Transparency of modified vinyl-silsesquioxane films and its validation by computing energy-band structure
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Di Wang, De-Rong Lin, Qun Zhang, and Li-Jiang Hua) Chemistry Department, Harbin Institute of Technology, Harbin 150001, China (Received 15 May 2009; accepted 28 August 2009)
Using vinyl-silsesquioxane modified with various amounts of tetraethoxysilane (TEOS) and titanium tetrabutoxide (TTB), two kinds of hybrid films, film-vinyl-silsesquioxaneTEOS (f-VSTE) and film-vinyl-silsesquioxane-TTB (f-VSTT), were prepared. The average transparency (AT) of the modified films was measured in the ranges of the visible light region (400–750 nm) and in the near-infrared region (750–2500 nm). The AT values in these ranges are about 88% to 94%, indicating that these high-AT films can provide crops with growth energy and improvement of the photosynthetic process efficiency. The TEOS additions result in a hybrid structure (containing SiO2); an adequate addition can cause an increase in the AT radiation from sunlight. On the other hand, the TTB additions result in a hybrid structure (containing TiO2) that causes a decrease in the AT. These results were validated using molecular dynamic simulation and were calculated (with Materials Stutio software) using the density of states and the energy-band structure of the vinyl-SSO, SiO2, and TiO2 building blocks.
I. INTRODUCTION
Both the visible light (VIS) (in the region of 400– 750 nm) and the near-infrared light (NIR) (in the region of 750–2500 nm) from sunlight radiation can give crops growth energy and improve the efficiency of photosynthesis (the initial process driving the growth of crops and plant ecosystems).1,2 Therefore, building greenhouses is a useful and efficient means of assisting crop growth in cold areas rather than an extension of the growth season.3,4 Consequently, materials for the greenhouse covers are an important research target.5 Silsesquioxane (SSO) compounds have an important role in coating film applications.6,7 Because of their nanostructures and properties,8,9 these attractive engineering materials provide new opportunities to incorporate and release transmittance hybrid films. An interesting type of organically modified silicates (Ormosils) is based on the hydrolytic condensation of a tetraethoxysilane or titanium tetrabutoxide with a trialkoxysilane having an organic moiety with a polymerizable group (epoxy, vinyl, etc.).10,11 In these kinds of hybrid materials, two different types of networks may be formed: (i) an organic network produced by the cross-linking of the polymerizable groups and (ii) an
inorganic network based on Si–O–Si or Ti–O–Ti bonds.12,13 The fraction of TEOS or TTB in the initial formulation will elucidate the prevalent network in the final structure that will determine the resulting optical properties of the hybrid materials. This study has two aims: (i) to determine whether the transparency of vinyl-SSO films for greenhouse covers could be improved by varying the amount of additional TEOS and TTB and (ii) to validate the measured transparency using molecular dynamic simulation to calculate the density of states (DOS) and the energy-band
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