The spontaneous formation of surface-induced micrometerscale patterns is of significant interest in the fabrication of surfaces with configurable optical properties [1] and of components in microfluidic devices, [2] or for the analysis of materials properties at the nanometer scale. [3] A range of different strategies have been explored to produce patterns in thin polymer films, such as controlled phase separation on surfaces patterned into regions of different surface tension [4] and spontaneous buckling of thin stiff films on a soft substrate. [5,6] However, thin films under compressive strain are frequently observed to delaminate and buckle, which is of significant importance not only in coatings technology (see, for example, the paint blister in Fig. 1f), but also in the fabrication of polymer electronics where multilayer devices, such as flexible displays, should not fail when bent through a small radius of curvature. This general phenomenon of buckle-driven delamination [7][8][9] has not been previously studied as a tool for patterning thin polymer films because it is difficult to predict the precise onset of the process. [10] In this work, we will demonstrate that pre-patterning the thin film under strain, in combination with a triggered release of the adhesion of the film to the substrate, allows for the design of well-controlled sub-micrometer pattern formation ( Fig. 1). A number of strategies exist to fabricate ultrathin polymer films with well-defined lateral patterns, [11][12][13] but two crucially important concepts are introduced in this paper: the introduction of eigenstrain (i.e., "stress-free" strain inherent in the material) in the polymer films, and the tuning of their adhesion energy to the substrate in order to allow controlled and triggered delamination. The thin films that are the subject of this study were prepared in a three-step process (Scheme 1) that allows good control of both the lateral dimensions and the thickness of the polymer films, whilst also providing a reliable method of lifting these objects from the substrates on which they are prepared. [14] First, initiator-terminated thiols were deposited into micrometer-sized patterns on gold using microcontact printing. Second, poly(glycidyl methacrylate) (PGMA) brushes were grown from the surface via atom transfer radical polymerization (ATRP).[15] The thickness of the brush films was controlled to be between 15 and 150 nm. Last, the PGMA brushes were cross-linked by opening the epoxide moieties using a methanolic NaOH solution. To facilitate further characterization, the films were then dyed with Rhodamine B. The patterned, cross-linked polymer brushes were then placed in a simple electrochemical cell, exploiting the Au substrate as the cathode. The adhesion between the polymer film and the gold surface was weakened by a short (less than 1 s) pulse of cathodic reduction of the gold-sulfur bond, [16] immediately producing striking buckling patterns as visualized by fluorescence microscopy. Figure 1 shows a range of different microme...

Here, we report the preparation of hierarchically structured polymer brushes with well‐defined geometries via multiple step microcontact printing (MS‐µCP) of inks containing different ratios of initiator‐terminated thiols and non‐reactive alkylthiols. Thick (and dense), polymer brushes grew from self‐assembled monolayers (SAMs) with high concentration of initiator‐terminated thiols, and these brushes exhibited high chemical etch‐resistance, compared to thin (and less dense), brushes grown from more dilute initiator‐terminated SAMs. Upon etching, patterned crosslinking polymer brush films decorated with thin layers of Au, could be lifted off the surface to form geometrically well‐defined free‐standing hierarchical films. These polymer brush films showed interesting buckling instabilities when compressed. Areas with different brush thicknesses and Au backing showed markedly different buckling behavior, leading to unusual patterns of wrinkles with different wavelengths and orientations toward the force field.

Soft nanotechnology requires new approaches and materials to efficiently convert chemical energy into mechanical motion and vice versa. A number of key design parameters, such as responsiveness to external stimuli, directionality of response through alignment, transduction via surface stresses or changes in ionic conductivity can be found in polymer brushes and several recent examples of actuation and transduction in polymer brushes will be explored.magnified image

This paper describes a fabrication strategy based on polymer brushes (20-150 nm thick) and soft lithographic techniques, for creating hydrophobic, cross-linked, laterally patterned polymer films. The hydrophobicity of the resulting micrometer-scale "quasi-2D" objects is shown to allow the polymer to act as an etch resist. By adjusting the etching time, we demonstrate that underetching of the gold from underneath the edges of the laterally patterned films can be used to create free-standing polymer-gold hybrid structures. These structures retain their structural integrity when lifted wholly or partially from the substrate and can hence be imaged in suspension. Characterization of the quasi-2D objects was carried out using atomic force microscopy (AFM), ellipsometry, optical microscopy, and Fourier transform infrared spectroscopy (FTIR). A continuous film, containing embedded polymer-gold objects, can be lifted, folded, and re-deposited onto a substrate without damaging the conductivity of the embedded metallic objects.

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