Memories of paste
- Weitz, D., Nature 410, 32-33 (2001).
In his article, Weitz primarily describes the following paper:
- Cloitre, M., Borrega, R. & Leibler, L. Phys. Rev. Lett. 85, 4819-4822 (2000).
Key Words: Paste, Glass, Microgel, Stress, Relaxation, Ageing
Weitz's article draws attention to the findings of Cloitre, Borrega, and Leibler and goes on to list related questions for future exploration.
Cloitre, Borrega, and Leibler studied the rheology of a paste consisting of pieces of microgel suspended in a fluid. These researchers found that the relaxation to stress applied to the paste depended on the history or age of the paste. MORE HERE
The related questions Weitz lists are:
- 1) What causes the ageing affect?
- 2) How much impact does the surprising rheology have?
- 3) Is the ageing affect specific to the particular microgel paste, or does it apply to other pastes or even other kinds of soft matter?
Soft Matter Details
Types of Soft Matter
As the title suggests, Memories of Paste focuses primarily on a class of soft materials called pastes. However, the author remarks on a similarity between pastes, gels, and glasses. "...the way a paste recovers from an applied stress is remarkably like the behaviour of glasses and gels" (Weitz p.32).
- What is the difference between pastes, glasses, and gels? What about colloids?
"Pastes typically consist of a suspension of small particles in a background fluid. These particles are crowded, or jammed together like grains of sand on a beach, forming a disordered, glassy, or amorphous structure" ( Wetiz p.32). In the experiment described above, the particles in the paste are made of micro-gel. At low particle concentrations, the particles act like hard colloidal particles; however, at high concentrations the material acts like a paste (Cloitre et a. p. 4819).
A colloid is a suspension of solid particles in a liquid, so it seems that a paste is a type of colloid where the volume fraction of solid particles is quite high.
Cloitre et al. made bulk rheological measurements using a rheometer to study a paste's response to stress. See their paper Rheological Aging and Rejuvenation in Microgel Pastes for more details.
author: Becca Perry