Molecular dynamics study of nanobubbles in the equilibrium Lennard-Jones fluid

Abstract

We employ a model, in which the density fluctuations in a bulk liquid are represented as presence of the clusters of molecules with the lowered number of nearest neighbors (number of bonds). The nanobubble size distribution is calculated on the basis of a close analogy between the surface part of the work of formation for a cluster and for a nanobubble. The pre-exponential factor for this distribution is related to the fluid compressibility. Estimates made for different liquids show that it can be noticeably different from that adopted in the classical nucleation theory (CNT). Molecular dynamics (MD) simulation is performed for a liquid inside a macroscopic droplet of molecules interacting via the Lennard-Jones potential plus a long-range tail. The nanobubbles are identified by clusters of bond-deficient particles with the optimum number of bonds that provide the maximum nanobubble number density and maximum resolvable nanobubble equimolar size. The results of MD simulation are in qualitatively better agreement with proposed theory than with CNT.

Advanced dynamic-equilibrium model for a nanobubble and a micropancake on a hydrophobic or hydrophilic surface

“…Several hypotheses have been proposed to explain the surprisingly long lifetime of surface nanobubbles [14,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. * k.yasui@aist.go.jp One explanation is that the gas-water interface of a nanobubble is shielded by a layer of impermeable contamination [19].…”

“…It hinders diffusion of gases from a nanobubble, thereby increasing the lifetime. However, German et al [29] experimentally showed that gas transfer actually took place across the surface of a nanobubble on a soild surface by measuring the rotational fine structure of CO 2 in the IR spectrum when nanobubbles formed in air-saturated water were perfused with CO 2 -saturated water. In another experiment, the CO 2 gas inside nanobubbles quickly dissolved into the surrounding air-saturated water, while nanobubbles remained stable for hours although CO 2 nanobubbles on a solid surface shrank upon exposure to air-saturated water.…”

The cluster model of a hot dense vapor

“…In contrast, as the critical point is approached, both the models of atoms and dimers [Eq. (32) with the upper summation limit k = 2 instead of ∞] and of the lightest clusters disagree with the experimental data. However, even the model of arbitrary size clusters flaws in the neighborhood of the critical point (Fig.…”

“…Given the temperature dependences of the surface tension, 34 the saturation vapor pressure, 30 the liquid density, 35 and the equilibrium constant of the dimer formation 11,12 , we solve Eq. (31) to find λ = 2.98 from the best fit of the compressibility factor of cesium vapor at the saturation line (32) to the experimental compressibility factor for the temperature interval 950 K ≤ T ≤ 1600 K 7 (Fig. 7).…”

Time-dependent cavitation in a viscous fluid

“…While often destructive [2], cavitation also offers a remarkable glimpse into the world of elementary particles via the bubble chamber [3,4] and has a direct link to such puzzling phenomena as sonoluminescence [5] and, more generally, to sonochemistry [6]. Recent advances in molecular dynamics (MD) studies of cavitation in nonmetallic [7][8][9][10][11][12] and metallic [13,14] fluids can clarify the elusive properties of the smallest subnano bubbles which provide a key boundary condition for the classical-type nucleation-growth equations and alternatively can reveal situations where the classical approach has to be reassessed.…”