Abstract
In the present study, the effect of atmospheric pressure plasma treatment (APPT) on polymethyl methacrylate (PMMA) substrates was investigated in terms of both the chemical and topographical changes introduced to the polymer surface and its influence on PMMA-to-glass adhesion. The use of a silane-based primer in this bonding system was also studied. The changes introduced to the PMMA surface, as a result of plasma processing, were identified using a combination of: X-ray photoelectron spectroscopy (XPS); atomic force microscopy (AFM), and; contact angle analysis (CA). Degreased only and APPT treated PMMA was then bonded to glass using a polydimethylsiloxane (PDMS)-based adhesive and the influence of plasma processing on adhesion performance was determined using the single lap shear (SLS) test geometry. SLS testing of the as-bonded PMMA-to-glass structures was performed as a function of various PMMA surface treatment conditions, and, after exposure of the bonded joints to multiple temperatures in order to assess the effect of the surface treatment on the strength of these joints. It was found that APPT treatment, with various gas mixtures, lowers the water contact angle of PMMA, and increases its surface free energy. The plasma gases used were argon, helium and oxygen, either on their own or in combination. The chemical composition of the plasma modified PMMA surfaces showed an increase in the level of oxygen present and a corresponding decrease in carbon content, as observed by XPS. Furthermore, AFM indicated a significant change in the topography of the PMMA surface after APPT exposure with a 100–200% increase in mean roughness values with optimised plasma conditions.The above-mentioned physicochemical changes to the PMMA surface led to much improved adhesion of the PMMA-to-glass. APPT treatment improved the strength of the SLS joints from 0.28 MPa to 0.58 MPa. In addition, plasma treated PMMA used in combination with a silane-based primer gave a significant further enhancement in observed adhesion levels with SLS values increasing up to 1.56 MPa. Moreover, the adhesion strength of the bonded samples remained stable after both high temperature exposure at 70 °C and temperature cycling with exposure of the bonded joints from −50 °C to 70 °C. This temperature range had negligible effect on the strength of the adhesive joints after 30 thermal cycles.
Published Version
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