Abstract
Dicationic ionic liquids (DILs) of diverse structural architectures (including symmetrical and asymmetrical ammonium, phosphonium and heterodications and the bis(trifluoromethylsulfonyl)amide (NTf2−) anion) have been prepared and used as additives to N-methyl-N-ethoxyethylpyrrolidinium (P1EOE) NTf2, a relatively high-performing IL in terms of its transport properties (viscosity 53 mPa s). The three-ion, binary IL mixtures were characterized for their thermal and transport properties using differential scanning calorimetry, temperature dependent viscosity, conductivity and Pulsed Gradient Spin Echo (PGSE) NMR. Variable temperature 1H, 19F and 31P self-diffusion coefficients were determined at 25, 60 and 75°C. The order of the diffusion coefficients was D(P1EOE+) > D(anion) > D(dication), and the composition of the dication had a strong effect on the degree to which diffusion of all three species is more or less coupled. IL mixtures containing about 30 mol % of the dicationic NTf2 and 70 mol % of P1EOE NTf2 resulted in a significant decrease in glass transition temperatures and viscosities compared to the pure DIL. The mixtures extended the liquid range and potential for practical applications significantly. The data obtained here provides insight into the future design of dicationic salts tailored to exhibit lower viscosity and higher conductivities.
Highlights
Dicationic ionic liquids (DILs) have received far less attention compared to the popular monocationic Ionic liquid (IL) based on imidazolium, pyrrolidinium or tetraalkylammonium
The synthesis and properties of symmetrical and asymmetrical DILs based on imidazolium, pyrrolidinium and ammonium ions have been reported by Armstrong and co-workers.[7,8]
In this work we focus on the synthesis and characterization of IL mixtures containing symmetrical and asymmetrical DILs as additives to a high-performing, etherfunctionalized monocationic IL
Summary
Dicationic ionic liquids (DILs) have received far less attention compared to the popular monocationic ILs based on imidazolium, pyrrolidinium or tetraalkylammonium. Variable temperature 1H, 19F and 31P self-diffusion coefficients (D) were determined at 25, 60, and 75 °C for mixtures of the dication ILs (MimC6Mim (NTf2)[2], (CH3)3NC5Mim (NTf2)[2], (CH3)3NC5Mpyrr (NTf2)[2], (Ph)3PC4Mim (NTf2)[2], and (Ph)3PC4Mpyrr (NTf2)2) with the common solvent P1EOE NTf2.
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