Synopsis: Gels settle down

Light scattering measurements provide a microscopic picture of particle motion in a slowly sedimenting gel.

Depending on the kind of colloidal particles it contains, a gel will sediment in a matter of minutes or days. Understanding how shifts in the positions of the typically submicron sized particles affect the more macroscopic sedimentation process (and vice versa) could be helpful in designing industry-use gels. So far, however, no experiments have provided simultaneous access to these vastly different length scales.

Now, a group of scientists in France and Italy report in Physical Review Letters the use of light scattering to capture both the microscopic and macroscopic pictures of a gel collapsing under its own weight.

Giovanni Brambilla of the Université Montpellier, France, and colleagues filled a tall glass column with about 10mm of a water-based gel. The sticky, colloidal particles in the gel slowly rearranged as the gel started to sediment, altering the specklelike pattern of laser light that the team scattered through a vertical slice of the gel. Over the course of ten days, Brambilla et al. captured this speckle pattern at various heights along the column and used an algorithm to extract such parameters as the particle relaxation rate, sedimentation velocity and density.

The team finds, at least in the slowly settling gels they studied, that both the microscopic and macroscopic dynamics mimic what is found in glassy polymers. Brambilla et al.’s data should thus provide a solid basis on which to test the theory of gels. – Jessica Thomas


Features

More Features »

Announcements

More Announcements »

Subject Areas

Soft Matter

Previous Synopsis

Next Synopsis

Related Articles

Viewpoint: Active-Matter Thermodynamics Under Pressure
Soft Matter

Viewpoint: Active-Matter Thermodynamics Under Pressure

Experiments show that, unlike an ideal gas, an active-matter system comprised of self-propelled disks does not have a well-defined mechanical pressure. Read More »

Viewpoint: Tube Model Under Tension
Soft Matter

Viewpoint: Tube Model Under Tension

Results from a new method of analyzing neutron-scattering data from polymer samples under deformation may challenge the prevailing “tube model” of polymer motion. Read More »

Focus: “Gas Marbles” Store Air in Strong Spheres
Soft Matter

Focus: “Gas Marbles” Store Air in Strong Spheres

A spherical shell made of plastic microspheres can store pressurized gas in a tiny volume and might be used to stabilize foams or to deliver specialized gases. Read More »

More Articles