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Keywords
- Femtosekundenlaser (6)
- Kohlendioxidlaser (2)
- Polymethylmethacrylate (2)
- Dreidimensionale Geometrie (1)
- Laser (1)
- Laserschweißen (1)
- Oberflächenstruktur (1)
- Quarzglas (1)
- Ultrakurzzeitlaser (1)
Year of publication
- 2018 (11) (remove)
Document Type
- Article (8)
- Conference Proceeding (3)
We report on laser generation of microchannels by focused femtosecond laser pulses inside PMMA bulk material. This process enables direct fabrication of three dimensional microfluidic channel architectures with generally unlimited channel length. Based on nonlinear ultrashort pulse laser absorption of high intensities around the focal volume, a material modification including a refractive index shift is triggered. After laser exposure the channel is created by a gaseous degradation of exposed areas during an annealing process. The 3D channel layout can easily be realized by moving the specimen using 3D motorized stages, allowing freely chosen complex shaped channel architectures. In this report, the creation of inner lying vertical microchannels is examined. In addition to previously shown horizontal channel architectures vertical channels are necessary to fulfill the definition of an internal three-dimensional microfluidic structure and to create interconnections in multilevel lab on chip devices. The cross section and geometry of vertical channels are strongly influenced by laser parameters such as pulse duration, laser power and writing speed. The influence of these process parameters on the channels diameter is determined and parameters are optimized regarding a controllable, stable and reproducible process. The functionality of vertical microchannels as an interconnection between multilayer microfluidic devices is demonstrated using a Rhodamine B solution.
Control of femtosecond laser generated microfluidic channels inside poly (methyl methacrylate)
(2018)
In this study, the authors report on femtosecond laser direct generation of microchannels inside poly(methyl methacrylate) with variable dimensions ranging from a channel height of 20 to 350 μm and an aspect ratio down to 1.2. Focused ultrashort laser pulses are used to trigger a material modification in the focal area which can be selectively opened by a subsequent annealing process. A 3D microchannel architecture can easily be realized by moving the specimen using motorized stages, allowing freely chosen complex shaped channel layouts. While the laser wavelength is identified as one of the main parameters determining process effectiveness, another core of this study is the variation of channel dimensions by the numerical aperture of the applied objective to focus the laser. The authors find that both size and shape of the modified region and the resulting microchannel can be controlled by altering the numerical aperture.
In this contribution, we report on surface functionalization by introducing laser induced periodic surface structures on 100Cr6 bearing steel to modify complex tribological properties. The advanced approach of this study is the measurement of the coefficient of friction by performing a ball-on-disk Stribeck test on laser structured surfaces with polytetrafluoroethylene balls in a lubricant environment. The Stribeck test reveals the modified friction behavior using translation speeds up to 106 mm/min and load forces between 100 mN and 5000 mN. Our results show increased stiction and coefficient of friction for laser structured surfaces in the regime of boundary lubrication which is attributed to the laser induced surface asperities. Decreased coefficient of friction is observed in the regime of mixed and hydrodynamic lubrication, i.e. for velocities higher than 1000 mm/min, for surfaces covered by laser induced periodic surface structures with low spatial frequency.
The laser beam welding of transparent plastic components is still a challenge
according to the state of the art. A new approach for the joining of two transparent
polymeric components using ultrashort laser beam pulses is presented in
this report. In this respect, the high peak pulse intensity associated with these
lasers permits non-linear absorption processes and thus the production of a
locally well-defined heat source in the interior even of a transparent material or
at the boundary layer between two transparent substrates. Welding results for
transparent plastics of the cycloolefin copolymer and polycarbonate types are
shown in this study. In addition to the investigation into the influences of fundamental
process parameters on the weld geometry, the leak tightness is
demonstrated in this study using a microfluidic system.