ABSTRACT The elasticity of Tetra‐PEG chemical gel deformed by the oscillation of a laser‐induced microbubble was obtained through comparison to a bubble dynamics model. An infrared nanosecond laser pulse was focused into the gel to nucleate a spherical microbubble whose subsequent free oscillation (at frequency of order ) was recorded using a high‐speed camera. The evolution of the bubble radius is found to be symmetric between the growth and shrinkage phases, suggesting that the gel structure is not damaged by finite‐amplitude oscillations of the bubble. The radius evolution in the first collapse phase (from the maximal to the minimal size) was compared with the Rayleigh–Plesset (RP) equation equipped with neo‐Hookean and quadratic Kelvin–Voigt (qKV) constitutive models, allowing for the determination of the shear modulus under high‐frequency deformation. When the maximum radius of the bubble is sufficiently small, the measured shear modulus agrees with values from previous conventional rheometer studies, indicating frequency‐independent behavior of the chemical gel above a certain deformation rate threshold. On the other hand, when the maximum radius exceeds a threshold, the neo‐Hookean model fails to capture the elastic response, and comparison with the RP equation with the qKV model, reveals pronounced stiffening under large deformation.
Zhao et al. (Thu,) studied this question.