科研之友
微信
新浪微博
Facebook
分享链接
摘要
The effects of laminar shear on crystalline orientation and the nanostructure of triglyceride crystal networks were quantified by using different microscopic techniques. Cocoa butter (CB) was crystallized in the presence and absence of an external shear field. Two different dynamic samples were crystallized under a shear rate of approximately 340 s(-1) by using a continuous Couette-type laminar shear crystallizer and by using a standard paddle mixer. To improve imaging resolution, liquid oil was removed from crystallized samples using isobutanol and aqueous solutions of different surfactants such as AOT, Teepol, and Fatsolve. Using cryogenic scanning electron microscopy (Cryo-SEM), oriented sheets of crystalline cocoa butter were observed in the sample obtained in the laminar shear crystallizer, while spherulitic structures were observed in the statically crystallized sample. The strong influence of the applied laminar shear on the nanoscale structure is demonstrated by characterization of CB platelet size using cryogenic transmission electron microscopy (Cryo-TEM). Shear crystallization caused a reduction in the platelets' length from 2000 to 300 nm and width from 165 to 130 am. The platelets' thickness, obtained from Scherrer analysis of the 002 SAXS reflection, yielded a domain size of 54.8 am for the specimen crystallized under laminar shear and 58.2 nm for the statically crystallized sample. This work demonstrates the large effects of shear during the crystallization process on,the microstructure of polycrystalline materials.
- 出版日期2011-6
