Study on the Characteristics of Macromolecular Chains of Cellulose in Dilute Solutions

The characteristics of macromolecular chains of cellulose in dilute solutions are discussed. Viscometry was used for the measurement of the intrinsic viscosity [η] of four cellulose samples, which were respectively dissolved in the solvent Tri-ethylenediamine cadmium hydroxide Cadoxen (Cadoxen), Cupriethylenediamine hydroxide(Cuen), iron sodium tartrate complex(EWNN) and N,N-dimethylacetamide(DMAc)with lithium chloride(LiCI, 9% w/w). The intrinsic viscosity of the four solutions decreased in the following manner:[η]DMAc/LiCl>[η]EWNN>[η]Cuen>[η]Cadoxen. The stability of cellulose (Sample α-cellulose) dissolved in solvents Cuen and EWNN was tested by plotting the intrinsic viscosity vs. time. The values of Huggins constant K_H for the cellulose samples dissolved in solvents Cadoxen,Cuen,EWNN and DMAc/LiCl (9% w/w ) were calculated.     

Sensitivity gains in chemosensing by lasing action in organic polymers

Societal needs for greater security require dramatic improvements in the sensitivity of chemical and biological sensors. To meet this challenge, increasing emphasis in analytical science has been directed towards materials and devices having highly nonlinear characteristics; semiconducting organic polymers (SOPs), with their facile excited state (exciton) transport, are prime examples of amplifying materials. SOPs have also been recognized as promising lasing materials, although the susceptibility of these materials to optical damage has thus far limited applications. Here we report that attenuated lasing in optically pumped SOP thin films displays a sensitivity to vapours of explosives more than 30 times higher than is observed from spontaneous emission. Critical to this achievement was the development of a transducing polymer with high thin-film quantum yield, a high optical damage threshold in ambient atmosphere and a record low lasing threshold. Trace vapours of the explosives 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) introduce non-radiative deactivation pathways that compete with stimulated emission. We demonstrate that the induced cessation of the lasing action, and associated sensitivity enhancement, is most pronounced when films are pumped at intensities near their lasing threshold. The combined gains from amplifying materials and lasing promise to deliver sensors that can detect explosives with unparalleled sensitivity.