Ultrasonication, effect, flocculation

Attempts have also been made to include the effects of droplet flocculation in ultrasonic scattering theory [63]. 

The attenuation coefficient in the flocculated emulsion is lower at low frequencies and higher at high frequencies than that of the nonflocculated emulsions. The decrease in attenuation at low frequencies on flocculation as a result of the thermal overlap effects mentioned earlier, whereas the increase at high frequencies results from increased scattering of ultrasound by the floes. The same ultrasonic spectroscopy technique has been used to study the disruption of floes in a shear field (38). As the emulsions are exposed to higher shear rates the floes become disrupted and their attenuation spectra become closer to that of nonflocculated droplets. 

The colloidal properties of emulsions are responsible for the quality of many foods. Ultrasound is sensitive to most of the properties of interest and can be used as both a research and a process-control tool by food scientists. As a research tool, ultrasonic measurements are particularly powerfid as they can be used to generate information not readily available by other methods - importantly, physical state, particle size, concentration, and flocculation in concentrated and optically opaque emulsions. In a process environment, ultrasonic measurements can be effected noninvasively in process lines and are therefore compatible with the stringent hygiene and cleaning requirements of food production. 

Currently, suspensions prepared from micronised active substances are the only marketed dehvery system for nebulisation of poorly water soluble substances such as steroids and cyclosporine [53]. Several problems are inherent in nebulising micro-suspensions and they vary from non-optimised lung deposition for the active substance to heterodispersity of the active substance concentration in the aerosol droplets and poor compatibility with different types of nebulisers, particularly ultrasonic devices. Suspensions may also have poor stability and the two components (solid and liquid) tend to separate with time within the formulation by sedimentation or flocculation, depending on the particle density relative to that of the liquid. Several jet nebulisers can deliver suspensions quite effectively, even independently of the primary particle size [54], but ultrasonic devices may convert primarily the continuous phase into aerosol whereas vibrating mesh inhalers can be blocked by particles being larger than the pore diameter of the membrane. 

Another field of an advanced separation is the flocculation and efficient dewatering of ultrfine coal (>150 pm) with a polymer blend (tmmodified and sonicated flocculant) as dual system [31]. The authors proved that ultrasonic conditioning may be an effective alternative for a dual system in which two different flocculants are used. 

Below we describe the use of the ultrasonic monitor to detect creaming in a polydisperse concentrated emulsion, and to characterise flocculation from the creaming behaviour. The effects of added polymers on the flocculation and creaming processes are also described. 

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