The determination of the size of paraffin-chain salt micelles from diffusion measurements

In aqueous solution of paraffin-chain salts-salts, one of the ions in which is a long paraffin-chain with the ionic group at the end-there exists a fairly well defined "critical" concentration (about N/1000 when the chain has 16 C atoms), below which the salt behaves as a normal electrolyte. In the neighbourhood of the critical concentration, all physical properties which have been measured with sufficient accurancy suffer a rather abrupt and Shute 1938). At concentrations well above the critical, the behaviour is that of a colloidal electrolyte and there is no doubt that the paraffin-chain ions are almost all aggregated into "micelles". The abruptness of the transition is satisfactorily explained, according to the reasoning of Bury and collaborators (Bury and Jones 927; Bury and Grindley 1929; Bury and Davies 1930; see also Murray and Hartley 1935), if the micelles have a large optimum size, much smaller aggregates not being formed in appreciable amount.