47
For agarose gels, the maximum radial stretch ratio is between 3 and 8. Lower concentrations of agarose have larger maximum radial stretch ratios and higher expansion-collapse oscillating frequencies.
To measure the sphericity of the cavitated bubble, we define the roundness of the bubble shape as:
Roundness:
Area
Perimeter
= p
4
2
which is shown in Fig. 8.2b–f for soft polyacrylamide, 0.5%, 1.0%, 2.5%, and 5.0% agaroses, respectively. The roundness
of circular shape is 1, while smaller roundness number implies serious nonspherical shape. Images of cavitated bubbles at
Fig. 8.1 Experimental setup
and schematic of inertial
microcavitation rheometry. A
single 6 ns, Q-switched
532 nm Nd:YAG laser pulse
of 1–10 mJ passes through a
beam expander to fill the back
aperture of an objective
mounted into an inverted
TI-Eclipse microscope, and
(inset, star) converges into a
cylindrical hydrogel sample.
Bright-field illumination is
supplied by a SILUX640 laser
illumination system. Bubble
images are recorded using a
Kirana high-speed camera.
(Image is modified based on
Estrada et al. [8])
Fig. 8.2 Experimentally measured laser-induced cavitation in polyacrylamide and agarose hydrogels. (a) Measured bubble radial stretch ratio λ
vs. normalized time t
* = t p ¥ / r r /R max . (b–f) Measured bubble “radius vs. time” and “shape roundness vs. time” curves in the cases of polyacrylamide, 0.5% agarose, 1% agarose, 2.5% agarose, and 5% agarose, respectively. (Vertical lines (i–vi) in (b–f) are selected time points where associated bubble image frames are shown in Fig. 8.3)
8 Dynamic Rugae Strain Localizations and Instabilities in Soft Viscoelastic Materials During Inertial Microcavitation
For agarose gels, the maximum radial stretch ratio is between 3 and 8. Lower concentrations of agarose have larger maximum radial stretch ratios and higher expansion-collapse oscillating frequencies.
To measure the sphericity of the cavitated bubble, we define the roundness of the bubble shape as:
Roundness:
Area
Perimeter
= p
4
2
which is shown in Fig. 8.2b–f for soft polyacrylamide, 0.5%, 1.0%, 2.5%, and 5.0% agaroses, respectively. The roundness
of circular shape is 1, while smaller roundness number implies serious nonspherical shape. Images of cavitated bubbles at
Fig. 8.1 Experimental setup
and schematic of inertial
microcavitation rheometry. A
single 6 ns, Q-switched
532 nm Nd:YAG laser pulse
of 1–10 mJ passes through a
beam expander to fill the back
aperture of an objective
mounted into an inverted
TI-Eclipse microscope, and
(inset, star) converges into a
cylindrical hydrogel sample.
Bright-field illumination is
supplied by a SILUX640 laser
illumination system. Bubble
images are recorded using a
Kirana high-speed camera.
(Image is modified based on
Estrada et al. [8])
Fig. 8.2 Experimentally measured laser-induced cavitation in polyacrylamide and agarose hydrogels. (a) Measured bubble radial stretch ratio λ
vs. normalized time t
* = t p ¥ / r r /R max . (b–f) Measured bubble “radius vs. time” and “shape roundness vs. time” curves in the cases of polyacrylamide, 0.5% agarose, 1% agarose, 2.5% agarose, and 5% agarose, respectively. (Vertical lines (i–vi) in (b–f) are selected time points where associated bubble image frames are shown in Fig. 8.3)
8 Dynamic Rugae Strain Localizations and Instabilities in Soft Viscoelastic Materials During Inertial Microcavitation