Surface Chemistry And Wettability Of Copolymer Coatings Of Acrylic Acid And Octafluorocyclobutane Deposited By Radio Frequency Plasma

Various methods of polymer surface tailoring have been studied to control the changes in wetting behavior.Polymers having precisely controlled wetting behavior in a specific environment are of great interest in biomaterial engineering.The controlled wetting behavior can be obtained by combining surface chemistry and morphology.Plasma assisted polymer surface modification technique have played a significant part to control surface chemistry and morphology.This dissertation focuses on radio frequency(RF)plasma copolymerization of octafluorocyclobutane and acrylic acid(C4F8-co-AA)and investigations regarding surface chemistry,surface wettability,coating kinetics,as well as coating stability.Main achievements in this dissertation are summarized below.Novel and intelligent C4F8-co-AA polymers with tunable wettability and pH-responsiveness are demonstrated.A series of plasma C4F8-co-AA polymer coatings based on various hydrophilic/hydrophobic monomer feed ratio on the flat and nanotextured low-density polyethylene(LDPE)surfaces are deposited via capacitively coupled RF plasma(CCP).The static water contact angles(SWCA)of C4F8-co-AA polymer coatings on flat LDPE surfaces tuned from 1190 to 11 °,while this surface wetting tunability dramatically enhanced from superhydrophobicity(SWCA=163°)to superhydrophilicity(SWCA=4°)for nanotextured LDPE surfaces.The C4F8-co-AA polymer coatings also showed pH-responsive wetting behavior caused by the combined effect of the pH-responsive component(carboxylic acid functional group)and nanotextured surface.The increase of carboxylic acid functional groups in C4F8-co-AA polymers shifted the switchable pH-responsive wetting behavior towards low SWCA range.The magnifying effect of the nanotextured surface on pH-responsiveness is also observed.The influence of duty cycle in pulsed plasma process with the monomer feed rate on the surface chemistry and wettability of C4F8-co-AA polymer coatings is studied.The concentration of the carboxylic acid(hydrophilic)groups increases,and that of fluorocarbon(hydrophobic)groups decreases by lowering the duty cycle.The combined effect of surface chemistry and surface morphology of the RF pulsed plasma copolymer coatings causes tunable surface wettability and surface adhesion.The gradual emergence of hydrophilic contents leads to surface heterogeneity by lowering duty cycle causing an increased surface adhesion in hydrophobic coatings.The C4F8-co-AA plasma polymer coatings on the nanotextured surfaces are tuned from repulsive superhydrophobicity to adhesive superhydrophobicity,and further to superhydrophilicity by adjusting the duty cycles with the monomer feed rates.The surface wettability of plasma polymer coating is traditionally considered as a substrate independent property.We present the substrate effect for ultrathin polymer coatings on surface wettability of C4F8-co-AA coatings.The high concentration of the carboxylic acid functional groups give rise to hydrophilicity via lowering duty cycle and substrate impact give rise to hydrophobicity for ultrathin coatings.The X-ray photoelectron spectroscopy(XPS)and coating thickness measurements confirmed that the sudden increase in water contact angle for lower duty cycle is influenced by the hydrophobic substrate for ultrathin polymer coatings.It is highlighted that the precise control over the surface wettability is attained by tuning the plasma parameters.The substrate-dependent wettability for flat substrate persisted for longer than 8 weeks,which demonstrates wetting stability for ultrathin coatings.