Acoustic Characterization of Polydimethylsiloxane for Microscale Acoustofluidics

Polydimethylsiloxane (PDMS) is widely used in acoustofluidic devices among other lab-on-a-chip systems, but a systematic study of its acoustic parameters is lacking, making it difficult to study the acoustic-PDMS interactions accurately during device designs and evaluations. Here the phase velocities and attenuation coefficients of longitudinal and shear acoustic waves propagating in Sylgard^TM 184 samples are measured throughout the frequency band from 3.0 to 7.0 MHz. Five sample groups are prepared, corresponding to different base-agent mixing ratios σ and curing temperatures T, (σ,T)=(10:1,85°C), (7:1, 85 °C), (5:1, 85 °C), (10:1, 65 °C), and (10:1, 100 °C). The shear wave measurements involved examining the change of the reflection coefficient at a solid surface caused by the attachment of the samples. For longitudinal waves, the parameters are obtained by analyzing their round-trip transmissions inside double-layered solid-PDMS structures. Apart from these, the influence of sample aging on the concerned parameters are also examined. With the measured results, the parameters lead to fitted functions based on the Kramers-Kronig principle, which should benefit users working outside the studied frequency range. Finally, the two independent parameters in the elastic matrix of PDMS are provided.