Many unusual phenomena in surfactant solutions below the critical micelle concentration have been attributed to the existence of premicelles. Here we investigate the properties of premicelles in aqueous solutions of non-ionic surfactants surrounding the critical micelle concentration (CMC) using advanced computer simulations. The concentration of premicelles increases with total concentration up to the CMC, above which the concentrations of free monomers and premicelles remain nearly constant. Analysis shows premicellar structures ranging from spherical to chain-like. Monomer exchange kinetics are observed to depend strongly on the aggregate size, with premicelles exhibiting extremely short (1.3 ns) relaxation times relative to full sized micelles (72 ns). (C) 2011 Elsevier B. V. All rights reserved.