Change in surface properties of polydimethylsiloxane/polyurethane/carbon nanotubes elastomeric coatings

Abstract

Addition of polydimethylsiloxane (PDMS) to polyurethane (PU) improves mechanical, surface and bulk properties. PDMS plays the role of a soft segment in PU because of its low surface tension and glass transition temperature. This polymer blend shows highly segregated morphology allowing production of thermoplastic elastomers with properties in between a crosslinked elastomer and thermoplastic depending on composition. In this study, PDMS/PU blends were synthesized in situ and the effects of PDMS composition, the type and content of catalyst, solvent and isocyanates molecular weight as well as carbon nanotubes (CNTs) incorporation on the surface properties of the resulting elastomeric coatings were discussed. Different measurements including contact angle, SEM, AFM, FTIR and elemental composition analyses were used for interpretations. The competition between OH terminating groups of PDMS and polycaprolactone was the key controlling over the hydrophilicity of the resulting PDMS/PU coatings. Such effect was studied by monitoring the changes in surface properties of the cured coatings. The results revealed that by adjusting the above-mentioned parameters, surface chemistry of the cured films were changed. PDMS introducing to PU resulted in a rise in water contact angle from 93° to 113°, which indicated a considerable surface hydrophobicity. Moreover, solvent selection exhibited a crucial role on surface roughness. CNTs incorporation resulted in surface hydrophobicity enhancement, as featured by a rise in water contact angle from 100 to 135°, suggesting the possibility of surface tailoring by optimizing PDMS and CNTs concentrations.