Fluorinated Copolymers Gas / Liquid Interface Structure And Its Influence Factors

Fluorinated polymers were widely employed in the coating and biomimetic materials fields owing to their effect of building low interfacial free energy surfaces,therefore, they have attracted a lot of attentions in the past few years. As we known, polymer surface structure and properties is mostly determined by the structure of polymer at air/solution interface, so it is very important to investigate the molecular structure of polymer chains at the air/solution interfaces. Molecular structure and the distribution of groups for these interfaces were still poorly understood, which can be attributed to the complexity of polymer molecules and difficultly division between interface and solutions. There are only a few interface techniques available to probe air/solution interface at molecular level.In this dissertation, the structure of fluorinated polymer on the air/solution interface was investigated by sum frequency generation (SFG) vibrational spectroscopy which has unique interfacial selectivity and submonolayer sensitivity. The effect of fluorinated polymer structure and solvent on the molecular structure at air/liquid interfaces was also explored and the conclusion was obtained as follows:(1) The structure of fluorinated polymer on the air/solution interface was influenced by the fluorinated block length of diblock copolymer. For PMMA144-b-PFMAn (poly(methyl methacrylate)-block-poly(2-perfluorooctylethyl methacrylate)) cyclohexanone solutions, when the PFMA block length was short, the molecules packed at the air/solution interface with the PFMA on the outmost surface, the PMMA block dissolved into solution. When the PFMA block was long, two-dimensional surface aggregates composed of a PMMA corona and a PFMA core were formed at the air/solution interface. As to the PBMA₁₆₄-b-PFMA_n (poly(butyl methacrylate)-block-poly(2-perfluorooctylethyl methacrylate)) toluene solution, when the PFMA block length was short, the molecules also packed at the air/solution interface with the PFMA on the outmost surface, and the PFMA display as horizontal orientation. While for PFMA with long block, the PFMA displays as vertical orientation on the outmost surface and assembles more ordered. (2) When the fluorinated block length of diblock fluorinated copolymer is similar, the surface tension of PBMA₁₀₁-b-PFMA_3.63,PBMA₁₆₄-b-PFMA_3.06 and PBMA₃₀₀-b-PFMA_3.08 was 21.4dyn/cm, 20.5dyn/cm and 25.0dyn/cm, respectively. Compared the SFG results, it is easy to found that the interface of PBMA₁₀₁-b-PFMA_3.63 toluene solution was covered by the loose PFMA blocks. As to the PBMA₁₆₄-b-PFMA_3.06, the interface was covered by tight vertical arrayed PFMA blocks, it is the most advantageous to make fluorinated groups enrichment to the interface. While for the PBMA₃₀₀-b-PFMA_3.08 solutions, the PBMA blocks were detected on the interface by SFG. The longer nonfluorinated block in triblock fluorinated copolymer PFMAn-PMMA91-PFMAn,PFMAn-PMMA355-PFMAn and PFMA_3.2-b-PBMA₁₁₆-b-PFMA_3.2,PFMA_3.2-b-PBMA₃₀₃-b-PFMA_3.2 was in favor of the PFMA block assembling and arranging horizontally.(3) It was also revealed that block polymer chain conformations at the air/solution interface were affected by the nature of the solvents. PMMA₁₄₄-b-PFMA_10.4 formed a surface segregation that PFMA was core and PMMA was shell at the air/solution interface with cyclohexanone as solvent. As to the PMMA₁₄₄-b-PFMA_10.4 toluene solutions, it was covered by PFMA blocks. At the air/solution interface of the PMMA₁₄₄-b-PFMA0 cyclohexanone solution, PFMA backbone arranged vertically, and as to the PMMA₁₄₄-b-PFMA0 toluene solutions, it arranged horizontally.(4) It is found that the triblock copolymer(PFMA₃-b-PBMA_m-b-PFMA₃) would like to reduce the surface tension much more than that of diblock copolymer (PBMA_m-b-PFMA₃)with the same fluorinated block length and nonfluorinated block structure. And the chain conformations at the air/solution interface of triblock copolymer is in favor of assembling more ordered than diblock copolymer, which illustrated the triblock copolymer would be propitious to the fluorinated moieties segregate to the surface.(5) The structures of the fluorinated diblock copolymer with different kinds of nonfluorinated units at the air/solution interface existed discrepancies. The interface of air and PMMA₁₄₄-b-PFMA_0.7 or PBMA₁₆₄-b-PFMA_0.98 toluene solution was covered by horizontal PFMA block, and the former polymer chain was more close-packing. However, the long alkyl side chain of PODMA dominated the interface of air and PODMA₁₆₀-b-PFMA_1.29 toluene solution and the perfluorinated side chain was buried in the long alkyl side chain of PODMA.(6) The solvent nature also affected the random copolymer(PMMA-r-PFMA) chain conformations at the air/solution interface. When cyclohexanone was used as solvent, the polymer chain at air/solution kept a compact coil conformation. The fluorinated moieties segregated to the air/solution interface as the FMA content increase to 9%. As to the toluene solutions, the chain conformation of the random copolymer was more extended, The fluorinated moieties segregated to the air/solution interface when the FMA content was just above 3%.(7) The chain structures of diblock copolymer at air/solution interface is quite different from that of random copolymers. PMMA₁₄₄-b-PFMA_0.7 polymer chain with cyclohexanone as solvent stand vertical at the air/solution interface, and the interface was covered by PFMA block. However, PMMA-r-PFMA with 2.51% or 2.52% FMA content performed a coil conformation at the air/solution interface, and the interface was covered by MMA units.