Study On The Surface Mobility Of Acrylate Polymer Films Labelled By Fluorinated End Groups

With the fast growth of nanotechnology, nanoscale polymer films have widespreadapplications, including surface coating, lubrication, adhesives, microelectronics, biomedicalenginnering, etc. The films on supporting substrate were influenced by interface effects andentanglement and the chain mobility deviating from that in polymer bulk. For this reason, theunderstanding of factors that influence surface chain mobility of polymer films is essential todesign new materials with distinctive surface structure and property.In this thesis, we choosed the functional poly(methylmetharylate)s (PMMA-ec-PFMA)labelled with fluoroalkane end groups that was synthesized by atom transfer radicalpolymerization (ATRP) as the model system and investigated the effect of chain entanglementand polymer/substrate interaction on the surface dynamics and glass transition temperature (Tg)of polymer films by contact angle, X-ray photoelectron spectroscopy (XPS), atomic forcemicroscope (AFM) and ellipsometry measurements. The conclusions were obtained as follows:(1) The effect of the concentration and quality of casting solution on surface mobility ofPMMA labelled with fluoroalkane end groups films had been systematically studied. It wasfound that the films surface onset temperature of chain rearrangement (TRonset) increased from55℃to70℃when the concentration changed from0.8%(wt%) to8.0%, and the surfacerelaxation activation energy (Ea) also increased from126kJ/mol to175kJ/mol. When the solventquality was changed from good to bad by control the volume ratio of ethanol in the solvent, thecorresponding surface TRonsetof spin-coated films decreased from68℃to55℃. The result thatthe zero-shear viscosity (η0) of solutions decreased with the decreaing concentration or qualityindicated the degree of chain entanglement also decreased in the solutions and it caused theenhanced surface mobility of films. When a polymer solution is subject to rapid drying, asspin-coating, the polymer chains in the solution may not have enough time to adjust and somememory of the chains conformation in the solution can get carried over to the dried film. Thedegree of chain entanglement in the spin-coated films decreased with decreaing concentration orquality of the casting solutions and it induced the enhanced surface mobility. Therefore, theproperty of casting solution determined the interchain interactions in the films and could influence the surface chain motion.(2)The effect of polymer/substrate interaction on the surface relaxation behavior and glasstransition temperature (Tg) of PMMA labelled with fluoroalkane end groups films wereinvestigated by contact angle and ellipsometry measurements. The Tgof films on nativeoxide-covered wafer (Si/SiO2) increased with decreasing film thickness caused by the strongpolymer/substrate interaction, while on hydrogen-passivated silicon (Si/Si-H) the influence ofsubstrate was weak and Tgof films decreased with decreasing thickness because of the effect offree surface. The corresponding thickness (h0) of films when Tgdid not change was the effectiverange of substrate. It was found that h0had a dependency on the molecular weight (Mw) and h0increased from15nm to32nm when Mwincreased from23K Da to92K Da. The h0for PMMAfilms with Mwof23K Da and43K Da were both below20nm, and their surface onsettemperatures of chain rearrangement (TRonset) on Si/SiO2and Si/Si-H were the same whenthickness was between20and110nm. But if Mwincreased to92K Da and h0was32nm, theTRonseton Si/SiO2was higher than that on Si/Si-H when the thickness was between20and30nmand the gap increased with decreasing thickness. The result demonstrated the effective range ofpolymer/substrate interaction was around30nm and it influenced the films surface mobility. As aconsequence, the effective range of substrate on the chain mobility in the film increased withincreasing Mw.