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SUMMARY:Magneto-optic tweezers and their application in soft mater researc
 h -  Assistant Professor Igor Poberaj\, Faculty of Mathematics and Physics
 \, University of Ljubljana\, Slovenia
DTSTART:20070608T131500Z
DTEND:20070608T141500Z
UID:TALK6870@talks.cam.ac.uk
CONTACT:Jurij Kotar
DESCRIPTION:Magneto-optic tweezers are extension of well known laser tweez
 ers. They combine optical gradient force of tightly focused laser beam(s) 
 and magnetic forces between super-paramagnetic particles induced by modula
 ted magnetic field. Depending on the modulation type\, both attractive and
  repulsive magnetic interactions can be achieved. Magneto-optic tweezers o
 ffer great flexibility in particle manipulation and enable experiments tha
 t can not be performed with laser tweezers only. This talk will present th
 e working principle of magneto-optic tweezers and results of two experimen
 ts in two different soft matter systems.\nIn the first experiment the inte
 raction between colloidal particles suspended in liquid crystal (LC) was i
 nvestigated. LC colloids exhibit a rich variety of phenomena that arise fr
 om long-range anisotropic interactions between them. Optical tweezers are 
 usually used for noncontact interparticle potential measurements. However\
 , a strong electric field of a highly focused laser beam used in optical t
 weezers can distort the local ordering of LC molecules making experimental
  results unreliable. A combination of optical and magnetic tweezers is use
 d to improve the measurement quality and to extend the measurement range t
 o smaller particle separations.\nIn the second experiment a water based co
 lloid was used as a model system to experimentally study the phase diagram
  of colloidal particles interacting with a hard core and repulsive soft sh
 oulder potential. In this experiment magnetic interaction was used to gene
 rate the soft shoulder potential which is very difficult to generate by ot
 her methods. The results confirmed the existence of several different phas
 es that were predicted by numerical simulations. 
LOCATION:IRC in Superconductivity Seminar Room\, Cavendish Laboratory
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