Liquid-crystal-droplet-based Monitoring System for Water-soluble Inorganic Acidic Gases from the Atmosphere
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Original Article
Liquid-crystal-droplet-based Monitoring System for Water-soluble Inorganic Acidic Gases from the Atmosphere Zongfu An & Chang-Hyun Jang
*
Received: 18 March, 2020 / Accepted: 15 May, 2020 / Published online: 18 August, 2020 ⒸThe Korean BioChip Society and Springer 2020
Abstract A liquid crystal (LC)‐based pH sensor for real‐time monitoring of variations in localized pH values near the LC droplets was developed, and its applicability for the detection of acidic gases was explored. It was found that 4‐cyano‐4′‐pentylbiphenyl (5CB), when doped with hexanoic acid (HA), shows a bright-fan-shaped (planar orientation of LCs) to dark-cross (homeotropic orientation of LCs) optical response to a minimal change of the pH value (from 6.5 to 6.6). The fast and intensive pH‐driven optical response can be explained mainly with the orientational transitions of 5CB, induced by the protonation and deprotonation of HA at the interface of aqueous/LC droplet. Because of its high pH sensitivity, the LC‐based sensor was further exploited for monitoring the local pH changes, which were originated from concentration changes of acidic gases. The results suggested that at an industrial scale/production environment, the sensor shows excellent performance for long-term monitoring and sensing of acidic gases. This type of LC‐based sensor may find to fulfill its applicability potential in the trace measurement of acidic gases. Keywords: Liquid crystal droplet pattern, 4-cyano4′-pentylbiphenyl (5CB), Gas sensor, Acidic gas
Department of Chemistry, Gachon University, Seongnam-daero 1342, Sujeong-gu, Seongnam-si, Gyeonggi-do 13120, Republic of Korea *Correspondence and requests for materials should be addressed to C.H. Jang ( [email protected])
Introduction Acidic gases are common byproducts in industrial production of various agents, such as disinfectant, cleaning agent, etc.1 Acidic gases such as hydrogen sulfide (H2S), carbon dioxide (CO2), hydrogen chloride (HCl), and sulfur dioxide (SO2) can have a high impact on human health2. The release of these pollutants and acidic gases into the atmosphere can also drastically affect the ecological environment. Moreover, when an industrial accident occurs, acute and severe injuries can result from the inhalation of acidic gases and fumes, and such accidents have a very high mortality rate. On the other hand, patients with acid smoke inhalation injuries can often suffer from respiratory irritation, such as cough and dyspnea3,4. In severe cases, acute respiratory distress syndrome (ARDS), pneumothorax, and mediastinal emphysema may also occur5,6. During the acute acid smoke exposure period, the body may suffer from transient hypercapnia, and there may be affected the lung functions such as small airway dysfunction, mild obstructive ventilatory dysfunction, and decreased gas diffusion function; patients subjected to acute exposure may suffer from pneumonia. In the long term, there may be airway hyperresponsiveness, occlusive bronchiolitis, and even pulmonary fibrosis7,8. The leadi
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