Dual approach of bimodality and nano-reinforcement towards toughened PDMS based foul release coatings

It is well established that crosslinked polydimethylsiloxane (PDMS) based coatings have efficacious foul release characteristics. However, a trade-off between mechanical integrity of filled and crosslinked PDMS based coatings and their foul release performance has been a bottleneck for producing efficient and durable coatings. In the present study, we report a dual approach of nano-reinforcement of a bimodal PDMS network as a strategy to produce simultaneously reinforced and toughened PDMS networks with facile release of macrofoulants from their surfaces. The nanocomposites of both unimodal and bimodal PDMS networks were prepared using oligomeric dihydroxyl functional PDMS precursor chains differing in their molecular weights by a factor of five and commercial Cloisite-20A nanoclay as the nanofiller. The clay layers were found to be mildly intercalated in the PDMS matrix, as revealed from investigations by scattering and imaging techniques at different length scales. While the unimodal PDMS networks did show nanoclay induced simultaneous reinforcement and toughening, at equivalent clay loadings, the bimodal PDMS nanocomposites seemed to stretch further with characteristic strain hardening before fracture. Dynamic mechanical analysis (DMA) and swelling studies of the nancomposites further confirmed the nanoclay induced reinforcement effect of the bimodal PDMS host matrix. The intrinsic low surface energy characteristics of PDMS were retained by bimodal blending of long and short chains and its subsequent nano-reinforcement. Macrofouling studies by panel immersion and release force measurements revealed that the macrofoulants could be dislodged from the nanocomposite coatings with a shear force < 0.05 MPa.