Dependence of the Quality of Adhesion between Poly(dimethylsiloxane) and Glass Surfaces on the Conditions of Treatment with Oxygen Plasma

Abstract

Treatment with oxygen-containing plasma is an essential step for the fabrication of devices containing components of polydimethylsiloxane (PDMS). Such oxidative treatment chemically modifies the surface of PDMS allowing it to permanently adhere to glass, quartz, PDMS and other silica-based substrates. Overexposure of PDMS to oxidative gas plasma, however, compromises its adhesiveness. Therefore, regulation of the duration and the conditions of the plasma treatment is crucial for achieving sufficient surface activation without overoxidation. Using a semiquantitative ternary approach, we evaluated the quality of adhesion ( QA) between flat PDMS and glass substrates pretreated with oxygen plasma under a range of different conditions. The quality of adhesion manifested good correlation trends with the surface properties of the pretreated PDMS. Examination of the QA dependence on the treatment duration and on the pressure and the RF power of the plasma revealed a range of oxidative conditions that allowed for permanent adhesion with quantitative yields.

Dependence of the quality of adhesion between poly(dimethylsiloxane) and glass surfaces on the composition of the oxidizing plasma

“…The surface properties of the plasma-treated siloxane elastomer correlated well with its ability to adhere permanently to glass substrates (Millare et al 2008). On the other hand, the use of oxidizing plasma composed of air or of other oxygen-containing gas mixtures, instead of pure oxygen, is a prevalent approach in the PDMS surface activation for the fabrication of lFDs (Gou et al 2010;Anderson et al 2000;McDonald and Whitesides 2002).…”

“…By applying pulling force, in the direction of lifting the PDMS from the glass slides, we examined the quality of adhesion (QA). The values of QA were estimated from ternary semiquantitative evaluation of PDMS-glass adhesion (Millare et al 2008): i.e., QA = 2 for permanent adhesion throughout the whole contact area; QA = 1 for partial adhesion (i.e., the regions of permanent adhesion are randomly distributed over the contact area); and QA = 0 for lack of any permanent adhesion. The QA for each set of the plasma composition and for plasma-treatment conditions was calculated by averaging the values of QA for all samples pretreated under these conditions.…”

“…The fabrication of microdevices, comprising PDMS components, involves controlled oxidation of the dimethylsiloxane surfaces to ensure a permanent adhesion to other silica-based substrates (Millare et al 2008;Bhattacharya et al 2005;Hui et al 2005). Oxidative conversion of the methylsiloxane to siloxy functionality (Si-CH 3 ?…”

“…A nucleophilic siloxy oxygen from one of the substrates attacks an electrophilic silicon from the other, forming a covalent bond across the interface between the two materials. For example, a noncovalent reversible adhesion between PDMS and glass, essential for a range of patterning fabrication steps (Hong et al 2008), does not sustain stress exceeding about 10 kPa (Millare et al 2008). The interfacial covalent enhancement of the PDMS-glass adhesion, however, can sustain stress of 1 MPa or larger (Millare et al 2008).…”

“…Recently, we examined the changes that treatments with plasma, composed solely of oxygen, induced on the PDMS surface (Millare et al 2008). The surface properties of the plasma-treated siloxane elastomer correlated well with its ability to adhere permanently to glass substrates (Millare et al 2008).…”