Polystyrene Surfaces Terminated with a Single Functionality of Alcohol
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I. INTRODUCTION Polymeric materials form the largest class of biomaterials. They have desirable chemical and mechanical bulk-properties, but their surfaces are often terminated with C-H bonds and are highly hydrophobic. Surface modifications are thus often needed to improve the surface properties and customize them to specific applications without changing the material's desirable bulk characteristics. Several methods such as low energy ion beam [1], gaseous plasmas [2,3], UV excimer-laser [4], electron beams [5] and gamma radiation [6] treatment of polymer surfaces are known to be efficient in functionalizing the surfaces. However, many of these modified surfaces have a mixture of chemical functionalities and are often highly reactive in a subsequent air exposure because of the presence of surface dangling bonds. The purpose of this work is to engineer a polymer surface with a desirable single chemical functionality. The presence of a single surface functionality allows a better prediction of the surface chemical reactivity at a certain pH value of the reaction system. Such a functionality may also be used as chemically reactive sites for a controlled binding of other molecules. Polystyrene is chosen for its optical transparency, durability, low cost, good mouldability, and rather unique spectral and chemical properties due to its aromatic system.
53 Mat. Res. Soc. Syrup. Proc. Vol. 414 ©1996 Materials Research Society
It is known that water dissociates into H, 0 and OH when adsorbed on a hot metal surface [7,8]. The majority of the adsorbed 0, H, OH react on the surface to give back water. The desorption of OH, however, remains a minor but significant channel. The H20/OH desorption yield ratio can be in the order of 10' [8], In this work, OH radicals were generated in vacuum by reacting water vapor with hot filaments, and used to form a single alcohol functionality on polystyrene. X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) were used to confirm the feasibility of such a surface engineering with a precise control. Furthermore, laser-induced fluorescence spectroscopy was used to confirm the OH radical generation in gas phase. II. EXPERIMENT The experiments heated to about 1500°C Torr. Polystyrene was 15nm. Such a thickness and HREELS analyses.
were carried out in a vacuum system in which filaments resistively were used to dissociate water vapor at a pressure of 0.2 - 0.0001 spun onto a p-Si(100) wafer with a final film thickness of about control prevents excessive surface charging during subsequent XPS
XPS was performed in a Surface Science Instrument Model SSX-100 spectrometer. An X-ray spot of about 300m in diameter was used in the analysis. Binding energy data collected from this spectrometer were calibrated by using the Au 4f 7, 2 peak at 83.93eV of a sputter-cleaned gold foil. Curve fitting was performed with a common chi-square minimization routine and constrains derived from the polystyrene spectra prior to any surface modification. HREELS analys
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