Sensing parameters as a function of the chemical structure and thickness of two poly(styrene)-type based composites with carbon black

Sensing parameters of polymer composite layers were studied as a function of the polymer matrix structure and the initial resistance of the composite layers. Composites of Poly(styrene) and 4-Chloro-poly(styrene) at the same volume fraction of carbon black (8.7% V/V) were prepared by ultrasonic dispersion. Composite layers with different thicknesses and resistances were deposited by spin coating technique on flexible substrates from commercial cellulose acetate foils. Both kind of composite layers with initial resistances of 10, 50 and 100 k? were exposed to Acetone, Tetrahydrofuran, Chloroform and Toluene. Results evidenced that selectivity is very dependent on the chemical structure of the polymer matrix and sensitivity to the initial film electrical resistance. PS-based composite series were selective to Tetrahydrofuran whereas that 4ClPS-based composite series were selective to Acetone as expected due to their solubility parameters. For both composite series sensitivity increased for layers with less than 100 k? resistances. For all tested solvents 4ClPS-based composites showed higher sensitivities than PS-based composites. The response times for both series were into the range of 2 to 150 s and recovery times were in the range of 30 to 2000 s.

Study of Catalytic Effect of Nanolayered Montmorillonite Organoclays in Epoxy Polymer

This paper is about the study of catalytic effect of nanolayered montmorillonite- (MMT-) based organoclays (OCs) in epoxy polymer by directly monitoring their exothermic temperature versus time during curing. Untreated clays (UCs) of MMT were also filled in the epoxy polymer for comparative study. OCs and UCs were individually filled in epoxy polymer from 0 wt.% to 5 wt.%, and the curing characteristics were examined. The cure behavior of epoxy-OC composites changes as a function of OC concentration. Among the epoxy-OC systems, improved curing reaction was observed at 3 wt.% OC-filled epoxy composites. Addition of OC above 3 wt.% in epoxy reduces its catalytic effect due to presence of two types of cross-linking, namely, intergallery and extragallery cross-linking reactions. The curing behaviours of epoxy-UC composites were almost similar to those of pure epoxy polymer, and hence the results suggest that UC does not act as catalyst in epoxy polymer. The cured composite series was examined by studying their structure and morphology using X-ray diffraction (XRD), transmission electron microscopy (TEM) analysis, and the Fourier transform infrared (FTIR) spectroscopy.

The Svalbard Airport Temperature Series

In the Isfjorden region of Spitsbergen in the Svalbard archipelago, the air temperature has been observed continuously at different sites since 1911 (except for a break during WW II). The thermal conditions at these various sites turned out to be different so that nesting the many series together in one composite time series would produce an inhomogenous long-term series. By using the SNHT (Standard Normal Homogeneity Test) the differences between the sites were assessed and the series adjusted accordingly. This resulted in an homogenised, composite series mainly from Green Harbour (Finneset in Grønfjorden), Barentsburg (also in Grønfjorden), Longyearbyen and the current observation site at Svalbard Airport. A striking feature in the series is a pronounced, abrupt change from cold temperature in the 1910s to warmth in the 1930s, when temperature reached a local maximum. This event is called the early 20th century warming. Thereafter the temperature decreased to a local minimum in the 1960s before the start of another increase that still seems to be ongoing. For the whole series, statistically significant positive trends were detected by the Mann-Kendall test for annual and seasonal values (except for winter). Quite often the Norwegian Meteorological Institute receives queries about long-term temperature series from Svalbard. Hopefully, the Svalbard Airport composite series will fulfil this demand for data. It may be downloaded free of charge from the Institute’s home page: http://sharki.oslo.dnmi.no and should be used with reference to this article.