School of Chemistry - Research Publications
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ItemMechanisms for the ultrasonic enhancement of dairy whey ultrafiltration(ELSEVIER SCIENCE BV, 2005-08-01)
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ItemThe use of ultrasonic cleaning for ultrafiltration membranes in the dairy industry(ELSEVIER SCIENCE BV, 2004-10)
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ItemMinimising oil droplet size using ultrasonic emulsification(ELSEVIER, 2009-08)The efficient production of nanoemulsions, with oil droplet sizes of less than 100nm would facilitate the inclusion of oil soluble bio-active agents into a range of water based foods. Small droplet sizes lead to transparent emulsions so that product appearance is not altered by the addition of an oil phase. In this paper, we demonstrate that it is possible to create remarkably small transparent O/W nanoemulsions with average diameters as low as 40nm from sunflower oil. This is achieved using ultrasound or high shear homogenization and a surfactant/co-surfactant/oil system that is well optimised. The minimum droplet size of 40nm, was only obtained when both droplet deformability (surfactant design) and the applied shear (equipment geometry) were optimal. The time required to achieve the minimum droplet size was also clearly affected by the equipment configuration. Results at atmospheric pressure fitted an expected exponential relationship with the total energy density. However, we found that this relationship changes when an overpressure of up to 400kPa is applied to the sonication vessel, leading to more efficient emulsion production. Oil stability is unaffected by the sonication process.
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ItemEffect of surfactants on the rate of growth of an air bubble by rectified diffusion(AMER CHEMICAL SOC, 2005-08-04)The rectified diffusion growth of a single air bubble levitated in an acoustic field (frequency = 22.35 kHz) in water and in aqueous solutions containing surfactants (sodium dodecyl sulfate and sodium dodecylbenzene sulfonate) was investigated. As reported by Crum (J. Acoust. Soc. Am. 1980, 68, 203), the presence of surfactants at the bubble/liquid interface enhanced the growth rate of the bubble by rectified diffusion. It is suggested in this paper that in addition to the effect of surfactants on the surface tension and interfacial resistance to mass transfer, the effect of surface rheological properties may also contribute to the cause of the enhancement observed in the bubble growth rate.
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ItemDetermination of the size distribution of sonoluminescence bubbles in a pulsed acoustic field(AMER CHEMICAL SOC, 2005-12-07)A simple method is described for determining the size of sonoluminescence bubbles generated by acoustic cavitation. The change in the intensity of sonoluminescence, from 4 ms pulses of 515 kHz ultrasound, as a function of the "off" time between acoustic pulses, is the basis of the method. The bubble size determined in water was in the range of 2.8-3.7 mum.
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ItemThe dissolution of a stationary spherical bubble beneath a flat plate(PERGAMON-ELSEVIER SCIENCE LTD, 2006-12-01)