GOALI: Collaborative Research: Non-invasive measurement of kinematics and rheology in a drying complex fluid

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Coatings impact many applications, including consumer products, medicine, food, and engineering applications, typically serve one of three purposes: to protect and extend the life of a product, to improve aesthetics, or to add new functionality. Small defects that form during solidification of a fluid film coating can harm the ultimate functionality of the coating. In a single automotive plant, painting accounts for 60% of the energy consumption, and refinishing to repair defects can cost more than $10 million/year. There are few methods capable of non-invasive tracking of the coating properties during drying. The objective of this project is to develop the capability to measure the transient viscosity and flow of a drying coating with time- and space- resolved optical measurements. The underlying knowledge gained via this project in relation to how transient rheology affects fluid flow will be applicable to a multitude of coating manufacturing processes. The project will have significant impact on coatings design and processing, help to bridge the gap between academia and industry, and include outreach to the science, technology, engineering, and math communities.The research objective of this proposal is to measure the transient rheology and kinematics of a drying complex fluid. Traditional macroscopic rheological techniques require physical contact with the coating during the measurement (i.e. the technique is invasive and alters drying) and are unable to spatially resolve rheological changes within the coating. This project will be enabled by non-invasive, high temporal and spatial resolution optical techniques to measure the time- and space-resolved rheology and flow in model complex fluids. Specifically, the research goals are to (1) measure the spatial dependence of rheology in a drying thin film with varied viscosity, (2) to determine and implement a suitable method of convection correction for thin films of drying viscoelastic fluids, and (3) to measure the impact of formulation and substrate angle on the transient convection cell structure and related microstructure formation in thin films of drying viscoelastic fluids. The proposed work on model ~0.100 mm thin films will be applicable to a broad set of applications and will complement ongoing work the industrial partner, PPG. When successful, this research will significantly enhance the design and processing of coatings for a wide range of applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.