Measurement of dynamic surface tension by the oscillating droplet method

Determination of dynamic surface tension and viscosity of non-Newtonian fluids from drop oscillations

“…The initial oscillation amplitude, a 2 (0), is less than 10% of the drop radius for which a linear theory is expected to hold. 15,16 The surface tension and viscosity of the fluid were derived from Eqs. (2)- (4), respectively, on the assumption that they were invariant over the measured time interval.…”

“…One approach is to look at free-falling drop immediately after its formation from orifice. [11][12][13][14][15] Trinh et al 13 and Hiller and Kowalewski 14 studied freely oscillating drops with small oscillation amplitudes experimentally and validated the OD theory within the linear approximation for the fundamental mode. Stückrad et al used the OD method to determine the temporal development of the DST of heptanol-water solutions and interpreted the results by a diffusion-controlled adsorption mechanism.…”

“…Stückrad et al used the OD method to determine the temporal development of the DST of heptanol-water solutions and interpreted the results by a diffusion-controlled adsorption mechanism. 15 Becker et al experimentally and theoretically investigated the nonlinear dynamics of viscous droplets with large initial amplitudes of oscillation, exceeding 10% of the drop radius for the fundamental mode. They found that nonlinear effects were most evident for higher oscillation modes (l > 2) while the fundamental mode conformed to the linear theory even for initial amplitudes exceeding 50% of the drop radius.…”

Mixing with bubbles: a practical technology for use with portable microfluidic devices

“…At intermediate concentrations of surfactant, the device generated irregular bursts of bubbles (with a frequency of approximately 10 21 to 10 22 Hz, and with tens to hundreds of bubbles generated in a single burst), interrupted by pauses with typical intervals on the order of tens of seconds. We associate this behavior with dynamic surface tension effects: [35][36][37] as bubbles break off from the tip of the stream of gas, the concentration of surfactant on the tip is diminished and the value of interfacial tension increases, pulling the tip upstream-into the gas inlet channel-and reducing the rate of formation of bubbles. As liquid flows by the tip, surfactant molecules adsorb onto the interface, lower the capillary pressure and formation of bubbles starts again.…”

Experimental and Computational Methods Pertaining to Surface Tension of Pharmaceuticals

“…By adjusting the osciallation frequency, the liquid vibrates to forms a jet having a series of stationary waves which depends chiefly on the characteristics of the orifice, its position, wave number, rate of flow and the surface tension of the liquid (Chang and Franses, 1995;Defay and Pétré, 1962;Stückrad et al, 1993;Thomas and Potter, 1975 …”