An Optical Sensor for Volatile Amines Based on an Inkjet‐Printed, Hydrogen‐Bonded, Cholesteric Liquid Crystalline Film

Abstract

A printable hydrogen‐bonded cholesteric liquid crystal (CLC) polymer film is described, which can be used as a sensor for detection of gaseous trimethylamine (TMA). In this optical sensor the virgin CLC polymer network reflects green light. When anhydrous TMA gas penetrates the film, disruption of the hydrogen bonds occurs, with the simultaneous formation of carboxylate salts. The consequent reduction of the molecular order causes the green reflecting CLC film to become colorless. However, exposure to TMA in water‐saturated nitrogen gas results in a red reflecting film. Due to the hygroscopic nature of the polymer salt that is formed by TMA, water vapor which is present in the environment is absorbed by the films. This leads to swelling of the film, resulting in an increase in pitch size and therefore a red shift of the reflection band. Interestingly, after exposure to ambient conditions, restoration of the green reflecting film takes place, showing that the sensor can be used multiple times. In a proof of principle experiment, it was shown that these CLC films can be used as optical sensors to detect volatile amines, that are produced by decaying fish.

An Optical Sensor Based on a Photonic Polymer Film to Detect Calcium in Serum

“…− , [ 25 ] which is consistent with complete deprotonation of the benzoic acid groups to form a K + -carboxylate salt. [ 24,25,29,30 ] This polymer potassium salt fi lm swells by absorbing water from KOH solution leading to an increase in pitch and thus a change in color with the refl ection band at λ = 540 nm ( Figure 1 ), which is around the same wavelength as the pristine fi lm.…”

“…[ 24,25,29,30 ] This polymer potassium salt fi lm swells by absorbing water from KOH solution leading to an increase in pitch and thus a change in color with the refl ection band at λ = 540 nm ( Figure 1 ), which is around the same wavelength as the pristine fi lm. The bandwidth is narrower which might be due to the absorbed water lowering the birefringence in the fi lm.…”

“…The FT-IR (Fourier Transform Infrared) spectrum of the polymer fi lm (see Figure S1, Supporting Information) showed the absence of C C double bond of the acrylate as no peaks are present at 809 or 985 cm −1 . [ 25 ] A highly intense peak centered at 1696 cm −1 was observed due to the stretching vibration of hydrogen bonded C O. The broad nature of this peak suggests the presence of more than one type of H-bonded carboxylic acids, [ 26 ] i.e., H-bonded MAAs, H-bonded benzoic acids, and mixed MAA-benzoic acid complexes.…”

“…The FT-IR spectrum showed a sharp vibration peak at 1680 cm −1 indicating the presence of H-bonded dimer of 6OBA and 6OBAM ( Figure S1, Supporting Information). [ 25 ] Upon removal of the chiral dopant, the refl ection band shifted to λ ≈ 380 nm indicating that the helical structure is still present and that a chiralimprinted polymer network has been formed (Figure 1 a,b). The blue shift of ≈130 nm of the SRB suggests a collapse of the polymer coating which resulted in a decrease in pitch length as the number of pitches is invariant after polymerization.…”

Stimuli-responsive photonic polymer coatings

“…More recently, a CLC coating has been used to detect gaseous trimethylamine (TMA). 69 The sensor works similar as the CLC-based amino acid sensor (see above). TMA is absorbed by the carboxylic acid functionalised coating (Fig.…”