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SUMMARY:Colloidal Gas-Liquid-Solid phase transitions induced by the Critic
 al Casimir Effect - Dr. Peter Schall\, University of Amsterdam
DTSTART:20110520T130000Z
DTEND:20110520T140000Z
UID:TALK31316@talks.cam.ac.uk
CONTACT:Erika Eiser
DESCRIPTION:Control over the assembly of colloidal particles has important
  applications for the design of structures at micrometer and nanometer len
 gth scales. While typically\, colloidal assembly is governed by geometric 
 exclusion and charge interactions that are fixed and cannot be adjusted wi
 th external control\, the increasing need for ever more complex nanoscale 
 structures calls for new techniques that allow precise control over the as
 sembly process.\nIn this talk\, I will present a new technique to control 
 the assembly of particles with temperature using the Critical Casimir effe
 ct. This effect allows direct control over particle interactions via tempe
 rature-dependent solvent fluctutions: In analogy to the confinement of flu
 ctuations of the electromagnetic field between two conducting plates (quan
 tum mechanical Casimir effect)\, the confinement of fluctuations of a crit
 ical solvent leads to an attraction between surfaces that are immersed in 
 this solvent. This allows exquisite temperature control over the interacti
 ons of colloidal particles. We show that this temperature control allows u
 s to “freeze” a dilute colloidal gas into a dense colloidal liquid\, a
 nd a crystalline solid. By using confocal microscopy\, we follow these pha
 se transitions directly in real space\, and we measure the particle pair p
 otential directly. We find that the gas-liquid condensation is accurately 
 described by the Van der Waals theory used for molecular gases. We also ob
 serve that these phase transitions are reversible: the colloidal solid “
 melts”\, and the colloidal liquid “evaporates”\, when the temperatur
 e is changed back to reduce the attractive force. This reversible control 
 opens new routes for the growth and annealing of perfect nanoscale structu
 res.\n\n
LOCATION:Small Lecture Theatre\, Cavendish Laboratory
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