Confinement of Lauric Acid into the Lumen of Halloysite Nanotubes

This document is the unedited author's version of a manuscript submitted for publication in Part. Part. Syst. Character. (Wiley) after peer review.

Abstract: Molecules confined within nanometer-scale environments frequently exhibit a distinct physical response in contrast to those found in bulk conditions. In this study, intercalates of lauric acid (LA) were synthesized within halloysite nanotubes (HNT), successfully trapping 12 wt% of LA within the internal HNT tube, as demonstrated by transmission electron microscopy (TEM), and wide-angle and small-angle X-ray scattering (WAXS/SAXS) techniques. Furthermore, we noted that the confinement of LA within the HNT lumen resulted in a significant reduction in LA crystallinity, consistent with the impact of geometric constraints on crystallization behavior. The presence of a significant amorphous phase in the intercalates proved beneficial for the gradual release of LA into water, as evidenced by pH changes. Remarkably, the necessity of employing a vacuum method and extended contact time (72 h) for the physical entrapment of LA in ethanol within the HNT lumen was found to be unnecessary, as similar physical characteristics were observed in an intercalate generated without vacuum and with very short contact time (< 1 h). Finally, we observed that the source of HNT is crucial in determining the final properties of the confined material.