Observation of the internal network structure of a polymer-stabilized liquid crystal via transmission electron microscopy

The internal structure of the network component of a polymer-stabilized liquid crystal has been observed for the first time. These are systems in which a small amount of a monomer is dissolved within a LC host and then polymerized in situ to produce a network. Studies performed on a system prepared using the diacrylate monomer RM60 and the nematic mixture BL087 are presented. The concentration of the monomer was 1 wt %. After formation of the network through photopolymerization of the monomer between Melinex layers within a glass cell, the LC host was removed by dissolving it in heptane. Subsequent observation of the internal network structure by transmission electron microscopy was made possible by bromine staining of the network, followed by embedding and ultramicrotomy. A collection of solid, near-circular objects was observed, of mean diameter 0.13 μm. These objects were found to be highly permeable to bromine vapour, suggesting an open, but homogeneous structure.     

Real‐time measurement of peroxyacetyl nitrate using selected ion flow tube mass spectrometry

The on‐line detection of gaseous peroxyacetyl nitrate (PAN) using selected ion flow tube mass spectrometry (SIFT‐MS) has been investigated using a synthetic sample of PAN in air at a humidity of ～30%. Using the H₃O⁺ reagent ion, signals due to PAN at m/z 122, 77 and 95 have been identified. These correspond to protonated PAN, protonated peractetic acid and its water cluster, respectively. These products and their energetics have been probed through quantum mechanical calculations. The rate coefficient of H₃O⁺ has been estimated to be 4.5 × 10^?9 cm³ s^?1, leading to a PAN sensitivity of 138 cps/ppbv. This gives a limit of detection of 20 pptv in 10 s using the [M+H]⁺ ion of PAN at m/z 122. Copyright © 2010 John Wiley & Sons, Ltd.     

Interference properties of a light beam having a helical wave surface

The spatial wave front characteristics of a laser were examined by two beam interference after amplitude division. Complex interference patterns were observed and are interpreted as due to a helical form of the phase front. This unusual form is implicit in previous analyses of cavity eigenfunctions, but the properties of such a helical co-phasal wavefront have not apparently been previously studied.     

Measurement of the interlayer elastic constant in a liquid crystal close to the smectic A—nematic transition

Brillouin scattering has been used to obtain first order elastic constants in 8CB. In contrast to earlier measurements the interlayer constant is found to be finite as T approaches the smectic A—nematic transition. These results confirm recent theoretical predictions.     

Cavity-enhanced absorption: detection of nitrogen dioxide and iodine monoxide using a violet laser diode

We present an application of cavity-enhanced absorption spectroscopy with an off-axis alignment of the cavity formed by two spherical mirrors and with time integration of the cavity-output intensity for detection of nitrogen dioxide (NO₂) and iodine monoxide (IO) radicals using a violet laser diode at λ=404.278 nm. A noise-equivalent (1σ≡ root-mean-square variation of the signal) fractional absorption for one optical pass of 4.5×10^-8 was demonstrated with a mirror reflectivity of ∼0.99925, a cavity length of 0.22 m and a lock-in-amplifier time constant of 3 s. Noise-equivalent detection sensitivities towards nitrogen dioxide of 1.8×10¹⁰ molecule cm^-3 and towards the IO radical of 3.3×10⁹ molecule cm^-3 were achieved in flow tubes with an inner diameter of 4 cm for a lock-in-amplifier time constant of 3 s. Alkyl peroxy radicals were detected using chemical titration with excess nitric oxide (RO₂+NO→RO+NO₂). Measurement of oxygen-atom concentrations was accomplished by determining the depletion of NO₂ in the reaction NO₂+O→NO+O₂. Noise-equivalent concentrations of alkyl peroxy radicals and oxygen atoms were 3×10¹⁰ molecule cm^-3 in the discharge-flow-tube experiments. Received: 4 February 2003 / Revised version: 10 March 2003 / Published online: 12 May 2003 RID="*" ID="*"Corresponding author. Fax: +44-1865/275-410, E-mail: vlk@physchem.ox.ac.uk