Abstract
Heterogeneous nucleation is the preferential means of formation of a new phase. Gas and vapor nucleation in fluids under confinement or at textured surfaces is central for many phenomena of technological relevance, such as bubble release, cavitation, and biological growth. Understanding and developing quantitative models for nucleation is the key to control how bubbles are formed and to exploit them in technological applications. An example is the in silico design of textured surfaces or particles with tailored nucleation properties. However, despite the fact that gas/vapor nucleation has been investigated for more than one century, many aspects still remain unclear and a quantitative theory is still lacking; this is especially true for heterogeneous systems with nanoscale corrugations, for which experiments are difficult. The objective of this focus article is analyzing the main results of the last 10-20 years in the field, selecting few representative works out of this impressive body of the literature, and highlighting the open theoretical questions. We start by introducing classical theories of nucleation in homogeneous and in simple heterogeneous systems and then discuss their extension to complex heterogeneous cases. Then we describe results from recent theories and computer simulations aimed at overcoming the limitations of the simpler theories by considering explicitly the diffuse nature of the interfaces, atomistic, kinetic, and inertial effects.
Highlights
The formation and evolution of vapor and gas bubbles in a liquid body is a phenomenon of vast fundamental and applicative interest
The main difference between DENSITY FUNCTIONAL THEORY (DFT) and cCNT results is quantitative, with the latter theory significantly overestimating the barrier when the spinodal is approached (Fig. 8(c)). This behavior is due to the fact that the critical nucleus shrinks in moving towards the spinodal conditions becoming of size comparable to the thickness of the diffuse interface, a phenomenon that cannot be captured in the capillarity approximation
We have considered theories and computer simulations of nucleation of vapor in confined systems and at textured surfaces
Summary
The formation and evolution of vapor and gas bubbles in a liquid body is a phenomenon of vast fundamental and applicative interest. II-IV present theories that can be considered a classical description of vapor nucleation or of its opposite phenomenon, in which gas is replaced by liquid They are based on the simple sharp interface model of the liquidvapor system and on the assumption that the transition takes place via a quasi-static process in which the volume of the vapor bubble is the observable monitoring of the state of the system. It is worth remarking that the assumptions on which any CNT theory, bulk, heterogeneous, and confined, is based on (quasi-static process, sharp interface model, volume of the vapor bubble as the order parameter) are rather general and are valid for other nucleation processes as well. Overall the relevance of the line tension in nanoscale heterogeneous nucleation can still be considered an open question deserving additional experimental, theoretical, and computational investigations
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