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Abstract The interfacial interactions between 2D materials and polymer substrates receive increasing interest due to the surge of flexible electronics, multifunctional coatings, and nanocomposites. Although the strain effect on electrical, optical, and mechanical properties of 2D materials is extensively investigated, understanding the interfacial mechanics of 2D material‐polymer systems by dynamic loading is still a challenge. Here, the interfacial degradation and pattern evolution of mechanically exfoliated single‐ and few‐layer graphene on polydimethylsiloxane (PDMS) substrates by cyclic mechanical loading, are reported. It is found that the tensile strain leads to interfacial slippage between graphene and PDMS, whereas the compressive strain can be transferred to graphene with a transfer efficiency above 80%. Through cyclic loading, the graphene surface is seriously deformed by formation of multiple instability patterns including wrinkles and cracks. The morphological characteristic and evolution mechanism of the wrinkles and cracks are analyzed and discussed in detail. The interfacial adhesion energy is evaluated by wrinkle profiles and it decreases from ≈23 to ≈2 mJ m−2 as the cycle number increases. This work can promote better understanding of the interfacial effect of 2D materials on polymer substrates and controllable fabrication of various wrinkled or crumpled surfaces of 2D functional materials by cyclic mechanical loading.

Smart surfaces with dynamically tunable wettability place an important role in microfluidics, biomedical engineering and flexible electronics. Mechanical strain is a promising stimulus to tune the surface wettability, however, it is still a great challenge to achieve both wide-range reversible wettability and high sensitivity. In this study, highly ordered and quasi-periodic ridge patterns with cracks at their peaks were tailored based on a film-substrate system by sputter deposition of zinc (Zn) nanofilm on prestretched polydimethylsiloxane (PDMS). The contact angle (CA) on the ridged Zn/PDMS surface is well tunable between 115° and 143° by adjusting the applied strains. It is remarkable that such a structure possesses wide-range CA variation (~28°) under just 28.6% applied strain, indicating a high responsive sensitivity (η = 98°). This result is attributed to the cracked ridges with both wide-range aspect ratios from 0.07 to 0.54 and high rate of change (~1.70). Moreover, the responsive reversibility of the ridged Zn/PDMS surface remains up to 1000 cycles and 60 days without special protection. The outstanding performances make the ridged surface could be a promising component for various technological applications, especially in small strain required situations.

Telephone cord blisters constitute a well-known example of patterns generated following buckling in thin films. Here the authors develop an analytical approach that can model the sectional height profiles along the blisters that they measure experimentally and simulate numerically.

A characteristic wrinkled Fe film system has been prepared on silicone oil surfaces by a direct current magnetron sputtering method. The experiment shows that the Fe film is under a large compressive stress induced by the thermal contraction during deposition, which is relieved by the formation of wrinkling patterns. It is found that the wrinkling patterns, such as straight strips and herringbones, are formed in networked domains. The straight strips are perpendicular to the domain edges and the herringbones are located in the center of the domains. The morphologies of the wrinkled patterns are characterized by the optical microscopy and atomic force microscopy. It is found that the average length d of the domains remains nearly unchanged and the wavelength λ of the wrinkling patterns increases linearly with the film thickness h, which obeys an equation λ = 14h + 1440. The amplitude z of the herringbones increases firstly with the film thickness h for h ≤ 450nm and decreases quickly for h > 450 nm. The characteristic, structure evolution and formation mechanisms of the wrinkled patterns have been described and discussed in detail. [ABSTRACT FROM AUTHOR]

We report on the morphology and structure evolutions of silver (Ag) atomic islands deposited on liquid substrates by vapor deposition. It is found that, as the nominal film thickness h is less than or equal to the critical value hc, the morphology of the islands evolves gradually from compact to branched islands, and the apparent Ag surface coverage p of the total area increases linearly with h. For h > hc, however, network-structural islands form and the corresponding decreases sharply and then shows a fluctuation behavior. Meanwhile, the average number density n of the islands decreases rapidly. These interesting phenomena mirror the fact that the percolation behavior is observed at hc = 0.8 nm and the condensation behavior appears for h > 0.8 nm. Atomic force microscopy measurements reveal that the Ag islands tend to show three-dimensional growth. Finally, the detailed growth mechanism of the Ag islands is presented. [ABSTRACT FROM AUTHOR]

A new crystal growth theoretical model is established for the low-dimensional nanocrystals on an isotropic and quasi-free sustained substrate. The driven mechanism of the model is based on the competitive growth among the preferential growth directions of the crystals possessing anisotropic crystal structures, such as the hexagonal close-packed and wurtzite structures. The calculation results are in good agreement with the experimental findings in the growth process of the low-dimensional Zn nanocrystals on silicone oil surfaces. Our model shows a growth mechanism of various low-dimensional crystals on/in the isotropic substrates. [ABSTRACT FROM AUTHOR]

Controlled cracks are useful in a wide range of applications, including stretchable electronics, microfluidics, sensors, templates, biomimics, and surface engineering. Here we report on the spontaneous formation of hierarchical crack patterns in metal (nickel) films sputter deposited on soft elastic polydimethylsiloxane (PDMS) substrates. The experiment shows that the nickel film generates a high tensile stress during deposition, which is relieved by the formation of disordered crack networks (called primary cracks). Due to the strong interfacial adhesion and soft substrate, the cracks can penetrate into the PDMS substrate deeply. The width and depth of the primary cracks both increase with increasing film thickness, whereas the crack spacing is insensitive to the film thickness. The film pieces dividing by the primary cracks can fracture further when they are triggered by an external disturbance due to the residual tensile stress, resulting in the formation of fine crack networks (called secondary cracks). The width and spacing of the secondary cracks show different behaviors in comparison to the primary cracks. The morphological characteristics, growth behaviors, and formation mechanisms of the primary and secondary cracking modes have been discussed in detail. The report in this work could provide better understanding of two distinct cracking modes with different sizes and morphologies. [ABSTRACT FROM AUTHOR]

Fascinating crack and wrinkle patterns driven by stresses are ubiquitous in natural and artificial systems. It is of great interest to control the morphologies of stress-driven patterns by using facile techniques. Here we report on the spontaneous formation of hierarchical wrinkles and oscillatory cracks in metal films deposited on liquid (or soft polymer) stripes. It is found that the metal film is under a tensile stress during deposition owing to the thermal expansion of the liquid substrate. As the film thickness is beyond a critical value, oscillatory cracks with sawtoothlike shapes form on the liquid stripes. The ratio of crack oscillation period to amplitude is independent of the stripe width and film material, which can be well explained by the "brittle adhesive joints" model. After deposition, the metal film is under a compressive stress, which is relieved by formation of various wrinkle patterns. Hierarchical wrinkles with changing wavelengths form near the stripe edge while labyrinth or wavy wrinkles form at the center. Energy analysis was adopted to explain the formation and evolution of the wrinkle patterns. This study could promote better understanding of the formations of crack and wrinkle patterns in constrained film structures and controllable fabrication of stress-driven patterns by prefabricating liquid (or soft polymer) interlayer arrays. [ABSTRACT FROM AUTHOR]