Effects of pH During the Base Catalyzed Reaction of Two-Step Acid/Base Catalyzed Process on the Microstructures and Physical Properties of Poly(dimethylsiloxane) Modified Silica Xerogels

Poly(dimethylsiloxane) (PDMS) modified silica xerogels were prepared by two-step acid/base catalyzed sol-gel process. By keeping the acid amount and hydrolysis period in acidic environment fixed, and adding different amounts of base to the sol afterwards, attempts had been made to study the effect of the different amounts of base catalyst on the micro-structure and physical properties of the prepared ORMOSILs. DTA, SEM, BET, FTIR were performed to characterize the derived specimens. The microstructure and physical properties are greatly influenced by the amount of base added to the sol. With increasing base content the crystallite size and porosity increase and the pore size distribution takes a broad spectrum. Whereas, the glass transition temperature seems to decrease with increasing of base catalyst amount. This is explained in terms of the change in the relative amounts of hydrolysis and condensation reactions due to the addition of different amount of base catalyst, which predominantly influences the condensation reactions. The results are reported in this communication along with possible explanations behind the observations.     

Capillary electrophoresis of baclofen with argon-ion laser-induced fluorescence detection

A capillary electrophoretic method with laser-induced fluorescence detection for baclofen (4-amino-3-p-chlorophenylbutyric acid) has been developed. 6-Carboxyfluorescein succinimidyl ester was used for precolumn derivatization of the non-fluorescent drug. Optimal separation and detection were obtained with an electrophoretic buffer of 50 mM sodium borate (pH 9.5) and an air-cooled argon-ion laser (excitation at 488 nm, emission at 520 nm). Linearity (r > or = 0.99) over three orders of magnitude was generally obtained and the lowest derivatizable concentration limit for baclofen in aqueous solution was 10 nM (2 ng baclofen/ml). Coupled with a simple clean up procedure, the method can be applied to the analysis of baclofen in human plasma at micromolar level. Recovery of spiked baclofen in plasma was 95%. The relative standard deviation values on peak size (0.5 microM level) and migration time were 8.2 and 1.0% (n=7), respectively. The limit of detection of baclofen in plasma was 0.1 microM (21 ng/ml).     

Vibrational spectroscopic studies of sol-gel derived physical and chemical bonded ORMOSILs

Fourier transform infrared (FT-IR) and FT-Raman Spectroscopy have been utilized to characterize the structure of physical and chemical bonded ORMOSILs (organically modified silicates) and to compare with the physical properties, reported earlier. The classic and sono ORMOSILs were synthesized by sol-gel method via traditional- and sono-catalysis routes, respectively. The physical and chemical bonding is established by Poly(ethylene glycol) (PEG) and Poly(dimethoxysilane) (PDMS), respectively. Existence of band at ∼560 cm⁻¹ (FT-IR) and ∼490 cm⁻¹ (FT-Raman) for the sono and classic gels with 5-10 wt% of PEG indicates the presence of structural defect due to the four-membered siloxane rings. Application of long molecular PEG chain and PDMS increases this defect. Modification in the intensity and peak position of siloxane (Si-O-Si) bands is found correlative with the physical properties. The xerogels with 5-10 wt% of PEG possess a large number of residual surface silanol groups than the xerogels with long molecular PEG chains and PDMS and is found related with the ν(OH) band at ∼3470 cm⁻¹. These results are attributed to the way of hydrolysis-condensation reactions and discussed with the help of Percolation and DLVO models.     

Determination of Butyltins in Sea Water by Gas Chromatography with Flame Photometric Detection

Use of a gas chromatograph with a flame-photometric detector (GC-FPD) is described to determine butyltin compounds in sea water. The butyltins in an acidified water sample (pH 3.0) are first complexed with tropolone, followed by solid-phase extraction (SPE) with a tropolone-treated C₁₈ cartridge. HCI at a small concentration is then added to the concentrated SPE eluate before GC analysis. This procedure is simple and off-column derivatization of analytes is not required. The organotins, viz. mono-, di- and tributyltin, are separated as their respective chlorides on a capillary column (HP-1) and are detected with a flame-photometric detector and an interference filter at 610 nm. Recoveries of the three butyltin species are quantitative (> 90%). Based on a sea water sample 200-mL, the detection limits for mono-, di- and tributyltin are 6,4 and 3 ng tin L^?1, respectively. This method is applied to analysis of trace butyltins in various samples of sea water.     

Experimental study of the Na2 3Πg state

The 3¹Π_g state of Na₂ is experimentally investigated by using high resolution cw optical-optical double resonance spectroscopy. A single line Ar⁺ laser (total of 9 lines) is used to pump the sodium dimers from thermally populated ground state to the intermediate B¹Π_u state. Then a single mode Ti:sapphire laser is used to probe the 3¹Π_g state. Violet fluorescence from highly Rydberg excited states (mainly 2³Π_g or 3³Π_g states which are transferred from 3¹Π_g state via collisions) to the state is monitored by a filtered photomultiplier tube and a lock-in amplifier. Compared with previous studies [C.C. Tsai, J.T. Bahns, W.C. Stwalley, J. Chem. Phys. 99 (1993) 7417], a wider range of rotational quantum numbers of data field are observed. A set of Dunham coefficients and the Rydberg-Klein-Rees potential energy curve of the 3¹Π_g state are deduced from all the observed rovibrational levels.     

High uniform illumination of light-emitting diodes lighting with applying the multiple-curvature lens

Light-emitting-diode (LED) sources will play a very important role in the future. Nowadays, there are many traditional light sources gradually being replaced by LED sources. From the viewpoint of illumination, different environments have the same requirement uniformity of illumination. The basic reason for this is to insure human comfort. Therefore, the promotion of illumination uniformity is an especially important key issue. In this article, we propose one effective design to improve the uniformity of illumination of LEDs with Lambertian radiation profiles by inserting into the lighting system, multiple-curvature lens. The enhanced illumination uniformity of LEDs, in this system, is due to energy redistribution by controlling the direction of incident light, using geometrical optics theory. Ray tracing was applied for the simulations required. Finally, the uniformity of illumination is 76.17% in LEDs using multiple-curvature lens, which is twice the uniformity of conventional LEDs. Furthermore, the phenomenon of overload in the multiple-curvature lens is reduced by increasing the numbers of rings on the lens. The overload is less than 0.02 lm in the case of lens designed with 23 rings.     

The Interplay of Photophysical Properties in Carbazole Fluorescent Oligomers

The photophysical properties and the organic synthesis using effective palladium‐catalyzed Suzuki coupling reactions from a series of carbazole derivatives are described and the relationships of the donor and acceptor groups are also investigated. The purification of the materials and its applications along with the corresponding photo‐physical characterizations were presented. With the advantages gained from 2D‐COSY spectra, which provide more correlated information between immediate atoms than ¹H‐NMR spectra and a series of further investigations were undertaken including powder X‐ray diffraction analysis, Infrared and Raman spectroscopy, constructing the composition conformation and chemical structure of the materials is more easily to achieve. Additionally, the optimized structure of the minimized energy geometries and spatial distributions of carbazole derivatives was calculated using density functional theory (DFT), new materials can be developed and designed selectively based on the method proposed in this work.     

Spectroscopic Study of the Na2 2Σg State by cw Perturbation-Facilitated Optical-Optical Double-Resonance Spectroscopy

The Na₂(3sσ_g)(4sσ_g) 2³Σ⁺_g state of Na₂ has been observed and studied by cw perturbation-facilitated optical-optical double-resonance (PFOODR) spectroscopy for the first time. A single-mode dye laser and a Ti-sapphire laser served as the pump and the probe lasers, respectively. A total of 543 PFOODR excitation signals have been assigned to the 2³Σ⁺_g ← b³Π_1u transitions. Absolute vibrational numbering was determined by counting nodes in the 2³Σ⁺_g → a³Σ⁺_u bound-free spectra. Spectroscopic constants and the corresponding RKR potential energy curve are presented in this vsork. The values of T_e, R_e, and D_e, are found to be 25 551.237(49) cm⁻¹, 3.53463(35) Å, and 6211.5(1) cm⁻¹ respectively.