Petia M. Vlahovska Group


My research explores the mechanics of soft and biological materials: from self-assembled bilayer membranes to structured fluids such as emulsions and blood. I am a theorist interested in the analytical modeling of the interrelation between the microscale physics, microstructure and macroscopic behavior of these so called complex fluids under non-equilibrium conditions. I also have a Lab, which has been an amazing source of discoveries and inspiration for new theories!


Lipid bilayer membranes play a central role in living systems: all cells are encapsulated by membranes; membranes divide the eukaryotic cell into compartments to sequester specific cellular functions; membranes are the sites where many cellular machineries carry out their tasks. Since living cells function out-of-equilibrium and are constantly subjected to stresses (e.g. cells in the blood flow), the non-equilibrium behavior of membranes is emerging as an important research area at the forefront of biophysics research.

Voltage driven extreme deformations, instability and poration of biomembranes

An electric potential difference across the plasma membrane is common to all living cells and is essential to physiological functions such as generation of action potentials for cell-to-cell communication. While the basics of cell electrical activity are well established (e.g. the Hodgkin-Huxley model of the action potential), the reciprocal coupling of voltage and membrane deformation has received limited attention. In recent years, studies of biomimetic membranes (lipid bilayers) in externally applied electric fields have revealed plethora of intriguing dynamics (formation of edges. pearling, and phase separation) that challenge current understanding of membrane electromechanics.

We are conducting a systematic investigation of bilayer deformations in response to changes in the transmembrane potential, and, in particular, of the small thermally-driven bilayer undulations and the large buckling-like deformations in an applied electric field. This work is in close collaboration with Dr. Rumiana Dimova, who directs the Membrane Biophysics Lab at the Max Planck Institute of Colloids and Interfaces (Germany).

Vesicle deformation and poration in a DC electric pulse
Reference: P. F. Salipante and P. M. Vlahovska “Vesicle deformation in DC electric pulses”, Soft Matter 10:3386-3393 (2014)

Electrohydrodynamic instabilties

A classic result due to G.I.Taylor is that a weakly conducting drop bearing zero net charge placed in a uniform electric field adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. We have found some intriguing symmetry--breaking instabilities (Quincke rotation resulting in drop steady tilt or tumbling, and pattern formation on the surface of a particle-coated drop), and the streaming from the drop equator that creates visually striking "Saturn-rings" around the drop.

See Videos and these videos from the Gallery of Fluid Motion

The Saturn-ring instability of a drop in an electric field

Electrohydrodynamics of a particle-coated drop

Active fluids

Active matter (systems of motile interacting units) is a new frontier of material science with new opportunities to design functional systems with collective properties not achievable by simply summing the individual components. Active systems can exhibit many emergent phenomena such as self-organization and directed motion at large scales. Most attention has been focused on the collective motion of translating units such as bacteria (at the microscale) and birds (at the macroscale). Only recently rotating units have been realized experimentally (the Quincke rotor) or identified in biology (Thiovulum majus) thereby prompting interest in their behavior.

We computationally and experimentally examine the collective dynamics of microrotors immersed in viscous fluid. In numerical simulations, we have considered a monolayer of rotors driven by a constant magnitude CW or CCW torque. We are finding that hydrodynamic interactions dramatically affect the collective dynamics, and the phase behavior is completely different from the one of rotors that interact solely through friction. We also observe the emergence of cooperative, superdiffusive motion, which can transport inactive test particles.

Segregation of a 50-50 mixture of CW and CCW rotating spheres
Reference: K. Yeo, E. Lushi and P. M. Vlahovska “Collective dynamics in a binary mixture of hydrodynamically coupled microrotors”, Physical Review Letters 114, 188301 (2015))