Acoustic attenuation characteristics of surface-modified polymeric porous microspheres

Porous microspheres (30-50 mu m) of poly (styrene-co-divinylbenzene) (SD), poly(styrene-co-2-hydroxyethyl acrylate-co-divinylbenzene) (SDH), and poly(methyl acrylate-co-divinylbenzene) (MD) have been synthesized as the basic unit of acoustic shielding medium. To improve their acoustic insulating property, the structural modifications involving deposition of Ni particles (d < 100 nm) by in situ reduction or electroless plating and incorporation of soft poly(ethyl acrylate) chains into SD microspheres to form a semi-IPN have been attempted. The effect of these modifications was assessed using acoustic sources of pink/white noises and an audio band (4000-5000 Hz). Different internal porous structures of the pristine microspheres cause indistinct divergences of acoustic insulating capabilities in the pink and white noise fields. The surface metallization enhances the reflection and scattering actions but dismantle the viscoelastic absorption feature of polymer bulk. Therefore, metallization on relatively soft MD microsphere could create a better effect than on SD and SDH beads. Embedding soft poly(ethyl acrylate) into individual SD bead demonstrates a clear improvement in the sound proof performance. Additionally, the disk constituted by semi-IPN beads displays a downshift of the panel resonance frequencies relative to the disk made of the corresponding SD beads. (c) 2006 Wiley Periodicals, Inc.