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Mixtures of polyethylene oxide (PEO, M.W.~900,000) and imidazolium ionic liquids (ILs) are studied using high-pressure Fourier-transform infrared spectroscopy. At ambient pressure, the spectral features in the C-H stretching region reveal that PEO can disturb the local structures of the imidazolium rings of [BMIM] + and [HMIM] + . The pressure-induced phase transition of pure 1-butyl-3-methylimidazolium bromide ([BMIM]Br) is observed at a pressure of 0.4 GPa. Pressure-enhanced [BMIM]Br-PEO interactions may assist PEO in dividing [BMIM]Br clusters to hinder the aggregation of [BMIM]Br under high pressures. The C-H absorptions of pure 1-hexyl-3-methylimidazolium bromide [HMIM]Br do not show band narrowing under high pressures, as observed for pure [BMIM]Br. The band narrowing of C-H peaks is observed at 1.5 GPa for the [HMIM]Br-PEO mixture containing 80 wt% of [HMIM]Br. The presence of PEO may reorganize [HMIM]Br clusters into a semi-crystalline network under high pressures. The differences in aggregation states for ambient-pressure phase and high-pressure phase may suggest the potential of [HMIM]Br-PEO (M.W.~900,000) for serving as optical or electronic switches.

Ionic liquids (ILs) have been considered as "green" substitutes for traditional organic solvents in many existing biological and chemical areas. However, they have high solubility and poor biodegradability in water, suggesting that they could become persistent chemical pollutants in aquatic environment. The ability of two widely used imidazolium-based ILs to affect the growth and physiological characteristics of a marine diatom (Phaeodactylum tricornutum) was investigated in this study. The diatom was exposed to different concentrations of 1-butyl-3-methylimidazolium tetrafluoroborate ([C 4 mim]BF 4 ) and 1-octyl-3-methylimidazolium tetrafluoroborate ([C 8 mim]BF 4 ) for 96h within a batch-culture system. Results showed that [C 4 mim]BF 4 and [C 8 mim]BF 4 were very stable in seawater during 96h of exposure, and the compounds significantly inhibited the growth of P. tricornutum with 24, 48, 72 and 96h EC 50 values of 30.81, 28.53, 39.92, 45.88mgL -1 and 30.17, 23.36, 28.62, 31.37mgL -1 , respectively. In addition, the photosynthetic activity and chlorophyll a synthesis of P. tricornutum were inhibited by [C 4 mim]BF 4 and [C 8 mim]BF 4 , indicating that the structural integrity of chloroplasts of the diatom may be disrupted or damaged by the two ILs. Compared with that of the controls, reactive oxygen species (ROS) level was increased by 0.65, 1.17, 1.85, 3.13, 2.94 times and 0.55, 1.77, 2.42, 3.45, 3.47 times in 5, 10, 20, 40 and 60mgL -1 [C 4 mim]BF 4 and [C 8 mim]BF 4 treatments, respectively. The excessive ROS may cause lipid peroxidation, shortage of metabolic energy and decline of photosynthetic efficiency, which may be the main reason for toxicity of the two ILs to marine diatoms. To withstand the damaging effects of excessive ROS, remarkable physiological and biochemical responses occurred in treatments with the two ILs to protect the cells of P. tricornutum. Parameters such as soluble protein content, soluble sugar content, and superoxide dismutase (SOD) and peroxidase (POD) activities of the diatom increased significantly with increasing concentrations of the two ILs at 96h of exposure relative to the controls. These findings not only provide strong background for evaluating the ecological risks and toxicity of ILs in marine environment, but also help to unravel the toxic mechanism of the two ILs to marine diatoms., (Copyright © 2017 Elsevier B.V. All rights reserved.)

In this study, we used high-pressureinfrared spectroscopy to probe the local structures formed betweenthe ionic liquid [BMI][PF6] and the triblock PEO–PPO–PEOcopolymer P123. The signals for the imidazolium C–H units of[BMI][PF6] underwent anomalous frequency shifts upon dilution,induced by order-to-order transitions. Appreciable changes in therelative band intensities of the signals for the imidazolium moietiesoccurred upon compression. Upon increasing the pressure, the etherC–O–C stretching band underwent dramatic changes, witha shoulder peak appearing near 1097 cm–1with relativelyincreasing intensity. It appears that high pressures somehow stabilizethe hydrogen bonds formed between [BMI] and P123, possibly forcingthe P123 molecules to dissociate the clusters of ionic liquid throughenhanced hydrogen bonding with the imidazolium C–H units. Analogousto temperature-dependent behavior, we suggest the possibility of pressure-inducedassociation of P123 molecules through elevation of pressure. [ABSTRACT FROM AUTHOR]