| The effects of laminar shear on the nano/meso-scale structure, oil migration, and physical properties of crystalline materials (cocoa butter) were studied. Cocoa butter (CB) was crystallized under the presence and absence of external shear field. Two different dynamic samples were made under a shear rate of approximately 340 s-1 using a continuous couette-type laminar shear crystallizer, and a standard paddle mixer.;After oil removal from crystallized samples by isobutanol and aqueous solutions of different surfactants such as TeepolRTM and FatsolveRTM, using cryogenic scanning electron microscopy (Cryo-SEM), oriented sheets of crystalline cocoa butter were observed in the sample crystallized in the laminar shear crystallizer. The strong influence of the applied laminar shear on nanoscale structure was demonstrated by characterization of CB nanoplatelets size using cryogenic transmission electron microscopy (Cryo-TEM). Shear crystallization caused a reduction in the nanoplatelets' length from 2000 mn to 300 mn and width from 165 mn to 130 mn. The nanoplatelets' thickness, obtained from Scherrer analysis of the 001 SAXS reflection yielded a domain size of 54.8 mn for the specimen crystallized under laminar shear and 58.2 mn for the statically crystallized sample.;Here we also showed that the size of the component nanocrystals strongly influenced the migration rate of oil through a cocoa butter matrix. A smaller diffusion coefficient and lower oil migration rate were observed in crystallized under shear. Liquid oil diffusivity was decreased by about 4.6 to 30 times in samples that exhibited alignment of the crystalline material along a given axis. Moreover, the tortuosity of the diffusive path in the sheared samples was approximately 4 to 12.5 times higher than that of the static sample. The relationships between the structural factors (nanoparticle size, domain size, tortuosity and particle distribution) and the permeability coefficients suggest that shear crystallization can retard oil migration by reducing the network's permeability by about a factor of 100.;Furthermore, using different tensile mechanical testing and ultrasonic spectrometry, we demonstrated that cocoa butter crystallized under an external shear field had a stronger network with higher breaking force, Young's and storage moduli than statically crystallized samples. It was also shown that the arrangement of the crystalline component influences the material's strength. The Young's modulus was increased by about 30% in samples that exhibited crystalline alignment. Moreover, a higher average peak melting temperature (∼0.8 °C) and FWHM of the thermogram (∼0.9 °C) were observed for the statically crystallized samples. In the presence of crystalline alignments, cocoa butter melting temperature was decreased slightly, about 0.5 °C. |
