Shear-reversible and super-thickening starch Janus particles.

Starch Janus particles, with oppositely-charged hemispheres, were fabricated to increase thickening capacity and shear resilience. A 3D masking approach was used to chemically modify a face of amaranth starch granules (1-μm): Starch granules were embedded at the surface of oil droplets (~320 μm) via emulsification and the exposed surface was cationically treated with 2,3-epoxypropyltrimethylammonium chloride (ETMAC) at high pH. The oil template was removed by successively rinsing with water, ethanol, and hexane. The resulting starch had one hemisphere that was positively charged due to the presence of a quaternary ammonium group, confirmed by XPS, CLSM, and SEM, while the other hemisphere remained negatively charged. After modification, the surface of the starch granule was positively charged. The Janus balance, which describes the amount of each surface trait, was 60 % positive charge. The charge asymmetry of Janus particles causes self-assembly via electrostatic interactions that manifests as particle aggregation. Granular suspensions of Janus particles surpass native starch by more than a 30-fold viscosity increase, 220 Pa·s > 6.70 Pa·s. When disrupted by shear, the initial viscosity of Janus particles recovered over time. Given their unique properties, Janus particles have exciting potential to be used as shear-reversible super-thickeners in foods.