The surface of micro nano structured materials can give many unique properties to materials, which has been a research hotspot in the field of materials. At present, biomimetic technology, photolithography technology, self-assembly technology, optical fluidization technology, microfluidic technology and many other "top-down" or "bottom-up" micro nano structure preparation technologies have been able to realize the controllable construction of different complex high-level micro nano composite structure surfaces, which are widely used in optics, flexible electronics, functional coating, biology and other fields. Among them, the development of surface wrinkling technology based on the instability of material surface makes the preparation of material surface microstructure more simple, efficient and low cost. However, this technology still faces the technical bottleneck of batch preparation, and continuous commercial production is still a challenging work.
Recently, daeyeon Lee, Shu Yang and Kathleen J. stebe of the University of Pennsylvania in the United States and other researchers simply realized the continuous and large-scale preparation of the wrinkle morphology of a series of materials based on the strategy of in-situ wrinkling on the surface of uv-pdms caused by bending strain / stress during the preparation of roll to roll. Based on different experimental parameters, PDMS surface can be constructed in one dimension or chessboard shape. The research team conducted in-depth research and Simulation Analysis on the internal mechanism of the formation of PDMS surface wrinkles. The surface micromorphology based on this strategy can improve the photoelectric conversion efficiency of solar cells.
Schematic diagram of continuous preparation process of wrinkle morphology on uv-pdms surface. Photo source: ACS appl. Mater. Interfaces
The research team took PDMS as the elastic substrate, coated uv-pdms prepolymer on the surface, uv-pdms polymerized and solidified to form a soft / hard composite system during the rotation of the round roller; the surface formed corresponding wrinkles after the bending stress release of the composite system with the continuous rotation of the cylinder. Further research shows that the wrinkles on the surface of PDMS depend on the thickness of the material film and the curvature of the roller (cylinder diameter); therefore, based on the adjustment of the thickness of the PDMS basement film and the diameter of the cylinder, the controllable preparation of the checkerboard like wrinkles and one-dimensional wrinkles with parallel or vertical orientation on the surface of the material can be realized.
The influence of PDMS thickness and cylinder diameter on the surface wrinkle morphology. Photo source: ACS appl. Mater. Interfaces
The internal mechanism and finite element analysis of the formation of different fold morphology on the surface of uv-pdms are studied. In the uv-pdms curing process, the modulus of the surface layer is higher than that of the bottom layer due to the decomposition of UV ozone, thus forming the hard uv-pdms / soft uv-pdms / PDMS three-layer structure soft hard system; the bending stress parallel to the bending direction caused by the rotation of the round roller and the compression stress introduced by the swelling of the uv-pdms prepolymer PDMS substrate Both of them depend on the parameters of material and equipment, and the comprehensive effect leads to the formation of different fold shapes on the surface of the material.
Analysis of the formation mechanism of uv-pdms surface fold morphology. Photo source: ACS appl. Mater. Interfaces
In terms of optical properties, the diffuse transmission caused by the scattering of folded structure of PDMS with folded surface is about 50% of the total incident light, which shows that PDMS with folded surface can be used as an effective optical diffuser. When the incident angle of light is 60 °, the folded PDMS film shows a higher current density. At the same time, compared with the solar cells with smooth package surface, the photovoltaic conversion efficiency of the solar cells with folded PDMS package is more stable with the change of the angle of thermal radiation.
Pleated shape improves the photoelectric conversion efficiency of solar cells. Photo source: ACS appl. Mater. Interfaces
summary
In the field of material surface micro nano morphology construction, surface wrinkling technology has obvious advantages in operation steps, preparation costs and so on. Based on the "roll to roll" processing technology, this research further realizes the continuous and large-scale preparation of uv-pdms surface wrinkle morphology, which will undoubtedly further promote the commercial application of surface wrinkle technology in optics, electronics and other fields. At the same time, the research results can be further extended to the construction and application of other polymer based materials.
Original text (scan or long press QR code, and then go to the original page after identification): scalable manufacturing of bending induced surface wrinklesxu A. Zhang, Yijie Jiang, R. Bharath Venkatesh, Jordan R. Raney, Kathleen J. stebe *, Shu Yang *, daeyeon Lee * ACS apply. Mater. Interfaces, 2020, 12, 7658-7664, DOI: 10.1021/acsami.9b23093
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