No abstract

Deposition of particular layers of solid materials on a swelling polymer leads to the formation of functional wrinkles after the release of polymer strain. Unlike traditional mechanical stretching, polymer swelling could introduce uniform wrinkle structures on complex substrates as a result of isotropic polymer elongation. In this work, conductive silver wrinkles are grown on an elastomer by combining polymer swelling with electroless deposition. By adjusting the crosslinking ratio of polymer substrate or deposition time, the amplitude and wavelength of wrinkles can be tuned to meet demands for ultrasensitive pressure sensors. The detectable pressure limit is successfully reached below 1.0 Pa. C omplex wrinkle patterns exist in many thin-film systems typically with layered structures, such as natural wrinkles in aging skin, drying fruits, and fingerprints. 1 In the past decades, fabrication of artificial microwrinkles with tunable periodical structures has become a steadily developing field. 2 Some particular wrinkle structures offered fascinating promise for serving as optical devices, 3 self-cleaning coatings, 4 selfassembly templates, 5 or microchannels. 6 To expand their more attractive and challenging potentials, great concerns have been paid to the wrinkles with predictable topologies grown on soft substrates. 7 Such an integration leads to a tremendous increase of possibilities for flexible and stretchable devices. 8 Among them, a striking possibility is a skin-like piezoresistive pressure sensor, 9 which is routinely based on the lamination of two deformable conductive layers. The strain-gauge sensitivity relies on the degree of conformal contact between two conductive layers upon an external pressure. 10 In this regard, conductive layers with nonplanar morphologies become extremely more sensitive compared with planar films. However, practical examples of ultrasensitive pressure sensors assembled by nonplanar conductive wrinkles are sparse due to the lack of "wave"-like layout with remarkable surface buckling and satisfactory adhesion on soft substrates.The formation of surface wrinkles is a process of mechanical instability whereby a flat film develops out-of-plane undulations on a substrate with different Young's modulus. 11 Amplitude referring to the degree of surface buckling is limited in a narrow range because of its correlation with film thickness and Young's modulus. Wrinkles grown on nonplanar or patterned substrates become more deformable which may meet the demands for ultrasensitive pressure sensors. 12 Mechanical stretching has been exploited as one effective way to prepare two-dimensional surface wrinkles. 13 Periodical wrinkles as a result of compression of a stiff thin film are typically generated along the relaxation of a prestressed soft substrate. 14 However, this method is invalid for the preparation of periodical wrinkles on the nonplanar and patterned substrates. The tensile stress from edges is only allowed to be delivered in the direction parallel to the applied force. Wrinkles are ...

To date, high-performance organic electrochemical transistors (OECTs) are mostly based on polythiophene systems. Donor-acceptor (D-A) conjugated polymers are expected to be promising materials for OECTs owing to their high mobility...