Fabrication of Multiscale Gradient Polymer Patterns by Direct Molding and Spatially Controlled Reflow

Authors

  • Jae Joon Chae,

    1. School of Mechanical and Aerospace Engineering, World Class University (WCU) Program on Multiscale Design, Seoul National University, Seoul 151–742, Republic of Korea
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  • Sung Hoon Lee,

    1. School of Mechanical and Aerospace Engineering, World Class University (WCU) Program on Multiscale Design, Seoul National University, Seoul 151–742, Republic of Korea
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  • Kahp Y. Suh

    Corresponding author
    1. School of Mechanical and Aerospace Engineering, World Class University (WCU) Program on Multiscale Design, Seoul National University, Seoul 151–742, Republic of Korea
    • School of Mechanical and Aerospace Engineering, World Class University (WCU) Program on Multiscale Design, Seoul National University, Seoul 151–742, Republic of Korea.
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Abstract

Size variations of pattern spacing as well as gradient control of the as-formed polymeric pattern via a spatially controlled reflow process are presented. Micro- and nanopatterns of polymethyl methacrylate (PMMA) in the form of line-and-space strips are first generated by capillary force lithography (CFL), and the residual layers are removed by ashing process. Subsequently, the exposed PMMA strips underwent a controlled reflow process above the glass transition temperature (Tg) while heating single or both sides of the substrate either in parallel to the line pattern (parallel reflow) or perpendicular to the line pattern (perpendicular reflow). As a result of this controlled reflow, a linear or a parabolic profile of pattern spacing is achieved depending on the heating mode. Furthermore, multiscale gradient patterns are formed with the spacing ranging from 98 nm to 4.23 μm (a difference of two orders of magnitude) in a single patterned layer using the original micropattern of 16 μm width and 8 μm spacing. In order to explain reflow behaviors, a simple theoretical model relating the normalized pattern width to the polymer viscosity is derived based on a leveling kinetics of polymer melt. Also, gradient PMMA channels are fabricated and bonded to a glass substrate, which are used to flow a liquid inside the channels by capillarity-driven flow.

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