Photochromic properties of spirooxazine dyes in ormocer gels and coatings

The wet- and "cold"-chemical characteristic of sol-gel process makes the sol-gel derived materials offer exciting potentials as hosts for photochromic dyes. In the present work, using mixed organically modified silicon alkoxides as starting compounds a novel ORMOCER material has been prepared via the sol-gel process as a host for spirooxazines. The photochromic properties of the dyes in the ORMOCER gel and coating are compared with those in ethanol. The experimental results show that both the photochromic performance and the thermal stability of the dyes are apparently improved in the ORMOCER matrix, while the temperature dependence of the photochromic intensity at higher temperatures need further improvement

Photochromic organic-inorganic hybrid nanocomposite hard coatings with tailored fast switching properties

A recently developed photochromic organic-inorganic nanocomposite (Nanomer) coating system is investigated, which is based on an epoxysilane as network former, different bisepoxides as spacer and an organic amine as thermal cross-linker. This coating system is compatible with different photochromic dyes like oxazines, pyrans and fulgides and also with surface modified ceramic nanoparticles as filler in order to obtain macroscopic hard properties\u27 without changing the photochromic kinetics. In order to investigate the dye-spacer interactions and influence on the switching kinetic behavior, the matrix composition was diminished to the network former, the thermal cross-linker and two types (polar and nonpolar) of spacers in different concentrations. Four commercially available spirooxazines with different molecular sizes and polarities were incorporated into the matrices and coatings on glass slides were prepared by float-coating and cured at 130 °C for 2 h. The half darkening and half fading times of the coatings were measured by a fast diode array spectrometer as a function of spacer type and concentration for the four different dyes. The nonpolar\u27 spacer CHMG did not influence the switching kinetic of the dyes significantly and fast switching times of 2 s-4 s were obtained. The polar\u27 spacer PCF (aromatic character) showed interactions with the dye molecules, which led to an increase in the switching times of up to 25 s. The retardation of the switching process increased with increasing spacer content and with increasing polar character of the dye molecule. From these results, it could be concluded that the photochromic behavior of the spirooxazines could be adjusted to different applications by interactions with polar spacers

Effect of glass substrates on the formation of gold-silver colloids in nanocomposite thin films

A sol-gel route to synthesize nanocomposite thin films containing phase separated metal colloids of gold (Au) and silver (Ag) was developed. Ag - Au colloids were prepared in silica films using dip coating technique. The annealing of the samples in air results in the formation of phase separated Ag and Au colloids in SiO2 thin films, showing the surface plasmon peaks at 410 nm and 528 nm. For the synthesis of phase separated Ag and Au colloids on float glass substrates, formation of the silver colloids was found strongly dependent on the surface of the float glass. On the tin rich surface formation of both gold and silver colloids took place, whereas, on the tin poor surface the formation of only gold colloids was observed. The surface dependence of the formation of silver colloids was attributed to the presence of tin as Sn2+ state on the glass surface, which oxidizes into Sn4+ during heat treatment, reducing Ag+ into silver colloids

Development of fast switching photochromic coatings on transparent plastics and glass

A new photochromic organic-inorganic nanocomposite (Nanomer(R)) coating system has been developed. It is based on an epoxysilane as network former, an organic bisepoxide as spacer, an organic amine as thermal cross-linker and surface modified SiO2 nanoparticles as fillers. This coating system is compatible with different photochromic dyes, like oxazines and pyrans. Photochromic coatings with blue, yellow, red, green, violet and neutral tints were prepared on flat glass and PMMA substrates by dip coating and cured for 3 h at 100 degrees C. The photochromic coatings show the following properties: the transmittance changes reversibly between 80 and 20% with half fading times of about 2-20 s (comparable to the half fading time of the appropriate dye in ethanolic solution) after UV irradiation for 15 s with 5 mW/cm(2). The coatings show a scratch hardness of about 15 g (scratch test with Vickers indenter, coating thickness 10 mu m). The addition of only 3 wt.% SiO2 nanoparticles relative to epoxysilane increases the scratch resistance of the coatings to about 20 g without changing the fast kinetics of the incorporated photochromic dye(s). The long term stability of the photochromic dye(s) in the matrix system can be considerably improved by the introduction of additives like antioxidants, hindered amine light stabilizer (HALS) and UV stabilizers. The half lifetime (decay to 50% of the initial photochromic intensity) of a blue spirooxazine dye (Blue A) measured in a dry sun-test (75 mW/cm(2)) could be increased from 20 h without any additive up to 200 h with an UV absorber (Tinuvin 327) as a stabilizer, which is assumed to be sufficient for ophthalmic applications

Preparation and photochromic properties of dye-doped aluminosilicate ORMOCER gels and coatings

Aluminosilicate and ORMOCER gels and coatings containing photochromic dyes, 1, 3-dihydro-1, 3, 3-trimethylspiro-[2H-indole-2, 3\u27-[3H]-naphth-[2, 1-b][1, 4]-oxazine] (SO) and 1\u27, 8a\u27-dihydro-2\u27, 3\u27-dimethoxycarbonyl-spiro [fluorene-9, 1\u27-indolizine] (DHI), were prepared by the sol-gel method and the photochromic activity was monitored in the course of the sol-wetgel-xerogel transformation. The photochromic activity of the aluminosilicate gels decreases rapidly and even vanishes in the wetgel-xerogel stage while that of ORMOCER gels and coatings levels off in the early wetgel-xerogel stage at a reasonably high photochromic intensity with the colour-fading speed similar to that in ethanol and the photostability being considerably improved. The experimental results are discussed in terms of the matrix effect on photochromism of organic dyes

A solid state 29Si and 13C NMR study on the synthesis of thin silicon-oxycarbide glass sheets by a sol-gel route

29Si and 13C MAS NMR spectroscopy, DTA-TG and elemental analysis were used to study the evolution of metastable oxycarbide phases starting from thin gel sheets derived from methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS) and a colloidal silica containing sol, up to 1450°C under a nitrogen atmosphere. The stoichiometric formulae of the glasses obtained by the semi-quantitative analysis of 29Si MAS NMR spectra were found to be in good agreement with those obtained by chemical analysis. It was found that the addition of colloidal silica sol delays the decomposition of methyl groups in MTEOS containing condensates. This delayed decomposition of the methyl groups was attributed to facilitate the strengthening of the matrix, thus leading to crack free sintering of sheets up to 400°C in air and for T>900°C under nitrogen. A significant portion (>40%) of the total carbon present in the glasses was found to exist as free carbon. 13C NMR showed that unsaturated C=C bonds exist in gels heat treated at 1000 °C, but they disappear in heat treated gels at 1200 and 1450°C. Both 29Si and 13C NMR spectra indicate the formation of a ca. 15 atom% SiC phase in the glass sheets sintered at 1450°C, which were found to be amorphous up to 1200°C