Effect of side chains and solvents on the film surface of linear fluorosilicone pentablock copolymers

The linear fluorosilicone pentablock copolymers PDMS-b-(PMMA-b-PFMA)₂ are synthesized via two-step ATRP approaches by dimethylsiloxane (DMS), methyl methacrylate (MMA) and fluorinated methacrylate (FMA). Trifluoroethyl methacrylate (3FMA), hexafluorobutyl methacrylate (6FMA), octafluoropentyl methacrylate (8FMA) and dodecafluoroheptyl methacrylate (12FMA) are used as FMA. The effect of different fluorinated side chains on the surface properties of PDMS-b-(PMMA-b-PFMA)₂ films indicates that 3FMA, 6FMA and 8FMA behave the similar surface properties as lower water contact angles (θ(H₂O) = 105–106°) and higher surface free energy (26.83–27.55 mN/m) than P12FMA (θ(H₂O) = 116°, 19.52 mN/m) due to the competing migration between the PFMA and PDMS chains. Therefore, the effect of chloroform (CHCl₃), tetrahydrofuran (THF), trifluorotoluene (TFT) and CHCl₃–TFT solvents on the self-assembly and surface properties of PDMS-b-(PMMA-b-P12FMA)₂ film is investigated by DLS, TEM, SCA, XPS, SEM, AFM and QCM-D. A typical bimodal distribution with high content of micelles (310 nm, 93%) in CHCl₃ solution and high content of unimers (17 nm, 70%) in CHCl₃–TFT solution are formed, but a special unimodal distribution of unimers (15 nm) in THF solution and micelles (75 nm) in TFT solution are found. The micelles are confirmed by TEM as P12FMA core–PDMS/PMMA shell in CHCl₃ solution, but PDMS core–PMMA/P12FMA shell in TFT and CHCl₃–TFT solutions. The results reveal that the higher content of unimers contributes much to the fluorine-rich surface, higher cetane contact angle, lower surface energy and lower viscoelasticity for the film, but the higher content of micelles promote forming the roughness surface. Therefore, the most hydrophobic surfaces are the films casting from THF and CHCl₃–TFT solution.