Yield stress and microstructure of composite halloysite-LAPONITE® gels: Effects of mixing ratio, surface chemistry, and ageing time

Pengfei Liu, Mingyong Du, Peta Clode, Peng Yuan, Jishan Liu, Yee Kwong Leong

Research output: Contribution to journalArticlepeer-review

Abstract

The dependences of yield stress and microstructure of composite halloysite (Hal)-LAPONITE® (Lap) gels on the Lap/Hal mixing ratio, surface chemistry (pH and ionic strength), and ageing time were investigated in this study. The yield stress was measured using the vane technique and the microstructure was revealed by the cryogenic scanning electron microscopy (cryoSEM) images. At a fixed solid loading, the yield stress of composite Hal-Lap gels first quickly decreased to a lowest point and then kept increasing as Lap/Hal mixing ratio increased. The corresponding microstructure changed from Hal dominated network to Lap dominated network showing strong interactions between Hal and Lap particles through heterogeneous charge attractions. Six stages, each with distinct features, were identified during the transition. The maximum of yield stress displayed at around pH 11 for composite Hal-Lap gels and pure Hal gel. The attractive interactions between pure Hal-Hal and Lap-Lap particles and composite Lap-Hal particles were still present in a significant manner at pH 12 as reflected by the high yield stress. The microstructure of composite Hal-Lap gels and pure Hal gel displayed a high content of fibre end-face interactions even at high pH. However, “phase separation” occurred at low pH 4. Increasing ionic strength resulted in higher bond strength due to the van der Waals attraction and heterogeneous charge attraction, so it produced higher yield stress gels of pure Hal gel and composite Hal-Lap gels with low Lap content. At high ionic strength, small Hal particles formed aggregates with large Hal nanotubes while Lap particles formed large agglomerates. The H18L2 showed microstructure with circular agglomerates dispersed in a suspension of Hal rods. The agglomerates consisted of a mixture of tightly packed Hal rods and Lap particles. The microstructure of composite Hal-Lap gels was also strengthened during ageing due to the particle rearrangement. A water-gel phase separation due to the Hal particles sedimentation was observed for composite gels with low Lap/Hal mixing ratio as increasing ageing time.

Original languageEnglish
Article number128472
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume640
DOIs
Publication statusPublished - 5 May 2022

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