Low-distortion, high-strength bonding of thermoplastic microfluidic devices employing case-II diffusion-mediated permeant activation

Abstract

We demonstrate a new method for joining thermoplastic surfaces to produce microfluidic devices. The method takes advantage of the sharply defined permeation boundary of case-II diffusion to generate dimensionally controlled, activated bonding layers at the surfaces being joined. The technique is capable of producing bonds that exhibit cohesive failure, while preserving the fidelity of fine features in the bonding interface. This approach is uniquely suited to production of layered microfluidic structures, as it allows the bond-forming interface between plastic parts to be precisely manipulated at micrometre length scales. Distortions in microfluidic device channels are limited to the size scale of the permeant-swollen layer; 6 microm deep channels are routinely produced with no detectable cross-sectional distortions. Conventional thermal diffusion bonding of identical parts yields less strongly bonded microfluidic structures with increasingly severe dimensional compressions as bonding temperatures approach the thermoplastic glass-transition temperature: a preliminary rheological analysis is consistent with the observed compressions. The bond-enhancing procedure is easily integrated in standard process flows, uses inexpensive reagents, and requires no specialized equipment.

Bonding of thermoplastic polymer microfluidics

“…In one example of COC solvent bonding, a tailored mixture of ethanol and decalin was used to introduced a well-defined volume of solvent into a COC chip surface by timed immersion (Wallow et al 2007). The solvent mixture exhibited case-II permeation, in which the solvated region of the polymer surface is separated from the unsolvated bulk by a sharp boundary.…”

High-strength thermoplastic bonding for multi-channel, multi-layer lab-on-chip devices for ocean and environmental applications

“…However, in a vapour process, its high vapour pressure and solvent capability offer optimal exposure times for process control. The permeant (CHCl 3 )-polymer interaction is thought to lead to a swollen layer and the possibility of channel distortion upon pressure (Wallow et al 2007), depending on the extent of the permeation, which in our case is ~60 µm. However, subsequent heating to the reduced T g of the permeated (PMMA + CHCl 3 ) surface (~80 °C) causes vapour loss, improves the channel profile resilience while permitting interaction with the permeant layer for bonding.…”

“…The latter approach has been reported for a number of polymersolvent combinations, e.g. temperature-activated isopropyl alcohol (Ng et al 2008) or ethanol (Rahbar et al 2010), 1,2-dichloroethane/ethanol at room temperature (Lin et al 2007), dimethyl sulfoxide/H 2 O/methanol (Brown et al 2006), decalin-ethanol COC (Wallow et al 2007), CHCl 3 (De Marco et al 2013;Ogilvie et al 2010), ethanol with UV (Tran et al 2013) and where the solvent interaction is obtained via immersion or vapour exposure. High-strength bonding is achievable by these processes at temperatures sufficiently low to minimise temperature-induced channel deformation.…”

Reliable magnetic reversible assembly of complex microfluidic devices: fabrication, characterization, and biological validation

“…Taking into account this severe limitation, most of the devices are based on direct bonding methods that mate the substrates without any additional materials added at the interface (Herold and Rasooly 2009). Among direct bonding methods, thermal (Taberham et al 2008;Hromada et al 2008;Buch et al 2004;Arroyo et al 2007), solvent (Wallow et al 2007;Unger et al 2000;Sun et al 2006;Griebel et al 2004;Brydson 1999), and surface modification (Johansson et al 2002;Brown et al 2006;Abgrall et al 2006) techniques have been successfully applied. The latter approach, based on plasma treatment, increases surface adhesiveness removing surface contaminants, roughening bonding surfaces, and increasing surface energy by introducing reactive chemical groups.…”