Preparation and rheological characterization of imogolite hydrogels

Abstract

Imogolite, one of the aluminium silicates, has a nanotube structure and has been known to form gel under alkaline condition. Imogolite nanotubes were synthesized in an acidic solution with various tube lengths by controlling the aging time from 1 d to 14 d. The length of the nanotubes grew from 100 nm to several μm as the aging time. Pure imogolite hydrogels were prepared by applying a salting-out method and centrifugation from its dispersed solutions with various tube lengths and solution pH. Imogolite hydrogel can be classified as the physically cross-linked one; the structure of the gel network is considered to be the entanglements and hydrogen bonding among nanotubes. The theoretical water contents of the prepared hydrogels were calculated as ∼99.7% in average. Gelation percentage significantly increased as the length of imogolite nanotubes. Whereas hydrogel prepared from 4 d aging sample showed the highest storage modulus of ∼970 Pa, it was found that the hydrogel could be prepared in the pH range from 6 to 10. The gel strength reached the highest value of 1000 Pa when the gel was prepared from the imogolite dispersed solution of pH 8. It could be explained by the surface charge variation of the imogolite.