Ultrasonic homogeniser

Ultrasound is known to generate extremely fine emulsions from mixtures of immiscible liquids. Ultrasonic homogenisation has been used for many years in the food industry for the production of tomato sauce, mayormaise and other similar blended items. In chemistry such extremely fine emulsions provide enormous interfacial contact areas between immiscible liquids and thus the potential for greater reaction between the phases. This can be particularly beneficial in phase transfer catalysis. 

Only a selection of commercially available mixing equipment has been described here. Indeed, the devices described all exist in a variety of configurations. In a ition, there are many items of equipment based on altogether different principles typical examples include jet mixers, in-line dynamic mixers, mills, valve homogenisers, ultrasonic homogenisers, etc. These, as well as many other types, have been discussed by Harnby et alp-K Oldshue and Nagata ... 

It is liquid-liquid reactions involving phase transfer catalysts which generally benefit from the use of ultrasound. Sonication produces homogenisation - i. e. very fine emulsions - which greatly increase the reactive interfacial area and allows faster reaction at lower temperatures. Davidson has reported an example of this with the ultrasonically enhanced saponification of wool waxes by aqueous sodium hydroxide using tetra n-heptyl ammonium bromide as a PTC [124]. 

Homogenisation method none mechanical or ultrasonic none... 

A laboratory-built Wilhelmy film balance was used to determine the U-A isotherms of monoparticulate layers at 23 1 °C ambient temperature. The sols used for spreading were prepared by diluting the silica suspensions with chloroform (1 vol alcosol and 2 vol chloroform) this was then homogenised in an ultrasonic bath for 10 min. An appropriate amount of sol was spread on the surface of the water in the film balance. After evaporation of the spreading liquid, the 11- 4 isotherms were obtained at a rate of 3.35 cm/min of the moving barrier (corresponding to 33.5 cm /min). The film balance experiments were repeated five times to assess the reproducibility. 

Fig. 6.18. Average droplet diameters obtained in various emulsifying machines as a function of energy consumption p. The number near the curves denotes the viscosity ratio A the results for the homogeniser are for = 0.04 (solid line) and = 0.3 (broken line) ( us = ultrasonic generator).

Their preparation requires, in many cases, special application techniques such as the use of high-pressure homogenisers as well as ultrasonics. Such equipment (such as the Microfluidiser) has became available only in recent years. 

SEM analysis of the AlCeOs nanoparticles (Aldrich, 99%) showed them to have diameters varying from a few nanometres (<25 nm) to 300 nm. They were added to a hexamethyldisiloxane (HMDSO > 98% grade) solution, purchased from Aldrich. The concentration of nanoparticles was calculated in weight percent. The solutions were homogenised by ultrasonic stirring at room temperature for 30 min. 

The fust pre-treatment procedure for non-aqueous formulations is represented by the homogenisation of the sample that is obtained by stirring, ultrasonication or centrifugation and filtration. Sometimes, heating or cooling processes are employed, to favour substance transport between phases or to induce precipitation. 

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