The EACN scale for oil classification revisited thanks to fish diagrams.

The phase behavior of C(10)E(4)-oil-water systems at constant o/w ratio and variable temperature (fish diagram) has been investigated for several homologous oil families. The temperature T( *) and surfactant concentration C( *) at the critical point were determined for 10 n-alkanes varying from C(6) to C(28) as well as for a series of alkylcyclohexanes and alkylbenzenes. On the basis of T( *), equivalent alkane carbon numbers (EACN) were assigned to nonlinear alkanes, alkylbenzenes, and alkylcyclohexanes. The consistency of the method was shown by corroborating that the EACN values of oils previously investigated with other C(i)E(j) (dibutyl ether, squalane, isopropyl myristate, and dodecylbenzene) are the same when determined with C(10)E(4). The fact that two oils of different nature but with the same EACN (i.e., the same T( *)) do not exhibit the same C( *) is discussed in terms of monomeric solubility of the surfactant in the oil (CMC(oil)).