Stargazing: In the sky and in the lab

 

Illuminating the dark: looking for answers in the stars

This week we have all been able to see some real stars on TV for a change.

The BBC 2 programme Stargazing Live featuring Professor Brian Cox and Dara O Briain hosted three nights of stargazing and discussion. With guest experts, and link-ups to observatories around the world, we saw some of the amazing sights of the universe from the comfort of our sofas (you can catch the programme again this Saturday).

But it's not the only place to see something extraordinary. Anyone with a microscope is uniquely privileged to see a world that a great number of individuals will never see - from the swirling of the cosmos to the slow almost imperceptible movement of a colloidal star glass.

A colloidal star glass is a polymer composed of repeating chemical units arranged in the shape of a star.

Michel Cloitre from the Matter and Soft Chemistry, ESPCI Paris Tech, together with scientists from the Institute of Electronic Structure and Laser, have been studying the response of a colloidal star glass to large-amplitude oscillatory stress (LAOS) and strain fields using the the Linkam Optical Shearing System - the CSS450.

The scientists use a recently published framework for analyzing non-linear responses to LAOS based on the analysis of the whole stress waveforms as a sequence of physical processes, in order to measure the points of static and dynamic yielding. By doing so, they have shown that the stress-amplitude dependence of the dynamic yield stress can be linked to the strain-rate-amplitude dependence via the form of the steady-state flow curve.

To read about their experiments please see the paper: “Oscillatory yielding of a colloidal star glass” Journal of Rheology / Volume 55 / Issue 4 available
here

For further reading on the physics of colloidal glass click here.

Happy stargazing

By Caroline Feltham