Experimental analysis of the porosity of randomly packed rigid fibers

The study focuses on the characterization of randomly packed monodispersed rigid fibers. We show that porosity can vary over a wide range of values, depending on the size of the fibers. A systematic study was carried out for fiber aspect ratios r (length-to-diameter) ranging between 4 and 70. Analysis and discussion of these results are presented in this paper. It is shown that the porosity law is dependent only on the fiber aspect ratio. This result was analyzed using the concept of excluded volume developed by Onsager in 1948 for systems at a molecular scale. In this work, we propose a simple law linking porosity to the aspect ratio of the fibers on the basis of experimental results and on the expression of excluded volume: epsilon = 1 - 11/pi/2r + 6 + 2r. (C) Academie des sciences/Elsevier, Paris