Water droplet excess free energy determined by cluster mitosis using guided molecular dynamics

Lau, Gabriel V.; Hunt, Patricia A.; Müller, Erich A.; Jackson, George; Ford, Ian J.

doi:10.1063/1.4935198

Cited by 17 publications

(14 citation statements)

References 45 publications

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“…Using γ lv for a flat interface could be inapropriate when dealing with curved drop surfaces. However, using a Tolman length of 1Å-larger than the values typically reported [36][37][38] -to correct for curvature effects only yields changes of less than 2 mN/m for the smallest drops considered. We therefore neglect any curvature effects in γ lv .…”

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confidence: 90%

Homogeneous Ice Nucleation Rate in Water Droplets

2018

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To predict the radiative forcing of clouds it is necessary to know the rate with which ice homogeneously nucleates in supercooled water. Such rate is often measured in drops to avoid the presence of impurities. At large supercooling small (nanoscopic) drops must be used to prevent simultaneous nucleation events. The pressure inside such drops is larger than the atmospheric one by virtue of the Laplace equation. In this work, we take into account such pressure raise in order to predict the nucleation rate in droplets using the TIP4P/Ice water model. We start from a recent estimate of the maximum drop size that can be used at each supercooling avoiding simultaneous nucleation events [Espinosa et al. J. Chem. Phys., 2016]. We then evaluate the pressure inside the drops with the Laplace equation. Finally, we obtain the rate as a function of the supercooling by interpolating our previous results for 1 and 2000 bar [Espinosa et al. Phys. Rev. Lett. 2016] using the Classical Nucleation Theory expression for the rate.This requires, in turn, interpolating the ice-water interfacial free energy and chemical potential difference. The TIP4P/Ice rate curve thus obtained is in good agreement with most droplet-based experiments. In particular, we find a good agreement with measurements performed using nanoscopic drops, that are currently under debate. The

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confidence: 90%

Homogeneous Ice Nucleation Rate in Water Droplets

2018

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“…The excess free energies of water droplets of different sizes have recently been calculated by means of a statistical mechanical approach at a temperature T = 300 K. 45,46 Considering that calculations using the TIP4P/2005 molecular model could successfully estimate the surface energy in agreement with experiments, 36 we use the calculations of Lau et al 46 to validate our model following the ensuing procedure: i) we deduce the values of λ by comparing the effective surface tension determined by our model, Eq. 24, with those obtained from statistical mechanics, and ii) use these results to calculate nucleation rates and compare them against experimental results at T = 300 K obtained by Brus et al.…”

Section: A Water Droplet Nucleationmentioning

confidence: 99%

“…Effective surface energy (γeff ) at different λ calculated by Eq. 24 at T = 300 K. ▲: Statistical mechanical simulations46 at cluster size of n = 3, 6, 12, 24, 48, 76, 96. Solid black curve shows the best fit to statistical mechanical simulations.…”

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confidence: 99%

Modelling the effect of acoustic waves on nucleation

Haqshenas

Ford

Saffari

2016

The Journal of Chemical Physics

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A phase transformation in a metastable phase can be affected when it is subjected to a high intensity ultrasound wave. In this study we determined the effect of oscillation in pressure and temperature on a phase transformation using the Gibbs droplet model in a generic format. The developed model is valid for both equilibrium and non-equilibrium clusters formed through a stationary or non-stationary process. We validated the underlying model by comparing the predicted kinetics of water droplet formation from the gas phase against experimental data in the absence of ultrasound. Our results demonstrated better agreement with experimental data in comparison with classical nucleation theory. Then, we determined the thermodynamics and kinetics of nucleation and the early stage of growth of clusters in an isothermal sonocrystallisation process. This new contribution shows that the effect of pressure on the kinetics of nucleation is cluster size-dependent in contrast to classical nucleation theory.

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“…We employ a reference initial tether strengthκ i of 0.09 kJ mol -1 Å -2 . This is small enough that the elevation in energy for a molecule at the edge of the cluster is less than k B T [23], and slight variations have been shown elsewhere [26] to have little effect on the extracted cluster free energy. We define κ iW = 2κ i m W /M W A and κ iA = 2κ i m A /M W A , where M W A = m W + m A .…”

Section: Determining the Free Energy Of Disassembly Of Binary CLmentioning

confidence: 96%

“…External forces are used to pull a cluster apart into its constituent molecules in a controlled or guided fashion. A variation, denoted cluster mitosis, has also been developed where a cluster is separated into two subclusters, again to characterise the change in free energy associated with the process [26]. The methods have been successfully tested against calculations of free energies, obtained by other techniques, for model argon and water clusters.…”

Section: Introductionmentioning

confidence: 99%

Free energy of formation of clusters of sulphuric acid and water molecules determined by guided disassembly

Parkinson

Lau

Ford

2016

Molecular Simulation

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We evaluate the grand potential of a cluster of two molecular species, equivalent to its free energy of formation from a binary vapour phase, using a nonequilibrium molecular dynamics technique where guide particles, each tethered to a molecule by a harmonic force, move apart to disassemble a cluster into its components. The mechanical work performed in an ensemble of trajectories is analysed using the Jarzynski equality to obtain a free energy of disassembly, a contribution to the cluster grand potential. We study clusters of sulphuric acid and water at 300 K, using a classical interaction scheme, and contrast two modes of guided disassembly. In one, the cluster is broken apart through simple pulling by the guide particles, but we find the trajectories tend to be mechanically irreversible. In the second approach, the guide motion and strength of tethering are modified in a way that prises the cluster apart, a procedure that seems more reversible. We construct a surface representing the cluster grand potential, and identify a critical cluster for droplet nucleation under given vapour conditions. We compare the equilibrium populations of clusters with calculations reported by Henschel et al. [J. Phys. Chem. A 118, 2599(2014] based on optimised quantum chemical structures.

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Water droplet excess free energy determined by cluster mitosis using guided molecular dynamics

Cited by 17 publications

References 45 publications

Homogeneous Ice Nucleation Rate in Water Droplets

Homogeneous Ice Nucleation Rate in Water Droplets

Modelling the effect of acoustic waves on nucleation

Free energy of formation of clusters of sulphuric acid and water molecules determined by guided disassembly

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