Abstract
Investigation on the mechanism of impact-contact occurred at multiphase interface is of great importance in technique control of mechanical polishing as it is the basic dynamic process connected with mass transfer and interfacial pressure. Classical continuum mechanics is not fit for study the physical essence of complex dynamic behavior in the impact-spreading at nano length scale because of the small thickness of fluid film and the discrete property of surface morphology. Molecular dynamics method has already been proved to be one of the most efficient toolkit on atomic scale discrete phenomenon and thus being employed in this research to study the complex mechanism of nano-scale impact-spreading. The study shows that the liquid film behaves like a stretched membrane under the unbalanced forces and the real traverse spreading is an anisotropic process resulted by the anisotropic surface structure which also influences the nonuniform distribution of film. The result justifies that boundary lubrication at the interface is resulted by poor spreading behavior on rough surface and will affect the transportation of abrasive particle and materials removal rate. The results also justify that the mechanical similarity can be difficult to hold because of the complexity of surface texture (rough surface) and the different contour profiles resulted by random movement of molecule. Furthermore, energy distribution shows that physical adsorption plays an important role in the impact-contact process which is also justified by the adsorption structure of water. With the increasing of impact velocity, part of outer molecules breaks away the constraints generated by the surface tension and forming a free-state water layer.
Highlights
The impact-contact dynamic behavior of single and clouds of drops on solid surface has been studied for over a century because of the great scientific interest and due to its relevance in industrial applications as diverse as spray coating, spray painting, inkjet printing, fuel injection, soil erosioPn due to rain drop impact: F Heslot et al.[1] found that the final stage of spreading is not a pancake but rather is a twodimensional gas; PJ Smith et al.[2] investigated the track of organometallic ink spreading at room temperature; T Mao et al.[3] studied the spread and rebound of liquid droplets on flat surface using CCD camera and found that the maximum spread has intense relationship with
Advances in Mechanical Engineering liquid viscosity; YY Yan[4] and M Voue and J De Coninck[5] studied the spreading problems at different scales; H Gau et al.[6] studied the liquid morphology on different structured surfaces; H Dong et al.[7] developed an apparatus for visualizing the drop formation and impaction on substrate; P Lenz and R Lipowsky.[8] found that the morphology of wetting layers on imprinted surface was determined by the geometry of the underlying surface domain; F Heslot et al.[9] studied the influence of surface energy on the profiles of drop on the substrate; the multibody contact-sliding and the dynamic evolvement mechanism at the interface were investigated by the author.[10,11]
molecular dynamics (MD) is a computer simulation method for studying the physical property of ensemble composed of atoms and molecules; the atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamical evolution of the ensemble
Summary
The impact-contact dynamic behavior of single and clouds of drops on solid surface has been studied for over a century because of the great scientific interest and due to its relevance in industrial applications as diverse as spray coating, spray painting, inkjet printing, fuel injection, soil erosioPn due to rain drop impact: F Heslot et al.[1] found that the final stage of spreading is not a pancake but rather is a twodimensional gas; PJ Smith et al.[2] investigated the track of organometallic ink spreading at room temperature; T Mao et al.[3] studied the spread and rebound of liquid droplets on flat surface using CCD camera and found that the maximum spread has intense relationship with. One of the most important research topic in polishing is the relation of the droplet diameter and its contact angle with spreading dynamics on rough surface. Most research on the dynamics of spontaneous drop spreading have been done by assuming ideal cases because of the complexity of influence of rough surface. Experiments justify that the spreading liquid consists of distinct monomolecular layers which advance across the solid with different velocities but not varying smoothly. Such films are too thin to be described by lubrication equations. We have been motivated thereby to conduct molecular dynamics (MD) simulations to investigate the spreading characteristics of nano-scale water-droplet on rough surface. The large-scale classical MD method is adopted in this work to investigate the dynamic process and gain insights into the atomistic scale multiphase process
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