The effect of freezing-assisted cross-linking on structural and rheological properties of potato starch.

In order to achieve preparation of cross-linked (CL) potato starch with the maximum degree of substitution, freezing pre-treatment (FS) in different modes as three days freezing (3D), two freezing-thawing cycles (3D + 3D) and 6 days freezing (6D) were conducted. Thereafter, native, frozen and cross-linked starches were characterized for morphological, structural and pasting properties as well as alkaline and intrinsic viscosity. Regarding obtained result, freezing pre-treatment as 3D + 3D was found to be an efficient method to achieve high level of cross-linking than native and other modes of freezing pre-treatments when exposed to POCl3 reagent. The crystallinity (%) and ratio of 1047/1022 cm-1 increased from 38.6 % and 1.112 (native potato starch; NPS) to 41.6 % and 1.269 (cross-linked native potato starch; CL) and 41.3 and 1.292 (cross-linked freeze- thawed starch 3D + 3D + CL) after being treated with POCl3. Data obtained by intrinsic viscosity was in line with the power-law model. Cross-linked starch with POCl3 exhibited the lowest k value and the highest n value, implying lower shear-thinning behavior of cross-linked starch after freezing pre-treatment than CL native starch. To sum up, low peak viscosity (determined by RVA) and intrinsic viscosity (by U-tube viscometer) could also explain the high level of cross-linking and low swelling power of 3D + 3D + CL.

Origin of Room-Temperature Ferromagnetism in Hydrogenated Epitaxial Graphene on Silicon Carbide.

The discovery of room-temperature ferromagnetism of hydrogenated epitaxial graphene on silicon carbide challenges for a fundamental understanding of this long-range phenomenon. Carbon allotropes with their dispersive electron states at the Fermi level and a small spin-orbit coupling are not an obvious candidate for ferromagnetism. Here we show that the origin of ferromagnetism in hydrogenated epitaxial graphene with a relatively high Curie temperature (>300 K) lies in the formation of curved specific carbon site regions in the graphene layer, induced by the underlying Si-dangling bonds and by the hydrogen bonding. Hydrogen adsorption is therefore more favourable at only one sublattice site, resulting in a localized state at the Fermi energy that can be attributed to a pseudo-Landau level splitting. This n = 0 level forms a spin-polarized narrow band at the Fermi energy leading to a high Curie temperature and larger magnetic moment can be achieved due to the presence of Si dangling bonds underneath the hydrogenated graphene layer.