Dynamics of gas bubbles in monolayers

Abstract

We present a study of the temporal evolution of a two-dimensional bubble pattern in the liquid-gas coexistence region of monolayers. Using fluorescence microscopy of pentadecanoic acid or dipalmitoyl phosphotidylcholine on the surface of water, we study the coarsening of the pattern for several days. Two different regimes appear, depending on the percentage of gas phase observed on the surface. At high gas coverage (∼75%), we observe ‘‘polygonal’’ gas bubbles separated by thin liquid lines like a two-dimensional soap froth. We confirm the results of Glazier and co-workers [J. A. Glazier, S. P. Gross, and J. Stavans, Phys. Rev. A 36, 306 (1987); J. Stavans and J. A. Glazier, Phys. Rev. Lett. 62, 1318 (1989)] on the nature of the asymptotic scaling states, but find a growth exponent α≊1.0 for the time evolution of the mean area. At intermediate gas coverage (∼50%), we observe weakly interacting ‘‘circular’’ gas bubbles, which grow at a slower rate with an exponent α≊0.6. This state does not reach a scaling regime: The probability distribution for bubble areas broadens continuously and develops a power law at late-stage. The pattern itself evolves toward a critical object. Also, secondary nucleation of tiny liquid droplets in the gas bubbles is observed. The relevance of long-range dipolar interactions is discussed.