Abstract
Molecular dynamics is used to investigate the thermocapillary motion of a water nanodroplet suspended in benzene subjected to a constant temperature gradient. This framework lets us identify the average behavior of the fluid particles by revealing their mean evolution. We connect such statistics to the behavior of the temporally evolving nanodroplet, thereby providing a microphysical foundation to existing macroscopic models that rely on the assumption of continuum. It is shown that, despite the significant Brownian effects, the droplet exhibits the macrophysical expected behavior, i.e., it migrates toward the direction of the imposed temperature gradient. Thermophoretic effects are negligible and the functional relationships involved in such a process well resemble those of available analytical results. Additionally, we provide molecular dynamics calculations of the viscosity, thermal conductivity, and interfacial tension of benzene [using the Optimized Potentials for Liquid Simulations—All Atom (OPLSAA) molecular model] and water using the Transferable Intermolecular Potential with 4 Points (TIP4P) model at different temperatures and pressures. These findings will serve as a good reference for future simulations of similar molecular models.
Highlights
Surface-tension-driven flows, called Marangoni convection after the Italian physicist Carlo Giuseppe Matteo Marangoni[1], refer to convective effects generated by a non-uniform distribution of surface tension along the boundary separating two fluids
Relevant examples range from the synthesis of metal alloys, microfluidics[13,14,15,16,17,18], manipulation of particles[19,20], combustion[21] and nano-systems[22] to the production of drugs and medicines and other relevant biotechnological applications
We present the calculations of the thermodynamic properties that are relevant to this study
Summary
Surface-tension-driven flows, called Marangoni convection after the Italian physicist Carlo Giuseppe Matteo Marangoni[1], refer to convective effects generated by a non-uniform distribution of surface tension along the boundary separating two fluids (e.g., a liquid and a gas or two immiscible or partially miscible liquids, see, e.g., Gaponenko et al 2, Shevtsova et al 3). This non-uniformity can be caused by different possible root causes, such as active compounds at the interface (e.g., surfactants4,5); solvent evaporation (leading to a variation of solute concentration at the interface),[6] or temperature gradients[7,8]. Such symmetry can be broken either as a result of a bifurcation, i.e., an instability able to make an initially isotropic state unstable,[32,33] or due to the presence of an imposed (“external”) gradient of concentration or temperature
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