Mechanical properties of bulk polydimethylsiloxane for microfluidics over a large range of frequencies and aging times

The dynamic mechanical characterization of polydimethylsiloxane (PDMS) over a large range of frequencies (10(-2) < f < 10(5) Hz) and long aging times at room temperature (4 h < t(v) < similar to 60 000 h) has been presented. Three samples with different curing conditions have been studied and three different techniques, dynamic mechanical analysis at different temperatures, nano-indentation and scanning micro-deformation microscopy, have been used. Although the three techniques work at different scales and at different frequencies all the results match the same master curve. As expected, the storage and the loss moduli greatly increase with the frequency. Moreover, these moduli moderately increase with the aging time tv depending on the curing temperature. A simple model which takes the frequency and the aging time into account, and which is based on the Havriliak-Negami model, has been presented and identified. Hence, values of the relaxed and instantaneous moduli at tv = 0 and tv = infinity are proposed. Only the relaxed moduli depend on the curing conditions and moreover it has been shown that the tangent of the phase lag is independent of the aging time and thus of the curing process.