Characterisation of flow behaviour and velocity induced by ultrasound using particle image velocimetry (PIV): Effect of fluid rheology, acoustic intensity and transducer tip size.

Acoustic streaming phenomena of ultrasound propagation through liquid media was investigated experimentally employing particle image velocimetry (PIV). Parameters associated with the ultrasonic processor of ultrasonic amplitude (i.e., acoustic power) and transducer tip diameter (i.e., surface area), as well as, fluid rheology (i.e., water, glycerol solution and CMC solution), were studied for their effects on overall flow behaviour and fluid velocity. PIV yielded velocity gradient maps, demonstrating the acoustic streaming phenomena of ultrasound and its associated flow behaviour as a function of ultrasonic amplitude and fluid rheology, whereby increasing amplitude allowed for greater penetration of the acoustic-beam through the bulk of the fluid, and increasing fluid rheology yielded the converse effect. Moreover, upon impingement of the acoustic-beam with the base of vessel, vortex formation occurred, yielding a recirculation pattern. The maximum observed fluid velocities for water, glycerol solution and CMC solution were 0.329 m s-1, 0.423 m s-1, and 0.304 m s-1, respectively (large diameter sonotrode tip for an ultrasonic amplitude of 80%). Furthermore, shear rates were attained (maximum values of 24.25 s-1), and Reynolds numbers were determined in order to assess the degree of turbulence as a function of investigated parameters.

Dissolution of lamellar phases.

Dissolution of surfactant liquid crystals is an important process both at the manufacturing stage of surfactant based formulated products and during their use. Dissipative particle dynamics simulations were employed to study the production of surfactant-oil-water systems under both temperature and water quenches. Upon the dissolution of a high concentration lamellar phase surfactant, wormlike micelles are formed, which differ from the spherical micelles produced at the same concentration with a temperature quench. The surfactant molecules have a tendency to remain within their initially formed lamellar phase sheets and just rearrange into wormlike micelles. When a hydrophobic additive (oil) is added to the initial system, longer cylindrical micelles are formed, with the creation of some spherical micelles under dissolution. These micelles detach from the long cylinders as a result of their natural oscillations.