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A conceptual model for shear-induced phase behavior in crystallizing cocoa butter

机译：可可脂结晶过程中剪切诱导相行为的概念模型

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摘要

We propose a conceptual model to explain the quantitative data from synchrotron X-ray diffraction experiments on the shear-induced phase behavior of cocoa butter, the main structural component of chocolate. We captured two-dimensional diffraction patterns from cocoa butter at crystallization temperatures of 17.5, 20.0, and 22.5 degrees C under shear rates from 45 to 1440 s(-1) and under static conditions. From the simultaneous analysis of the integrated intensity, correlation length, lamellar thickness, and crystalline orientation, we postulate a conceptual model to provide an explanation for the distribution of phases II, IV, V, and X and the kinetics of the process. As previously proposed in the literature, we assume that the crystallites grow layer upon layer of slightly different composition. The shear rate and temperature applied define these compositions. Simultaneously, the shear and temperature define the crystalline interface area available for secondary nucleation by promoting segregation and affecting the size distribution of the crystallites. The combination of these factors (composition, area, and size distribution) favors dramatically the early onset of phase V under shear and determines the proportions of phases II, IV, V, and X after the transition. The experimental observations, the methodology used, and the proposed explanation are of fundamental and industrial interest, since the structural properties of crystalline networks are determined by their microstructure and polymorphic crystalline state. Different proportions of the phases will thus result in different characteristics of the final material.
机译：我们提出了一个概念模型来解释同步加速器X射线衍射实验对可可脂（巧克力的主要结构成分）的剪切诱导相行为的定量数据。我们在结晶速率为17.5、20.0和22.5摄氏度，剪切速率为45至1440 s（-1）和静态条件下，从可可脂中捕获了二维衍射图。通过对积分强度，相关长度，层状厚度和晶体取向的同步分析，我们提出了一个概念模型，为相II，IV，V和X的分布以及该过程的动力学提供了解释。如先前在文献中提出的，我们假设微晶逐层生长，其组成略有不同。施加的剪切速率和温度定义了这些组成。同时，剪切力和温度通过促进偏析并影响微晶的尺寸分布，定义了可用于二次成核的晶体界面区域。这些因素（组成，面积和尺寸分布）的组合极大地促进了剪切作用下相V的早期发作，并确定了转变后相II，IV，V和X的比例。实验观察，所使用的方法和提出的解释具有根本的工业意义，因为晶体网络的结构特性取决于其微观结构和多晶型态。因此，不同比例的相将导致最终材料的不同特性。

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