Morphological modulation of starch chains from nanorod to nanospindle via temperature-controlling rearrangement

Polymorphic nanoparticles, including starch nanoparticles (SNPs), have increasingly attracted attention, particularly rod-shaped variants, which are used for constructing anisotropic systems. Compared to symmetrically spherical particles, they show superior properties such as gastrointestinal retention for functional nutrients/drugs delivery and mechanical enhancement of filled materials, but their controlled fabrication remains a challenge. In this study, we yielded polymorphic SNPs with nearly axisymmetric geometries through a combined alkaline hydrolysis and nanoprecipitation method, followed by temperature-controlling rearrangement. The change from starch nanorod (SNR) to starch nanoellipsoid (SNE) and starch nanospindle (SNSP) was obtained when heat-induced rearrangement of starch chains occurred from temperature 90 °C to 20 °C. Interestingly, the sodium ions introduced by NaOH solution could be separated from the samples to varying extents. Both raw materials of normal and high-amylose starches have the above rules of nano-morphological alternation and salting out phenomenon, whereas their microstructures are not totally the same. Compared to SNR/SNE/SNSP fabricated from normal starch, those from high-amylose starch have a higher proportion of long chains (DP > 24) while less short chains (DP 6-12), with higher degrees of order and crystallinity.