Related Experiment Video
Updated: Jul 4, 2026
11:51
Visually Based Characterization of the Incipient Particle Motion in Regular Substrates: From Laminar to Turbulent Conditions
Published on: February 22, 2018
Instabilities and pattern formation in active particle suspensions: kinetic theory and continuum simulations
David Saintillan1, Michael J Shelley
1Courant Institute of Mathematical Sciences, New York University, New York, New York 10012, USA.
Physical Review Letters
|June 4, 2008
Summary
Suspensions of self-propelled particles are always unstable, leading to density fluctuations and efficient fluid mixing. This study analyzes collective dynamics using kinetic theory and nonlinear continuum simulations.
Area of Science:
- Physics of complex fluids
- Statistical mechanics of active matter
Background:
- Collective dynamics in suspensions of self-propelled particles are crucial for understanding emergent behaviors.
- Previous work by Simha and Ramaswamy predicted certain instabilities.
Purpose of the Study:
- To investigate the collective dynamics and stability of suspensions of self-propelled particles.
- To analyze the behavior of both aligned and isotropic suspensions under nonlinear conditions.
Main Methods:
- Utilizing kinetic theory to analyze suspension stability.
- Employing nonlinear continuum simulations to study long-time dynamics.
- Examining the effects of fluctuations on suspension behavior.
Main Results:
- Aligned suspensions are universally unstable to fluctuations, generalizing prior findings.
- Isotropic suspensions exhibit an instability in particle stress.
- Nonlinear simulations reveal strong density fluctuations and efficient fluid mixing over long times.
Conclusions:
- Suspensions of self-propelled particles exhibit inherent instabilities.
- Collective dynamics lead to significant density fluctuations and mixing.
- The findings have implications for understanding active matter systems.
Related Concept Videos
01:29The Colloidal State
The formation of a colloidal system is exemplified by an aqueous solution containing Cl− ions is introduced to another containing Ag+ ions, resulting in the precipitation of solid AgCl as extremely tiny crystals. Instead of settling out as a filterable precipitate, these crystals remain suspended in the liquid, showcasing a colloidal system.A colloidal system involves colloidal particles within the approximate range of 1 to 1000 nm in at least one dimension, dispersed in a medium called the...
01:17Colloids and Suspensions
Children at play often make suspensions such as mixtures of mud and water, flour and water, or a suspension of solid pigments in water known as tempera paint. These suspensions are heterogeneous mixtures composed of relatively large particles visible to the naked eye or seen with a magnifying glass. They are cloudy, and the suspended particles settle out after mixing. The suspended particles in a suspension settle out after some time of mixing. The separation of particles from a suspension is...
01:23Equilibrium Conditions for a Particle
When an object is in equilibrium, it is either at rest or moving with a constant velocity. There are two types of equilibrium: static and dynamic. Static equilibrium occurs when an object is at rest, while dynamic equilibrium occurs when an object is moving with a constant velocity. In both cases, there must be a balance of forces acting on the object.
To understand the concept of equilibrium, let us first consider the forces acting on an object. When different forces act on an object, they can...
To understand the concept of equilibrium, let us first consider the forces acting on an object. When different forces act on an object, they can...
02:43Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision
The ideal-gas equation, which is empirical, describes the behavior of gases by establishing relationships between their macroscopic properties. For example, Charles’ law states that volume and temperature are directly related. Gases, therefore, expand when heated at constant pressure. Although gas laws explain how the macroscopic properties change relative to one another, it does not explain the rationale behind it.
01:18First Law: Particles in Two-dimensional Equilibrium
Recall that a particle in equilibrium is one for which the external forces are balanced. Static equilibrium involves objects at rest, and dynamic equilibrium involves objects in motion without acceleration; but it is important to remember that these conditions are relative. For instance, an object may be at rest when viewed from one frame of reference, but that same object would appear to be in motion when viewed by someone moving at a constant velocity.
Newton's first law tells us about the...
Newton's first law tells us about the...
01:09Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model
Various dissolution theories provide insight into the factors that influence the dissolution rate. Danckwerts' Model suggests that turbulence, rather than a stagnant layer, characterizes the dissolution medium at the solid-liquid interface. In this model, the agitated solvent contains macroscopic packets that move to the interface via eddy currents, facilitating the absorption and delivery of the drug to the bulk solution. The regular replenishment of solvent packets maintains the concentration...