Study On The Morphology, Struture And Application Of Self-assembled Block Copolymer PS-b-PLA Thin Films

Block copolymer generally refers to macromolecular polymer which connected with two or more diverse polymer chain segments of different chemical composition and properties by chemical bond(covalent bonds). Due to the thermodynamic incompatibility of different polymer chain segments, block copolymer can develop nanometer range ordered structures by micro phase separation. This structure is under the control of itself molecular parameters, thin film thickness, substrate properties, the external field and so on.In this paper, the Polystyrene-b-Polylactide(PS-b-PLA) thin film were prepared on Si substrate by spin-coating. We studied the influence of substrate properties, solution concentration, film thickness, annealing temperature and time, annealing solvent and the addition homopolymer Polylactide(PLA) on the morphology and structure of block polymer film self-assembly. It was found that the difference of substrate properties influences the morphology and structure of PS-b-PLA self-assembly film. Selective solvent contributed to the micro phase separation of PS-b-PLA film,while cosolvent had no obvious influence on phase separation. Temperature annealing at 130℃ couldn’t bring ordered structural film. After being annealed at 150℃, the mixture order structure of the strip, ‘parallel rod-like’ perpendicular to the substrate could be obtained, while the temperature is 170℃, the strip ordered structure perpendicular to the substrate could be obtained. The addition of PLA, the micro phase separation of PS-b-PLA together with PLA film occurred, and the time of developing order structure extended.In addition, in this paper the PS-b-PLA thin film were prepared on hydrophobic Si substrate, then the film was annealed at 170℃ for 2h to acquire parallel strip structure perpendicular to the substrate. Moreover, the film was annealed at 170 ℃ for 30 h to acquire elongated cylinders perpendicular to the substrate. After the film with parallel strip structure was immersed in NaOH solution, the PLA phase was removed and the Si substrate with ‘dendritic’ surface was obtained, the light reflection rate to visible light was 60%. After the same handling on the elongated cylinders film, we acquired the porous Si substrate, the light reflection rate was 30%.