Related Experiment Video
Updated: Jun 18, 2026
05:46
3D Printing Bacteria to Study Motility and Growth in Complex 3D Porous Media
Published on: January 19, 2024
Three-dimensional model for the effective viscosity of bacterial suspensions
Brian M Haines1, Andrey Sokolov, Igor S Aranson
1Department of Mathematics, Penn State University, McAllister Bldg, University Park, Pennsylvania 16802, USA.
Physical Review. E, Statistical, Nonlinear, and Soft Matter Physics
|November 13, 2009
Summary
Swimming bacteria suspensions exhibit reduced effective viscosity due to self-propulsion aligning with background flow. This phenomenon, observed in Bacillus subtilis, is explained by microscopic interactions and bacterium shape.
Area of Science:
- Fluid dynamics
- Microbiology
- Soft matter physics
Background:
- Dilute suspensions of swimming microorganisms present complex rheological behaviors.
- Bacterial motility, involving flagellar rotation and random tumbling, influences fluid properties.
- The asymmetric shape of bacteria interacts with background flows, affecting suspension dynamics.
Purpose of the Study:
- To derive the effective viscosity of dilute bacterial suspensions from fundamental principles.
- To elucidate the relationship between bacterial self-propulsion, reorientation, and bulk fluid properties.
- To explain experimental observations of viscosity reduction in bacterial suspensions.
Main Methods:
- Microscopic analysis of the interaction between an elongated bacterial body and background flow.
- Theoretical derivation of effective viscosity based on individual bacterium dynamics.
- Consideration of generic background flows like planar shear and straining.
Main Results:
- Bacterial shape and self-propulsion lead to preferential alignment in specific flow directions.
- This alignment significantly reduces the effective viscosity of the suspension.
- The derived model aligns with experimental data for suspensions of Bacillus subtilis.
Conclusions:
- Microscopic details of bacterial motility and shape govern the macroscopic rheology of suspensions.
- Self-propulsion-induced alignment is a key mechanism for viscosity reduction in active matter.
- The findings provide a theoretical framework for understanding the fluid dynamics of swimming microorganisms.
Related Concept Videos
01:17Viscosity
When water is poured into a glass, it falls freely and quickly, whereas if honey or maple syrup is poured over a pancake, it flows slowly and sticks to the surface of the container. This difference in the flow of different kinds of liquids arises due to the fluid friction between the liquid layers and the liquid and the surrounding material. This property of fluids is called fluid viscosity. In this example, water has a lower viscosity than honey and maple syrup.
The SI unit of viscosity is...
The SI unit of viscosity is...
01:27Viscosity
Viscosity is a property of fluids that measures their resistance to flow. It is influenced by factors such as the surface area of contact, the gradient of flow speed, and the fluid's viscosity constant, called the coefficient of viscosity. The coefficient of viscosity, also known as dynamic viscosity, is denoted by the symbol η. It determines the proportionality between the viscous force and the gradient of flow speed.Newton's law of viscosity states that the viscous force on a faster-moving...
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...
01:15Theories of Dissolution: Diffusion Layer Model
Dissolution, the process by which drug particles dissolve in a solvent, is explained by the diffusion layer model, a theoretical framework that simulates the absorption of oral drugs and allows us to analyze experimental data.
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
This process starts with a thin layer, saturated with the drug, forming at the interface between the solid and liquid. The solute then diffuses from this layer into the main solution. The Noyes-Whitney equation suggests that the rate of dissolution relies on the diffusion...
01:19Viscosity of Fluid
Viscosity measures the resistance a fluid offers to flow and deformation. It results from internal friction between layers of fluid moving relative to one another. Dynamic viscosity, denoted by the Greek letter mu (μ), quantifies the force needed to move one fluid layer over another. For Newtonian fluids like water and air, the relationship between the shearing stress and the rate of shearing strain is linear, meaning their viscosity remains constant regardless of the applied stress.
01:20Stokes' Law
Viscous forces, like friction, are intermolecular forces that resist the relative motion of molecules over each other. When a solid body moves through a liquid, viscous forces drag it in the opposite direction. The force's magnitude depends on the solid's shape and size, as well as its speed and the liquid's coefficient of viscosity, density and temperature.
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only for low Reynolds...
The expression for the force on a solid spherical object in a fluid is called Stokes' law. Stokes' law is valid only for low Reynolds...