Complex Fluids and Active Matter

This course unit provides an introduction to the field of complex fluids and active matter, with applications in both the physical chemistry of soft matter and the physics of living systems and biological objects.

It is common to both the PhyMV and SoftMat tracks.

To provide a modern introduction to the classical fields of complex fluid rheology and their applications, as well as to the emerging field of active matter: self-propelled fluids exhibiting collective behavior, which can be found at various scales in living or physicochemical systems—such as flocks of birds, schools of fish, and crowds...

- Hydrodynamics

Recommended prerequisites: 

- Surfaces, Interfaces, Colloids,

- Statistical Physics

- Physics, Biology

Continuous Integral Control

A) Complex fluids:

Overview of non-Newtonian fluids: rheofluidizers, rheo-thickeners, viscoelastic fluids, and thixotropic fluids.

Examples of practical systems: colloidal suspensions, polymers, biological fluids (blood, mucus, etc.), liquid crystals, pastes, giant micelles, transient networks, and biological applications.

Phenomenological models of non-Newtonian fluids: Maxwell's model, Voigt's model (visco-plastic solid), Bingham's model (threshold fluid).

Measurement methods: different types of rheometers and different types of tests. Single-point and two-point microrheology.

Microfluidics: microfluidic flow and rheology, capillary flow, stagnant and contracting flow. Instabilities (Saffman-Taylor, etc.)

B) Active Ingredient:

Examples of active matter: swarms, schools, hordes, crowds, bacterial colonies; mechanical examples (vibrators); physicochemical examples; actin gel; SPV; ABS partitioning system.

Vicsek's model, simulations, and phenomenology.

Hydrodynamic description, conservation laws, symmetries, slow variables.

"Dry" active ingredient

• Polymer: The Toner & Tu model; study of the model’s properties: phase transition, 2D order, giant fluctuations, “sound” waves…
• Nematode: Model by Ramaswamy, Simha, and Toner.

"Wet" active material. Hydrodynamics of active gels.

Optional: Choose from the following examples:

- Janus particles

- Active growth. Active sedimentation.

- Active-membrane fluctuation spectra.

- The parABS system, equations, equilibrium, quasi-static limit, oscillations, stability, traveling waves.

- Self-Propelled Voronoi Model.