Preparation of Oleic Acid/Water Emulsions in Surfactant-Free Condition by Sequential Processing Using Midsonic−Megasonic Waves

Abstract

Emulsifying action of high-frequency acoustic waves was investigated on surfactant-free oleic acid/ water mixtures using megasonic irradiation (200 kHz and 1 MHz) in baths manufactured for precision cleaning. While the droplet size distribution was bimodal for single irradiation at 40 kHz or 1 MHz, a unimodal distribution was obtained at 200 kHz irradiation. The whole amount of dispersed oil was evaluated with the total organic carbon measurement. The largest dispersed amount was obtained for the 40 kHz treatment, while the amount was quite small for 200 kHz or 1 MHz treatment. Then, a tandem emulsification method was devised for oleic acid/water emulsion, in which the first irradiation was made at 40 kHz, followed by the second one at 200 kHz over varying exposure times. A primary peak appeared at 100 nm droplet size accompanying with a subpeak at 400 nm in the first dispersion. The latter population decreased with increase in exposure time in the second dispersion until it disappeared. This indicates that the large droplets are disrupted to form or release the smaller ones as a result of sonic acceleration. The averaged droplet size showed a preliminary increase before being stabilized within 2 days in the 40 kHz f 200 kHz and 40 kHz f 200 kHz f 1 MHz sequential processing. Contrary to a low stability for the emulsion obtained at 40 kHz exposure, the turbidity for these emulsions could be observed for 1-2 years. A slight rise in the ζ potential was noticed for the droplet at the early stage. These results demonstrate that sequential processing with megasonic waves has a high potential to improve characteristics of unstable emulsions in surfactant-free condition.

Suspension Polymerization of Styrene Monomer without Emulsifier and Initiator.

“…The generation of H and OH radicals was also confirmed in the present experimental setup (19). The radical polymerization of styrene was then conducted using these radical species generated from water by the ultrasonic irradiation.…”

“…Meanwhile, formation of radical species such as OH radical has been shown to occur on irradiating aqueous solution with high frequency ultrasonic waves (>200 kHz) (13)(14)(15)(16)(17)(18)(19).…”

Charge of water droplets in non-polar oils

“…The electrical generator, which is connected to the mains, converts the input electricity into an alternating electrical signal (ranging from 20 kHz to tens of MHz), which drives the transducer [64][65][66]. A transducer contains piezoelectric crystals, which, upon receiving the electrical signal, start to oscillate, causing the horn or probe to longitudinally expand and contract.…”

Nanoparticles and Nanoemulsions

“…The size of the droplets depends on the sonication time and the energy used (Anton et al, 2008;Ghosh et al, 2012). In fact, it is possible to form a nanoemulsion using megasonic irradiation (Kamogawa et al, 2004). The emulsion was sonicated at 40 kHz followed by a series of irradiation at 200 kHz and 1 MHz to form small droplets.…”