Phase transition kinetics in colloidal systems

Solid-solid transformations are technologically important in shape-memory materials, metals, and alloys. A deep understanding of the microstructural changes and the underlying kinetic mechanisms is still lacking. The kinetics of fluid-gel transitions are difficult to study because of the lack of a convenient control parameter. In our group, we use electric-field-induced dipolar interactions as a switch to induce phase transition quenches, in addition to polymer-induced depletion interactions, allowing us to study kinetics, and to probe reversibility and irreversibility. [PhD work of Ashish Joy and Shivani Semwal. Collaborator: Ivan Saika-Voivod (MUN). Past collaborators: Alfons van Blaaderen (Utrecht), Priti Mohanty (KIIT-Bhubaneswar), Peter Schurtenberger (Lund), Surajit Sengupta and Saswati Ganguly (TIFR-Hyderabad)]

Macromolecular crowding

The living cell is a crowded macromolecular environment. While crowding has been viewed primarily as an excluded volume hard-sphere effect, proteins are charged and have hydrophobic and polar groups, so non-specific soft interactions are important. In our research, we have used diffusion NMR to study diffusion in macromolecular complex fluids [see our review: Barhoum, S., Palit, S., & Yethiraj, A. (2016). Progress in Nuclear Magnetic Resonance Spectroscopy, 94, 1-10.].

Combining diffusion NMR with small-angle neutron scattering (SANS) and rheology, we study structure and microscopic dynamics in a polymer-colloid model system for crowding. [PhD work of Swomitra Palit (2018) and Venketesh Thrithamara. Collaborators: Stefan Wallin (MUN), Yun Liu (NIST)]

Swomitra Palit, Lilin He, William A. Hamilton, Arun Yethiraj, Anand Yethiraj, “Combining diffusion NMR and SANS enables precise measurements of polymer chain compression in a crowded environment”, Phys. Rev. Lett, 118, 097801 (2017).

Swomitra Palit et al., "Combining diffusion NMR and SANS enables precise measurements of polymer chain compression in a crowded environment", Phys. Rev. Lett, 118, 097801 (2017)

Electrohydrodynamics and Driven Emulsions

PhD work of Majid Bahraminasr, Somayeh Khajehpour and Atul Varshney. Past collaborators: Shankar Ghosh (TIFR-Mumbai)

We stumbled upon a beautiful model system for tunable hydrodynamics by
re-discovering the electrohydrodynamics of oil drops in an immiscible leaky dielectric oil, originally discovered by G. I. Taylor [Melcher, J. R., & Taylor, G. I. (1969). Annual Review of Fluid Mechanics, 1, 111-146.]. There were two key differences in our point of view: (a) While previous work on electrohydrodynamics studied individual drops, we examined collective behaviors and interactions of many drops; (b) In our work, we have employed high-speed imaging and used electric field frequency as a tuning parameter to control the hydrodynamic lengthscale. The outcome of this new point of view was rich dynamical phenomena as a function of field strength and frequency, with ordered drop arrays at high frequency, chaotic flows at low frequency, and multiscale turbulence at DC arising from anomalous super-diffusion in the fluid. The design of new materials using these novel interactions remains un-explored.

Nanoscale active matter

We are making active nanoparticles that could serve as active crowders and can be studied by new(-ish) optical techniques such as fluoresecence dynamic difference microscopy or fluoresence correlation spectroscopy. [PhD Anas Alhasanat and Will Seavey, with the help of undergraduate students. Collaborators: Francesco Piazza & Josef Hamacek (Centre Biophysique Moléculaire, Orléans), Valerie Booth (MUN)]

Funding

  • Canadian Foundation for Innovation (2025)
  • Canada Research Chairs Programme (2025 – )
  • NSERC Discovery Grant (since 2005)
  • NSERC Discovery Accelerator Grant (2019)
  • Canadian Foundation for Innovation (2006)