Abstract
Water at normal conditions is a fluid thermodynamically close to the liquid-vapor phase coexistence and features a large surface tension. This combination can lead to interesting capillary phenomena on microscopic scales. Explicit water molecular dynamics (MD) computer simulations of hydrophobic solutes, for instance, give evidence of capillary evaporation on nanometer scales, i.e., the formation of nanometer-sized vapor bubbles (nanobubbles) between confining hydrophobic surfaces. This phenomenon has been exemplified for solutes with varying complexity, e.g., paraffin plates, coarse-grained homopolymers, biological and solid-state channels, and atomistically resolved proteins. It has been argued that nanobubbles strongly impact interactions in nanofluidic devices, translocation processes, and even in protein stability, function, and folding. As large-scale MD simulations are computationally expensive, the efficient multiscale modeling of nanobubbles and the prediction of their stability poses a formidable task to the'nanophysical' community. Recently, we have presented a conceptually novel and versatile implicit solvent model, namely, the variational implicit solvent model (VISM), which is based on a geometric energy functional. As reviewed here, first solvation studies of simple hydrophobic solutes using VISM coupled with the numerical level-set scheme show promising results, and, in particular, capture nanobubble formation and its subtle competition to local energetic potentials in hydrophobic confinement.
Highlights
The modeling and description of aqueous properties such as water structure, dynamics, and eventually thermodynamics are obviously of fundamental interest as water is the most abundant fluid on our planet, and governs biological evolution and geomechanical and atmospheric phenomena (Ball 1999)
Given the large surface tension of water, we find for the nanometer plates a large mutual hydrophobic attraction of G γ nm2 20kBT in agreement with atomistic computer simulations (Koishi et al 2004)
In this paper we review selected examples in the explicit and implicit modeling of nanobubbles in hydrophobic confinement and present a method – the variational implicit solvent model (VISM) – which is potentially capable of predicting nanobubbles in arbitrary confinement without any a priori assumption of the interface location
Summary
The theoretical modeling of water can be performed by explicitly resolving its atomic and molecular degrees of freedom by quantum-mechanical (QM) methods (Jensen 2006) or classical molecular dynamics (MD) computer simulations (Allen and Tildesley 1987, Frenkel and Smit 1996). The phenomenon of nanobubble formation in hydrophobic confinement has been confirmed in the last decade by a large number of explicit computer simulations of, e.g., plate-like solutes (Chandler 2005), homopolymers (ten Wolde and Chandler 2002), or channels and pores (Beckstein et al 2001, Dzubiella and Hansen 2004b, 2005, Rasaiah et al 2008, Vaitheesvaran et al 2004). In this paper we review selected examples in the explicit and implicit modeling of nanobubbles in hydrophobic confinement and present a method – the variational implicit solvent model (VISM) – which is potentially capable of predicting nanobubbles in arbitrary confinement without any a priori assumption of the interface location It is the first implicit water model that can predict nanobubble formation as it is based on a geometric minimization procedure and does not need the interface location in the confining system as input, as used by conventional methods. Parts of this paper have been published elsewhere (Cheng et al 2007, Dzubiella and Hansen 2003, 2004a, b, 2005, Dzubiella et al 2006a, b)
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