The Effect of Surface Tension and the Surface Plasmonic Resonance of Gold Nanoparticles on Cavitation Bubble Dynamics

The effects of surface tension and surface plasmonic resonance of gold nanoparticle colloidal solutions on laser induced cavitation bubbles have been investigated. High-speed photography was used to measure the diameter of the bubbles. The collapse time was obtained by spatial transmittance modulation method for bubbles formed in ethanol, deionized water and gold nanoparticle solutions. Water and ethanol were selected for their similar viscosity but difference in surface tension by more than a factor of three. An Nd:YAG laser of 6 ns was used with an attenuator to alter the energy. The optical breakdown threshold for plasma formation in these solutions was investigated. The differences can be attributed to the variation of infrared absorption between the liquids as well as the plasmonic properties of gold nanoparticles. The duration and the amplitude of the plasma were also studied. We observe that the cavitation bubbles in ethanol have longer lifetimes and grow larger in size than bubbles in water. Liquids with lower surface tension display lower resistance to deformation, therefore the bubbles grow larger. Similarly, bubbles in gold nanoparticles demonstrate larger diameter compared to ones formed in water, which is due to the plasmonic effect of these nanoparticles.