Anomalous Thermal Characteristics of Poly(Ionic Liquids) Derived from 1-Butyl-2,3-dimethyl-4-vinylimidazolium Salts

The synthesis of 1-butyl-2,3-dimethyl-4-vinylimidazolium triflate, its polymerization, and ion exchange to yield a trio of 1-butyl-2,3-dimethyl-4-vinylimidazolium polymers is described. Irrespective of the nature of the anion, substitution at the 2-position of the imidazolium moiety substantially increases the distance between the anion and cation. The methyl substituent at the 2-position also served to expose the importance of H-bonding for the attractive potential between imidazolium moiety and anions in polymers without a methyl group at the 2-position. The thermal characteristics of poly(1-butyl-2,3-dimethyl-4-vinylimidazolium) salts and corresponding poly(1-ethyl-3-methyl-4-vinylimidazolium) salts were evaluated. While the mid-point glass transition temperatures, Tg-mid, for 1-ethyl-3-methyl-4-vinylimidazolium polymers with CF3SO3−, (CF3SO2)2N− and PF6− counterions, were 153 °C, 88 °C and 200 °C, respectively, the Tg-mid values for 1-butyl-2,3-dimethyl-4vinylimidazolium polymers with corresponding counter-ions were tightly clustered at 98 °C, 99 °C and 84 °C, respectively. This dramatically reduced influence of the anion type on the glass transition temperature was attributed to the increased distance between the center of the anions and cations in the 1-butyl-2,3-dimethyl-4-vinylimidazolium polymer set, and minimal H-bonding interactions between the respective anions and the 1-butyl-2,3-dimethyl-4-vinylimidazolium moiety. It is believed that this is the first observation of substantial independence of the glass transition of an ionic polymer on the nature of its counterion.

Anion substitution and influence of sulfur on the crystal structures, phase transitions, and electronic properties of mixed TiO2/TiS2 compounds

Recent studies of TiO2/TiS2 nanostructures with various morphologies have been reported, usually showing improved properties with applications from electronics and catalysis to solar cells and medicine. However, there is a limited number of studies on the crystal structures of TiO2/TiS2 compounds with corresponding properties. In this research, relevant crystal structures of TiO1–x S x (x = 0, 0.25, 0.5, 0.75 and 1) solid solutions were investigated using an ab initio method. For each composition, crystal structures adopting anatase, rutile and CdI2 structure type were calculated on LDA-PZ and GGA-PBE levels of theory. Novel phase transitions and predicted structures are presented, and apart from several interesting metastable structures, a very interesting pressure-induced phase transition is found in the TiOS compound. Furthermore, electronic properties were studied through the dependence of semiconducting properties on dopant concentration. The first description of the electronic properties of the mixed TiO1–x S x compounds in crystal form has been presented, followed by a detailed study of the structure–property relationship, which will possibly have numerous industrial and technological applications.

Isosymmetric compression of cubic halide perovskites $$\mathrm{ABX}_{3}$$ ($$A=K, Rb, Cs$$; $$B=Ge, Sn, Pb$$ and $$X=Cl,Br,I$$)-influence of cation–anion exchange: a first principle study

Halide perovskites are potential candidates for their use in solar cells. In this study, an investigation of the structural, mechanical and electro-optical properties of $$\mathrm{ABX}_{3}$$ ABX 3 ($$A=K, Rb, Cs$$ A = K , R b , C s ; $$B=Ge, Sn, Pb$$ B = G e , S n , P b and $$X=Cl,Br,I$$ X = C l , B r , I ), under isosymmetric compression, is presented. All the calculations are performed with generalized gradient approximation schemes. We have examined the effect of cation and anion substitution on their overall properties.

Compositional Heterogeneity in CsyFA1-yPb(BrxI1-x)3 perovskite films and its Impact on Phase Behavior

Hybrid organic inorganic lead halide perovskite semiconductors of the form CsyFA1-yPb(BrxI1-x)3 are promising candidate materials for high-efficiency photovoltaics. Notably, cation and anion substitution can be used to tune the band...