Tailorable low modulus, reversibly deformable elastomeric thiol–ene materials for microfluidic applications

The ability to form low-moduli materials with sensitive modulus control over a wide range is advantageous for a variety of applications, including membranes and valves for microfluidic devices. This paper examines the impact of monomer functionality and stoichiometry on the network properties of thiol–vinyl systems from both experimental and theoretical perspectives. Agreement is observed between the model predictions, based on the probability of forming finite polymer network chains, and the measured Youngʹs modulus values for polymer networks ranging in moduli from 1 to 10 MPa. The highest modulus is obtained for polymers containing tetrathiol, and lower-modulus polymers were obtained by copolymerizing monothiol or dithiol monomers. These novel elastomeric systems are also shown to have strain-at-break values of over 1000%. To illustrate one application of these low-modulus materials, the contact liquid photolithographic polymerization (CLiPP) method was used to fabricate thiol–ene valves in a polymeric microdevice. For an applied pressure of 5 psi, the maximum deflection of the valve was varied from 100 to 320 μm simply by tailoring the modulus of the thiol–ene membrane.