RESUMO
Hydrogen is well known to embrittle high-strength steels and impair their corrosion resistance. One of the most attractive methods to mitigate hydrogen embrittlement employs nanoprecipitates, which are widely used for strengthening, to trap and diffuse hydrogen from enriching at vulnerable locations within the materials. However, the atomic origin of hydrogen-trapping remains elusive, especially in incoherent nanoprecipitates. Here, by combining in-situ scanning Kelvin probe force microscopy and aberration-corrected transmission electron microscopy, we unveil distinct scenarios of hydrogen-precipitate interaction in a high-strength low-alloyed martensitic steel. It is found that not all incoherent interfaces are trapping hydrogen; some may even exclude hydrogen. Atomic-scale structural and chemical features of the very interfaces suggest that carbon/sulfur vacancies on the precipitate surface and tensile strain fields in the nearby matrix likely determine the hydrogen-trapping characteristics of the interface. These findings provide fundamental insights that may lead to a better coupling of precipitation-strengthening strategy with hydrogen-insensitive designs.
RESUMO
Although natural emulsifiers often have many drawbacks when used alone, their emulsifying ability and stability can usually be improved unexpectedly when used in combination. In this study, monodisperse emulsions stabilized by combining two natural protein emulsifiers, i.e., whey protein isolate (WPI) and sodium caseinate (SC), in different proportions were prepared using microchannel (MC) emulsification. The influences of temperature, pH, ionic strength, and storage time on the microstructure and stability of the emulsions were examined. Analysis of the microstructure and droplet size distribution revealed that the WPI-, SC-, and mixed protein-stabilized emulsions exhibited uniform droplet distribution. The droplet size and ξ-potential of the MC emulsions stabilized by mixed protein emulsifiers were higher than those of the emulsions stabilized by WPI or SC separately. The emulsions stabilized by the two types of proteins and mixed emulsifiers had better stability under high salt concentrations than the synthetic emulsifier Tween 20. WPI-SC-stabilized emulsions were more resistant to high temperatures (70-90°C) and exhibited excellent stabilization than those stabilized by WPI and SC, which was attributed to the more sufficient coverage provided by the two types of protein emulsifier layers and better protein adsorption at the oil-water interface. These results indicate that WPI-SC is a potential stabilizer for MC emulsion requirements. This study provides a basis for the formulation of monodisperse and stable natural emulsion systems.
RESUMO
The effect of natural emulsifiers (whey protein isolate, WPI; modified lecithin, ML; and gum arabic, GA) on the formulation, stability, and bioaccessibility of fucoxanthin-loaded oil-in-water (O/W) emulsions was determined in this study. The fine emulsions were prepared under high-pressure homogenization at 100 MPa for 4 passes, using 2 wt % WPI, ML, and GA, resulting in emulsions with the droplet sizes of 136, 140, and 897 nm, respectively. The chemical stability of fucoxanthin in the emulsions after long-term storage at ambient temperature decreased in the following order: WPI > GA > ML. The release of free fatty acids of fucoxanthin, studied by in vitro digestion, decreased in the following order: WPI > ML > GA > bulk oil. The bioaccessibility of fucoxanthin in emulsions stabilized by WPI, ML, and GA after in vitro digestion were 92.5 ± 6.8%, 44.6 ± 0.4, and 36.8 ± 2.5, respectively. These results indicate that natural emulsifier type and concentration used significantly affects the formulation, stability, lipid digestion, and fucoxanthin bioaccessibility, which may be ascribed to the different properties of each emulsifier. The bioaccessibility of fucoxanthin was improved by using emulsion-based delivery systems.
