Nanoscale Engineering And Functionalization Of Polymer Thin Films Using Vapor-based Approach

Functional polymer thin films plays a significant role in a wide variety of fields.Their fabrication methods have evolved over the past decades with the tendency of focusing on the enhancement of film durability along with enrichment of functionality.In this work,initiated chemical vapor deposition(iCVD)technique was used to fabricate functional polymer thin films.Through in situ adjustment of deposition conditions,we engineered film structure and chemical composition at nanoscale.Hydrophilic/superhydrophilic surface and hydrophobic/superhydrophobic surface have been fabricated on various substrates,realizing desired functionalities.The detailed research results are as follows:1.Anti-biofouling poly(N-vinyl pyrrolidone)(PVP)coatings with tailored cross-linking degrees were synthesized and grafted onto planar and microporous substrates via a one-step vapor-based approach.N-Vinyl pyrrolidone was copolymerized with ethylene glycol diacrylate(EGDA)at different ratios in the vapor phase,resulting in conformal PVP coatings with a wide spectrum of crosslinking degrees.To improve coating adhesion,direct and hybrid grafting of poly(vinyl pyrrolidone-co-ethylene glycol diacrylate)P(VP-co-EGDA)copolymer were conducted on planar and non-planar substrates,respectively.The surface hydrophilicity of the resultant coatings along with their protein and bacteria repellency increased monotonically with the decrease of crosslinking degree.Coatings with the lowest crosslinking degree showed water contact angles of 33 ± 1oand 0o on planar and nonplanar surfaces,respectively.The modified microporous membranes adsorbed 92% less bovine serum albumin compared to the control,and readily prevented the attachment of Escherichia coli cells.The grafted copolymer coatings are robust against continuous washing and ultrasonication.2.PVP chains were grafted on top of the reactive sites of P(VP-co-EGDA)copolymer to further improve surface hydrophilicity and biocompatibility.XPS spectra show that the N element in the grafted PVP surface is 37% higher than that of the P(VP-co-EGDA)copolymer with the lowest crosslinking degree,indicating a higher content of hydrophilic lactam group.Water contact angle on planar surface grafted with PVP decreases from 33o to 22o compared to the copolymer-coated surface.We deposited both copolymer and PVP-grafted coatings on medical PVC catheters.Similarly,the water contact angle on catheter surface grafted with the extra PVP layer is 28o,compared with 38o of copolymer coated surface.An in vivo biocompatibility test wasconducted by subcutaneously implanting pristine and modified PVC catheters in mice.It was observed that the two modified catheters both exhibit improved histocompatibility compared with the pristine catheter,while the catheter grafted with PVP shows even superior histocompatibility.3.Polymer nanocone array structures were constructed on arbitrary substrates using iCVD for the first time.By flowing both EGDA and 1H,1H,2H,2H-perfluorodecyl acrylate(PFDA)precursors on top of a highly crosslinked PEGDA layer,P(PFDA-co-EGDA)nanocone arrays were fabricated in the vapor phase.The density and shape of the nanocones can be tailored by adjusting the partial pressure of EGDA and PFDA monomers,while the size of the nanocones increases with the increase of deposition time.Due to the ultralow surface free energy of perfluoro side chains of PFDA unit along with the nanostructured surface,the resultant surfaces reached superhydrophobic and superoleophobic state.Such nanostructures can be formed onto a variety of substrates including planar and nonplanar surfaces.When applied onto silicon wafer surface,superhydrophobicity with advancing and receding water contact angles of 162o and 158o were achieved respectively,while the sliding angle is less than 1o.Superamphiphobicity was achieved on nonplanar surfaces,including cotton fabrics and stainless steel meshes,exhibiting repellency towards most liquids such as water,glycerol,ethylene glycol,diiodomethane,vegetable oil,and octane.To summarize,we engineered the structure and chemical composition of polymer thin films at nanoscale,realizing enhancement of both durability and functionality.We hope this work would shed light on the research and industrial fabrication of functional polymer thin films,leading towards a wider variety of applications..