Detection of organic vapours employing droplets having nanoparticles

In this paper, a droplet based organic vapour detection technique is discussed. The detection was based on solutal Marangoni effect where a strong circulation of fluid was observed inside a droplet once an organic vapour source was introduced near the vicinity of the droplet surface. The reason behind the rotational motion was the surface tension gradient created on the air-droplet and vapour-droplet interfaces. Different organic vapours produced rotational motion of different magnitudes inside the droplet based on the surface tension gradient created on air-droplet and vapour-droplet interfaces. In order to electrically detect the motion, a nanoparticle laden salt solution droplet was placed in between two copper electrodes and the electrodes were further connected to a digital multimeter for measuring the electrical resistance across the droplet. It was observed that there was a change in resistance when the droplet was set in motion by introducing an organic vapour source. A similar to 95% change in resistance was observed due to the flow circulation. It was also observed that the magnitude of change in resistance was different for different organic vapours. Thus, the system had the capability of being used as organic vapour sensor. A computational study was also performed in order to explain the phenomenon and to illustrate the effect of contact angle of the droplet.