Langmuir, Vol.18, No.26, 10163-10167, 2002
Self-assembly of surface-active powder at the interfaces of selective liquids. 1: Multiple structural polymorphism
A ternary system consisting of a surface-active powder (fluorinated silicone resin powder), fluorinated oil (perfluoropolymethylisopropyl ether, PFPE), and silicone oil (dimethylpolysiloxane, DMS) has been studied and found to exhibit multiple structural polymorphism in the mixed states. The mixed states were classified into seven different regions and ruled roughly by the composition ratio of the powder and the PFPE. For PFPE compositions which exceed the absorption limit of the powder, the continuous phase was PFPE and four mixed states were observed, that is, a network-structured state, an ON emulsion state (O/F emulsion means a DMS-in-PFPE type emulsion), an ON emulsion state with excess PFPE and DMS phases, and a powder dispersion state with excess PFPE and DMS phases. On the other hand, in the region in which the amount of PFPE was less than the absorption limit of the powder the continuous phase was DMS and three mixed states, powdery state, granular state, and dispersion state containing the PFPE/powder mixture, were observed. Such self-assemblies of the resin powder and the multiple structural polymorphism were observed only when the degree of fluorination on the silicone resin powder was balanced. According to the results of X-ray photoelectron spectroscopy and sinking time measurements, the wettabilities of powder with PFPE and DMS are the governing factors to control the mixed state. The powder is dispersed in DMS or PFPE when it has too high an affinity to DMS or PFPE,and the O/F type emulsion is formed when it has balanced affinity to both oils. The multiple polymorphism of the mixed state is interesting not only from the scientific point of view but also for applications in the chemical and cosmetic industries.