Paper PS-TuP5
Measurement of the Isoelectric Point of Plasma Modified Surfaces and Plasma Polymerized Thin Films

Tuesday, October 21, 2008, 6:30 pm, Room Hall D

Plasma polymerization and plasma modification are often used to tailor the surface properties of materials. One important, but often overlooked property of materials is the isoelectric point, which is a critical measure of the acid/base properties of a variety of surfaces, most notably metal oxide surfaces. The isoelectric point for surfaces can be determined using contact angle methods as a function of the pH of the water solution used for the measurements. Here, we have treated a variety of metal oxide surfaces, including SiO₂, SiO_xN_y, and ZrO₂ with Ar plasmas to determine the effect of plasma treatment as well as aging on the isoelectric point of the surfaces. SiO₂ substrates exhibit a significant increase in isoelectric point upon treatment, from ~4.9 to ~6.0, depending on substrate location in the plasma. Upon aging, there is no change in the isoelectric point. In contrast, the SiO_xN_y substrates exhibit little change in isolectric point upon treatment, and no subsequent changes are observed upon aging. XPS compositional data will also be presented to corroborate changes in surface composition upon treatment as well as upon aging of the substrates. Additional contact angle and XPS data will be presented on plasma-deposited metal oxides (e.g. SiO_x and SiO_xC_y) and polymers (e.g. poly(allyl alcohol) and polyamides) for comparison.