![]() ![]() However, colorimetric humidity sensor based on electrospun fibers was rarely investigated. Typical colorimetric RH indicator such as silica gel self indicator and CoCl 2-based optical humidity sensor have been presented. In addition, cobalt chloride has been applied as colorimetric RH indicator for its color changes when contaminated by water. At present, several intermediate agents have been adapted to realize colorimetric indicator for humidity including photonic crystal, polymer electrolyte thin films, doped cholesteric liquid crystal, and crystalline covalent organic framework nanofibers. Since RH do not have measurable intrinsic optical properties, some intermediate agent will be introduced to show a change in optical property. Optical humidity sensors will be a possible solution. While the sensitivity of the above humidity sensors based on electrospun fibers were detected by precise instrument, it may do not work in practical application limits to conditions. Moreover, ceramic LiCl-doped ZnO electrospun fibers were also fabricated as humidity sensor, with response time and recovery time about 3 and 6 s. It shows high sensitivity and the response and recover times are 120 and 50 s, respectively, with RH changing from 2 to 35%. For example, electrospun polyamide 6 nano-fiber/net modified by polyethyleneimine was investigated as RH indicator detected by quartz crystal microbalance (QCM). It is now believed that RH sensors based on the electrospun nanofibrous membranes (NFMs) show improved sensor sensitivity due to their large surface area to volume ratio, providing an increased number of sites for analyte interaction or signal transduction. Among these types of sensors, the optical type has attracted a lot of interests since it is supplying a change in optical properties, easily detectable with the naked eye (visual) which is suitable for applications in daily life. Until now, various types of humidity sensors have been reported, such as resistance type, capacitor type, field-effect-transistor type, optical type, and so on. But under unfavourable conditions, errors may amount to as much as ± 5% R.H., unless the corrections are used.Relative humidity (RH) sensor is mainly used for monitoring atmospheric humidity environment and shows important applications in warehousing, environmental monitoring, instruments and meters, and meteorology. teat papers can be estimated to about the nearest 1% R.H. The standards cover humidities above 50% R.H. Corrections are given for use when exposures other than 30 min. is sufficient except at very high humidities, where up to 2 hr. The influence of temperature and humidity on the time taken to reach colour equilibrium is described. Approximate corrections for temperature are given. Methods of impregnating the paper are described, also the above-mentioned method of preparing standards. A further improvement is the use of pure cotton tissue paper. Papers more suitable for use at high humidities have been prepared with cobalt thiocyanate solution. Alternatively, the addition of zinc chloride or certain other salts adapts the method for use at low humidities. The method can thus be adapted for accurate use at higher humidities. Certain salts, such as potassium thiocyanate and sodium thiosulphate, produce a similar, but much greater effect, and also produce stronger colours. Various colloid substrates other than paper, including mercerized cotton, cause the blue colour to persist at somewhat higher humidities possible uses of this are suggested. to the nearest 2% R.H., and above this range to the nearest 5%, except for low humidities at low temperatures. It is possible to measure humidities from 40 to 70% R.H. ![]() Colour standards for the matching of test papers are prepared by exposing papers over constant humidity solutions and then sealing them up in liquid paraffin between opal and clear glass. The time required for a piece of CoCl 2, paper to reach equilibrium with the atmosphere depends chiefly on humidity and temperature up to 2 hr. The paper is impregnated by dipping in a solution of CoCl 2.6H 2,O. It is shown that the colour is determined chiefly by the relative quantities of cobalt chloride and water in the paper. There is a close correspondence between colour and relative humidity, although the colour is influenced slightly by temperature. Cobalt chloride paper is blue at low and pale red at high humidities, with a series of lilac colours between. To meet the need for a simple method of measuring humidity in small spaces, a new method of using paper impregnated with cobaltous salts has been developed. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |