Content area
Full Text
Microuid Nanouid (2011) 10:225229 DOI 10.1007/s10404-010-0662-8
SHORT COMMUNICATION
Femtosecond laser-induced modication of surface wettability of PMMA for uid separation in microchannels
Z. K. Wang H. Y. Zheng H. M. Xia
Received: 19 April 2010 / Accepted: 21 June 2010 / Published online: 2 July 2010 Springer-Verlag 2010
Abstract The modication of polymer surface wettability is receiving increasing interest in recent years. As surface wettability affects the owing resistance, and thus the separation ratio and/or mixing ratio of samples in different microchannels, the controlled modication of surface wettability is highly desirable. In this study, microuidic channels with controlled surface wettability were achieved and fabricated using femtosecond (fs) laser direct ablation of polymethyl methacrylate at various uences. Varied ow velocities and separation ratio of water in microuidic channels have been successfully obtained through fs laser-induced modication in wetting characteristics of the microchannel surfaces. A concave ow front was observed in a microchannel with hydrophilic surface. Correspondingly, a convex ow front was observed with hydrophobic surface. For an untreated channel, a straight ow front was observed. These results would be attractive for various microuidic chip applications, such as control of the reagent reaction through controlling liquid medium separation or control of mixing ratio in different channels.
Keywords Microuidic channel Surface wettability
Femtosecond laser Sample separation PMMA substrate
1 Introduction
Surface wettability would inuence the reagent ow behavior in microuidic channels (McCarley et al. 2005; Hao et al. 2008) and the ease of adhesion of cells (Yang 2006). Polymethyl methacrylate (PMMA) has excellent optical transparency and is a commonly used substrate for various applications in microuidic devices (Becker and Gartner 2008). Therefore, modication of PMMA surface wettability remains an important research topic (Lin and Burns 2005; Noma et al. 2007; Qi et al. 2008). Approaches that have been used to improve surface wetting characteristics include chemical treatment (Postema et al. 1986), mechanical and ame methods (Fourche 1995), DC glow discharge (Schulz et al. 2001), ion-assisted reaction (Cho et al. 2003), irradiation using a low-pressure mercury lamp that mainly emits 254 nm light (Wei et al. 2005; Hu et al. 2010), electron beam irradiation (Nathawat et al. 2009), plasma treatment (Holmes and Schwartz 1990), and laser irradiation (Lawrence and Li 2001). Plasma treatment is considered to be an effective method...