Sphere caging by a random fibre network

We analyse the remarkable efficiency of a random distribution of rigid thin rods (with diameter sigma) to 'cage' a test sphere (with diameter D>>sigma ) by purely geometric hindrance due to rod-sphere contacts. The average num ber of random contacts which traps a sphere in three dimensions corresponds to a volume fraction phi(c) = 7(D/sigma)(2) of very long rods or fibres. S ome implications for confinements and dynamics of(colloidal) particles in f ibre structures are discussed. (C) 1999 Elsevier Science B.V. All rights re served.