Abstract
A responsive hydrogen-bonded cholesteric liquid crystal polymer (CLCP) film with controlled porosity was fabricated as an optical sensor to distinguish between methanol and ethanol in alcohol solutions. To facilitate responding the alcohols, porosity was generated by removing the nonreactive liquid crystal agent, and the hydrogen bridges of CLCP were broken. The sensitivities of CLCPs to ethanol and methanol were obtained by monitoring the wavelength shifts of the transmission spectrum at different alcohol concentrations and ratios of methanol/ethanol. Changes in the central wavelength of the CLCP network transmission spectrum allowed the methanol–ethanol ratio to be discriminated. A linear relationship between wavelength shift of CLCP networks and alcohol concentration was obtained experimentally, and the sensor characteristics were explored. The sensitivities of the CLCPs were 1.35 and 0.18 nm/% to ethanol and methanol, respectively. The sensing sensitivity of cholesteric networks to alcohol molecules increased as the methanol–ethanol ratio declined. Therefore, CLCP could act as a stimuli-responsive material to distinguish the concentrations of acetone and ethanol in mixed solutions. Furthermore, the impact of UV intensity for curing a CLC mixture on the sensing sensitivity to the different alcohol concentrations was also studied. The higher UV intensity could enhance the sensitivity to alcohol molecules and distinguishing ability between methanol and ethanol.
Highlights
Methanol and ethanol are colorless, flammable, and soluble in water, and are commonly used in medical sterilization, chemical synthesis, and industrial fuels
Various methods to distinguish between methanol and ethanol have been reported, such as gas chromatography-mass spectrometry [1], spectrofluorometric [2], optical fiber sensing [3,4,5], high performance liquid chromatography (HPLC) [6], electrochemical methods [7], Raman spectroscopy [8], and multifunctional nanomaterials [9,10]
During the bond-breaking process, the reflected color of cholesteric liquid crystal polymer (CLCP) film cured at UV intensity of 20 mW/cm2 was observed to gradually change from blue through purple to orange-red
Summary
Methanol and ethanol are colorless, flammable, and soluble in water, and are commonly used in medical sterilization, chemical synthesis, and industrial fuels. Since these two alcohol solutions are easy to obtain and the price of methanol is lower than that of ethanol, some unscrupulous manufacturers maliciously make alcoholic beverages mixed with methanol. The high similarity of methanol and ethanol makes methanol sensing surprisingly challenging. A method allowing simple, convenient, and selective distinction between ethanol and methanol in aqueous solutions is urgently required
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