The nature of bioadhesive bonding between barnacles and fouling-release silicone coatings

The failure mechanism of bioadhesive bonding between a marine macrofouler, the Balanus improvisus barnacle, and room-temperature vulcanized poly(dimethylsiloxane) (PDMS)-based elastomers was investigated and compared with poly(methylmethacrylate) (PMMA) panels. The strength of barnacle bioadhesive bonds measured in the shear mode when barnacles were detached from PDMS coatings was much lower than on PMMA and was comparable to the adhesion strength obtained in a 'pseudobarnacle test' in which an epoxy adhesive was used. The failure surfaces were analyzed by scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA), contact angle measurements, and atomic force microscopy (AFM). Analysis of the fracture surfaces indicated that the failure mode was a cohesive failure within the PDMS coatings. It is suggested that the fouling-release properties of the silicone elastomers are facilitated by disentanglement and displacement of surface-enriched uncross-linked PDMS chains. The failure mode when barnacles were detached from PMMA was complex. The major difference from PDMS was the cohesive failure observed in the biofilm attached between the barnacle base plate and the PMMA surface. Preliminary results of the surface characterization of barnacle cement are also reported.