Abstract
Polydimethylsiloxane (PDMS) is hailed as one of the foundational materials that have been applied to different products in various fields because of its chemical resistance, low cost, excellent flexibility, and high molding capability. With the aim to achieve surface texture with high efficiency by means of electrochemical micromachining with PDMS mask, a femtosecond laser is utilized to process a precision array of micro-through-holes on PDMS films as the molds. The ablation process of PDMS with a femtosecond laser was investigated via numerical simulation verified with experiments indicating a laser energy density of 4.865 mJ/mm2 as the ablation threshold of PDMS with the melting temperature of 930 K. The spiral scanning path with optimized radial offset was developed to ablate materials from the PDMS film to form the laminated profiles, and a tapered through hole was then formed with multilayer scanning. The profile dimension and accuracy were examined as control targets in terms of laser pulse energy and scanning speed, showing that a 12 μJ femtosecond laser pulse energy and 1000 mm/s scanning speed could bring about a nearly circular laminating profile with expected smaller exit diameter than the entry diameter. All the cross-section diameters of the microcone decreased with the increase of laser scanning speed, while the taper increased gradually and then saturated around a laser scanning speed of 800 mm/s due to the energy absorption resulting in smaller ablation in diameter and depth.
Highlights
Polydimethylsiloxane (PDMS) microstructured components have been widely used in many fields, especially in microfluidics, optical microelectromechanical systems, micro fabrication techniques, and biomedical applications due to PDMS’s chemical resistance, low cost, low interfacial free energy, excellent flexibility, and high molding capability [1,2,3,4].A novel hydrophobic and superhydrophobic surface prepared with microhole-arrayedPDMS was able to realize an underwater bubble unidirectional self-transportation in the direction of both buoyancy and antibuoyance [5]
PDMS with through-holes was first employed as a mask in through mask electrochemical micromachining (TMEMM) for obtaining microstructures, and the PDMS mask was fabricated through two steps of photolithography and molding, where the photolithography process for achieving the SU-8 mold with the micropillar array was complex, timeconsuming, and expensive, including spin coating, prebaking, exposure, development, and postbaking [20,21]
When the laser energy is higher than 0.55 μJ, indicating the ablation threshold of the femtosecond laser on PDMS film
Summary
Polydimethylsiloxane (PDMS) microstructured components have been widely used in many fields, especially in microfluidics, optical microelectromechanical systems, micro fabrication techniques, and biomedical applications due to PDMS’s chemical resistance, low cost, low interfacial free energy, excellent flexibility, and high molding capability [1,2,3,4]. PDMS with through-holes was first employed as a mask in through mask electrochemical micromachining (TMEMM) for obtaining microstructures, and the PDMS mask was fabricated through two steps of photolithography and molding, where the photolithography process for achieving the SU-8 mold with the micropillar array was complex, timeconsuming, and expensive, including spin coating, prebaking, exposure, development, and postbaking [20,21]. The femtosecond laser, with extremely short pulse width, ultrahigh instantaneous power, micro/nanoprocessing accuracy, almost nonexistent thermal effects to the adjacent materials around the ablation spot, and three-dimensional direct writing nature, is an ideal processing technology for achieving through-holes on PDMS mask [23]. The present work focuses on the fabrication and profile control of the microhole array by means of femtosecond laser for PDMS mask so as to obtain micro structures and surface morphology with high efficiency and high quality in electrochemical micromachining. The influence of processing parameters on the cone profiles and dimensions of PDMS micro-through-holes were examined for controlling the profile and the size of the exit holes
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