In numerous applications in microfluidics, cell growth, soft lithography, and molecular imprinting, the surface of
poly(dimethylsiloxane) (PDMS) is modified from a hydrophobic methyl-terminated surface to a hydrophilic hydroxylterminated
surface. In this study, we investigated molecular structural and orientational changes at the PDMS-air
interface in response to three commonly used surface modification processes: exposure to long-wavelength ultraviolet
light (UV), exposure to short-wavelength UV that generates ozone (UVO), and exposure to oxygen plasma (OP). The
surfaces of two PDMS compositions (10:1 and 4:1 of base polymer/curing agent) were probed during modification,
using monolayer-sensitive IR + visible sum frequency generation (SFG) vibrational spectroscopy, with two different
polarization combinations. During PDMS surface modification, the peak intensities of CH3 side groups and CH2
cross-link groups decreased, while peak intensities of Si-OH groups increased. There was no significant change in
the average orientation of the CH3 groups on the PDMS surface during modification. The concentration of CH3 groups
on the surface decreased exponentially with time, for all three UV, UVO, and OP modification processes, with first
order kinetics and time constants of approximately 160, 66, and 0.3 min, respectively. At steady state, residual CH3
groups were detected at the PDMS surface for UV and UVO treatments; however, there were negligible CH3 groups
detected after OP modification. 表面和频光谱分析系统(SFG) PL2230系列高能量全固态锁模皮秒Nd:YAG激光器 Ekspla CARS 相干反斯托克斯拉曼显微光谱仪
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