Controlled surface patterns are useful in a wide range of applications including flexible electronics, elastomeric optics, fluidic channels, surface engineering, measurement technique, biological templates, stamps, and sensors. In this work, we report on the controlled formation of surface patterns in metal films deposited on elasticity-gradient polydimethylsiloxane (PDMS) substrates. Because of the temperature gradient during the curing process, the PDMS substrate in each sample successively changes from a purely liquid state at one side to a purely elastic state at the opposite side. It is found that surface folds appear in the liquid or viscous PDMS region while wrinkles form in the elastic region. In the transition region from the liquid to elastic PDMS, a nested pattern (i.e., the coexisting of folds and wrinkles) can be observed. The folding wave is triggered by the intrinsic stress during the film deposition and its wavelength is independent of the film thickness. The wrinkling wave is induced by the thermal compression after deposition and its wavelength is proportional to the film thickness. The report in this work could promote better understanding of the effect of substrate elasticity on the surface patterns and fabrication of such patterns (folds and wrinkles) by tuning the substrate property.

Controlled wrinkled surface is useful for a wide range of applications, including flexible electronics, smart adhesion, wettability, stamping, sensoring, coating, and measuring. In this work, thickness-gradient-guided spontaneous formation of ordered wrinkling patterns in metal films deposited on soft elastic substrates is revealed by atomic force microscopy, theoretic analysis, and simulation. It is observed that in the thicker film region, broad cracks form, and the film surface remains flat. In the thinner film region, the cracks attenuate along the direction of the thickness decrease, and various wrinkle patterns including branched stripes, herringbones, and labyrinths can coexist. The interplay between the residual compression and the thickness gradient leading to the formation of such wrinkling patterns is discussed based on a nonlinear wrinkling model. The simulated wrinkling patterns as well as the variation trends of the wrinkle wavelength and amplitude along the gradient direction are in good agreement with the experimental observations. The report in this work could promote better understanding and fabrication of such ordered wrinkling patterns by tunable thickness gradient.

The spindle checkpoint delays the onset of anaphase until all of the chromosomes properly achieve bipolar attachment to the spindle. It has been shown that unattached kinetochores are the site that emits a signal for activation of the checkpoint. Although the components of the checkpoint such as Bub1, Mad1 and Mad2 selectively accumulate at unattached kinetochores, the answer to how they recognize unattached kinetochores has remained elusive. Mps1 pombe homolog (Mph1) kinase has been shown to function upstream of most of the components of the checkpoint and thus it is thought to recognize unattached kinetochores by itself and recruit other components. In this study we have expressed a fusion protein of Mph1 and Ndc80 (a kinetochore protein of the outer plate) and shown that the fusion protein arrests cell cycle progression in a spindle-checkpoint\x{2013}dependent manner in fission yeast. When expression of Mad2 is turned off, the cells grow normally with Mph1 constitutively localized at centromeres/kinetochores. Under this condition, Bub1 can be found with Mph1 throughout the cell cycle, indicating that localization of Mph1 at centromeres/kinetochores is sufficient to recruit Bub1. In contrast, Mad1 is found to transiently localize at kinetochores, which are presumably unattached to the spindle, but soon it dissociates from kinetochores. We propose that Mph1 is a sufficient marker for recruitment of Bub1. Mad1, in contrast, requires an additional condition/component for stable association with kinetochores.

Formation of telephone cord blisters as a result of buckling delamination is widely observed in many compressed film-substrate systems. Here we report a universal morphological feature of such blisters characterized by their sequential sectional profiles exhibiting a butterfly shape using atomic force microscopy. Two kinds of buckle morphologies, light and heavy telephone cord blisters, are observed and differentiated by measurable geometrical parameters. Based on the Föppl-von Kármán plate theory, the observed three-dimensional features of the telephone cord blister are predicted by the proposed approximate analytical model and simulation. The latter further replicates growth and coalescence of the telephone cord into complex buckling delamination patterns observed in the experiment.

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...