Structure–property correlations of foul release coatings based on low hard segment content poly(dimethylsiloxane–urethane–urea)

We report the foul release characteristics of model poly(dimethylsiloxane–urethane–urea) (PDMSPU)-based coatings with a relatively lower hard segment content of 9 to 13.7 wt%. The PDMSPUs were prepared by facile moisture curing of isophorone diisocyanate-capped hydroxyalkyl-terminated PDMS. The surface free energies of the coatings were tuned (20–25 mJ/m2) by varying the hard segment content to be in the minimum adhesive regime (20–30 mJ/m2) of Baier’s curve pertaining to the relative amount of biofouling vs the critical surface tension of various chemical substrates. A series of complimentary analytical tools, namely 1H NMR spectroscopy, small-angle x-ray scattering (SAXS), FTIR-attenuated total reflectance spectroscopy (FTIR-ATR), contact angle goniometry, marine field tests, and quantitative biofouling adhesion in shear, have been employed to deduce several physicochemical parameters of importance to establish the structure property correlations. Further, the time-dependant changes in surface wettability and surface concentration of polar functional groups of the coatings (immersed in 3.5 wt% aqueous solution of NaCl) were investigated by FTIR-ATR and contact angle goniometry. The extent of surface restructuring was found to increase with increasing hard segment content of the PDMSPUs and consequently increasing attachment strengths of macrofoulants with the coatings, which were in the range 0.12–0.5 MPa.