Richards Jeffrey J, Gagnon Cedric V L, Krzywon Jeffery R, Wagner Norman J, Butler Paul D
NIST Center for Neutron Research, National Institute of Standards and Technology.
Department of Materials Science and Engineering, University of Maryland.
J Vis Exp. 2017 Apr 10(122):55318. doi: 10.3791/55318.
A procedure for the operation of a new dielectric RheoSANS instrument capable of simultaneous interrogation of the electrical, mechanical and microstructural properties of complex fluids is presented. The instrument consists of a Couette geometry contained within a modified forced convection oven mounted on a commercial rheometer. This instrument is available for use on the small angle neutron scattering (SANS) beamlines at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR). The Couette geometry is machined to be transparent to neutrons and provides for measurement of the electrical properties and microstructural properties of a sample confined between titanium cylinders while the sample undergoes arbitrary deformation. Synchronization of these measurements is enabled through the use of a customizable program that monitors and controls the execution of predetermined experimental protocols. Described here is a protocol to perform a flow sweep experiment where the shear rate is logarithmically stepped from a maximum value to a minimum value holding at each step for a specified period of time while frequency dependent dielectric measurements are made. Representative results are shown from a sample consisting of a gel composed of carbon black aggregates dispersed in propylene carbonate. As the gel undergoes steady shear, the carbon black network is mechanically deformed, which causes an initial decrease in conductivity associated with the breaking of bonds comprising the carbon black network. However, at higher shear rates, the conductivity recovers associated with the onset of shear thickening. Overall, these results demonstrate the utility of the simultaneous measurement of the rheo-electro-microstructural properties of these suspensions using the dielectric RheoSANS geometry.
介绍了一种新型介电流变体小角中子散射仪的操作程序，该仪器能够同时检测复杂流体的电学、力学和微观结构特性。该仪器由置于安装在商用流变仪上的改进型强制对流炉内的库埃特几何结构组成。此仪器可用于国家标准与技术研究院（NIST）中子研究中心（NCNR）的小角中子散射（SANS）光束线。库埃特几何结构经加工后对中子透明，可在样品发生任意变形时测量夹在钛圆柱体之间的样品的电学特性和微观结构特性。通过使用可定制程序来同步这些测量，该程序可监测和控制预定实验方案的执行。这里描述的是一种执行流动扫描实验的方案，其中剪切速率从最大值对数递减到最小值，在每个步骤保持指定的时间段，同时进行频率相关的介电测量。给出了由分散在碳酸亚丙酯中的炭黑聚集体组成的凝胶样品的代表性结果。当凝胶经历稳定剪切时，炭黑网络发生机械变形，这导致与构成炭黑网络的键断裂相关的电导率初始下降。然而，在较高剪切速率下，电导率随着剪切增稠的开始而恢复。总体而言，这些结果证明了使用介电流变体小角中子散射几何结构同时测量这些悬浮液的流变 - 电 - 微观结构特性的实用性。
