Spreading over heterogeneous surfaces is an important part of many natural and technological processes, including welding, soldering and composite material production. In [1] we studied spreading of simple (Lennard-Jones) and polymer nanosized droplets over structured (heterogeneous) solid substrates using the isothermal molecular dynamics. Three types of modeling substrates with mesoscopic nanosized heterogeneities have been used: stripped surfaces, high-energy surfaces with regularly quadratic low-energy inclusions and low-energy ones with quadratic high-energy inclusions. It has been shown that spreading kinetics and final droplet configurations may be greatly influenced by the mesoscopic structure of the substrate. It has been also found that the macroscopic Cassie law is not always qualitatively satisfied for substrates with mesoscopic heterogeneities. In the present presentation a special emphasis is made on simplest but basic case of striped surfaces. This case reproduces, to a greater or less extent, the case of unidimensional spreading: high energy stripes play role of grooves bounded by neighboring low energy stripes. Usually [2] the case when the droplet size is greater or equal to the stripe width has been investigated. Respectively, the initial droplet is located over one or several high-energy stripes. In [3] we studied a more interesting, in our view, case when a spherical droplet is put over the gap between two neighboring high-energy stripes. Such a modeling system demonstrates a bifurcation behavior: in dependence on values of some critical parameters the droplet in question forms a bridge between neighboring high-energy stripes. In [3] the modeling system under consideration was interpreted in terms of the soldering of neighboring conductive ways of a nanosized bus, i.e. the bus with the way width of about 1 nm, was simulated using the isothermal molecular dynamics. Conductive ways and dielectric gaps between them were reproduced by a heterogeneous surface with high- and low-energy stripes, respectively. The role of main controlling parameters (the solder droplet size, the width of the dielectric gap and others) was investigated. In [3] our investigation was restricted by using the Lennard-Jones model of the interatomic interaction. In this work we present our recent results on molecular dynamics of the metal nanodroplets spreading over stripes surfaces. The interatomic interaction in the droplet itself and the droplet-substrate interaction were described by the tight-binding many body potential [4]. Some specific features of the spreading behavior are revealed in comparison with Lennard-Jones systems.
Acknowledgments
Financial support of Ministry for Education and Science of Russian Federation is acknowledged (grant program ‘Scientific and pedagogical stuff of the innovation Russia, 2009-2013’).
References :
1. V.M. Samsonov et. al., Surface Science, 2003, 532-535, 560-566
2. G.S. Grest, D.R. Heine and E.B. Webb III, Langmur, 2006, 22, 4745-4749.
3. V.M. Samsonov, D.G. Zykov, Adhesion of melt and soldering of materials. Kiev, Nauk Dumka, 2009, 42, 54-62.
4. F. Cleri, V. Rosato, Phys. Rev., 1993, 48, 1, 22-33.