Finite amplitude effects on drop levitation for material properties measurement

Abstract

The method of exciting shape oscillation of drops to extract material properties has a long history, which is most often coupled with the technique of acoustic levitation to achieve non-contact manipulation of the drop sample. We revisit this method with application to the inference of bulk shear viscosity and surface tension. The literature is replete with references to a “10% oscillation amplitude” as a sufficient condition for the application of Lamb's analytical expressions for the shape oscillations of viscous liquids. Our results show that even a 10% oscillation amplitude leads to dynamic effects which render Lamb's results inapplicable. By comparison with samples of known viscosity and surface tension, we illustrate the complicating finite-amplitude effects (mode-splitting and excess dissipation associated with vorticity) that can occur and then show that sufficiently small oscillations allow us to recover the correct material properties using Lamb's formula.

Shape oscillations of single blood drops: applications to human blood and sickle cell disease

“…When the modulation is turned off, the drop undergoes free-decay oscillations. The free-decay technique has been calibrated in our previous study for viscous liquids 44 . In this study we designed an assay that quantified the viscosity of whole blood versus hematocrit (Hct), the main factor affecting blood viscosity 45 .…”

“…In order to maintain very small oscillations (less than 0.5% oscillatory strain amplitude) we do not use the camera images for dynamic shape oscillation data. More detailed descriptions of this technique can be found in an earlier publication 44 . Figure 7(a) shows a levitated drop undergoing very large amplitude quadrupole mode shape oscillations for illustration.…”

Monitoring of blood coagulation with non‐contact drop oscillation rheometry

“…The semi‐infinite medium assumption is justified here because the radius of the droplets was typically two orders of magnitude larger than the amplitude of vibration. For the range of droplet radii studied (1‐1.5 mm), the oscillation amplitudes were typically observed to be <0.01 mm . We were not able to see this small oscillation amplitude with a camera.…”

“…Figure shows a blood drop levitated in the acoustic field and a schematic of the experiment setup. A more detailed description of the apparatus and method is given in may be found in Ansari Hosseinzadeh et al and Ansari Hosseinzadeh and Holt …”

“…A method allowing both non‐contact containment and manipulation in coagulation measurement was introduced by Holt et al This method, referred to as quasi‐static acoustic tweezing thromboelastometry (QATT), inferred changes in tensile elasticity (elastic modulus or firmness) of a coagulating drop of blood by employing imaging to measure its static deformation during acoustic levitation. Hosseinzadeh et al added an optical scattering diagnostic in order to measure the viscosity of normal and sickled blood. By optically measuring the dynamic shape oscillations of blood drops at small strain amplitudes, they employed longstanding theoretical formulations of drop oscillations to infer surface tension and viscosity.…”