Nucleation Of Liquid Droplets Research Articles

Nucleation and growth of droplets at a liquid-gas interface

The nucleation of liquid droplets at a liquid-gas interface from a saturated vapor in the gas phase, as well as the droplet growth after the nucleation are studied. These two processes determine the formation of a regular hexagonal array of drops on the surface of an evaporating film of polymer solution that is used for the fabrication of polymer membranes with a regular microporous structure. The free-energy barrier for the nucleation of a droplet at a liquid-gas interface is found as a function of the droplet radius and the contact angles, and the critical nucleation radius is computed. It is shown that the heterogeneous nucleation is thermodynamically more preferable than the homogeneous one. The role of the line tension between the phases is also estimated. Further growth of a droplet nucleated at the liquid-gas interface is studied. Two growth mechanisms are considered: by the vapor diffusion flux from the gas phase and by the surface diffusion of the vapor molecules adsorbed at the liquid-gas interface outside the droplet. Two cases, corresponding to unsaturated and saturated condensation, are considered. The droplet growth is described by a free-boundary problem which is solved analytically and numerically. The droplet growth exponents at different stages of growth are found.

On the Becker/Döring Theory of Nucleation of Liquid Droplets in Solids

Nucleation of liquid precipitates in semi-insulating GaAs is accompanied by deviatoric stresses resulting from the liquid/solid misfit. A competition of surface tension and stress deviators at the interface determines the nucleation barrier.

Nucleation through a Double Barrier on a Chemically Patterned Substrate

We study nucleation of liquid droplets from a one-component vapor phase on a planar lyophobic substrate, δ, patterned with a number of lyophilic (easily wettable) circular domains, γ. The wettabilities of the lyophilic domains and the lyophobic substrate are characterized by contact angles θγ and θδ, respectively. Depending on the supersaturation of the vapor and on the contact angles θγ and θδ, nucleation of a droplet on one of these circular domains proceeds through a free energy barrier with one or two maxima (a double barrier). Barriers with two maxima occur for intermediate values of the supersaturation. In terms of the dimensionless supersaturation Δ, this intermediate regime is given by sin θγ < Δ < sin θδ for θγ < θδ < π/2 and by sin θγ < Δ < 1 for θγ < π/2 < θδ. We extend classical nucleation theory to account for the kinetics of nucleation through a double barrier and apply this extension to the nucleation of droplets on lyophilic circular domains.

Nanobubbles: the big picture

Nanobubbles, whose existence on hydrophobic surfaces immersed in water has previously been inferred from measurements of long-ranged attractions between such surfaces, are directly imaged by tapping mode atomic force microscopy. It is found that the nanobubbles cover the surfaces in an irregular, interconnected or close-packed network whose morphology is dependent on pH and whose lifetimes are at least of the order of hours. Their height is of the order of 30 nm and their radius of curvature is of the order of 100– 300 nm . It appears that the nanobubbles form from a solution supersaturated with air. A thermodynamic and statistical mechanical analysis of the homogeneous nucleation of liquid droplets from a supersaturated vapour shows that although a single droplet can be in equilibrium with a finite volume of gas, for a gas reservoir the equilibrium state is represented by a single macroscopic droplet, which grows by collisions and by Ostwald ripening. It is concluded that the electric double-layer repulsion between neighbouring nanobubbles on the hydrophobic surface plays a role in their stabilisation.

The fundamental equations of gas-droplet multiphase flow

This paper describes the derivation of an equation set for the multiphase flow of small polydispersed liquid droplets in a continuous gas-phase consisting of either a pure vapour (of the same chemical species as the liquid droplets) or a mixture of pure vapour and an inert gas. Some difficulties of previous formulations are resolved by more judicious definitions of the interphase transfer terms. The analysis includes a consistent model to represent the surface energy and entropy of the liquid droplets. Surface effects are normally neglected but must be included if consistency is to be maintained with droplet growth models in which the droplet temperature depends on its radius due to the effects of capillarity. A derivation of the equation for the rate of entropy creation due to departures from equilibrium is also presented. Entropy production in non-nucleating flows can be represented by precisely four terms, three of which are associated individually with the interphase transfer of mass, momentum and energy. The fourth term represents the entropy change due to the homogeneous nucleation of liquid droplets from the vapour and is in exact agreement with the results of classical nucleation theory. The form of the entropy creation equation allows an interpretation using the methods of linear irreversible thermodynamics and indicates that some mathematical models of droplet growth in common use, derived on an informal basis, may not be physically realistic in certain circumstances.

Radiation-induced nucleation in superheated liquid droplet neutron detectors

Superheated liquid droplet (“bubble”) dosimeters are relatively new devices which utilize the nucleation of liquid droplets to detect neutrons. A theoretical model was developed to predict the response of such detectors to both polyenergetic and monoenergetic thermal neutron fluxes. Experiments were conducted with spontaneous fission neutron sources as well as purely thermal neutrons at the National Institute of Standards and Technology, confirming the model. Additionally, an inhibition temperature was predicted, below which no response to thermal neutrons is expected. Data was obtained to verify this prediction.

Homogeneous Nucleation and Growth of Ethanol Drops in Supersonic Flow

Condensation of ethanol by homogeneous nucleation of liquid droplets has been studied in a supersonic nozzle. Continuous static pressure measurements on the nozzle centerline and light scattering measurements permit the condensation process to be resolved in detail for comparison with theory. Nucleation rates found in the present work are in general agreement with previous results obtained in diffusion and expansion cloud chambers. It is seen that the predictions of the classical theory of homogeneous nucleation or that of the statistical mechanical theory with the assumptions of Dunning roughly agree with the experimental results. Various terms entering different versions of nucleation theory are given quantitatively. The pressure variations in the flow found beyond the onset point of condensation are used to study droplet growth processes. It is shown that a simple kinetic growth law with a constant mass condensation coefficient describes the condensation process well.