Defect Sensitivity in Instability and Dewetting of Thin Liquid Films:  Two Regimes of Spinodal Dewetting

Abstract

The instability, dynamics, and dewetting engendered by the van der Waals forces in a thin liquid film sandwiched between a solid substrate and bulk fluid phase are investigated based on linear stability analysis and large-area, nonlinear 2D and 3D simulations. The effects of initial free-surface heterogeneities on the length scale of instability, morphology, order of the resulting structures, and their dynamic evolution are examined. The simulations clearly show two distinct regimes of spinodal instability: (a) deep inside the spinodal territory (DIST) and (b) a defect-sensitive spinodal regime (DSSR). The latter regime with increased sensitivity to the initial conditions and local ordering and clustering of holes is obtained toward the periphery of the spinodal region where spinodal destabilization becomes weak, or the force per unit volume ∂φ/∂h f 0. Thus, relatively thin and thick films close to the spinodal boundaries that do rupture by the spinodal mechanism may give the appearance of nucleation-induced rupture. Finally, the effects of simulation domain size (or number of holes) on the morphological and dynamic characteristics of spinodal instability are studied to assess the minimal sample size of simulations required to faithfully mirror some important aspects of thin-film rupture.

Submicrometer Pattern Fabrication by Intensification of Instability in Ultrathin Polymer Films under a Water–Solvent Mix

“…13 ), which possibly hints at the onset of a new-regime of dewetting for relatively thicker films which are known to be sensitive to the precise initial conditions and physico-chemical 13 heterogeneities. 17,21,22,27,56,57 As is also shown in Figure 1, relatively thinner films form a more dendritic structure compared to the well-defined polygons in thicker films, which indicates a change in the process of droplet formation.…”

Control of morphology in pattern directed dewetting of thin polymer films

“…Dewetting on a flat substrate Stability of a thin polymer film on a defect-free, flat and smooth surface and its subsequent dewetting is determined by the nature of van der Waals interaction between the polymer and its substrate. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In this study, a thin film of PS (surface energy, g 2 z 31 mJ m À2 ) on a crosslinked PDMS (polydimethylsiloxane) surface (g 1 z 20 mJ m À2 ) is considered. 53 Wetting of a surface is characterized by its spreading coefficient defined as: S LW ¼ g 1 À (g 2 + g 12 ), where g 1 and g 2 are the surface tensions of the substrate and the liquid, respectively and g 12 is the interfacial tension between the substrate and the liquid.…”

“…The average diameters of the dewetted structures as well as their dominant wavelength depend on the initial film thickness (h 0 ) and interfacial tension of the polymer film. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, randomness of the final dewetted structures and lack of long range order hinders the utility of dewetting as a viable surface patterning technique for engineering of small structures. Thus, the challenge is to bring long-range order and alignment to the dewetted structures with potential applications in fabrication of devices.…”

“…For example, the polymer films used here with thickness in the range of 20 nm to 80 nm, have spinodal lengthscales in the range of 10 mm to 100 mm. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Here, we explore conditions of film preparation other than spin coating where the lateral confinement effects of the substrate remain effective even when the pattern periodicity is much smaller than the spinodal length-scale. Thus far, the effect of the initial configuration of the film on the pattern formation has not been systematically studied.…”

Kinetics of spinodal phase separation in unstable thin liquid films

“…It is known that initial fluctuations greatly influence the kinetics for film thicknesses at the edge of the spinodal regime or in the defect sensitive spinodal region (DSSR), as opposed to thicknesses in the deep inside spinodal region (DISR). [12]. A new evolution coordinate found by dividing T by a time, T i , at which different films are at a given morphological event during their evolution, will account for the different initial fluctuations.…”