A Liquid Crystal-Based Passive Badge for Personal Monitoring of Exposure to Hydrogen Sulfide

Abstract

A new liquid crystal (LC)-based passive dosimeter badge for personal monitoring of exposure to hydrogen sulfide (H2S) gas is reported. When a thin film of LC supported on a surface functionalized with lead perchlorate Pb(ClO4)2 (the LC sensor) is exposed to H2S, the orientation of LC molecules in the film changes from perpendicular to parallel. This reorientation induces a change in the appearance of the LC film when viewed between crossed polarizers. A H2S dosimeter was fabricated by pairing a LC sensor with a glass substrate forming a headspace between the two surfaces, to control diffusion of H2S across the LC film. When the dosimeter is exposed to H2S, a bright front appears as a function of exposure time. An algorithm has been developed to correlate this response length and exposure dose. The dosimeters are functionally stable when subjected to extreme temperature and humidity fluctuations, and are immune to a number of potentially interfering chemicals, except mercaptans. These dosimeters detect H2S at 0.2 ppm TWA (8 hr) with ±20% overall accuracy. The dosimeters were used to monitor the personal exposure of personnel working in an oil refinery. The TWA concentrations measured by the LC-based dosimeters correlate strongly with the NIOSH 1063 method that uses a sorbent tube and a pump followed by laboratory analysis. Thus, the LC-based dosimeters can provide a sensitive tool for on-site assessment of personal exposure to H2S in different environments.

Seeing the Unseen: The Role of Liquid Crystals in Gas‐Sensing Technologies

“…[ 146,150,160,162 ] Additionally, gas or VOC interactions were also characterized by Fourier‐transform infrared spectroscopy (FTIR) [ 149,160,162 ] or Raman spectroscopy. [ 140 ] Other transduction methods include the use of custom‐made devices, [ 42,94,109,127,142 ] SPR [ 135 ] (used to detect subtle changes in LC birefringence), or quartz crystal microbalance [ 153 ] (used to detect mass changes when chiral LCs were coated on acoustic devices). As discussed in Section 3.6, discotic LCs films exhibit changes in their surface conductivity upon gas exposure.…”

“…Surface functionalization studies have extended to perchlorate salts of metal ions [ 125,126 ] such as, gallium, [ 102 ] lead, [ 127 ] or manganese. [ 128 ] Hunter and Abbott [ 129 ] have also explored the possibility of tuning the anion in perchlorate‐salt decorated surfaces in order to manipulate the LC anchoring to the binding surface, and hence increase the selectivity and sensitivity of surface‐induced LC transitions triggered by gas analytes.…”

Computational Chemistry‐Guided Design of Selective Chemoresponsive Liquid Crystals Using Pyridine and Pyrimidine Functional Groups

“…[1][2][3][4][5][6] Liquid crystals (LCs) provide the basis of a particularly promising class of chemoresponsive materials as they are fluid phases within which the molecules (mesogens) exhibit preferred orientations, a so-called director, at chemically functionalized interfaces. [7][8][9][10][11][12][13][14][15][16][17] For example, LC films supported on the surfaces of solids decorated with metal salts have been shown to report the binding of specific chemical targets, such as organophosphonates, [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] NO 2 [33] or H 2 S [34] . The LC ordering transitions, which are triggered by competitive binding of the mesogens and targeted chemical species with the metal salts, are easily transduced with optical and electrical methods.…”

A Zero‐Power Optical, ppt‐ to ppm‐Level Toxic Gas and Vapor Sensor with Image, Text, and Analytical Capabilities

“…Others have previously exploited this concept for the detection of H 2 S, [41] but the here-described patterning approach using ink-jet printing allows for smaller, distinct features that are easier to catalogue and compare and permit in principle the detection even of multiple gases on the same device.…”

“…[38] Taking advantages of functionalized surfaces, such as self-assembled monolayers, and the corresponding interfacial ordering of LCs, Abbott et al designed chemically triggered interfaces that reorient the nematic LCs under the influence of gases such as organoamines or organophosphonates. [39] This work opened the path of LC materials that respond to the presence of a variety of gases including nitrogen dioxide, [40] hydrogen sulfide, [41] or a simulant of organophosphonate chemical warfare agents, [42,43] as well as other vapor-phase chemicals and biological entities. [44] This approach led to the design of responsive, zero-power optical devices where LC molecules produce and enhance the optical output signal.…”