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SUMMARY:Crystallisation in the Energy Landscape - Vanessa de Souza
DTSTART:20111117T131000Z
DTEND:20111117T140000Z
UID:TALK33025@talks.cam.ac.uk
CONTACT:Dr Edward Cackett
DESCRIPTION:*Is Glass a Liquid?*\n\nThe observation that old windows are o
 ften thicker at the bottom than at the top has led to the popular myth tha
 t such glass has flowed over a matter of centuries\, and hence glass is a 
 liquid.\n\nThere are a number of materials that can not be simply classifi
 ed as solids or liquids. When a liquid is cooled\, it generally undergoes 
 a transition at its freezing temperature to form a crystalline solid. Howe
 ver\, it is possible to avoid this transition\, lowering the temperature o
 f a liquid below its freezing point\, without it becoming solid. The most 
 common method to form a 'supercooled liquid' is to cool the liquid very fa
 st. On further cooling\, the motion of the\nparticles within the liquid de
 creases and eventually\, when the structure appears frozen in experiments\
 , the system can be described as a solid\, specifically a noncrystalline s
 olid or glass.\n\n*Crystal or glass?*\n\nThe structure of a glass is liqui
 d-like. From the point of view of each individual atom\, there is order du
 e to chemical bonding but there is no long-range order or symmetry as foun
 d in a crystalline solid. In contrast\, the mechanical properties of a gla
 ss resemble those of a\nsolid i.e. it does not flow. In fact the shape of 
 old windows is due to the process of manufacture. It was hard to create a 
 completely flat pane of glass and when installing windows\, it was logical
  to place the\nthicker part at the bottom.\n\n*The Energy Landscape?*\n\nP
 articles interact with each other and this interaction has an energy cost 
 or gain. The total energy of an arrangement of particles changes with the 
 position of each individual particle. As each particle can\nmove\, this fo
 rms a multidimensional landscape. It is possible to move from one structur
 e to another and energy changes en route. By studying the energy changes w
 e can examine structures and the connections between different arrangement
 s of atoms\, and deduce how particular properties are related to underlyin
 g structure.
LOCATION:Entertaining Room\, Darwin College
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