文摘
The diffraction color of a gelatin holographic diffractiongrating changed as a function of the water activity whenimmersed in a "wet" hydrophobic liquid.Quantificationof the absorption maximum of the diffracted light showedthat it was related, after calibration, to either thewatercontent or the water activity of the solvent. Theholographic diffraction grating measured water contents ofhydrocarbon solvents at sensitivities comparable to thatof the Karl Fischer coulometric titrator and over a widerange of water contents. A grating immersed in xylenerevealed a visible color change when the water contentwas increased from 47 to 120 ppm. Conversely, theholographic grating responded to ethanol in water in therange 0-1% (w/w). The inexpensiveness andsimplicityof silver halide holographic reflection gratings, combinedwith their relatively high sensitivity, suggests thatthesedevices might find widespread application as immersiblewater activity sensors for hydrophobic liquids.