Measuring small forces using optics

In many areas of physical chemistry, we want to measure a small force.  Examples include the force needed to unravel folded domains in biopolymers, the adhesiveness of malarial-infected red blood cells, the attractiveness of colloids for surfaces, amongst many others  If the force is large (say, greater than 10 picoNewtons where 1 picoNewton is 10^{-12} Newtons ) and changes over nanometre-scale distances, then AFM or Atomic Force MIcroscopy is the appropriate technique.  However, if we are measuring smaller forces (less than a picoNewton) over roughly micron-scale distances - that is "soft forces", then optical techniques, commonly referred to as optical tweezers, are most appropriate. Both techniques are dynamic: you measure a force that changes  as you vary distance, that is you measure the work energy.  Our group is interested in soft matter, that is macromolecules,  molecular assemblies (such as liposomes), colloids - anything that deforms with $k_BT$ energy.  Our focus is upon measuring the work or energy needed to say, deform, detach, stretch  such soft systems.  
 
We have a number of projects that are primarily experimental but also rely upon the student's ability to comprehend concepts in thermodynamics, statistical mechanics, and soft matter.  Those projects that involve doing optical experiments include
1.  Mechanical instabilities
2.  Microrheology
3.  Dynamics of colloids
If you are interested, or might be interested, please contact Edie via email for an appointment.  These projects will progress through a team-like approach involving Dr. Vincent Daria (JCSMR/Physics) and Dr. Genmiao Wang (RSC).