Multifunctional Wrinkled Film Generation By Patterning Surface Material Properties

Department of Mechanical EngineeringDuctile composite consisting of a variety of materials having respective intrinsic mechanical property, such as human skin, may wrinkle on the surface by the physical or chemical stimulus, revealing intrinsic structural features. In order to mimic this natural wrinkles, many research have been actively conducted to generate wrinkles with the buckling method using bilayer, and multilayer system with various methods of fabrication process. Wrinkles composed of layered structure react to the external stimulus, show high surface to volume ratio, 1-D directionality and periodicity. Due to these advantages, wrinkle has received attention in the various research fields such as chemical sensors, optics and electronic devices. Furthermore, according to the possible controllability of the periodicity of the wrinkle, it is applicable to the structural color with the property of fast response and the repeatability. However, the fine-tuning of wrinkle periodicity remains a challenge mainly because of the low controllability offered by the fabrication processes which additionally require high-cost equipment and complicated process. In this study, we proposed an inkjet printing-based wrinkle generation method that could modulate wrinkle periodicity on the scale of several tens of nanometers. We employed a triple-layered flexible film and controlled the material properties of each layer. The inkjet printing method played a key role in generating various stiff interlayer patterns, which subsequently enabled the precise generation and local modulation of the micro/nano wrinkles. Then, this kind of multifunctional wrinkled surface has been firstly applicated to the study of mechanochromatographic response of triple layer structure under different volume fraction of the patterned layer, by controlling its periodicity in tens of nanometer scale. Periodic wrinkle array behaved as 1D grating, exhibiting angle dependent structure coloration. Because the light diffraction occur through the wrinkled triple layer system, the light transmission is wrinkle size dependent and also it is viewing angle dependent. As a result, each of the RGB colored patterns could be exhibited on the selected area in one plane at certain viewing angle. Additional application to the high throughput material patterning has been also conducted by fabricating the micro/nano fluidic device based on the high periodic nano wrinkled surface. Conjugating of respective wrinkle as a unit nano channel was able to be conducted with certain fabrication process, which maintained the wrinkled surface even after the adhesion to the micro channel mold. Injection of the nano particle has brought the result of high throughput 1D arrangement of each particles, which may be utilized as the new method for the material patterning process. Thus we believe that our study could provide a novel fabrication strategy for the high periodic nano patterning technology, and show high potential for the flexible electronics and next generation wearable systems.clos