David J. Castro

Magnetic Microrheology for Characterization of Viscosity in Coatings

This chapter reviews the technique of magnetic microrheology for the characterization of the viscosity of coatings. In magnetic microrheology, a liquid containing a dilute solution of micron-sized magnetic probe particles is placed in a magnetic field gradient and the motion of the probe particles is tracked with a microscope. The probe particle velocity found from image analysis is then used, along with the particle and system parameters, to find the local viscosity of the liquid. The application to coatings requires an apparatus designed for tracking particles in thin liquid coating layers. In the chapter, an overview of magnetic microrheology is provided, including the design of an apparatus for monitoring coating viscosity. Examples are provided for the use of the method to track viscosity as a function of time during drying and curing, and position through the thickness of the coatings. The chapter explores the application of the method to understand the effects of process variables on the viscosity development of a coating used in the manufacture of tissue paper.