Ultrasound assisted generation of foam

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Abstract

Foams represent an important class of structured liquids of relevance to a wide range of industries. Their quality is mostly determined by their complex cellular structure, which defines primarily their texture and to a large extent their rheology and stability, The foam structure is influenced not only by the formulation used but also crucially by the production process adopted, hence the need for production techniques that can assist in the generation of foams with controlled structures. The ability of high-intensity ultrasound waves to influence the mean bubble size and texture homogeneity of foam generated pneumatically has been investigated. An ultrasound probe located near the pneumatic foam generator and operating at a fixed frequency produced significant changes in the foam bubble size and foam homogeneity. Under certain conditions, foam exhibited a smaller bubble size and a narrower bubble-size distribution. Such enhanced homogeneity in texture is highly desirable to reduce the presence of aesthetically unattractive large cavities and to reduce the destabilizing effects of coarsening or Ostwald ripening, i.e., the growth of large gas bubbles at the expense of smaller ones due to gas diffusion driven by the higher Laplace pressure of the gas in the smaller cells. This enhanced stability was reflected in a slower rate of foam collapse and, hence, a longer foam lifetime. These effects are demonstrated for foams with a wide range of formulations.

Details

Original languageEnglish
Pages (from-to)3312-3320
Number of pages9
JournalIndustrial & Engineering Chemistry Research
Volume44
Issue number9
Publication statusPublished - 27 Apr 2005