Fabrication and Characterization of Stable Hydrophilic Microfluidic Devices Prepared via the in Situ Tertiary-Amine Catalyzed Michael Addition of Multifunctional Thiols to Multifunctional Acrylates

Abstract

In situ tertiary amine-catalyzed thiol-acrylate chemistry was employed to produce hydrophilic microfluidic devices via a soft lithography process. The process involved the Michael addition of a secondary amine to a multifunctional acrylate producing a nonvolatile in situ tertiary amine catalyst/comonomer molecule. The Michael addition of a multifunctional thiol to a multifunctional acrylate was facilitated by the catalytic activity of the in situ catalyst/comonomer. These cost-efficient thiol-acrylate devices were prepared at room temperature, rapidly, and with little equipment. The thiol-acrylate thermoset materials were more natively hydrophilic than the normally employed poly(dimethylsiloxane) (PDMS) thermoset material, and the surface energies were stable compared to PDMS. Because the final chip was self-adhered via a simple chemical process utilizing the same chemistry, and it was naturally hydrophilic, there was no need for expensive instrumentation or complicated methods to "activate" the surface. There was also no need for postprocessing removal of the catalyst as it was incorporated into the polymer network. These bottom-up devices were fabricated to completion proving their validity as microfluidic devices, and the materials were manipulated and characterized via various analyses illustrating the potential diversity and tunability of the devices.

Gelation and Cross-Linking in Multifunctional Thiol and Multifunctional Acrylate Systems Involving an in Situ Comonomer Catalyst

“…Additionally, f w,acrylate represents the weight-average functionality of the monomers containing acrylate functional groups, and f w,thiol represents the weight-average functionality of the thiol monomer. In agreement with previous reports, 18 we find that the concentration of DEA and the critical extent of reaction are directly proportional ( Figure 6). This relationship is due to a decrease in acrylate functionality caused by the increase in DEA concentration and can be used to explain the minimum observed in gel time ( Figure 5).…”

“…Figure 7a shows the thiol conversion, adapted with permission from Bounds et al, 18 and G′ as a function of time for PETA with 16.1 mol % DEA. In the initial stages of the reaction, the percent conversion of thiol increases rapidly, reaching a conversion of roughly 0.55 within 30 min after the addition of TMPTMP.…”

Tailorable, 3D structured and micro-patternable ionogels for flexible and stretchable electrochemical devices

“…A thiol acrylate mixture can proceed via an ionic Michael addition mechanism with a base catalyst, which deprotonates a thiol group and creates a reactive thiolate anion. 19 Addition of the thiolate anion to an electron-deficient unsaturated acrylate group generates a highly reactive carboanion, which deprotonates another thiol group for reactive thiolate anion regeneration. 20 The thiol acrylate Michael addition cycle continues until one of the reactants reaches full conversion.…”

“…These unique aspects of the thiol acrylate Michael addition reaction make it advantageous for fabricating micropatterns and micro-structures for instance for microfluidics. 19 Therefore, micro-patterning of thiol acrylate based ionogel was investigated using two complementary micro-patterning techniques: soft imprinting lithography and standard photolithography.…”

“…In principle, two ionogel films with different excess groups can be covalently bonded using the same chemistry as the catalyst needed for further thiol acrylate Michael addition is still available on this truly reactive surface. 19 However, two solid surfaces are difficult to conform to each other due to micro-and nano-irregularities, leading to inefficient bonding in the interface. 28 In addition, bonding two different surfaces together would result in a non-uniform layered structure with two different mechanical properties.…”