The
Chemical
Engineering
Department
is
hosting
a
special
graduate
seminar
about Multiphysics
across
Multiple
Scales
in
Soft
Matter.
Abstract:
Understanding physical phenomena at the right scale is the key to engineer soft materials. For example, fundamental concepts in solid mechanics are used to reveal the swelling dynamics of hydrogels when confined in tight porous space, whereas mean field theories are needed to explain the phase transition of thermoresponsive polymers. Following this overarching principle, I will discuss how some of global challenges can be addressed by understanding the behavior of soft materials.
In the first part of my talk, I bolster our perspective and understanding of the spread of microplastics in aquifers. By directly visualizing colloidal transport in transparent 3D porous media, I identify the fundamental mechanisms by which particles are distributed throughout a medium. At high injection pressures, hydrodynamic stresses cause particles to be continually deposited on and eroded from the solid matrix—notably, forcing them to be distributed throughout the entire medium. By contrast, at low injection pressures, the relative influence of erosion is suppressed, causing particles to localize near the inlet of the medium. Unexpectedly, these macroscopic distribution behaviors depend on imposed pressure in similar ways for particles of different charges, although the pore-scale distribution of deposition is sensitive to particle charge. These results reveal how the multiscale interactions between fluid, particles, and the solid matrix control the distribution of microplastics in aquifers.
Next, I discuss the dynamics of thermally induced phase transitions of functionalized cellulosics at the lower critical solution temperature (LCST). Above the LCST, hydroxypropyl substituents favor the spontaneous formation of liquid droplets, whereas methyl substituents induce fibrillation through a diffusive growth rate. In the coexistence of methyl and hydroxypropyl substituents, the fibrillation initiates after liquid drop formation, at a sub-diffusive growth rate. This alteration impacts the reversibility of thermally induced phase transition. Unlike for liquid droplets, the dissolution of fibrils back into the solvated state occurs with significant thermal hysteresis. This hysteresis is tunable by the content of substituted hydroxypropyl moieties. This work provides a systematic study to decouple competitive mechanisms during the phase transition of multi-functionalized macromolecules.
Finally, I provide an overview of innovative directions through which we can transition away from petroleum resources to create more sustainable and healthier environment.