Structures And Properties Of Polymer Thin Films And Water-soluble Polymer Mixtures Studied By Spectroscopy

Chemical structure in the molecular level determines the properties of surfacesand interfaces. Studying the molecular level structure of surface and interface is ofgreat importance, aiding in penetrating into the nature of surface and interfacialproperties. However, up to now，it is still challenge to accurately probe molecularlevel structure and alignment of surface and interface in situ. Fortunately, SumFrequency Generation (SFG) Vibrational Spectroscopy, with inherent interfacialselectivity and submolecular sensitivity, has been developed into a powerful techniquedetecting the surface and interfacial molecular structures in the past twenty-five years.What’s more, SFG also has the potential to study the bulk relaxation of polymer thinfilms, considering the special selectivity and sensitivity of surface and interfacialmolecules，it also can be employed to study the surface and interfacial relaxation.From my prospective, SFG would be developed into an effective means to study thesurface、interfacial and the bulk relaxation of polymer thin films.At present，ordinary materials have already failed to meet the people’s growingmaterial and cultural needs，materials science is developing in the direction ofintelligent and functional materials. Thermoresponsive polymers are importantfunctional materials due to its wide applications. Because water is unharmful andenvironmental friendly, thermoresponsive polymers which are water-soluble haveextensively attracted the scientists’ attention worldwide. Attenuated Total ReflectanceInfrared (ATR-FTIR) Spectroscopy and Ultraviolet-Visible Absorption Spectra (UV)are the effective techniques to study molecular structures and absorbances ofpolymers in aqueous solutions.The thesis mainly employed Sum Frequency Generation (SFG) VibrationalSpectroscopy to probe surface molecular structure and bulk glass transtiontemperature of polymer thin films. Attenuated Total Reflectance Infrared (ATR-FTIR)Spectroscopy and Ultraviolet-Visible Absorption Spectra (UV) were used to studythermoresponsvie interpolymer complexes in aqueous solutions, the concrete research contents and conclusions are as follows：(1) The Sum Frequency Generation (SFG) Vibrational Spectroscopy wasemployed to study the surface molecular chain conformation of spin coating PMA andcasting PMMA films prepared from solvents with different qualities. SFG spectra ofPMA and casting PMMA films prepared from solvents with different qualities werefound different. With the solvent from poor to good，the SFG intensity of ester methylgroups of spin coating PMA and casting PMMA films become more and more strong,which indicates that the ester methyl groups tend to stand on the surface in goodsolvent，On the contrary，the ester methyl groups prefer to lie down on the surface inpoor solvent. This suggests that the surface molecular structures of PMA and PMMAfilms are affected by the solvent quality. A simple phenomenological model was usedto describe the chain conformational order at the polymer surface by correlating theSFG resonant signals of the side chromophoric groups (ester methyl groups) to theintroduced chain arc included angle. The chain arc included angle decreased withexpanding molecular chain. This model is believed to be applicable for polymers withshort and rigid side chromophores active for the SFG spectroscopy.(2) The sum frequency generation (SFG) vibrational spectroscopy as a novelcharacterization means was used in studying glass transition temperature of thinpoly(methacrylate)s films supported by gold (Au) substrates for the first time. Theglass transition temperatures (Tg) of three kinds of polymer thin films which arepoly(methyl methacrylate)(PMMA), Poly(ethyl methacrylate)(PEMA) andPoly(benzyl methacrylate)(PBMA) have been investigated in this study. The resultsshowed that the bulk glass transition temperatures of all sorts of polymer thin filmswere in good accord with that measured by traditional differential scanningcalorimetry (DSC). The Tg values of given thickness of polymer thin films wereevaluated, it was found that all kinds of polymer thin films supported by goldsubstrates showed a decrease in Tg with decreasing films thicknesses, consistent withresults by others. The Tg value of26nm thick PBMA film is reduced from the bulkvalue of Tg by27K. The depression of the Tg value of17nm thick PEMA film isaround11K than the bulk value of Tg. Obviously, SFG is an effective tool to determine the bulk Tg. Due to the sensitivity of surface and interface of SFG, wefirmly believe that SFG will be developed into a popular technique to detect thesurface and interfacial relaxation in the near future.(3) Attenuated Total Reflectance Infrared (ATR-FTIR) Spectroscopy andUltraviolet-Visible Absorption Spectra (UV) were employed to studyThermoresponsive Complexation Between Poly(4-vinylpyridine)(P4VP) andPoly(acrylic acid)(PAA) via hydrogen bonding in aqueous solutions. Upper criticalsolution temperature (UCST) was found under appropriate conditions of PH,adjusting the PH of the solution can change the value of UCST. The value of UCSTincreases with increasing PH. Under the same conditions of PH, The value of UCSTincreases with increasing molecular weight of PAA and also increases with increasingpercentage contents of PAA.