Non-linear dynamics of particles in time-dependent non-Newtonian fluids

As we grapple with the environmental impacts of our technological advancements, finding green alternatives becomes crucial. My research dives into the fascinating world of cellulose nanofibrillated gels, revealing their complex properties from a fundamental point of view. The use of cellulose, sourced from wood, aligns with global efforts to reduce our carbon footprint and promote renewable resources.

Cellulose gels exhibit unique characteristics such as yield stress, elasto-visco-plasticity, thixotropy, and aging. These properties make them beneficial for a wide range of applications, from drug delivery to sustainable energy harvesting, cosmetic materials, wastewater treatment, and more. To optimize the use of cellulose material for such advanced technologies, a fundamental understanding of their flow behavior is important. For example, what happens when a solid object drops into such a complex fluid? What if we let the fluid age and then apply shear to it? What if we apply shear after mixing them? Are they homogeneous, and is it important? How do the shape and size distribution of the tiny solid particles forming the gel affect its flow properties? How can we explain their flow properties with mathematical models? These questions drive my research.
In my doctoral thesis, I explored cellulose nanofibrillated gels using both experimental and numerical methods. Through numerical modeling approaches, I explained the complex interactions between these gels and solid objects and compared the results with alternative complex gels such as Laponite. This understanding could be useful for applications where solid objects and complex fluids interact, such as in drilling.

Hakimeh Koochi received a 5000 euro grant from the Finnish Foundation for Technology Promotion to accomplish her doctoral project on "Nonlinear Dynamics of Particles in Time-Dependent Non-Newtonian Fluids. She defended her doctoral thesis successfully at Aalto University, School of Science, Department of Applied Physics in 2023.