Detection of volatile organic compounds (VOCs) is an important issue due to their harmful impact on human health. We developed two methods for increased sensitivity of polymeric, passive sensors templated from cholesteric liquid crystals (CLC). First, we showed that the presence of VOCs at concentrations in the order of 100 ppm can be identified based on the color shift of the polymeric films templated from CLCs taking advantage of elastic energy resulting from the anisotropic network (Figure 1). Specifically, we produced CLC-templated polymeric flat and strained films with programmed strain profiles and tested their response against VOCs in a controlled experimental system. To illustrate the relationship between strain and sensitivity, we developed the strain map of the polymeric films using a model based on the twist part of the elastic energy. Our results showed that in the presence of strain, up to 4 times higher signals could be obtained in 0-1000 ppm concentration range. We also showed efficient reversibility and the response time of the sensor. In the second part, we showed that filling the pores of the CLC-templated polymeric films with polydimethylsiloxane (PDMS) to increase the sensitivity of the CLC-templated polymeric films. Overall, this study provides a method to develop a passive sensor using CLC-templated polymeric films which is sensitive enough to be used in industry and daily life and is durable for integration into wearable technologies.

Enhanced sensitivity of polymeric sensors templated from cholesteric liquid crystals

ACS Fall 2021

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