Determining The Modified Region of Cold Plasma Treated Adhesive using Contact Angle

A key challenge of surface modification of polymers with atmospheric pressure cold plasma is understanding the size of the modified region, given the lack of visual change in the surface. This experiment aimed to gain a better understanding of the modified region of a pressure sensitive acrylic adhesive after being treated with a 2 mm atmospheric pressure cold helium plasma jet, a few millimeters above the surface. Data was collected using contact angle measurements. A 'contact angle map' was created by taking measurements of equally spaced water drops placed in a line on the substrate. Size and uniformity of the treated region were evaluated through changes in contact angle along this line. In addition, universal pH indicator paper was used to map the affected region, showing a region of high pH on the order of several square cm around where the jet makes contact with the paper. This matched our 'contact angle map', where the contact angle dropped significantly over areas on the order of several square cm. To characterize the modified region in detail, we are currently pursuing more selective techniques, such as x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. We will describe our methodology and preliminary results.