Control of Self-Organized Contact Instability and Patterning in Soft Elastic Films

Abstract

The surface of a soft elastic film becomes unstable and forms a labyrinth pattern when a rigid flat plate is brought into adhesive contact, without application of any external pressure. These isotropic undulations have a characteristic wavelength, lambda approximately 3H, where H is the film thickness. We present here technique of ordering, aligning, and modulating these micro-labyrinth structures by using a patterned stamp, by varying the stamp-film inter-surface distance, by a lateral confinement of the instability and even by a simple shear motion of a flat stamp. Many complex structures, such as an array of femto-liter beakers and doubly periodic channels, are generated from a simple stamp consisting of parallel channels. The elastic nature of the patterns allows an in-situ tuning, manipulation, and reconfiguration of the microstructures. Regardless of their precise morphology, the structures continue to have the elastic length scale, lambda approximately 3H. The structures can also be made permanent as required by UV-ozone-induced oxidation of the structures. The underlying principles of the elastic contact instability presented here have the potential to develop into a new soft lithography technique-elastic contact lithography (ECL), allowing a simple, rapid and large area patterning of soft solids.

Contact Instability of Elastic Bilayers: Miniaturization of Instability Patterns

“…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.…”

“…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. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][35][36][37][38][39] Theoretical studies [18][19][20][21][22][24][25][26][27][28][29][30][31][32] based on the linear stability analysis and simulations [24,26,28,30,37] reveal that this instability originates from the influence of inter-surface adhesive interactions such as the van der Waals force and opposed by the restoring elastic force because of the energy penalty in elastic deformation of the film. This short-wave elastic contact instability, which involves no material transport by diffusion or convective flow, is quite distinct from the long-wave instability and dewetting of viscous liquid films because of the residual stresses, [11,12] van der Waals [1,2,…”

“…In contrast, the wavelength (k) of adhesive field induced instability in a solid elastic films is largely independent of the nature and magnitude of the interaction forces and the surface tension. It has been shown both experimentally [18,19,23,29,[35][36][37][38][39] and theoretically [18][19][20][21][22][24][25][26][27][28][29][30][31][32] that the patterns form on a lateral length scale (k) of about three to four times the film thickness (h). Interestingly, the lateral pattern length scale is independent of all the material properties including the shear moduli of the film and the surface energy of the stamp for films thicker than about 1 lm.…”

“…The elastic contact instability and the pattern morphology can be modulated by application of an electric field, [36] and by stamp movements and the use of pre-patterned stamps. [37][38][39] The elastic contact lithography can thus have potential applications in self-organized meso-patterning of soft surfaces such as silicon rubbers and hydrogels. [38,39] However, a greater control on the feature sizes beyond the simple k ∼ 3 h offered by a single film is clearly desirable for a greater flexibility in meso-patterning and in engineering of optimal pressure-sensitive adhesives.…”

Photoinduced doughnut-shaped nanostructures

“…Micro-droplets of polystyrene solutions on surfaces were used to obtain typical structures like micro-size domes [6]. Other experiments have shown the possibility to create meso-patterning of thin film polymers by controlled dewetting [7]. A 2-D array of femto-litter beakers best described as nano-membrane were investigated by the dewetting of PS film on complex patterned surfaces and exposition to toluene vapor.…”