Optical fiber sensor for determination of methanol ratio in methanol-doped ethanol based on two cholesteric liquid crystal droplets embedded in chitosan

In this paper, an optical fiber sensor based on cholesteric liquid crystal (CLC) is designed to detect the proportion and concentration of methanol and ethanol in alcohol solution. Due to the different polarity of methanol and ethanol molecules, the pitch of CLC will swell in different degrees. Therefore, the reflected light wavelength of CLCs will shift differently when the sensor is put into the mixed solution of two alcohols with different proportions and concentrations. The function of chitosan polymer network is to fix and protect CLC droplets, it also allows small molecules to pass through and interact with CLC. The sensitivities of the two CLCs are 0.296nm/v% and 0.467nm/v% to methanol, and 0.764nm/v% and 1.133nm/v% to ethanol, respectively. The detection range of the sensor for alcohol solution is 0.5v/v% - 30v/v%. The linear relationship between wavelength shift and proportion and total concentration was obtained by least square method, and the related characteristics of the sensor were explored.