Brownian motion in typical microparticle systems
  Many studies on microscopic systems deal with Brownian particles embedded in media whose densities are different from that of the particles, causing them either to sink or float. The proximity to a wall modifies the friction force the particle experiences, being, instead of the Stokes force assumed by Einstein and Langevin, a function of the separation distance, as described by Faxen. In this work we present a thorough analysis of bidimensional Brownian motion using monodisperse suspensions of latex beads with controlled temperatures. By means of Langevin's model and Faxen's correction, we calculate the mean separation distance between the spheres and the bottom of the confining vessel. 
Silvana Palacios, Victor Romero-Rochin and Karen Volke-Sepulveda
physics.class-ph