Observation of interactions between hydrophilic ionic liquid and water on wet agar gels by FE-SEM and its mechanism

In the present study, an attempt is made to understand the mechanism of field emission electron microscopy (FE-SEM) observation of wet agar gel using a typical hydrophilic ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate; [BMIM][BF4]. The IL interaction with water molecules within agar gel during sample preparation condition for FE-SEM observation was investigated using Raman spectroscopy. Results showed that water molecules within agar gel form weak hydrogen bond such as BF4−⋯HOH⋯BF4− by interaction with BF4− of IL, and, it remained stable even under vacuum condition at 60 °C, 24 h. This interaction was found to be helpful for IL displacement of the water molecules within agar gel. From this study, it was found that the exact morphology of gel materials in FE-SEM condition can be observed by optimization of water concentrations of IL and gel mixtures. Thus, using IL, agar gel or any other material under wet condition can be observed without drying in FE-SEM chamber, and, present result gives an insight to the mechanism of FE-SEM observation of agar gel using IL without any conducting coating.

► The mechanism of SEM observation of agar gel using ionic liquid was investigated.
► Weak hydrogen bond between ionic liquid and water exist even under vacuum condition.
► Ionic liquid binding ability with water is useful for observing wet material using FE-SEM.
► We could optimize the water concentrations of sample of IL and wet material mixtures.
► SEM observation of fine morphology of agar gel in optimum water content.