Functional Polymer Films With Controlled Crosslinking Degree Through ICVD And Its Applications

In recent years,polymer films have been widely used in biomedicine,optoelectronic devices,protective coatings,and energy catalysis.As the preparation methods became mature,the control of function and stability has become the research focus in the field of thin films.In this paper,a series of functionally controlled polymer films were prepared by initiated chemical vapor deposition(iCVD),and their applications to the fields of surface patterning,hydrophilic surfaces and antifouling surfaces were discussed.The specific research contents are as follows:1.Photo-responsive poly(allyl methacrylate)film was successfully prepared by vapor-based route.Compared with the traditional polymerization methods,our conditions are milder,lower cost and simpler.The influence of deposition conditions on the structure of the film was explored to achieve structural regulation.The prepared film retains most of the allyl groups,providing a reaction site for further modification of the polymer.Under 254 nm ultraviolet light,the photoinitiating groups in the film were able to undergo crosslinking.Upon UV exposure of 3 h,films were cross-linked completely.Using a photomask,the as-deposited film was exposed to a mild UV source,and a high resolution optical pattern was obtained directly in one step.The optical patterns were characterized by AFM,which showed that the thickness of the film decreased with the increase of crosslink density,and the decrease was about 28.8%.In addition,we have found that the solubility of the film changes with the UV exposure time.In a highly polar organic solvent,light can convert the amount of dissolution of polymer film by more than 85%.By controlling the duration of UV light exposure,we can thus control the degree of crosslinking of the film,which enabled further possibility of functionalization.2.The optimal synthesis conditions of the ultra-thin hydrophilic film of P(EGDA-co-VP)and P(EGDMA-VP)cross-linking system were investigated.A series of polymer films of different crosslinking degrees were obtained by adjusting the flow ratio of monomer to crosslinking agent.We used a layered grafting strategy on both planar and non-planar substrates to enhance the bonding strength between the polymer film and the substrate,and avoid the instability of the hydrophilic film on the substrate.Through water contact angle test,films from both systems have a same trend: as the VP moiety in the polymer increases,the contact angle reduces in both P(EGDAco-VP)and P(EGDMA-VP)films.The contact angles on silicon wafer for the P(EGDA-co-VP)and P(EGDMA-VP)systems were about 34° and 38°,respectively.The contact angle approached to 0° on porous substrates coated with these films such as PVDF filter.In addition,by grafting an additional layer of PVP on the surface of the film,the contact angles can be further reduced to 31° and 33° for the two films,respectively.The excellent hydrophilicity of these films reduced the adsorption of 99% E.coli on the silicon wafer.It is also noted that the thickness of our films can be easily tuned to as thin as 20 nm.3.Upon coating with the most hydrophilic film,the water contact angle of commercial nanofiltration membranes can be reduced from 58° to 32°.At the same time,since the hydrophilic film is extremely thin(about 20 nm),no obvious change was observed on the surface of the polyamide membrane after iCVD coating.The ultrathin hydrophilic coating allowed the water flux of the nano-filtration membrane with only a 12% reduction.The water contact angle on the coated membrane was maintained at about 34° after 8 h of ultrasonic testing,indicating its stability.The salt rejection on the surface of the modified nanofiltration membrane was slightly increased,while the antibacterial adsorption reached 99%,indicating significant extension of the membrane life.In summary,we explored factors affecting the functionality of the iCVD films,and exploited its advantage of in situ crosslinking to fabricate hydrophilicity-tuned ultrathin coatings for nanofiltration membranes.These advantages of the iCVD method indicates its promising applications in various fields of functional polymer thin films.