A pressure sensitive device that can characterize gases using structural colors

NIMS, Harvard University, and the University of Connecticut have designed and manufactured a simple device that can display an injected gas in multiple colors according to the gas properties and provide chromatic separation of different gases. This user-friendly device displays the pressure created by an injected gas by converting it into structural colors. This technology could potentially have a wide range of applications, such as environmental monitoring, security assurance, and healthcare.

The imaging of gases is important in many gas-related basic and applied research projects because nearly all ambient gases are colorless and invisible. Only a few methods have been developed for imaging the ambient gas flow (for example, the use of infrared cameras that can detect temperature changes and airflow measurements by releasing tracer particles into the air).

These methods require detailed equipment and are not suitable for consistent imaging of different types of gases. In addition, the images they produce are not suitable for the analysis of gas properties. A simple method capable of imaging and analyzing all gas types could have a wide variety of applications, such as image-based measurements.

This research team has recently produced a device capable of imaging and distinguishing various gases using a wide variety of colors (i.e. structural colors) through a simple procedure: polydimethylsiloxane (PDMS) – a soft material – first shaped into a sheet. A portion of the PDMS surface was then treated with argon plasma. The plasma-treated PDMS sheet was placed on the surface of a glass substrate with the plasma-treated surface down, and they were fully in contact.

The plasma-treated PDMS surface creates a periodic fluctuation-like micropattern when compressed by an injected gas passing through the tight boundary between the PDMS and glass layers. This compression and the resulting micropattern formation leads to the production of structural colors. This mechanism is applicable for displaying and distinguishing any type of gas. Structural colors are completely lost when the incoming gas flow is interrupted.

The degree of PDMS deformation depends on the flow rates, viscosities and densities of the injected gases. Because all gases have unique viscosities and densities, this instrument can be used to distinguish and analyze gas samples based on these properties under a constant flow rate.

In future research, the team will work to optimize the device by increasing its sensitivity with the goal of making it compatible with a variety of applications (e.g. identification of ambient gases and biological samples). The team will also consider developing a new gas identification technique by combining it with image recognition and machine learning techniques and producing a small, CCD (charge-coupled device) integrated device with a simple structure.

The research was published in the journal Advanced Science.