| In recent years,major safety accidents caused by fake alcohol poisoning have caused many deaths in countries all over the world.Therefore,how to quickly detect the methanol concentration in ethanol environment has attracted much attention.At the same time,the liquid crystal drop sensor has become a hot research direction in the field of sensing due to its advantages such as high sensitivity,fast response speed,and low detection limit.However,the traditional drop sensor is mostly performed by observing its image changes under a polarizing microscope.For substance measurement,although this method is intuitive,it cannot accurately analyze the concentration of the analyte.Therefore,this paper designs a sensor that integrates liquid crystal droplets on the end of the optical fiber to detect the ratio and concentration of methanol and ethanol in the alcohol solution.Due to the different polarities of methanol and ethanol molecules,the pitch of the cholesteric liquid crystal will expand to different degrees.Therefore,when the sensor is put into different mixed alcohol solutions,the reflection wavelength of the cholesteric liquid crystal will change differently.The sensor integrates the polymer network and the cholesteric liquid crystal on the optical fiber at the same time.It has the advantages of high integration,simple measurement method,fast response speed,and good repeatability.It provides a method for measuring the methanol concentration in a high ethanol concentration environment.The new method has broad application prospects.The main research contents of this article are as follows:(1)Through experimental operations,chitosan hydrogel and cholesteric liquid crystal droplets are integrated in the hollow capillary at the end of the optical fiber,and a double cholesteric liquid crystal droplet fiber optic alcohol sensor is prepared to detect the concentration of methanol and ethanol in the solution.(2)The response characteristics of cholesteric liquid crystal droplets to methanol and ethanol solutions were explored,including the sensitivity to methanol and ethanol solutions,the response range,the lowest detection limit,etc.,and related experimental phenomena were theoretically analyzed,and the cholesteric liquid crystal liquid was obtained.The linearly corresponding concentration range of drops to methanol solution is 0.5 v/v%～30 v/v%;the linearly corresponding concentration range of ethanol solution is 0.3 v/v%～40 v/v%.Finally,the influence of the size of the cholesteric liquid crystal droplet on the sensing sensitivity is explored,and it is concluded that in the range of 0～75 μm,the size of the droplet has no effect on the sensing sensitivity.(3)The sensor’s response characteristics to a single solution and a mixed solution in the concentration range of 0.5 v/v% to 30 v/v% are explored,and the sensitivities of the two cholesteric liquid crystal droplets to methanol are 0.296 nm/v% and 0.467 nm/v%,respectively.The sensitivity to ethanol is 0.764 nm/v% and 1.133 nm/v%,respectively.The sensor parameters such as the response time and repeatability of the sensor are explored,and finally the contour map and calculation formula of the reflection wavelength of the sensor with the change of ethanol/methanol and total concentration are obtained through mathematical methods.Finally,the sensor was used to repeatedly measure the ethanol solution within 14 days,which proved that the sensor had a good stable response to methanol and ethanol solutions. |
