Kwang-Sun Kang

Fabrication of large area photonic crystal with surface modified silica spheres

Large area photonic crystal has been fabricated with monodisperse silica spheres modified the surface with 3-(trimethoxysilyl) propylmethacrylate (TMSPM). The surface of the spheres has been modified by hydrolysis and condensation reaction of TMSPM with base catalyst and acid catalyst. The Fourier transform infrared (FTIR) spectra, field emission scanning electron microscope (FESEM) images no evidence that the TMSPM is corporate on the surface of the silica spheres for the base catalyst process. However, FTIR spectra and FESEM images clearly presents the existence of hydrolyzed TMSPM on the surface of silica spheres for the acid catalyst process. The FTIR absorption peak at 1714 cm-1 representing C=O stretching vibration indicates that the hydrolyzed TMSPM is corporate on the surface of the silica spheres. Although generally the colloidal photonic crystal has large number of cracks, surface modification and photocross-linking process during the packing process can be avoided the crack process of the photonic crystal.

ENHANCED FIRE RETARDANCY BY USING LARGE SURFACE AREA OF POLYALUMINUM HYDROXIDE ON SILICA SPHERES

Fire retardancy was greatly enhanced by using large surface area of polyaluminum hydroxide (PAH) attaching on the surface of uniform size silica spheres. The PAH was synthesized on the surface of silica spheres by simple hydrolysis and condensation reaction using KOH or NH4OH as a catalyst. Although partial segregation between silica spheres and PAH was observed when KOH was used as a catalyst, there was no such segregation was observed when NH4OH was used as a catalyst. Characteristic absorption peaks of Al–OH and Si–O–Al were detected by FTIR spectra after completely washing silica spheres. Field emission scanning electron microscope (FESEM) images show large amount of long chain of PAH. Various amounts of PAH were attached on the surface of silica spheres and mixed with cellulose acetate for testing fire retardancy. The fire retardancy was greatly enhanced by increasing the amount of PAH and proved by FESEM images.

BRIGHT LUMINESCENCE OF FIRE RETARDANT ALUMINUM HYDROXIDE-SILICA SPHERE COMPOSITE

Bright luminescence was achieved with excess amount of aluminum hydroxide with silica spheres. Various amounts of aluminum hydroxide were attached to silica spheres to improve the performance of fire retardancy. Although silica spheres attached with 60wt.% of AlCl3 (AlOH-A) showed no color change and luminescent chromophores, silica spheres attached with 80wt.% of (AlOH-B) and 100% of (AlOH-C) of AlCl3 changed the color and produced luminescent chromophores. The solution colors became intense yellow and brown for AlOH-B and AlOH-C, respectively, after 15 days. The FTIR spectra showed the characteristic absorption peaks of Al–OH and Si–O–Al. The concentration dependent photoluminescence (PL) intensities were continuously increased until 242mg addition of the colored solution and then slightly decreased thereafter for both AlOH-B and AlOH-C. The PL peaks shifted toward red by increasing the excitation wavelength for both AlOH-B and AlOH-C. Large Stoke shifts, such as 73 and 68nm for AlOH-B and AlOH-C, respectively, were observed.

Highly Luminescent Aniline and TiO 2 Composite: The Effect of Weight Ratio of Aniline and TiO 2

Strong deep ultraviolet emitting aniline and TiO2 composite has been synthesized via hydrolysis and condensation reactions of titaniumisopropoxide (Ti(OPr)4), aniline, and acetic anhydride. Three different weight ratios of aniline and Ti(OPr)4 including 3:1 (TiO2An-A), 2:1 (TiO2An-B), and 1:1 (TiO2An-C) were synthesized and characterized their optical properties. The FTIR spectra of the TiO2An-A, -B, and -C showed the absorption intensities of the benzene ring stretching and bending vibrations, and benzene ring -CH stretching, bending, and deformation vibrations increased with the increase of the amount of aniline. The UV-visible absorption spectra showed that the UV region absorption was slightly increased with the increase of the amount of aniline. The photoluminescence (PL) intensities were exponentially increased with the increase the excitation wavelength from 307 to 317 nm, steadily increased from 300 to 313 nm and slowly increased from 302 to 308 nm for TiO2An-A, -B, and -C, respectively and decreased thereafter. Therefore, the PL intensity is strongly dependent on the weight ratio of Ti(OPr)4 and aniline.

Photoluminescence Characteristics of the Light-Emitting Chromophores Obtained from Organic-Inorganic Hybrid Silica Spheres

Light-emitting chromophores have been separated from silica spheres modified the surface with 3-(trimethoxysilyl)propylmethacrylate (TMSPM). The photoluminescence characteristics of the chromophores were investigated with various excitation wavelengths. The TMSPM was attached to the surface of silica spheres at 75°C. Large number of round shaped particles of the TMSPM was on the surface of silica spheres after 3 h reaction. The TMPSM was completely covered on the surface of the spheres after 6 h reaction. The surface modified silica spheres were soaked into acetone and stored for 20 days at ambient condition. The solution color slowly changed from light yellow to deep yellow with the increase of the storing time. The FTIR absorption peaks at 3348, 2869, 2927, 1715, 1453/1377, 1296, and 1120 cm -1 represent C-OH, R-CH₃, R₂-CH₂, -C=O, C-H, C=C-H, and Si-O-Si absorption, respectively. The FTIR absorption peak at 1715 cm -1 representing the ester –C=O stretching vibration for silica spheres stored for 20 days was increased compared with the spheres without aging. The UV-visible absorption peaks were at 4.51 eV (275 nm) and 3.91 eV (317 nm). There were two luminescence peaks at 2.51 eV (495 nm) and 2.25 eV (550 nm). The emission at 2.51 eV was dominant peak when the excitation energy was higher than 2.58 eV, and emission at 2.25 eV became dominant peak when the excitation energy was lower than 2.58 eV.

Controlled growth of CdSe quantum dots on silica spheres

Various sizes of CdSe quantum dots have been fabricated on the surface of the monodisperse silica spheres and five diffe rent photoluminescence (PL) peaks are observed from the CdSe quantum dots. The monodisperse silica spheres were syn thesized with Stöber synthetic method. The surface of the spheres was modified with 100:1 ratio of phenylpropyltrimeth oxysilane (PTMS) and mercaptopropyltrimethoxysilane (MPTMS). The MPTMS works as a covalent bond formation wi th CdSe quantum dots, and the PTMS acts as a separating quantum dots to prevent PL quenching by neighboring quantu m dots. The Fourier transform infrared (FTIR) spectrum of the surface modified spheres (SMSiO2) shows strong absorpti on peak at 2852 and 2953 cm-1 representing the characteristic absorption of –CH or -CH2. The FTIR absorption peak at 1 741 cm-1 represents the characteristic absorption of CdSe quantum dots. The field emission scanning electron microscope image shows the average diameter of the spheres ranging approximately 418 nm. The ultraviolet-visible transmittance s pectrum shows stop band at 880 nm. The PL spectrum shows five different emission bands at 434, 451, 468, 492 and 545 nm, which indicates the formation of several different sizes of CdSe quantum dots.

Cause of absorption band shift of disperse red-13 attached on silica spheres

A reversible color change and large absorption band shift have been observed for the disperse red-13 (DR-13) attached on the surface of the monodisperse silica spheres. Two step synthetic processes including urethane bond formation and hydrolysis-condensation reactions were used to attach the DR-13 on the surface of the silica spheres. After the reaction, the characteristic absorption peak at 2270 cm-1 representing the –N=C=O asymmetric stretching vibration disappeared, and the a new absorption peak at 1700 cm-1 corresponding the C=O stretching vibration appeared. A visual and reversible color change was observed before and after wetting in alcohol. Although the absorption peak of DR-13 in alcohol is at 510 nm, the absorption peak shifts to 788 nm when it is dried. The absorption peak shifts to 718 nm when it is wetted in alcohol. This result can be explained by the formation of intramolecular charge transfer band.

Temperature dependent surface modification of silica spheres with methacrylate

Surface modification of silica spheres with 3-(Trimethoxysilyl)propylmethacrylate (TMSPM) has been performed at ambient condition. However, the FTIR spectra and field emission scanning electron microscope (FESEM) images show no evidence of the surface modification. The reaction temperatures were varied from 60 to 80 °C with various reaction periods. Small absorption shoulder of the C=O stretching vibration was at 1700 cm-1, and slightly increased with the increase of the reaction time at 60 °C. The clear absorption peak appeared at 1698 cm-1 for the spheres reacted for 80 min at 70 °C and shifted toward 1720 cm-1 with the increase the reaction time. Strong absorption peak showed at 1698 cm-1 and shifted toward 1725 cm-1 with the increase of the reaction time at 80 °C. The spheres were dispersed to methanol and added photoinitiator (Irgacure-184). The solution was poured to a patterned glass substrate and exposed to the 254 nm UV-light during a self-assembly process. A large area and crack-free silica sphere film was formed. To increase the mechanical stability, a cellulose acetate solution was spin-coated to the film. The film was lift-off from the glass substrate to analyze the surface nanostructures. The surface nanostructures were maintained, and the film is stable enough to use as a mold to duplicate the nanopattern and flexible.

Strong photoluminescence characteristics of sulforhodamine B attached on photonic crystal

The optical properties of sulforhodamine B (SRH) impregnated in photonic crystal by two step synthetic processes including a urethane bond formation between a 3-isocyanatopropyl triethoxysilane (ICPTES, -N=C=O) and a SRH with elevated temperature in pyridine and hydrolysis-condensation reactions between synthesized ICPTES/SRH (ICPSRH) and tetraethoxyorthosilicate (TEOS) in NH4OH. The monodisperse silica spheres impregnated the ICPSRH (ICPSRHS) are fabricated. The reduction of the absorption peak at 2270 cm-1 representing asymmetric stretching vibration of –N=C=O indicates the progress of the reaction and new absorption peak at 1712 cm-1 characterizing –C=O stretching vibration indicates the formation of urethane bond. The UV-visible absorption spectra show the broadened spectral line width by intermolecular interaction. The photoluminescence (PL) peak of the SRH in methanol shows a hypsochromic shift with the increase the excitation wavelength. However, the PL peak for the ICPSRH exhibits a bathochromic shift as the excitation wavelength increases. The PL peak for the ICPSRH shows no hypsochromic or bathochromic shift. The PL peaks for SRH in methanol, ICPSRH and ICPSRHS are at 568, 598 and 572 nm, respectively. The main cause of the PL peak shift is due to the intermolecular interaction.

Optical properties of azo-chromophore attached on the surface of a silica photonic crystal

Optical properties of a azo-dye attached on the surface of the monodisperse silica photonic crystal have been investigated. The azo-chromophore was covalently attached to a 3-isocyanatopropyl triethoxysilane (ICPTES) having isocynate functional group by a urethane bond formation reaction. The resulting disperse red/ICPTES (DRICP) was attached on the surface of the silica photonic crystal by hydrolysis and condensation reactions. The FTIR spectrum of the resulting product DRICP/silica sphere (DRICPSS) shows no characteristic isocynate absorption peak at 2270 cm-1 and shows a new absorption peat at 1700 cm-1 corresponding the C=O stretching vibration. This result indicates the complete reaction between –N=C=O and –OH. The DRICPSS has weak brownish color when it is dried. The color of the DRICPSS changed to intense red when it is wetted in methanol, ethanol and 2-propanol. The near infrared absorption maximum at 788 nm shifted to 718 nm for the ICPDRSS after wetting in methanol. This system can be applicable to a sensitive alcohol sensor.