Laser Modification of Silicon and Borosilicate Glass Wettability for Micro-Fluidic Systems
Yuko Aono, Wataru Shinohara, and Hitoshi Tokura
Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology
2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
A laser modification method to control the surface wettability of a silicon and borosilicate glass substrate is proposed and demonstrated. The wettability of the silicon surface decreases after 2.5 W laser irradiation without a change in surface morphology. When the laser power is greater than 4 W, it results in the formation of a 10-nm-deep groove and the wettability increases. These phenomena are caused by changes in the number of surface groups and morphology, respectively. On the other hand, the glass surface is modified by infrared laser irradiation and the treated surface is highly hydrophilic. Surface analysis by FT-IR indicates that the modification is the result of an increase in the number of silanol groups. The proposed modification method is applied to micro-fluidic systems. A modified line can function as a surface micro-channel. Furthermore, with a gradient in wettability, the micro-channel has the ability to self-transport water droplets.
-  Y.-C. Tan, J. S. Fisher, A. I. Lee, V. Cristini, and A. P. Lee, “Design of microfluidic channel geometries for the control of droplet volume, chemical concentration, and sorting,” Lab on a Chip, Vol.4, pp. 292-298, 2004.
-  Y. Bellouard, A. Said, M. Dugan, and P. Bado, “Fabrication of high-aspect ratio, micro-fluidic channels and tunnels using femtosecond laser pulses and chemical etching,” Optics Express, Vol.12, pp. 2120-2129, 2004/05/17 2004.
-  T. N. Kim, K. Campbell, A. Groisman, D. Kleinfeld, and C. B. Schaffer, “Femtosecond laser-drilled capillary integrated into a microfluidic device,” Applied Physics Letters, Vol.86, p. 201106, 2005.
-  E. Váazquez, C. Rodr’iguez, A. El’ias-Z’u niga, and J. Ciurana, “An experimental analysis of process parameters to manufacture metallic micro-channels by micro-milling,” The International Journal of Advanced Manufacturing Technology, Vol.51, pp. 945-955, 2010.
-  B. H. Jo, L. M. Van Lerberghe, K. M. Motsegood, and D. J. Beebe, “Three-dimensional micro-channel fabrication in polydimethylsiloxane (PDMS) elastomer,” Microelectromechanical Systems, Vol.9, pp. 76-81, 2000.
-  K. Imamura and T. Yasuda, “Droplet Transportation on a Wettability Gradient Surface Generated by Electrowetting-on-Dielectric,” IEEJ Transactions on Sensors and Micromachines, Vol.130, pp. 1-5, 2010.
-  Q. Xie, J. Xu, L. Feng, L. Jiang, W. Tang, X. Luo, et al., “Facile Creation of a Super Amphiphobic Coating Surface with Bionic Microstructure,” Advanced materials, Vol.16, pp. 302-305, 2004.
-  Z. K. Wang, H. Y. Zheng, and H. M. Xia, “Femtosecond laser-induced modification of surface wettability of PMMA for fluid separation in microchannels,” Microfluidics and Nanofluidics, Vol.10, pp. 225-229, 2011.
-  V. Zorba, L. Persano, D. Pisignano, A. Athanassiou, E. Stratakis, R. Cingolani, et al., “Making silicon hydrophobic: wettability control by two-lengthscale simultaneous patterning with femtosecond laser irradiation,” Nanotechnology, Vol.17, p. 3234, 2006.
-  T. Nishino, M. Meguro, K. Nakamae, M. Matsushita, and Y. Ueda, “The Lowest Surface Free Energy Based on –CF3 Alignment,” Langmuir, Vol.15, pp. 4321-4323,1999.
-  J. Lawrence, L. Li, and J. T. Spencer, “Diode laser modification of ceramic material surface properties for improved wettability and adhesion,” Applied Surface Science, Vol.138-139, pp. 388-393, 1999.
-  D. Erickson and D. Li, “Integrated microfluidic devices,” Analytica Chimica Acta, Vol.507, pp. 11-26, 2004.
-  R. L. DeRosa, P. A. Schader, and J. E. Shelby, “Hydrophilic nature of silicate glass surfaces as a function of exposure condition,” Journal of Non-Crystalline Solids, Vol.331, pp. 32-40, 2003.
-  A. Kanta, R. Sedev, and J. Ralston, “Thermally- and Photoinduced Changes in the Water Wettability of Low-Surface-Area Silica and Titania,” Langmuir, Vol.21, pp. 2400-2407, 2005.
-  R. N. Wenzel, “Surface Roughness and Contact Angle,” The Journal of Physical and Colloid Chemistry, Vol.53, pp. 1466-1467, 1949.