A STUDY OF SEDIMENTATION EQUILIBRIUM USING POLYMER LTEXX PARTICLES - CRITICAL-ASSESSMENT OF THE ROLE OF THE DEBYE LENGTH

Perrin's experiment on sedimentation equilibrium was repeated with polymer latex particles, the charged state of which can be better characterized than gamboge particles. The particle distribution was confirmed to obey the well-known exponential equation, from which the particle radius was calculated using the Avogadro number (6.06 x 10(23)). The radius thus obtained was in good agreement with that determined by micrography, in accordance with Perrin's analysis. This agreement indicates that the use of enlarged particle sizes other than those obtained micrographically (for example, hard sphere radius plus the Debye length) will give an Avogadro number different from the accepted value. Thus we demonstrate that the often advanced interpretation of colloidal phenomena in terms of the enlarged effective sphere is incorrect, at least as far as the sedimentation equilibrium is concerned. By comparing our experimental procedure with that of Perrin, we argue that the so-called wall effect on the microscopic study, particularly on the interparticle spacing, is unimportant.