Thaddeus J. Novak

Use of Anisotropic Materials as Chemical Detectors

Abstract The visual detection between crossed polarizers, of organic vapors on various liquid crystal films is reported. Non-selective detection is achieved in the ppm range. However, opportunities exist for bettering selectivity and sensitivity as illustrated with a combined polymer-liquid crystal detection system for amines. Also described is the detection of liquid droplets by utilizing changes in the birefringence of polycarbonate membrane filters.

Effect of Bulk Impurities on the Transparency of Cholesteryl Nonanoate

Abstract The effect of bulk impurities on the transparency of cholesteryl nonanoate is described. In one variation, the transparency was measured at a fixed incident wavelength (500 nm) as the sample was cooled from the isotropic liquid to the smectic phase. The effects on transition temperature and temperature of maximum dichroic scattering by each of nine solutes at a concentration of 0.5% were determined. The effect of varying the concentration of an added solute (methyl benzilate) was investigated in a similar fashion. In another variation, the dependence of the wavelength of dichroic scattering on concentration of solute was investigated. Combined with results from measurements of the helix pitch and optical anisotropy, these types of data can provide valuable information on the structure of cholesteric materials and on solvent-solute interactions.

Fluorescence of Pyrene and Phenanthrene in Cholesteryl Nonanoate as a Function of Temperature

Abstract The fluorescence emission of pyrene and phenanthrene dissolved in cholesteryl nonanoate is examined as a function of temperature at various excitation wavelengths. Over the temperature range studied, the sample passed from the isotropic liquid phase through the cholesteric and smectic mesophases. The fluorescence curves exhibit intensity increases at temperatures corresponding to the mesomorphic transitions of cholesteryl nonanoate. The cholesteric-smectic transition is poorly defined except for emission at the excimer wavelength of pyrene. The major cause of the enhanced fluorescence is ascribed to the increased path length due to scattering of the exciting light.

Transparency Characteristics of Several Cholesteryl Esters

Abstract Transparency characteristics are reported for cholesteryl myristate, decanoate, and nonanoate from the solid to the isotropic liquid phases. The procedure involves heating a sample between calcium fluoride plates in a brass holder in a Cary 14 spectrophotometer. Changes in transmittance at fixed wavelengths (3000, 4000, 5000, 7000, and 25,000 A) were recorded continuously as the temperature was allowed to change slowly. The transparency characteristics of cholesteryl nonanoate while being cooled from the liquid phase are also described. All transitions which occur are observed. By comparison with other techniques this method compares very favorably with regard to the detection of transitions and dichroic scattering. The shapes of the transparency curves vary markedly between compounds; the degree of light scattering varies as a function of the incident light wavelength. However, the temperature ranges over which the transitions occur for a particular compound are reproducible irrespective of the ...

1,3-Diisonitrosoacetone and 4,4'-Bis(Diethylamino)Benzophenone Oxime as Methanesulfonyl Chloride Vapor-Sensing Coatings for Optical-Based Microsensors

Abstract The chromogenic detector reagents 1, 3-diisonitrosoacetone (DIA) and 4, 4l-bis (diethylamino)benzophenone oxime (EMKO) have been studied as solid-state coatings for sensing methanesulfonyl chloride vapor. The strength of the optical detection signals produced on contact of the coatings with methanesulfonyl chloride vapor are strongly affected by the composition of the solid reaction support; silica is the preferred support for coatings made with either reagent. When monitored with a fiber-optic spectrophotorneter, coatings made with DIA and EMKO are capable of sensing rnethanesulfonyl chloride vapor down to the low pprn level. At 25°C the DIA coatings are stable for up to five days while the EMKO coatings are stable for less than one day.

A Technique of Measuring the Transparency of Materials as a Function of Temperature

Abstract : A simple technique has been developed to measure the transparency of materials at any specific wavelength (ultraviolet to near infrared) versus temperature. The procedure involves heating a sample between calcium fluoride plates in a brass holder placed in a Cary-14 spectrophotometer. Changes in transmittance at a fixed wavelength are recorded continuously as the temperature is allowed to change slowly. As an illustration of the procedure, the transmission properties of the nematic liquid crystal butyl p-(p- ethoxyphenoxycarbonyl)-phenyl carbonate in its various states are described. For comparative purposes a description of the transmitance of phenyl benzoate (which does not possess a mesophase) is also included.

Detection Of Amines With Dichloroacetaldehyde And Chloral-Dichoroacetaldehyde Copolymer

Abstract Methods are described for the detection of amines as vapors and in solution. The lower limit of detection of diethylamine or triethylamine vapors by drawing the vapor through a detector tube containing silica gel impregnated with dichloroacetaldehyde and then heating is 25 μg. As low as 1 μg of the same amines can be detected In aqueous solution by the degradation of a chloral-dichloroacetaldehyde copolymer. Detection signal in the latter case is the appearance of fluorescence when liberated monomer dissolves a 2-diphenylacetyl-1,3-indandione derivative.

Vycor Porous Glass (Thirsty Glass) as a Reaction Medium for Optical Waveguide Based Chemical Vapor Detectors

Abstract Vycor Porous Glass (Thirsty Glass) has been studied as a reaction medium for several model chemical vapor detection reactions. It was also compared with Celgard 2400 microporous propylene film as a reaction medium. Using Thirsty Glass as the reaction support for the detector reagent 2,6-dichloroquinone-4-cnloroimide, 1-butanethiol was detected at concentrations as low as 0.1 ppm. With either 4,4′-bis(diethytamino)benzophenone oxime or 1,3-diisonitrosoacetone as the detector reagent, methanesulfonyl chloride was detected at concentrations in air as low as 1 ppm. When 4-(p-nitrobenzyl)pyridine was the detector reagent, high detection sensitivities for 2-chloroethylethylsulfide and dimethylsulfate were achieved only when a two-step test procedure was used.

Catalytic NBP spot test for the detection of trichothecene mycotoxin T-2

Abstract Thorium(IV)salts were found to act as catalysts for the alkylation of 4-(p-nitrobenzyl)pyridine by T-2 toxin. Using thorium(IV)chloride as the catalyst, a detection procedure for T-2 toxin was developed that required a heating step consisting of only 2 minutes at 90°C. The limit of detection of T-2 toxin with this procedure was found to be 1 microgram.

Detection of amines by using the depolymerization of poly(chloroaldehydes)

Abstract A detector tube is described in which amine vapors cause decomposition of a chloral-dichloroacetaldehyde copolymer. Detection signal is based on the dissolution of the dye pinacyanole by the liberated chloroacetaldehyde monomers. Of the 77 amines tested, ammonia, allylamine, n -butylamine, isobutylamine, sec -butylamine, cyclohexylamine, diethylamine, dibutylamine, dipropylamine, and piperidine gave strongest tests. The limit of detection of diethylamine is approximately 2 μg. The sensitivity is increased about one order of magnitude if solution techniques are employed. Interferences appear to be few since 71 compounds representing 21 classes of compounds did not give a test.