Fluorinated Acrylate Block Copolymer Surface Structure And Protein Adsorption Behavior Relationship

How to tailor the amount of adsorbed proteins on material surfaces for potential applications has become a great challenge. It is therefore important to study the interactions between artificial interfaces and proteins in the fields of biomaterials and marine antifouling materials. Fluorinated copolymers can reduce protein adsorption theoretically with its low surface energy property, though there many opposite results were reported. Conflicting results may be caused by poor characterization of the fluorinated surface and the lack of systemic study of the interactions between the surface structure and protein adsorption.In this paper, diblock and triblock fluorinated copolymers composed methyl methacrylate(MMA) and 2-per?uorooctylethyl methacrylate(FMA) were synthesized by atom transfer radical polymerization (ATRP). The structure of fluorinated copolymers on the air/solution interface was investigated by surface tension and sum frequency generation (SFG) vibrational spectroscopy which has unique interfacial selectivity and submonolayer sensitivity. The influence of air/solution interface structures on the property of films were systemic studied. In order to study the principle of protein adsorption on fluorinated copolymers surface, protein adsorption test on the surface with various properties was explored and the conclusion was obtained as follows:(1) The surface tension of diblock copolymers (PMMAm-b-PFMAn) were the same as that of PMMA homopolymer in cyclohexanone solutions. There were no surface activity for fluorinated copolymers were discovered. It was found that PMMA segments was adsorbed at the air/solution interface. This may be attributed to that the stable micelle was formed in the solution which stopped PFMA segments from adsorbing at the air\solution interface.(2) When PFMA or PMMA block were short, the surface tension of triblock copolymers(PFMAy-b-PMMAx-b-PFMAy) were much lower than that of PMMA homopolymer in cyclohexanone solutions. It was found that PFMA segments was adsorbed at the air/solution interface. When PFMA or PMMA block were long enough, the surface tension of the triblock were the same as that of PMMA homopolymer, no surface activity for fluorinated copolymers was discovered. It was found that PMMA segments adsorbed at the air/solution interface. These phenomenon were related to the stability of the micelle formed in cyclohexanone solutions.(3) It was found that the surface activity of the polymers in toluene solutions was different from that in cyclohexanone solutions. The surface tension of diblock copolymers PMMAm-b-PFMAn (besides PMMA920-b-PFMA0.9 and PMMA430-b- PFMA22.0) and triblock copolymer PFMA10.1-b-PMMA430-b-PFMA10.1 were lower than that of PMMA homopolymer in toluene solutions. Surface activity for fluorinated copolymers were found in toluene solutions. The SFG results showed that PFMA segments were adsorbed at the air/solution interface. The difference in the air/solution interfacial structure from various solvents was attributed to the stability of the micelle formed in the solvents. Compared with cyclohexanone, toluene was a much better solvent for PMMA and PFMA block, in which block copolymers could not form stable micelle.(4) The air/solution interface structure of the copolymers determined the surface properties of the films which was prepared by spin-coating. These may be caused by the fast evaporation of the solvent. In this way the chain of the copolymers were locked immediately. Films had high PFMA content at surfaces when the air/solution interface occupied by PFMA segments. Otherwise, the PFMA content at surface was much lower.(5) The air/solution interfacial structure of the copolymers had no significant effect on surface properties of the films which were prepared by cast. Cast films of PMMAm-b- PFMAn(n≈1) and PFMAy-b-PMMAx-b-PFMAy(y≈1) had high PFMA content no matter how long the PMMA segments were. The water contact angle of the cast films could reach to 120 degree.Cast films had best environmental stability when the length of PMMA block was as long as 430. In this PMMA length, copolymers had the best orders for both film surface and film bulk. This may be attributed to that the free energy of PFMA components of surface enrichment was influence by PMMA block length.(6) Fluorinated component on the film surface could reduce protein adsorption. The higher fluoride content was on the film surface, which resulted in the less protein adsorbance. Surface reconstruction of fluorinated copolymers film in protein solution would affect their anti-fouling ability. The excellent properties of fluorinate copolymers disappeared when it exposed to protein solution, the anti-fouling ability became weak.