Micro/Nano Fabrication of Surface Architectures on Polymers and Copolymers Using Direct Laser Interference Patterning
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Micro/Nano Fabrication of Surface Architectures on Polymers and Copolymers Using Direct Laser Interference Patterning Diego Acevedo1, Andrés Lasagni2,3, Cesar Barbero1, and Frank Muecklich3 1 Departamento de Química, Universidad Nacional de Río Cuarto, Río Cuarto, X5804ZAB, Argentina 2 W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0405 3 Functional Materials, Saarland University, Saarbruecken, Germany ABSTRACT Novel surface engineering techniques of polymeric materials are essential to produce advanced topographies which could for example serve to modulate cell and tissue response in bio-materials. Direct Laser Interference Patterning (DLIP) permits the fabrication of repetitive arrays and microstructures by irradiation of the sample surface with coherent beams of light. Furthermore, the most important advantage of this method is that no additional process steps are required in comparison with other top-down or bottom-up techniques. In this study, we report a novel method for the advanced design of architectures in polymers using a single step process, as well as photo-activation of polymers with low absorption coefficient using a second polymer with relative high absorption coefficient. Previously calculated interference patterns using the well known interference theory could be directly produced on polymeric surface. Moreover, the cross-section of the structured polymers changes depending on the intensity of the laser beams, and photomachinability of polymers is highly influenced by laser wavelength. High absorbance of the polymeric materials at specific wavelengths allows the reduction of the laser intensity required to achieve a determined structure depth. For (60:40 %) polymethylmetacrylate/polystyrene copolymer substrate, different structures types were observed depending on the laser intensity including swelling and ablation of the material. INTRODUCTION Patterning techniques represent important tools for the fabrication of functional structured surfaces with application in chemistry, biology, physics and material science. Various techniques have been utilised in the past to produce structured surfaces with controlled dimensions. Most of them require multiple steps (e.g. mask/mould fabrication, etching, etc.) in order to produce the final microstructure, which usually implies relatively long processing times [1, 2]. Direct laser interference patterning uses a single preparation step whereas other holographic methods comprise at least two different steps (irradiation, etching, developing, etc). In addition, in the case of laser interference patterning, no masks are required and relatively large areas can be directly structured (cm²) on the time scale of a few seconds. For example, considering a 50 Hz laser operating with a maximal energy per pulse of 250 mJ, a structuring speed of about 55 cm2/s can be achieved [3]. This method has been applied in the case of different materials such as semiconductors, metals, ceramics, and polymers [4].
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