Objective

Complex fluids, like colloidal dispersions, play an important role in many traditional technologies like chemistry (paints, coatings, adhesives) and life-science (pharma, cosmetics and nutrition). A key technological challenge is to control the flow properties in order to meet the manifold requirements during processing and application.

Operation principle

A self-built flow cell is used to determine flow profiles of the complex fluids on microscale. This microchannel is mounted on the inverse fluorescence microscope, which is also used for Video Particle Tracking. The cross-section of this microchannel depends on the material system and varies between 200 x 200 and 800 x 20 µm. A connected syringe pump provides the needed flow rates in order to get shear rates between 0.1 and 20 s^-1. Fluorescent particles are added to the probe for visualization of the flow profile. These tracer particles can be detected using the inverse fluorescence microscope Zeiss Axio Observer D1. A high-speed sCMOS camera (Andor Zyla) with a frame rate up to 100 fps is used to track the particles. The flow profile is determined based on the analysis of spatially-resolved particle velocity for different gap heights. A so-called z-scan is used to obtain the flow profile perpendicular to the flow direction for different gap heights. It is placed between the microscope revolver and the objective and has a travel range of 400 µm at a repetition accuracy of 5 nm.

Specifications

Application

Determination of flow properties of complex heterogeneous fluids like dispersions or clay suspensions on a µm scale.