Wettability Interpretation of Oxygen Plasma Modified Poly(methyl methacrylate)

Abstract

Poly(methyl methacrylate) (PMMA) has been modified via a dc pulsed oxygen plasma for different treatment times. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), optical profilometer, zeta potential, and advancing contact angle measurements. The measured advancing contact angles of water decreased considerably as a function of discharge. Several oxygen-based functionalities (carbonyl, carboxyl, carbonate, etc.) were detected by XPS, while zeta potential measurements confirmed an increase in negative charge for the treated PMMA surface. Evaluating the correlation between the concentration of polar chemical species and zeta potential, we found that increase in surface hydrophilicity results from the coeffect due to incorporation of oxygen functional groups and creation of charge states. The electrical double layer (EDL) effect was also considered in contact angle interpretation by introducing an additional surface tension term into Young's equation. We also found that EDL contribution to the solid-liquid interfacial tension is negligible and can be safely ignored for the systems considered here.

Oxygen and nitrogen plasma hydrophilization and hydrophobic recovery of polymers

“…[6][7][8][9]21,23,36 Several studies 9,21,23 have demonstrated that longer treatment times induce more hydrophilic surfaces. Similar results have been observed for higher plasma powers as compared with lower ones, 6 implicating that the higher the plasma dose the lower the measured contact angle.…”

“…[16][17][18] Typically, polymer surfaces exposed to oxygen or nitrogen plasmas become more hydrophilic due to formation of high energy surface groups in reactions between the native surface groups of the polymer and the reactive plasma species. 19,20 In addition to surface chemistry, plasma treatment also often affects the surface topography, [20][21][22][23] which further enhances the effect of the surface chemistry on the contact angle. However, the hydrophilization is typically not stable, and either a partial or complete hydrophobic recovery is usually observed.…”

Characterization and performance of injection molded poly(methylmethacrylate) microchips for capillary electrophoresis

“…As a consequence, hydrophobic plastic surfaces are typically difficult to wet with aqueous solutions [25,26]. These inter-related problems can be partially ameliorated by modifying the surface charge density by plasma oxidation [16,27,28], UV exposure [29], or dynamically modifying the plastic surface with surfactants [30]. Alternatively, the EOF can be eliminated or greatly suppressed by increasing the viscosity of the running buffer by adding a sufficient amount of a linear polymer, such as polyethylene oxide (PEO).…”

Low-Temperature Polymer Bonding Using Surface Hydrophilic Treatment for Chemical/Bio Microchips

“…Polymer surface modification methods are classified into two categories. One is modification of the original surface (e.g., plasma treatment (Lianos et al, 1994;Kamińska et al, 2002;Chai et al, 2004;Lai et al, 2006), UV irradiation (Peeling & Clark, 1981;Murakami et al, 2003;Hozumi et al, 2004;Diaz-Quijada et al, 2007;Kim et al, 2009). The other is coating with other materials (Ratner, 1995;Oehr, 2003;Liu et al, 2004;Bi et al, 2006).…”

“…C-H) on the polymer surface are expected to be dissociated and incorporated oxygen radicals. Polar oxidized components were increased because of the incorporation (Lianos et al, 1994;Chai et al, 2004). This surface state is considered to enhance the bonding reaction at the interface.…”