Studies on surface wettability of poly(dimethyl) siloxane (PDMS) and glass under oxygen-plasma treatment and correlation with bond strength

TLDR

Microfluidic channel fabrication in glass/PDMS lacks a systematic study of bonding strength, and existing work on oxygen‑plasma‑induced siloxane bonds uses parameters specific to individual setups. The study seeks a general, systematic method to predict bond strength between surfaces by correlating it with a common measurable parameter. Surfaces were treated first in an inductively coupled high‑density plasma system and then in a plasma‑enhanced chemical vapor deposition system, after which bond strength was measured with a standardized blister test. The wettability changes induced by varying plasma exposure levels correlate strongly with bond strength, as demonstrated by a clear relationship between water contact angle on PDMS and glass and the measured bond strength, offering a reliable, scalable approach for device manufacturing.

Abstract

An issue in microfabrication of the fluidic channels in glass/poly (dimethyl siloxane) (PDMS) is the absence of a well-defined study of the bonding strength between the surfaces making up these channels. Although most of the research papers mention the use of oxygen plasma for developing chemical (siloxane) bonds between the participating surfaces, yet they only define a certain set of parameters, tailored to a specific setup. An important requirement of all the microfluidics/biosensors industry is the development of a general regime, which defines a systematic method of gauging the bond strength between the participating surfaces in advance by correlation to a common parameter. This enhances the reliability of the devices and also gives a structured approach to its future large-scale manufacturing. In this paper, we explore the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces. We find that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength. We obtained a good correlation between contact angle of deionized water (a direct measure of wettability) on the PDMS and glass surfaces based on various dosages or oxygen plasma treatment. The exposure was done first in an inductively coupled high-density (ICP) plasma system and then in plasma enhanced chemical vapor deposition (PECVD) system. This was followed by the measurement of bond strength by use or the standardized blister test.