Inkjet printed colloidal photonic crystal microdot with fast response induced by hydrophobic transition of poly(N-isopropyl acrylamide)

This paper presents rapid response colloidal photonic crystal (PC) microdots fabricated by inkjet printing, which demonstrate a fastest response of ca. 1.2 s to water vapor. This remarkable improvement of response rate could be attributed to the combined effects of the intrinsic small size of the inkjet microdots and the hydrophobic transition of poly(N-isopropyl acrylamide) (PNIPAm) above its lower critical solution temperature (LCST). The reversible phase transition of PNIPAm modifies the hydrophilic–hydrophobic balance of the polymer interface, which leads to the modulation of wetting states/adhesion properties of adsorbed water on the polymer segments, resulting in the remarkable improvement of response rate. Moreover, the optimal response performance (including signal strength and response sensitivity) of the printed PC microdot is achieved by the coordination of a well-ordered latex assembly and full infiltration of the responsive polymer in the latex interstices. This simple fabrication of functional colloidal PC microdots opens new avenues for the construction of advanced microanalysis and microsensing devices. In addition, improving the response rate by the phase transition of the polymer segments is promising for the creation of high-performance sensors.