Determination of the critical values of flow parameters characteristic of the alignment of cylindrical nano-objects in suspensions

Abstract

A method for determining the critical values of the flow speed and the flow constriction degree characteristic of the alignment of cylindrical nano-objects in a flowing suspension is proposed. Previously, the alignment process of cylindrical nano-objects in suspensions was investigated by using birefringence of the polarized light and the small-angle X-ray scattering. While both methods are suitable for measuring the alignment degree of cylindrical nano-objects in suspensions diluted down to low concentrations, they are restricted for the application to undiluted concentrated suspensions because of non-transparency and multiple scattering of X-rays. In addition, the use of the second method requires an expensive synchrotron equipment. We present a simple and faster method based on the direct ultrasound attenuation measurements of longitudinal viscosity of a suspension containing cylindrical nano-objects, which decreases monotonically, approaching its asymptotic value with increase in the flow speed and the flow constriction degree. The principle and advantages of the proposed method are as follows: • The cylindrical nano-objects align along an accelerated flow at overcritical values of the flow speed and the constriction degree. • The critical values correspond to the state of a suspension possessing viscosity close to the asymptotic value. • The method is applicable to undiluted concentrated suspensions, including opaque ones.

Keywords

• Ultrasound attenuation
• Longitudinal viscosity
• Suspension
• Cylindrical nano-objects
• Alignment
• Critical parameters