Determination of Concentrations of Surface-Active Materials in Aqueous Solutions at Different pH Values Using Liquid Crystals

Abstract

Determination of the content of environment polluting chemical agents is of significant importance. The goal of this study was the development of experimental approaches for detection of concentrations of surfaceactive molecules (surfactants) such as sodium dodecyl sulfate (SDS) and

Thermotropic Liquid Crystal-Assisted Chemical and Biological Sensors

“…Surface-active materials classified as solubilizing agents, such as sodium dodecyl sulfate (SDS), are readily detected by LC cells: 5CB films normally remain stable at concentrations above those that drive the transition from hybrid into homeotropic alignment [ 5 , 47 ]. In contrast, Popov et al [ 55 ] showed that 5CB-based freely-suspended nematic and cholesteric sensing films collapse in the presence of the non-ionic surfactant Triton X-100 before showing any hybrid-to-homeotropic LC realignment as shown in Figure 16 :…”

“…As reported by Popov et al [ 55 ], freely-suspended LC films are not suitable for experiments where the grids are fully immersed in aqueous solutions containing certain surfactants. For example, the addition of the non-ionic oil-soluble emulsifying surfactant Triton X-100 into water did not facilitate the planar-to-homeotropic transition but instead led to 5CB film rupture.…”

“…In biological sensing, an important environmental parameter is the pH value. Popov et al [ 55 ] found that when the pH of the sub-phase was decreased with acetic acid, 5CB films become more sensitive to SDS; for example, the hybrid-to-homeotropic transition occurs at lower analyte concentrations. When the pH of the sub phase was increased with ammonium hydroxide, 5CB films became less sensitive to SDS, to the point that no hybrid-to-homeotropic transition was observed before the SDS concentration became so high that the freely suspended film collapsed.…”

“…To date a large variety of approaches of LC assisted biological and chemical sensing have been demonstrated [ 7 , 9 , 17 , 47 , 55 ] but examples of LC-based specific sensing of analytes remain scarce [ 14 , 57 , 112 , 113 ]. While non-specific LC-based sensor studies are interesting and insightful, “real life” applications require highly-specific LC assisted platforms for selective sensing of analytes.…”

Octylcyanobiphenyl Liquid Crystal Confined to Anisotropic Porous PET Films at Homeotropic Anchoring: Optical Textures and Internal Ordering

“…Liquid crystals (LCs) confined to micrometersized curvilinear (non-planar) geometries are attractive from both fundamental and applied points of view [1]. In this case, a strong confinement provides higher sensitivity to the external stimuli and lower switching times, respectively to flat LC layers, which is important at a practical elaboration of new LC devices for sensing [2,3] and photonic [4] applications. In the simplest case, LC materials comprise micrometer-sized droplets or cylinders surrounded by a polymer matrix.…”