Study of water sorption in rubbers by acoustic microscopy

Acoustic microscopy has been used to examine changes during water swelling at the surface of a rubber previously treated with an acrylic monomer. Surf ace modification was carried out with acrylic acid either in aqueous soluti on or in the vapour phase, and a photografting reaction was achieved with a n aqueous solution of acrylic acid in the presence of a photo-initiator. Wa ter sorption induces modifications of the mechanical properties, transformi ng a rigid polymer into a soft material. Therefore, the acoustic impedance of the material decreases during the swelling process and the evolution of acoustic reflection coefficient is followed. The potential of ultrasonic me asurements as an in situ and non-destructive dynamic analysis technique is demonstrated. Mapping of grafted and ungrafted areas on a rubber surface is obtained with acoustic microscopy. (C) 2000 Society of Chemical Industry.