The phase behavior of the middle-phase microemulsion for the quaternary system of the mixed-chain alkyl polyglucoside (C_8/10APG or C_12/14APG)/1-butanol/n-octane/water has been studied with Winsor phase diagram, δ-γ fishlike and modified ε-β fishlike phase diagrams. A series of phase changes Winsor I→Ⅲ→Ⅱ were observed from above three kinds of phase diagrams with increasing the concentration of alcohol. It was observed from the Winsor phase diagram that the phase types, the phase volumes and the concentrations of alcohol at the start point and end point of the Winsor microemulsion formation change with the increase of the concentration of alcohol. From the δ-γ fishlike phase diagram, some important parameters were calculated, such as the mass fraction of 1-butanol in the hydrophile-lipophile balanced interfacial layer, A^S, the coordinates of the start point and the end point of the Winsor microemulsion formation, and the solubilities of APG and 1-butanol in n-octane phase. The modified ε-β fishlike phase diagram was presented for the first time by us. With the ε-β fishlike phase diagram, the above experimental phenomena were observed and the physico-chemical parameters were calculated precisely. The ε-β fishlike phase diagram has some advantages over the Winsor and δ-γ fishlike phase diagrams in visual observations of the phase changes, and calculation of the related physico-chemical parameters.

Key words: middle-phase microemulsion, fishlike phase diagram, alkyl polyglucoside, solubilization