Surface instability films

The stability of flow in open channels has been investigated theoretically from a more macroscopic or hydraulic point of view by several workers (Cl7, D9, DIO, Dll, 14, J4, K16, V2). Most of these stability criteria are expressed in the form of a numerical value for the critical Froude number. Unfortunately, most of these treatments refer to flow in channels of very small slope, and, under these circumstances, surface instability usually commences in the turbulent regime. Hence, the results, which are based mainly on the Ch<5zy or Manning coefficient for turbulent flow, are not directly applicable in the case of thin film flow on steep surfaces, where the instability of laminar flow is usually in question. The values of the critical Froude numbers vary from 0.58 to 2.2, depending on the resistance coefficient used. Dressier and Pohle (Dll) have used a general resistance coefficient, and Benjamin (B5) showed that the results of such analyses are not basically incompatible with those of the more exact investigations based on the differential rather than the integral ( hydraulic ) equations of motion. The hydraulic treatment of the stability of laminar flow by Ishihara et al. (12) has been mentioned already. 

In addition, patterns created by surface instabilities can be used to pattern polymer films with a lateral resolution down to 100 nm [7]. Here, I summarize various possible approaches that show how instabilities that may take place during the manufacture of thin films can be harnessed to replicate surface patterns in a controlled fashion. Two different approaches are reviewed, together with possible applications (a) patterns that are formed by the demixing of a multi-component blend and (b) pattern formation by capillary instabilities. 

Electric fields A patterned top electrode generates a laterally inhomogeneous electric field [30], The replication of the electrode pattern is due to two effects. Since the time constant for the amplification of the surface instability scales with the fourth power of the plate spacing (Eq. (1.8)), the film becomes unstable first at locations where the electrode topography protrudes downward towards the polymer film. In a secondary process, the... 

THE PHYSICS OF ULTRATHIN SOLID-FLUID-SOLID FILMS FROM SURFACE INSTABILITIES TO ISOLATED POCKETS OF FLUID... 

Initially the van der Waals forces across the film drive undulation growth in these systems and cause the surface instability to occur. The growth is resisted by the elastic deformation of the solid capping layers, which also maintains the films structural integrity. Eventually, the solid capping layers locally meet and the fluid is ejected from these regions of the film to form isolated pockets of fluid. 

The Physics of Ultrathin Solid-Fluid-Solid Films From Surface Instabilities to Isolated Pockets of Fluid 217... 

Ultrasonic nozzles use a metal horn geometry to amplify a small peizoelectric vibration. These vibrations drive surface instabilities along a thin film and generate droplets of very uniform size, but at low flow rates. 

The dewetting rim is deformed by the morphological instability. The wave number of the deformation and the critical diameter of the dry patch depend upon the initial film thickness. The rim instability and the origin of the initial holes (e.g. spinodal surface instability) determine the final arrangement of the droplets. From the calculation of the surface free energy of deformed rims, we showed that the rim instability is due to the three-dimensional structure of the rims. However, estimation of the node density is complicated by the two kinds of kinetics, the expansion mte of the dry patches and Ae growth rate of the rim fluctuations. 

Mukherjee, R., Sharma, A., Steiner, U. Surface instability and pattern formation in thin polymer films. In del Campo, A., Arzt, E. (eds.) Generating Micro- and Nanopattems on Polymeric Materials. Wiley-VCH, Weinheim (2011)... 

In applications in the semiconductor industry, polymer structures are required on length scales down to individual molecules. A bottom-up approach is better than a top-down approach in order to achieve this. A lateral resolution less than 100 nm can be created by surface instabilities and pattern formation in polymer films. Steiner [6] discussed demixing of polymer blends and pattern formation by capillary instabilities for nanostructure formation. 

This last article is concerned with instabilities in multilayer films with a free upper surface. Instabilities in viscoelastic liquids at low Reynolds mrmbers are reviewed in... 

It is important to note that spinodal dewetting " - does not imply that the surface instability and consequent dewetting can occur only in the form of a bicontinuous structure composed of liquid ridges or "hills" and "valleys." The thin-film experiments presented here demonstrate that a rich variety of morphological patterns can evolve. 

U. Thiele, M. Mertig, and W. Pompe, Dewetting of an evaporating thin liquid film heterogeneous nucleation and surface instability, Phys. Rev. Lett, 80, 2869 [1998]. 

S.-Q. Huang and X.-Q. Feng, Spinodal surface instability of soft elastic thin films, Acta Mech. Sin., 24,289 (2008]. 

X.-H. Pan, S.-Q. Huang, S.-W. Yu, and X.-Q. Feng, Interfacial slippage effect on the surface instability of a thin elastic film under van der Waals force, /. Phys. D Appl Phys., 42,055302 (2009],... 

Surface Instability and Pattern Formation in Thin Polymer Films... 

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