. The origin of such a band has been ascribed to the convolution of donor-acceptor pair (D-A) recombinations that occur in the NH groups of the amide linkages and in the siliceous nanodomains. The maximum quantum yield value of the d-A(8) di-amidosil is 5.4%.
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| 19. |
- Nunes, S. C., et al.
(författare)
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Vibrational spectra and microstructure of poly(epsilon-caprolactone)/siloxane biohybrids doped with lithium triflate
- 2008
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860. ; 879:1-3, s. 72-80
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Tidskriftsartikel (refereegranskat)abstract
- Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies and Scanning Electron Microscopy (SEM) were used to investigate ionic association, hydrogen bonding and morphology in a family of sol-gel derived lithium triflate (LiCF3SO3)-doped di-urethane cross-linked poly(epsilon-caprolactone) (PCL(530))/siloxane hybrid electrolytes. The materials studied, with compositions infinity > n >= 0.5 (where n - composition - expresses the molar ratio of PCL(530) ester repeat units per Li+ ion), are non-porous and homogeneous. The Li+ ions interact with the urethane and ester carbonyl oxygen atoms within the whole range of salt concentration analyzed, promoting the formation of hydrogen-bonded aggregates. The composition dependence of the relative concentration of "free" anions and coordinated anions (weakly coordinated anions, Li+CF3SO3- ion pairs or [Li(CF3SO3)(2)](-) triplets, aggregates I ([Li-2(CF3SO3)](+)) and aggregates II ([Li-3(CF3SO3)](+)) in all the samples is in perfect agreement with the values of the room temperature ionic conductivity reported previously. (C) 2007 Elsevier B.V. All rights reserved.
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| 20. |
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