ZnS/Sulfur-Containing Polymer Nanocomposite Optical Materials With High Refractive Index

The organic-inorganic nanocomposites with high refractive index and transparency were desirable in the areas like high reflective and antireflection coatings, ophthalmic lenses, optical waveguides, filters, optical adhesives, prism's, non-linear optical materials, etc. In particular, transparent bulk nanocomposites more than 1 mm are required in several optical applications such as filters and ophthalmic lenses. However, it is hard to prepare high refractive index nanocompise with high transparency. On one hand, designing organic molecule structure to enhance material's refractive index is limited. These restrict their practical applications in optics field. On the other hand, because of the inherently hydrophilic character and high specific surface energies, the inorganic particles could aggregate easily in organic matrix. Thus, The development of high refractive index organic polymer matrix, especially bulk materials, with excellent optical properties and good compatibility is a challenging topic.In this dissertation, we used there means to prepare high refractive index nanocomposites including selecting higher refractive index nanoparticles, selecting higher refractive index organic matrix and increasing the content of the nanophase. The ZnS nanocarticles were used as nanophase, Sulfur-containing Polymer was used as organic phase. Sulfur-containing compound used to stablilize nanoparticles. Finally, we synthesized high refractive index bulk ZnS-polymer nanocomposites and films with high nanophase content and high transmittance. The optical, thermal, mechanical and physical properties of the obtained nanocomposites were characterized in detail. And the relationship between composition, structures (monomer structure, polymer structure, interaction between the two phases) and properties was also discussed intensively. The nanocomposites with well-balanced properties have potential application in fabricating optical materials with tunable refractive indices and high abrasion resistance.In chapter two, we used a simple method for the large scale production of 2-mercaptoethanol (ME)-capped ZnS nanoparticles (2-5 nm, nd20= 1.790), and then immobilized them into polymer matrix. We synthesized two types of high refractive index episulfide compounds including episulfide derivative of diglycidyl ether of bisphenol A (ESDGEBA, nd20=1.61) and bis(β-epithiopropylthioethyl) sulfide (ESGMES, nd20=1.635). ME-ZnS NPs were dispersed in N'N-dimethylacrylamide (DMAA), and then mixed with ESDGEBA, ESGMES, M-xylylene diisocyanante (XDI) and 2-hydroxyethyl methacrylate (HEMA) to prepare high refractive index bulk nanocomposites. XDI could also react with the hydroxyls on the surface of ZnS NPs. And the hydrophilic ZnS NPswere led into the hydrophobic polymerization system in this way. The monomer N,N-dimethylacrylamide (DMAA) plays an important role not only as a free radical polymerization monomer, but also as an effective dispersant and stabilizer of ME-capped ZnS NPs.2-hydroxyethyl methacrylate (HEMA) has both hydroxyl group and carbonecarbon double bond. It was used as comonomer and crosslinker for the two types of polymerization parts. The refractive index of the ZnS-polymer nanocomposites could be continuously regulated in the range from 1.5911～1.6410 by the content of ZnS NPs. And the refractive index could reach 1.6410 with 30 wt% nanophase content. The ZnS-polymer nanocomposite has a highest pencil hardness round about 6H. The results indicate that the introduction of episulfide as monomer to improve the refractive index of nanocomposite is very efficacious.In chapter three, we synthesized thiol compounds 3-mercaptopylene sulphide (MPS, nd20=1.58), and use ME-ZnS NPs as nanophase. Other comonomers are XDI, HEMA, DMAA. The monomer XDI could also react with the hydroxyls on the surface of ZnS NPs. And the hydrophilic ZnS NPs were led into the hydrophobic polymerization system in this way. The refractive index of the obtained bulk ZnS-polymer nanocomposites could be continuously regulated in the range from 1.5953～1.6475 by the content of ZnS NPs. And the refractive index could reach 1.6475 and the transmittance is 76% with 30 wt% nanophase content. The ZnS-polymer nanocomposite has a highest pencil hardness round about 6H. The nanocomposites obtained in our work could exhibit higher refractive indices in much lesser nanophase contents. The conclusion proved that use high refractive index polymer matrix could improve the refractive index of the nanocomposite effectively.In chapter four, we synthesized thiol compounds 4-thiomethyl styrene (TMSt, nd20=1.625) and TMSt-thiophenol (PhSH)-capped ZnS nanoparticles (5～10 nm). MES, TDI and TMSt were used to synthesize sulfur-containing polyurethane macromonomer. TMSt/PhSH-ZnS NPs were dispersed in DMF, and then complex with sulfur-containing polyurethane macromonomer. UV curing and thermal curing methods were used to prepare high refractive index nanocomposite films. The refractive index of the obtained ZnS-polymer nanocomposites films could be continuously regulated in the range from 1.6731～1.7960 by the content of ZnS NPs. The refractive index of TMSt/PhSH-ZnS NPs is calculated to be about 1.8103 by regression analysis. The transmittances of the nanocomposite films are all above 93%. AFM test results indicate that the nanocomposite films have high degree of smoothness. We also use TMSt/PhSH-ZnS NPs to prepare bulk nanocomposites. We fixed the TMSt/PhSH-ZnS NPs content at 20 wt%. The refractive index of the ZnS/TMSt/DMAA bulk nanocomposite is 1.6495, pencil hardness is 1H, the transmittance is 77%. We used XDI to improve the crosslinking degree. The refractive index of the ZnS/TMSt/ XDI/DMAA bulk nanocomposite is 1.6375, pencil hardness is 3H, the transmittance is 78%. The conclusion indicate that using high refractive index nanoparticle surface coating agent could improve the refractive index of the nanocomposite.