Entropic Splitter for Particle Separation
  We present a particle separation mechanism which induces motion of particles of different sizes in opposite directions. The mechanism is based on the combined action of a driving force and an entropic rectification of the Brownian fluctuations caused by the asymmetric form of the channel along which particles proceed. The entropic splitting effect shown could be controlled upon variation of the geometrical parameters of the channel and could be implemented in narrow channels and microfluidic devices. 
D. Reguera, A. Luque, P. S. Burada, G. Schmid, J. M. Rub\'i, and P.   H\"anggi
cond-mat.stat-mech cond-mat.soft