Supplementary material
Chip scale humidity sensing based on a microfluidic
infiltrated photonic crystal
A. Casas-Bedoya1, S. Shahnia1, D. Di Battista1, E. Mägi1 and B. J. Eggleton1
1
Centre for Ultrahigh bandwidth Devices for Optical Systems (CUDOS), Institute of Photonics and
Optical Science (IPOS), School of Physics, University of Sydney, New South Wales 2006, Australia.
SUPPLEMENTAL MATERIAL
The ability of the water molecules to bond to the ionic liquid molecules via hydrogen
bonding [1,2] is represented in Figure S1 (a). Here, a higher concentration of water molecules
increases the liquid’s probability to create a hydrogen bond with water. This, in turn reduces the
liquid’s effective refractive index, reducing n and changing the volume of the liquid in the PhC
hole.
To further explain the liquid’s ability to de-absorb [2] water according to a RH reduction, the
hydrogen bonds created between the ionic liquid and the air moisture or water vapour were
analysed. Here, we use the fact that in an isolated environment the RH decreases as the
temperature increases. Figure S1(b) for instance, shows (via Fourier transform infrared
spectroscopy) how a temperature rise reduces the intensity of the O-H bond at 3600 cm-1.
1
Figure S1(a) Schematic representation of an infiltrated PhC hole after exposed to different
water vapour concentrations. (b) Fourier transform infrared spectroscopy measurements of
the Ionic liquid used during this research. The different colors are associated with different
temperatures. The O-H bond present at 3600 cm-1 (b-Inset) is dominant at lower
temperatures due to the higher amount of water present in the surroundings.
Acknowledgment
We acknowledge the scientific and technical assistance of the Vibrational Spectroscopy facility,
in the School of Chemistry, at the University of Sydney.
References
1.
C. D. Tran, S. H. D. E. P. Lacerda, and D. Oliveira, "Absorption of Water by RoomTemperature Ionic Liquids: Effect of Anions on Concentration and State Water," Applied
Spectroscopy 57, 2–7 (2003).
2.
J. N. Decerbo, "1-alkyl-3-methylimidazolium bis(pentafluoroethylsulfonyl)imide based
ionic liquids:A study of their physical and electromechanical properties," Wright State
University (2008).
2