Vibrational Spectroscopy 75 (2014) 173–177 Contents lists available at ScienceDirect Vibrational Spectroscopy journal homepage: www.elsevier.com/locate/vibspec Wing wettability of Odonata species as a function of quantity of epicuticular waxes  Song Ha Nguyen a , Hayden K. Webb a , Jafar Hasan a , Mark J. Tobin b , David E. Mainwaring a , Peter J. Mahon a , Richard Marchant c , Russell J. Crawford a , Elena P. Ivanova a,∗ a Faculty of Science, Engineering, and Technology, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia b Australian Synchrotron, 800 Blackburn Rd., Clayton, VIC 3168, Australia c Melbourne Museum, 11 Nicholson St., Carlton, VIC 3053, Australia article info Article history: Available online 1 August 2014 Keywords: Insect wings Long-chain aliphatic hydrocarbons Surface topography Wettability abstract Dragonflies have gained much attention due to their sophisticated wing surface structure, and their associated superhydrophobic, self-cleaning and bactericidal properties. In this work, we compared and contrasted the chemical composition and surface morphology of the wing membranes of four species of dragonfly and damselfly from the Odonata family collected in 1970s (Diplacodes melanopsis and Xan- thagrion erythroneurum) and 2011 (Diplacodes bipunctata, and Ischnura heterosticta). Diplacodes species are dragonflies, whilst Xanthagrion and Ischnura are damselflies. Fourier-transform infrared spectroscopy data obtained from the Australian Synchrotron were used to classify the fundamental components of all four of the insect species’ wings. The spectra of all species were dominated by C H stretching, amide I and amide II and O H stretch absorbance indicating the presence of a similar membrane composition of chitin, protein and wax in all four species. Although the samples were collected 40 years apart, there was no evidence of degradation having taken place during this time. Despite the overall similarities in spectral profile, species-specific differences were observed, most notably in the intensity of the CH 2 peaks, which in part reflected the amount of waxes present on the wings, which appeared to be different between individual species. The surface topography also contained minor differences in the diameter and the spacial distribution of its nanopillars. It is postulated that the differences in surface wettability of the wings could be attributed to these minor differences in surface chemistry and surface topogra- phy. For example, X. erythroneurum presented the highest water contact angle (WCA) of 160 ◦ whilst the D. melanopsis wings exhibited the lowest WCA (138 ◦ ), and the wettability of their wings was found to directly correlate with the intensity of hydrocarbon peaks found in their respective IR specta. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Insects first evolved the ability to fly at least 400 million years ago and are one of the largest classes, representing half of all liv- ing organisms on Earth [1]. In order to adapt to ever-changing environments, they have developed strategies to cope with differ- ent stresses [2]. Investigation into the mechanisms that they have adopted to enable them to cope with these environmental stresses has provided the scientific community with great insights for many  Paper presented at the 7th International Workshop on Infrared Microscopy and Spectroscopy with Accelerator-Based Sources (WIRMS), Melbourne, Australia, 10–13th November 2014. ∗ Corresponding author. Tel.: +61 3 9214 5137. E-mail address: eivanova@swin.edu.au (E.P. Ivanova). useful applications [3–8]. For example, the mechanism by which some beetles collect water from fog-laden wind on their back can be applied in water-trapping systems, such as water condensers and engines [9]. The anti-reflective properties of the eyes of some moth species have been used as an inspiration for various optical applica- tions [10]. Colourful butterfly wings have been studied extensively as a template for the fabrication of smart materials [11]. Superhy- drophobicity and self-cleaning properties are also two important characteristics possessed by many insects. In order to maintain their high levels of functionality, their surfaces have evolved to possess highly specific structures and surface chemistries [12–19]. Dragonfly and damselfly species belong to the order Odonata, and their wing surfaces are known for their superhydrophobic- ity and self-cleaning properties. A surface that exhibits a WCA greater than 150 ◦ is considered to be superhydrophobic. When water droplets remain in a spherical shape and readily roll off a http://dx.doi.org/10.1016/j.vibspec.2014.07.006 0924-2031/© 2014 Elsevier B.V. All rights reserved.