Fluorosilicone polymers with tailored mechanical, acid resistant and adhesive properties: Role of ultrasonication and functionally active single walled carbon nanotubes

Though fluorosilicone polymers (FSP) are known for their excellent solvent resistance and broad service temperature, reports on single walled carbon nanotube (SWCNT) incorporated FSP coatings that are resistant to oxidative environments and at the same time possessing good adhesive characteristics are rare. In this paper we report some interesting results when functionalized single walled carbon nanotubes (FSWCNTs) were incorporated into FSP matrix where the nanotube chosen is the one having minimum defects with the maximum amount of functional groups attached on its surface. Ultrasonication is the process adopted for nanotube incorporation where the conditions were first optimized by subjecting the mixture to ultrasonication for different extent of time. Next, the concentration of FSWCNT in the FSP matrix is varied to optimize the nanotube loading. An ultrasonication time of 30 min and FSWCNT concentration of 0.1% displayed the highest storage modulus values which is taken as the basis for the second part of the study where the optimization of extent of functionalization of SWCNT was validated. Here, FSP nanocomposites were prepared using pristine SWCNT, SWCNT functionalized for 30 min (lower than optimum duration), SWCNT functionalized for 4 h (optimum duration) and SWCNT functionalized for 24 h (higher than optimum duration). Among the nanocomposites, the one containing optimally functionalized SWCNT (that is, SWCNT functionalized for 4 h) displayed superior adhesive properties and resistance to corrosive environment. The reason for this behaviour is established using computational studies where better interaction between FSWCNT and FSP matrix was shown when the nanotubes were functionalized for 4 h. Swelling studies were carried out to prove the role of better interaction of cyclic siloxane units of FSP with hydroxyl functionalities of optimally functionalized SWCNT along with free trifluoropropyl pendants in imparting excellent resistance to corrosive acidic environments. Lap shear strength evaluation on aluminium substrate proved the capability of FSP/FSWCNT nanocomposite as a promising adhesive.