Novel temperature-activated, humidity-sensitive optical sensor

A novel, colorimetric, temperature-activated humidity indicator is presented, with a colour change based on the semi-reversible aggregation of thiazine dyes (esp. methylene blue, MB) encapsulated within the polymer, hydroxypropyl cellulose (HPC). The initially purple MB/HPC film is activated by heat treatment at 370 °C for 4 s, at which point the film (with a colour associated with a highly aggregated form of MB; λmax = 530 nm) becomes blue (indicating the presence of monomeric and dimeric MB; i.e. with λmax = 665; 605 nm respectively). The blue, heat-treated MB/HPC films respond to an ambient environment with a relative humidity (RH) exceeding 70% at 21 °C within seconds, returning to their initial purple colour. This colour change is irreversible until the film is heat-treated once more. When exposed to a lower RH of up to ca. 47%, the film is stable in its blue form. In contrast, a MB/HPC film treated only at 220 °C for 15 s also turns a blue colour and responds in the same way to a RH value of ca. 70%, but it is unstable at moderate RH 37-50% values, so that it gradually returns to its purple form over a period of approximately 6 hours. The possible use of the high heat-treated MB/HPC humidity indicator in the packaging of goods that cannot tolerate high RH, such as dry foods and electronics, is discussed.

Ionic liquids as modulators of fragrance release in consumer goods

When organic esters or alcohols were dissolved in each of three novel ionic liquids (which have no effective vapour pressure), the vapour–liquid equilibria (as measured by infrared spectroscopy of the gas phase) revealed significant positive deviation from Raoult’s law for a wide range of perfume raw materials. The addition of water amplified the repulsive effect of the ionic liquid matrix, and this was exemplified by a series of ternary phase diagrams