Related Experiment Video
Updated: Jun 8, 2026
06:07
Studying Large Amplitude Oscillatory Shear Response of Soft Materials
Published on: April 25, 2019
Extensional rheology of active suspensions
1Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA. dstn@illinois.edu
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|September 28, 2010
Summary
This study models active particle suspensions, finding that self-propulsion alters viscosity. "Puller" active particles increase viscosity, while "pusher" particles decrease it, even becoming negative in weak flows.
Area of Science:
- Soft Matter Physics
- Fluid Dynamics
- Rheology
Background:
- Classical rheology models suspensions of passive particles.
- Active particles, like microswimmers, exhibit self-propulsion, influencing fluid dynamics.
- Understanding active particle suspensions is crucial for microfluidics and biological systems.
Purpose of the Study:
- To develop a simple model for the extensional rheology of dilute active particle suspensions.
- To extend classical rheological models to include active particle behavior.
- To analyze the impact of particle activity on viscosity and normal stresses.
Main Methods:
- Developed a model based on the orientation distribution of active particles.
- Utilized a Fokker-Planck equation to describe particle orientation dynamics.
- Calculated particle extra stress from force dipoles and configurational averages.
Main Results:
- Derived analytical expressions for the stress tensor in various extensional flows.
- Observed increased effective viscosity for 'puller' type active particles.
- Found decreased effective viscosity for 'pusher' type active particles, including negative viscosity in weak flows.
Conclusions:
- Active particle self-propulsion significantly modifies suspension rheology.
- The observed viscosity changes are linked to active power input, not dissipation.
- The model provides insights into the complex flow behavior of active matter.
Related Concept Videos
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...
01:18Residual Stresses in Bending
In the study of elastoplastic members subjected to bending moments, understanding the loading and unloading phases is crucial for assessing material behavior and structural integrity. During the loading phase, as the bending moment increases, the material initially responds elastically, adhering to Hooke's Law, where stress is directly proportional to strain. When the load exceeds the yield strength, plastic deformation occurs, resulting in permanent strain and deformation that remains even...
01:15Relation between Poisson's ratio, Modulus of Elasticity and Modulus of Rigidity
Deformation occurs in axial and transverse directions when an axial load is applied to a slender bar. This deformation impacts the cubic element within the bar, transforming it into either a rectangular parallelepiped or a rhombus, contingent on its orientation. This transformation process induces shearing strain. Axial loading elicits both shearing and normal strains. Applying an axial load instigates equal normal and shearing stresses on elements oriented at a 45° angle to the load axis.
01:20Elastic Strain Energy for Shearing Stresses
As discussed in previous lessons, strain energy in a material is the energy stored when it is elastically deformed, a concept crucial in materials science and mechanical engineering. This energy results from the internal work done against the cohesive forces within the material. When a material undergoes shearing stress and corresponding shearing strain, the strain energy density, which is the energy stored per unit volume, is calculated. Within the elastic limit, where the stress is...
01:19Members Made of Elastoplastic Material
The behavior of elastoplastic materials under bending stresses, particularly in structural members with rectangular cross-sections, is crucial for predicting material responses and understanding failure modes. Initially, when a bending moment is applied, the stress distribution across the section follows Hooke's Law and is linear and elastic. This distribution means the stress increases from the neutral axis to the maximum at the outer fibers, up to the elastic limit.
As the bending moment...
As the bending moment...
01:21Plastic Behavior
A material's elastic behavior is characterized by the disappearance of stress once the load is removed, allowing the material to return to its original state. However, when stress surpasses the yield point, yielding commences, marking the onset of plastic deformation or permanent set. This change from elastic to plastic behavior is influenced by the peak stress value and the duration before the load is removed. An intriguing observation occurs when a specimen is loaded, unloaded, and reloaded.