Date/Time
Date(s) - 24/01/2011
4:30 pm - 5:30 pm

Title: Light Induced Self Organisation of Molecular Materials

Speaker: Dr. Jean-Michel Nunzi, Queen’s University

Institute:

Location: ABB 102

Description:

CAP LECTURE
Glasses and more generally amorphous materials (plastics for instance) are the subject of intense research because unexpectedly, they do not differentiate from liquids by their structure. However, their dynamic properties are considerably different (glass is a solid at room temperature). Some glasses are known as photochromic; they can for instance change color under the action of light. In 1995, early researchers showed that it was possible to induce a significant macroscopic, visible to the naked eye, transport of matter by illuminating polymers containing peculiar photochromic molecules. Many models were then developed but none could really give a comprehensive view of the observations, nor to give an account of the very different material behaviors (glasses, plasticsâ?¦). A molecular dynamics simulation shows that the reversible action of light on a photochromic glass (photochromism) induces a diffusion of matter (a flow) which is similar to diffusion in the liquid state. We can find an analogy with a subway at rush hours: to exit from the car, it is necessary that other passengers agree to move. In the same manner, in order to move, the molecules which constitute the solid must wait until one of their neighbors moves. So-called cooperative movements are then observed. The latency which can be extremely long explains why the medium is a solid and not a liquid. The pressure that is exerted on the surroundings of the activated photochromic molecules can be as high as a GPa; enough to drill most materials. These results open the road to many new applications. Interestingly, study of the behaviour of the ensemble of molecules reveals similarities with the behaviour of groups of social animals.