Low-temperature direct bonding of two cyclo-olefin polymer (COP) plates is realized by pretreatments of vacuum ultraviolet (VUV) light irradiation, VUV irradiation in the presence of oxygen gas (VUV/O3), or oxygen plasma treatment. The bond strength was strong enough to observe bulk destruction on the fractured surfaces after the tensile test of the sample. To investigate the mechanism underlying the low-temperature direct bonding, attenuated total reflection Fourier-transform infrared spectrometer (ATR-FT-IR), X-ray photoelectron spectroscopy (XPS), contact angle measurements, and atomic force microscopy (AFM) surface analysis methods were carried out for the treated COP samples. These experimental results showed that polar functional groups (e.g., -OH, -COOH) are generated by each treatment. These groups are expected to generate dipolar interactions including hydrogen bonds on the surfaces of the pretreated COPs at room temperature. In case of VUV and VUV/O3 treatments, degradation of COP was also occurred and the degradation layer acted as an adhesive for the direct bonding. Thermal annealing enhances creation of strong covalent bonds (-C-O-C-) changed from hydrogen bonds.
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