Plasmonic Bubbles in n-Alkanes

In this paper, we study the formation of microbubbles upon the irradiation of an array of plasmonic Au nanoparticles with a laser in n-alkanes (C_nH_2n+2, with n = 5-10). Two different phases in the evolution of the bubbles can be distinguished. In the first phase, which occurs after a delay time δ_d of about 100 μs, an explosive microbubble is formed, reaching a diameter in the range from 10 to 100 μm. The exact size of this explosive microbubble barely depends on the carbon chain length of the alkane but more so on the laser power P_l. With increasing laser power, the delay time prior to bubble nucleation as well as the size of the microbubble both decrease. In the second phase, which sets in right after the collapse of the explosive microbubble, a new bubble forms and starts growing due to the vaporization of the surrounding liquid, which is highly gas-rich. The final bubble size in this second phase strongly depends on the alkane chain length; namely, it increases with a decreasing number of carbon atoms. Our results have important implications for using plasmonic heating to control chemical reactions in organic solvents.