Body And Interface Conditions Organosiloxane Hydrolysis - Condensation Process Of Aggregation Behavior Of A Comparative Study

It has been an increasing interest in employing Ormosils(Organically Modified Siloxanes) as precursors to prepare various Organic-Inorganic materials through sol-gel processe.These materials with chemical inertness,mechanical stability,optical transparency are becoming more and more widely used in optical and electrical materials,chemical biomedical sensors,catalyst, multifunctional coatings and films,and so forth.Organic component can be introduced into the sol-gel materials by two ways:precursor being organically modified and organic additives being incorporated in sol-gels.Being different from traditional sol-gel precursors with simple structure and lower molecular weight,Ormosils present the marked substituent effects on sol-gel process depending on the structure and property of the organic substituent R.In summary,R group has significant influences on reaction rate of hydrolysis and condensation,species distribution of the silanols and silicates,and type of self-organizations. Therefore,it is significant both in theory and application to systematically investigate the influences of the organic moiety on the sol-gel process,which assists in further understanding the organic modification mechanism in the sol-gel process,controlling the synthesis conditions of organicinorganic hybrid materials and taking deep insight into properties of the final products.With emphasis on the insights above mentioned,we carried out the research in this thesis mainly including two parts:(1) The aggregation behavior occurred in bulk phase and at air-water interface during hydrolysis and condensation processe of 3-methacryloxypropyltrimethoxysilane(MAPTMS) were comparatively investigated.The fluorescence spectra of pyrene probing the bulk phase and air-water interface for hydrolysis-condensation process of MAPTMS implied that there were aggregation of hydrolyzates in bulk phase and at air-water interface.Additionally,the variations in fluorescence spectra with time manifested that both hydrolysis and condensation occurred in bulk phase were faster than that at air-water interface.These conclusions were coincident with the results derived from In-situ ATR-FT-IR andπ-A isotherm measurement.The fluctuations in the emission intensity of pyrene were also observed for both cases of bulk phase and air-water interface,indicating that the aggregates were reversible and the fluctuation was more violent in bulk phase than at air-water interface.All findings related to the aggregation could be interpreted in terms of the hydrolyzed MAPTMS being similar to amphiphilic molecule and differences in the fluorescence spectra and IR spectra originating from the bulk phase and air-water interface could be attributed to the difference in the degree of molecular confinement in two cases which makes the hydrolysis and condensation of MAPTMS different.(2) The hydrolysis-condensation processes of 3-Glycidoxypropyltrimethoxysilane(GPTMS) in bulk phase and air-water interface were followed by means of fluorescent spectroscopy with pyrene as fluorescent probe and In-situ ATR-FT-IR.Additionally,theπ-A curve of the hydrolyzates of GPTMS LB film using the hydrochloric acid solution as the subphase was examined by the KSV Minitrough.In earlier stage of the reaction for GPTMS hydrolysis-condensation system,the fluorescence spectra of pyrene probing the bulk phase and air-water interface implied that there were not aggregations of hydrolyzates in bulk phase and at air-water interface.It indicates that species of hydrolysates dispersed in the solution and such systems are homogenous.Owing to the protonated expoxyl group of GPTMS,the silanols produced from GPTMS do not easily form aggregates because of the presence of two polar ends in the silanols.With the reaction,the spectra of pyrene appear distorted excimer emission at air-water interface,which was also confirmed byπ-A isotherm measurement.The spectroscopic results revealed that the condensation products are prone to form aggregates at air-water interface.That is to say,condensation products at air-water interface are similar to amphiphilic molecule.So all these results are very significant in the controllable preparation of a controlled material and surface modification.