Abstract
Photoresist is the key material in the fabrication of micropatterns or microstructures. Tuning the surface wettability of photoresist film is a critical consideration in its application of microfluidics. In this work, the surface wettability tuning of acrylic resin photoresist by oxygen plasma or ultra-violet/ozone, and its aging performance in different atmospheres, were systematically studied. The chemical and physical characterizations of the surfaces before and after modification show a dramatic decrease in the C–C group and increase in surface roughness for oxygen plasma treatment, while a decrease of the C–C group was found for the UV/ozone treatment. The above difference in the surface tuning mechanism may explain the stronger hydrophilic modification effect of oxygen plasma. In addition, we found an obvious fading of the wettability tuning effect with an environment-related aging speed, which can also be featured by the decrease of the C–C group. This study demonstrates the dominated chemical and physical changes during surface wettability tuning and its aging process, and provides basis for surface tuning and the applications in microfluidics.
Highlights
There are special requirements for the wettability of solid surfaces in many fields, including biological process [1,2], membrane [3,4], wastewater treatment [5], metal corrosion resistance [6,7], separation [8], absorbance [9], cleanness [10], sensor [11], etc
UV/ozone treatments with different exposure times led to a decrease of the water contact angle, which was a continuous decrease with the UV/ozone time, different from the fast decreasing and constant contact angles with oxygen plasma treatments
The C–C percentage in the carbon spectrum of X-ray photoelectron spectroscopy (XPS) observations decreases after oxygen plasma or UV/ozone treatment, indicating the chemical content variation, which is the chemical cause of superficial hydrophilic enhancement
Summary
There are special requirements for the wettability of solid surfaces in many fields, including biological process [1,2], membrane [3,4], wastewater treatment [5], metal corrosion resistance [6,7], separation [8], absorbance [9], cleanness [10], sensor [11], etc. When used in microfluidics or other fields, the stability of the hydrophilic polymer surfaces obtained by plasma or UV/ozone treatments should be paid attention to, because of the hydrophobic recovery with time [39,40,41]. Except for the hydrophilic modification performance, the wettability stability during aging of the acrylic photoresist surface is compared between oxygen plasma and UV/ozone treatments, while the storing atmosphere includes air and water, which plays an important role in the lifetime of applications. UP water (18.2 MΩ.cm) was used as the water droplet without further purification, prepared by a Laboratory Water Purification System (Ultrapure UV, Hitech Instruments Co., Ltd., Shanghai, China)
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