Mechanically tunable PDMS-based polyHIPE acoustic materials

Abstract

Porous PDMS elastomers were synthesized using emulsion templated thiol–ene “click” reactions to obtain materials with tunable storage moduli at a single porosity value that achieve low sound speed values of ∼40 m s−1.

Polydimethylsiloxane Polymerized Emulsions for Acoustic Materials Prepared Using Reactive Triblock Copolymer Surfactants

“…MIPEs were prepared using a modified procedure from our lab. , The continuous phase was first prepared in a 20 mL glass vial. Typically, thiolated-PDMS (0.25 g, 0.285 mmol thiol-functional group), vinyl-PDMS (0.857 g, 0.285 mmol alkene-functional group), and Silube (11 mg, 1.0 wt % with respect to weight of the continuous phase) were combined and vortexed.…”

“…Frequency sweep experiments were performed in rectangular tension mode (0.1–70 Hz; 0.01 mm strain) on three separate samples for all materials and presented as the average of the replicates. The acoustic characterization of samples was performed at ultrasonic frequencies following previously reported protocols. , For each material, two samples (32 mm in diameter) with different thicknesses (1 and 2 mm) were used. Each sample was placed between two identical broadband ultrasonic (US) transducers (emitter and receiver, Olympus V301) with a diameter of 30 mm and a central frequency of 500 kHz.…”

“…The porosity of PDMS appears to have an effect on C L , where a sudden drop of C L was observed with increasing porosity before a plateauing in the values observed over a porosity range of 0–35% porosity . Porous polysiloxanes have now been widely reported as acoustic materials, − but there remains a need for the development of porous siloxanes that can obtain a wide range of porosities, especially at higher porosities, and mechanical properties to access materials with new properties for acoustic lenses and metasurfaces. Acoustic metasurfaces consist of a single material with a subwavelength thickness that has a gradient of distinctly different acoustic properties, e.g., acoustic index, to act as a lens to focus or shape acoustic waves, and this can be achieved by producing gradients of stiffness or porosity using polymer-based acoustic metasurfaces .…”

“…Previously, we reported PDMS-based acoustic materials prepared from thiol- and ene-functionalized PDMSs using polymerized emulsion templating methods that obtain low C L values of ∼40–50 m/s. , In these reports, the thiol to ene ratio was varied to adjust the mechanical properties, and we were able to obtain materials with moduli differences of ∼200 kPa at a single porosity. We used the commercially available surfactant “Silube” to stabilize the emulsions in our previous work, and we were consequently limited to a single pore morphology in the final polymerized materials.…”

Synthesis and Applications of Elastomeric Polymerized High Internal Phase Emulsions (PolyHIPEs)

“…Our lab has synthesized PDMS polyMIPE polyHIPEs with tunable porosity and storage moduli using thiol- and ene-functionalized PDMSs. , Recently, we reported thiol–ene PDMS polyMIPEs that resulted in low longitudinal sound speeds of ∼40 m/s through the polyMIPEs at ultrasonic frequencies. The storage modulus ( G ′) was dependent on the thiol to ene ratio of the PDMS components and polyMIPEs, and G ′ values from ∼40 to 230 kPa could be obtained at a single porosity of ∼40%.…”