W-INK Colourimetric Indicator Design

Harvard University (HU) is a private research university located in Cambridge, Massachusetts. The School of Engineering and Applied Science (SEAS) at HU aims to bring discovery and innovation to bear directly on improving human life and society in the 21^st century [1]. As a part of this process, SEAS developed a Watermark Ink (W-INK) chip that identifies the surface tension of a liquid. The W-INK colourimetric indicator for organic liquids works based on the wettability of highly ordered Inverse Opal Films (IOF).  The indicators mutually distinguish methanol, ethanol, and isopropanol, as shown in Figure 1. Applications of the W-INK system range from forgery detection to in-field liquid identification.  To distinguish between highly similar liquids in the IOF (i.e., methanol, ethanol, and isopropanol), a quality control procedure must be developed to account for the variability between samples, ensuring reproducible liquid distinction results. Chemical tuning techniques for W-INK samples adjust the wettability of the IOF for use as a colourimetric indicator in a wide range of liquids. Resolution and distinction capabilities of each chemical tuning technique are suitable criteria for assessment.

Kevin Raymond, a co-op student from the University of Waterloo, was asked to investigate the W-INK quality control procedure and chemical tuning parameters that allow it to successfully identify a wide range of liquids and account for structural variability in samples.