Harnessing Heterogeneous Wrinkles in Metal/Polydimethylsiloxane Film System by Combination of Mechanical Loading and Heat Treatment

Abstract

dehydration, and atrophy. Controlling wrinkle morphologies including orientation, wavelength, and amplitude is very important and necessary for various practical applications.Generally, the orientation of wrinkles is determined by the stress distribution of the film. Unidirectional strain results in stripe-like wrinkles perpendicular to the strain axis [4,5] while multidirectional strain leads to disordered labyrinth-like or ordered herringbone wrinkles. [6,7] Introduction of film impurity can induce local strain anisotropy and guide wrinkle orientation, achieving highly ordered wrinkle arrays. [8,9] The wavelength of wrinkles depends on the film thickness [10] and the modulus ratio of film to substrate. [11] It can range from submicron to macroscale (kilometers in tectonic plates for instance). The amplitude of wrinkles is directly proportional to the wavelength and the square root of strain. [12,13] The aspect ratio of wrinkle (the ratio of amplitude to wavelength) is merely dependent on the strain. The previous studies showed that the wrinkle amplitude or aspect ratio is usually uniform for a homogeneous sample. [4][5][6][7] As the compression is beyond a critical value (20-30%), the homogeneous wrinkles evolve into localized patterns such as folds, ridges, and delaminations. [13][14][15][16][17] Localized wrinkles can be also observed in disordered or heterogeneous films such as single-wall carbon nanotubes, glassy polymers, and diblock copolymers due to spontaneous strain localization. [18,19] Artificial thickness or modulus inhomogeneities of film-substrate systems are frequently used to induce various complex arrays of localized patterns by mechanical loading. [20][21][22] Although localized patterns in disordered or artificially inhomogeneous systems have been extensively investigated, the formation and evolution of heterogeneous wrinkles (with unequal wavelengths or amplitudes compared with the sinusoidal wrinkles) in a homogeneous system remain unknown up to now. In this study, we report a novel way to tailor the heterogeneous wrinkles in metal/polydimethylsiloxane (PDMS) bilayer system by the combination of mechanical loading and heat treatment. The novelty of this work is concluded as following. First, the heterogeneous wrinkles in this study spontaneously form at small strain condition and evolve into homogeneous structures as the compression increases. This process is in contrast to Spontaneous wrinkled surfaces in nature usually possess unique physical and chemical properties. Inspired by nature and stimulated by practical application, artificial wrinkle patterns have received increasing interest recently. Here, the controllable heterogeneous wrinkles in metal films deposited on polydimethylsiloxane substrates by combination of mechanical loading and heat treatment is reported. It is found that the wrinkles are spontaneously localized at small strain condition due to the uneven distribution of wrinkle amplitudes on the film surface. The morphological features and underlying mechanisms of such wrink...

Tunable Friction Properties of Periodic Wrinkled BaTiO3 Membranes

“…Heating is another reliable way to create wrinkled patterns in bilayer systems for the compressive stress introduced to the upper stiffer film during the cooling process. [15,33] Hence, heating might also be an effective method to realize the dynamic control of wrinkled patterns and the friction property. The AFM and LFM measurements were taken in situ as the temperature rose from room temperature (25 °C) to 75 °C.…”

“…Surface wrinkled patterns with periodic or aperiodic topographies are widespread [ 1–4 ] due to their various and distinctive physical, [ 5,6 ] chemical, [ 7,8 ] and biotic properties, [ 9,10 ] such as human skins, blood cells, and dehydrated fruits, with random dimensions spanning across length scales from nanometers to meters. [ 11–13 ] In particular, the tunable morphologies of wrinkled surfaces enable the possibility of controlling the friction property, [ 14,15 ] thereby providing broad and fantastic potential applications in nanomechanical systems, microfluidic channels, and soft‐fingered robotics. [ 16–19 ] Recently, it has been reported that the friction of wrinkled surfaces is closely related to morphological features, including amplitude, wavelength, and orientation.…”

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In particular, the tunable morphologies of wrinkled surfaces enable the possibility of controlling the friction property, [14,15] thereby providing broad and fantastic potential applications in nanomechanical systems, microfluidic channels, and soft-fingered robotics. [16][17][18][19] Recently, it has been reported that the friction of wrinkled surfaces is closely related to morphological features, including amplitude, wavelength, and orientation.

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An asymptotic modeling and resolution framework for morphology evolutions of multiple-period post-buckling modes in bilayers

“…In-plane pre-tension induces a softening of the outward deflection of the substrate relative to the inward deflection, and hence may promote the formation of hierarchical wrinkles and periodic ridges. For a bilayer with the modulus ratio m f =m s = 200 under high pre-stretch l 0 1s = 1:75, we observe hierarchical wrinkling pattern (see Figure 5) in the form of alternating packets of large and small undulations (c) Surface morphology of a silver film sputter deposited on a PDMS substrate after heating/cooling process under prestretch and the profile of the film after annealing [40], where hierarchical wrinkles appear. [18,36,[39][40][41].…”

“…For a bilayer with the modulus ratio m f =m s = 200 under high pre-stretch l 0 1s = 1:75, we observe hierarchical wrinkling pattern (see Figure 5) in the form of alternating packets of large and small undulations (c) Surface morphology of a silver film sputter deposited on a PDMS substrate after heating/cooling process under prestretch and the profile of the film after annealing [40], where hierarchical wrinkles appear. [18,36,[39][40][41]. The surface morphology of hierarchical wrinkles is similar to the experimental measurement [40] of cross-sectional profiles of heterogeneous wrinkles in silver/PDMS bilayers (see Figure 5(c)).…”