Fig.1. Microstructure of chocolate and rheological property as a function of applied shear stress
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Recently there has been a growing interest in “complex fluids,” or “soft matter”, which include biological macromolecules, polyelectrolytes, surfactants, suspensions, emulsions, commercial polymer solutions, polymer melts [1]. These “complex fluids” are neither simple liquids nor simple crystalline solids, and thus they do not fall readily within the classical scheme of materials classification because they have unique internal structures with various sizes ranging from micro to nano meter. For example, block copolymers show self organize into periodic heterogeneous nanostructures on a length scale of 10-100 nm where spheres, cylinders, gyroid, and lamellae can appear. These complex fluids are used in fundamental science but also industry applications e.g. food products, personal care products, electronic and optical materials, plastic products, and for many biological applications.
They undergo a variety of deformations (shear, and extensional flow and so on) under the processing conditions. These deformations affect the microstructure, nanostructure induce anisotropy and orientation. Vice versa these structures can also affect the mechanical property, see Fig.1. Chocolate shows several different microstructure under applied stress or deformations. Thus, we need to investigate the coupling between internal structure and flow field.
Fig.1. Microstructure of chocolate and rheological property as a function of applied shear stress
A rheometer is a powerful instrument to study the flow and the deformation of materials because it controls various deformations e.g. steady shear flow, mechanical creep and recovery, and large amplitude oscillatory shear (LAOS). X-ray scattering experiments, on the other hand, have been widely used in the investigation of various scales structures. For a better understanding between internal structure and flow field, a new in-situ Rheo-SAXS was developed (see Fig. 2, combination of Rheometer and X-ray).This set-up use a unique vertical x-ray beam arrangement in combination with parallel plate or con plate geometry. A patent is suspending at DESY.
Therefore, we can investigate flow-induced microscopic or nanoscopic scale structure of complex fluid with this unique in-situ Rheo-SAXS set-up under applied shear.
Fig. 2. (a) The whole setup of in-situ Rheo-SAXS. (b) The 2D SAXS pattern under shear. (c) Top-view of the flow geometry.
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