Spinodal Theory: A Common Rupturing Mechanism in Spinodal Dewetting and Surface Directed Phase Separation (Some Technological Aspects: Spatial Correlations and the Significance of Dipole-Quadrupole Interaction in Spinodal Dewetting)

Hindawi Publishing Corporation Advances in Condensed Matter Physics Volume 2011, Article ID 526397, 14 pages doi:10.1155/2011/526397 Research Article Spinodal Theory: A Common Rupturing Mechanism in Spinodal Dewetting and Surface Directed Phase Separation (Some Technological Aspects: Spatial Correlations and the Significance of Dipole-Quadrupole Interaction in Spinodal Dewetting) Satya Pal Singh1, 2 1 Department of Physics and Electronics, Dr. R. M. L. Avadh University, Faizabad, UP 224001, India 2 Department of Applied Sciences, MMM Engineering College, Gorakhpur, UP 273010, India Correspondence should be addressed to Satya Pal Singh, Received 25 July 2010; Revised 11 January 2011; Accepted 11 February 2011 Academic Editor: Nigel Wilding Copyright © 2011 Satya Pal Singh. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The emerging structures in spinodal dewetting of thin nano films and spinodal decomposition of binary mixtures are found to be similar with certain differences attributed to the nonlinearities inherent in the wetting forces. This paper deals with the technological aspects of the spinodal processes by giving a brief account of the theory and to correlate the two phenomena termed as spinodal dewetting of thin nanofilms and surface-directed phase separation. The MC simulation micrographs at early stage of spinodal dewetting of a (linear) polymer film confined between two hard walls (using FENE potential between the beads on same chain and Morse potential between inter and intra chain beads) show similarities with surface-directed phase separation (using metropolis algorithm) in creation of holes. The spinodal dewetting is also criticized on the basis of global minimization of free energy emerging from dipole-quadrupole interactions. A novel molecular scale-driving mechanism coming from asymmetric interface formation in spinodal processes is also proposed. It can be believed that the modeling done with the films under confinement of two walls works as a classical mathematical ansatz to the dipole-quadrupole interaction coming from quantum origins and giving rise to lateral interactions in the process reflecting a colossal behavior in thin nano films though weak in nature. 1. Introduction Dewetting of thin films (<100 nm) have created great interest among physicists and chemists as they see this as new technique to produce nanodevices, for example, polymerbased nanosize organic devices such as nanoscale memory. The emerging structures at early stages in the spinodal dewetting of thin nanofilms in contact with a substrate has been found very much similar to those as in surface directed phase separation (SDPS) [1–4]. The MC simulation patterns in SDPS have shown close resemblance to phase separation followed by dewetting or wetting of one component of the polymer mixtures in contact with a substrate [5]. Thus, SDPS has found importance not only for the study of rupturing or pseudodewetting of spin domains (magnetic memory) but also in the study of the spinodal instabilities leading to dewetting of thin nanofilms or binary mixture of thin films on a surface. Spinodal dewetting of polymer surface by a thin polymer film give rise to patterns of remarkably well-aligned polymer lines with well-defined width and is controlled by the magnitude of the dispersion forces at the interface, which in turn can be varied by changing the thickness of the polymer substrate [6]. Such studies are helpful in understanding the adsorption properties of the (coated) substrates. It has been reported that patterns have shown significant dependence on the interaction of phases with the substrate [7], that is, chemical properties of the substrates. With the manifold developments in science and technology every year, the sizes of the applied devices are getting more and more compact, and thus the technologists are confronting more and more complications in the production of such devices. The problem comes in controlling the growth processes and in making these devices 2 stable. Several groups all over world are dedicated to the synthesis and investigation of functional materials, focusing on the novel size-dependent physics and chemistry that result when atoms and electrons are confined within nanoscale semiconductors and metal clusters. Remarkable variations have been observed in past decades in fundamental electrical, optical, and magnetic properties of functional materials as one progresses from an infinitely extended solid to small domain of material consisting of a countable number of atoms [8]. The cellular targets of versatile quantum-dot beads or polymer microarrays can be changed simply by changing their surface chemistry, and thus the surface must be tailored for different biological applications [9]. It is not easy finding a worthy successor to highly refined microchip technologies [10, 11]. Molecular-scale electronic devices and its biological counterparts are fast becoming a good bet. A controlled dewetting may be used in the synthesis of nanoscale structures, as G. Reiter at MaxPlanck Institute says that controlled dewetting of magnetized films may be used to make nanoscale memory [12]. The present microchips can be replaced by smarter nanochips in future. The researchers working in the area of dewetting of thin films see this area as a microscope for observing forces working at very small scale. Films formed by gold nanoparticle polyoctylthiophene blends exhibit fluorescence from the circular regions of the morphological structures. The dispersion of the circles can be a signature of the differences in the evaporation/dewetting processes of the two systems during the film formation resulting in the creation of local domains [13]. Wetting or growth has always been a focused area, but at saturation when sizes are getting compact, dewetting has developed a new interest in researchers. The tendency of thin films of liquids and solids to get ruptured or dewetted from surfaces challenges the ingenuity of the engineers and designers. An insulating glaze in a microelectronic chip may allow short-circuit of the film, as it breaks and can tease its manufacturers. Pierre Wiltzius of Lucent Tech. Bell Labs says, “Thin films often are finicky little beasts.” Dewetting/selfcleaning of the window glasses in multistory complexes, cars, and other transportation vehicles is always welcomed. Although self-cleaning surface have still got applications in household commodity sector and in biotechnology [14]. Thermal stability of thin polymer films is of importance for various technological applications like coatings and dielectric layers. Study of dewetting can help in understanding the adsorption properties of the (coated) surfaces [15] and a diversity of physical and biological thin film phenomena [4]. A brief introduction (...truncated)