SEM Observation of Hydrous Superabsorbent Polymer Pretreated with Room-Temperature Ionic Liquids

Tetsuya Tsuda,Kazuki Iwasaki,Katsuhiko Tsunashima,Susumu Kuwabata,Shoko Kishida,Eiko Mochizuki,Vipul Bansal

doi:10.1371/journal.pone.0091193

Tetsuya Tsuda, Kazuki Iwasaki + Show 5 more

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https://doi.org/10.1371/journal.pone.0091193

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Abstract

Room-temperature ionic liquid (RTIL), which is a liquid salt at or below room temperature, shows peculiar physicochemical properties such as negligible vapor pressure and relatively-high ionic conductivity. In this investigation, we used six types of RTILs as a liquid material in the pretreatment process for scanning electron microscope (SEM) observation of hydrous superabsorbent polymer (SAP) particles. Very clear SEM images of the hydrous SAP particles were obtained if the neat RTILs were used for the pretreatment process. Of them, tri-n-butylmethylphosphonium dimethylphosphate ([P4, 4, 4, 1][DMP]) provided the best result. On the other hand, the surface morphology of the hydrous SAP particles pretreated with 1-ethyl-3-methylimidazolium tetrafluoroborate ([C2mim][BF4]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) was damaged. The results of SEM observation and thermogravimetry analysis of the hydrous SAP pretreated with the RTILs strongly suggested that most water in the SAP particles are replaced with RTIL during the pretreatment process.

Highlights

Room-temperature ionic liquid (RTIL) that was once called ambient-temperature molten salt and room-temperature molten salt is a liquid salt at or below room temperature [1,2]
Because RTIL is often diluted with water and ethanol for the RTIL-based pretreatment process to form a uniform thin layer on the target specimens [10,11,12,13], we investigated the effect of the RTIL concentration in aqueous RTIL solution on scanning electron microscope (SEM) images of water-absorbed superabsorbent polymer (SAP) particles
Particles by employing the easy-to-use RTIL-based pretreatment process that can be completed within 5 min

Summary

Introduction

Room-temperature ionic liquid (RTIL) that was once called ambient-temperature molten salt and room-temperature molten salt is a liquid salt at or below room temperature [1,2]. Due to the moderate coulomb interactions, most RTILs show negligible vapor pressure. This property is encouraging the scientists in the field of the ionic liquid to create novel vacuum technologies with ionic liquid [3,4,5,6,7,8]. We revealed that it is possible to observe directly RTIL itself without accumulation of electrostatic charge by a common scanning electron microscope (SEM) observation technique that is one of useful vacuum technologies [9]. We found that a thin RTIL layer spread on insulating materials works as a conductive layer like a thin Au layer when such materials are observed by using a common SEM system [10,11,12,13]. Since our first report [9], a number of similar works have been reported by various research groups [14,15,16,17,18,19,20]

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