Free polymers which are added to suspensions of colloidal hard sphere
particles induce attractions among the particles. These depletion
attractions are rather well understood as long as the polymer coils are
much smaller than the particles. Considering the opposite limit in size
ratios, polymer coils which are much larger than the spheres, strikingly
contradictory predictions can be found in the literature.
Whereas de Gennes predicted that only weak attractions are induced which
cannot lead to phase separation, Sear recently predicted that phase
separation takes place at smaller and smaller colloid concentrations for
increasing polymer size.
Experimental observations and some theoretical arguments will be given
trying to disentangle the threads, and to stress the need for more
P.G. de Gennes, C. R. Acad. Sci. Paris 288B, 359 (1979)
R. Sear, Phys. Rev. Lett. 86, 4696 (2001)
other references can be found