Direct Observation of Flocculation/Coalescence of Metastable Oil Droplets in Surfactant-free Oil/Water Emulsion by Freeze-Fracture Electron Microscopy

Abstract

Direct imaging of flocculation/coalescence in surfactant-free oil/water emulsion was achieved by freeze-fracture electron microscopy (FFEM) on benzene oil droplets ultrasonically dispersed in water. Immediately after sonication, spherical droplets with diameters at 30−100 nm (S class) and aggregates consisting of S class droplets at 200−500 nm (M class) were observed. An hour later, we were able to obtain FFEM images, in which a number of S class droplets in flocculation coalesced into larger droplets. Additionally, two droplets of M class coalesced easily when these droplets were in contact with each other. These results support that M and L (≥1000 nm) class droplets are formed through flocculation of S class droplets and coalescence of M class droplets, respectively.

Soft Liquid Phase Adsorption for Fabrication of Organic Semiconductor Films on Wettability Patterned Surfaces

“…Figure 2b shows a photograph of a toluene/water emulsion prepared by adding a toluene solution of MDMO-PPV to water, followed by ultrasonication. Orange-colored emulsions were formed, and the size of the toluene droplets was estimated to be on the order of several micrometers by dynamic light scattering 22 . The emulsions were stable for several hours, which indicated that the emulsions could be used for the fabrication of MDMO-PPV films on the wettability-patterned substrates.…”

An Analysis on Multi-Step-Growth of Oil Droplets Dispersed in Water

“…2 (10). The model was supported by a direct observation of flocks and droplets with such sizes with a freezefracture electron microscope (11).…”

Nanoemulsion stability: Experimental evaluation of the flocculation rate from turbidity measurements

“…Sakai et al [69] studied the evolution of alkane-in-water nanoemulsions (R = 30 nm, φ = 2 ×10 −4 , where φ is the volume fraction of oil) in the absence of surfactants. According to the theory of Lifshitz, Slyozov and Wagner (LSW theory) [70,71], the Ostwald ripening rate (dR 3 /dt) is proportional to the solubility of the oil, and the interfacial tension of the drops.…”