Dependence of the molecular aggregation state of octadecylsiloxane monolayers on preparation methods

The molecular aggregation state of octadecylsiloxane monolayers on Si-wafer substrate surfaces prepared from octadecyltrimethoxysilane (OTMS) or octadecyltrichlorosilane (OTS) was investigated on the basis of grazing incidence X-ray diffraction (GIXD), Fourier transform infrared spectroscopy (FT-IR), contact angle measurement, field emission scanning electron microscopy (FE-SEM), and scanning force microscopy (SFM). The OTMS monolayer was prepared by using the chemical vapor adsorption (CVA) method, and the OTS monolayers, which were used as reference samples, were prepared either by chemisorption (OTS-S) or by the water-cast method (OTS-W). The GIXD, FT-IR, lateral force microscopic (LFM) measurements, and FE-SEM observation revealed that the alkyl chains in the OTMS monolayers prepared using the CVA method are in an amorphous state at room temperature. According to the LFM measurement, the transition temperature from the hexagonal crystalline phase to the amorphous phase was found to be ca. 333 K for the OTS-S monolayer prepared by the chemisorption method. However, the phase transition was not observed in the OTMS monolayer prepared by the CVA method. Also, the atomic force microscopic (AFM) observation and the contact angle measurement showed that the OTMS monolayer prepared by the CVA method has a uniform surface when compared to the OTS monolayers. These results indicated that organosilane compounds in the monolayer prepared by the CVA method were immobilized on the Si-wafer substrate surface in an amorphous state, which was quite different from the hexagonal crystalline state obtained by the chemisorption and water-cast methods.     

Flow of a single magnetic vortex in a submicron-size superconducting Al disk controlled by radio-frequency currents

We report the first observation of a single-vortex flow in a mesoscopic superconductor. A flow of a single vortex is successfully controlled by an rf current superimposed on a dc current, evidence of which is provided by voltage steps in current-voltage (I-V) characteristics. Irrespective of the number of vortices confined to the disk, we unambiguously observe that when a single vortex inside the disk is driven out of the disk, another vortex enters the disk similarly to two balls colliding in billiards: only one vortex passes through the Al disk at the same time in mesoscopic systems.     

Molecular orientation and optical anisotropy in drawn films of cellulose diacetate-<Emphasis Type="Italic">graft</Emphasis>-PLLA: comparative investigation with poly(vinyl acetate-<Emphasis Type="Italic">co</Emphasis>-vinyl alcohol)-<Emphasis Type="Italic">graft</Emphasis>-PLLA

Cellulose diacetate-graft-poly(L-lactide) (CDA-g-PLLA) and poly(vinyl acetate-co-vinyl alcohol)-graft-PLLA (P(VAc-co-VOH)-g-PLLA) were synthesized over a range of compositions, by ring-opening copolymerization of L-lactide at the original hydroxyl positions of the respective trunk polymers, CDA (acetyl DS = 2.15) and P(VAc-co-VOH)-g-PLLA (VAc = 64.2 mol%). All the products of both graft copolymer series were non-crystallizable and their solution-cast films showed no domain segregation of the two components that constituted the trunk and side-chains. A comparative study on the molecular orientation and optical anisotropy induced by uniaxial stretching of film samples was undertaken for the two copolymer series with various side-chain lengths. Overall behaviour of the orientation was estimated from the statistical second (<cos² ω>) and fourth (<cos⁴ ω>) moments obtained by a fluorescence polarization method using a rod-like probe of ~2.5 nm. Upon stretching, any film of both series imparted a positive orientation function, i.e., f = (3 <cos² ω> − 1)/2 > 0, which increased with the extent of deformation. The degree of molecular orientation was higher in the CDA-graft series with a semi-rigid trunk, and, in both series, it declined monotonically with increasing content of the PLLA side-chain. With regard to the optical anisotropy, CDA-g-PLLA films always exhibited a positive birefringence (Δn > 0) upon stretching, while drawn films of P(VAc-co-VOH)-g-PLLA displayed a negative one. This contrast in polarity reflects a difference in the intrinsic birefringence between the two trunk polymers. Of interest was the finding of a discontinuous change in Δn value with copolymer composition (PLLA content) for the respective graft series, when compared at a given stage of elongation of the films. Discussion took into consideration the locally different orientation manners of the attached PLLA chain segments.     

Optimization of an interface chip for coupling capillary electrophoresis with thermal lens microscopic detection.

This paper presents a capillary-to-microchip connection, which can be used as an interface for coupling capillary electrophoresis (CE) with a thermal lens microscope (TLM). It is difficult to directly apply TLM to samples in a capillary with a curved surface, and such an interface chip at the end of a CE separation column is needed for reliable TLM measurements. The dependence of the TLM signal intensity on the TLM detection point in the interface chip and the dependence of the theoretical plate number of CE separation on the channel dimensions of the interface chip were investigated and optimized with a mixture of 4-dimethylaminoazobenze-4'-sulfonyl (DABSYL)-derivatized amino acids (glycine, alanine, methionine, and proline) as a model sample. By using an optimized interface chip, theoretical plate numbers of DABSYL-glycine, -methionine, -alanine, and -proline were obtained to be 104000, 95000, 104000, and 95000, respectively.     

One-Pot System for Reduction of Epoxides Using NaBH4, PdCl2 Catalyst,and Moist Alumina

Reduction of epoxides with sodium borohydride, a catalytic amount of palladium(II) chloride, and chromatographic neutral alumina preloaded with a small amount of water (moist alumina) in hexane gave alcohols in good to excellent yields and good selectivity of the desired products under mild conditions. The reaction system was operationally simple and environmentally friendly. The alumina can be recovered simply and reused a number of times without any treatment and with good activity.     

Ultrastable cesium atomic clock with a 9.1926-GHz regeneratively mode-locked fiber laser

We describe an ultrastable cesium (Cs) atomic clock with a 9.1926-GHz regeneratively mode-locked fiber laser obtained by use of an optically pumped Cs beam tube. By adopting a 1-m-long Cs beam tube with a linewidth of 110 Hz, we have successfully obtained frequency stabilities of 4.8 x 10(-12) for tau = 1 s and 6.3 x 10(-13) for tau = 50 s for a 9.1926-GHz microwave output signal. This Cs atomic clock can generate an optical pulse train with the same stability as that of the obtained microwave, which allows us to deliver a frequency standard optical signal throughout the world by means of optical fiber networks.