Confined ionic liquid melts at higher temperature

In work that could lead to new types of carbon nanotube-based composites, scientists at the Chinese Academy of Sciences have shown that the melting point of an ionic liquid increases significantly when the liquid is encapsulated in multiwalled carbon nanotubes (J. Am. Chem. Soc., DOI: 10.1021/ja067972c). Guozhong Wu at Shanghai Institute of Applied Physics and coworkers impregnated nanotubes with the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF₆]. X-ray diffraction and electron microscopy revealed that stable crystals of [bmim][PF₆] formed inside the nanotubes. The melting point of pure [bmim][PF₆] is about 6 ^oC, but it is difficult to obtain stable crystals of the ionic liquid by cooling because solidification often results in glass formation. Differential scanning calorimetry showed that, inside the nanotubes, the ionic liquid's melting point is above 200 ^oC. The results will provide insight into phase transitions of materials confined in nanoscale environments, the authors believe.