Aggregation and Stabilization of Carboxylic Acid Functionalized Halloysite Nanotubes (HNT-COOH)

We modified the functional groups of holloysite nanotubes (HNT) from hydroxyl groups (HNT-OH) to carboxylic acids (HNT-COOH). Aggregation and dispersion properties of HNT-COOH under dry conditions were probed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Moreover, the degree of aggregation and dispersion of HNT-COOH in acidic, basic, and neutral solutions were measured by multiple angle polarized dynamic light scattering (MA-DLS). HNT-COOH formed aggregates in neutral solution; however, the material was dispersed in basic and acidic solutions. This occurrence is due to hydrogen bonds (HB) between the carboxyl groups of HNT-COOH in neutral solution, which decrease in acidic and basic solution due to charge dispersion.