Self-Assembly of Surface-Active Powder at the Interfaces of Selective Liquids. 1:  Multiple Structural Polymorphism

Abstract

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 O/F emulsion state (O/F emulsion means a DMS-in-PFPE type emulsion), an O/F 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.

Surface activity of solid particles with extremely rough surfaces

“…The solid particles are adsorbed at the interfaces and form self-assembled structures, i.e. emulsions, ball-like aggregates and foams, when the particles have suitable wettability to both liquids [3][4][5]. In recent years, some scientists have used the emulsions as a template of functional composite materials [6][7][8].…”

Preparation and Characterization of n-Alkane/Water Emulsion Stabilized by Cyclodextrin

“…The formation of Pickering emulsions is known to be related to the contact angle (q ow ) that the solid particle forms with the interface 11,12) . Binks et al investigated the relationship between q ow and oil-water interfacial tension (g ow ) by employing silica microparticles with different hydrophobicities and various oils 13) .…”

Formation and Characterization of Emulsions Using .BETA.-Cyclodextrin as an Emulsifier

“…The type of emulsion is governed by the contact angle (q ow ) which the solid particle makes with the interface. [9][10][11] That is to say, a solid particle of q ow Ͻ90°sta-bilizes O/W emulsion, and that of q ow Ͼ90°stabilizes W/O emulsion. Also, it is known that q ow varies with the oil-water interfacial tension (g ow ) of the compound used as the oil phase.…”