Pattern-Directed Dewetting of Ultrathin Polymer Films

Abstract

We utilize chemically patterned substrates with arrays of progressively narrower stripes (1-15 µm) to investigate the influence of pattern size on the morphology of ultrathin dewetting polystyrene films. The scale and orientation of the spinodal-like height fluctuations of the dewetting patterns are coupled to the imposed substrate chemical frequency, providing a powerful means of morphological control. Dewetting patterns are correlated to the substrate pattern period leading to the formation of droplet arrays. The measurements confirm recent numerical simulations by Kargupta and Sharma of the existence of upper and lower cutoff scales for pattern recognition of a dewetting fluid. For pattern dimensions less than the characteristic scale on nonpatterned substrates, the droplets become anisotropic as they coarsen to a scale comparable to the stripe width, and then undergo a morphological transition to circular droplets that cross multiple stripes. This leads to quantization of droplet size and contact angles, as indicated by theory.

Contact Instability of Elastic Bilayers: Miniaturization of Instability Patterns

“…Confinement of a soft liquid [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] or a soft solid surface by external fields and residual stresses [11,12,33,34] often engenders the surface instability and self-organized patterning of the film surface. Such instabilities can also be often controlled and guided, [3][4][5][6]9,10,[12][13][14][15][16][17]28,[36][37][38][39] which may allow their potential technological use in the applications involving meso-scale patterning of soft materials.…”

“…Such instabilities can also be often controlled and guided, [3][4][5][6]9,10,[12][13][14][15][16][17]28,[36][37][38][39] which may allow their potential technological use in the applications involving meso-scale patterning of soft materials. Of particular interest here is the surface of a soft thin elastic film, which, when brought in adhesive proximity of another rigid flat surface, undergoes spontaneous roughening with the formation of a short-wave isotropic structure.…”

Surface pattern based on an azobenzene-containing copolymer thin film and its light-driven morphology modulation

“…The fabrication of a well-defined pattern on film surfaces attracts considerable attention because of the numerous potential applications in electronic devices, sensors, information storage materials, and other functional surface materials (Reiter et al, 1996;Sehgal et al, 2002;Tokarczyk et al, 2011). Conventional means of constructing order pattern in the film is photolithography; however, photolithography requires a specific instrument and precise operation.…”

Dry-spot nucleation in thin liquid films on chemically patterned surfaces

“…They systematically studied the effect of initial film thickness, pattern dimensions, and surface energy contrast (Kargupta et al 2000;Kargupta and Sharma 2002;Kargupta and Sharma 2003). Sehgal et al (2002) and Zhang et al (2003) performed experiments regarding the dewetting of polystyrene layers on periodically heterogeneous substrates. Thiele et al considered the morphology evolution in a thin liquid film on substrates with one-and two-dimensional sinusoidal surface energy modulation (Brusch et al 2002;Thiele et al 2003;Pototsky et al 2004).…”

“…This allows parametrization of arbitrary experimental disjoining pressure isotherms, at least over a finite range of film thicknesses. While several groups have already studied dewetting of thin liquid films on structured surfaces (Kargupta et al 2000;Kargupta and Sharma 2002;Kargupta and Sharma 2003;Sehgal et al 2002;Zhang et al 2003;Brusch et al 2002;Thiele et al 2003;Pototsky et al 2004;Kao et al 2006;Julthongpiput et al 2007;Zhu et al 2010), most of the results have been obtained for small film thicknesses on order of ten times the precursor layer thickness, very specific disjoining pressure isotherms with more than one inflection point or neglecting the influence of gravity. For industrial applications relevant film thicknesses range typically between 1 and 10 lm, which is several orders of magnitude above the precursor layer thickness such that the influence of gravity can be substantial if not decisive.…”