Optical pH Sensor Based On Chemical Modification of Polymer Film

Fluorescence based fibre optic pH sensor for the pH 10–13 range suitable for corrosion monitoring in concrete structures

“…Prior work has shown that poor immobilization results in dye leaching and consequently a drifting of the calibration of the probe, which leads to the gradual breakdown of its useful sensing ability [17]. Among several widely used immobilization methods are included absorption or entrapment [45][46][47], layer-by-layer (LbL) electrostatic self-assembly [48,49] and covalent binding [18,[50][51][52][53]. The first two approaches are generally easier and simpler but not suitable for this type of application as they suffer from numerous disadvantages such as cracking, dye leaching and inhomogeneity of the material (in case of absorption or entrapment in a sol-gel matrix) or irreversible damage at extreme pH values and issue related to effect of ionic strength (in case of electrostatic attachment).…”

“…The covalent binding method can produce more reliable and durable sensors, as the indicators are virtually bonded to the substrate therefore they are unlikely to leach out under normal conditions, although the fabrication process is relatively complicated and time-consuming [54]. Regarding solid supports, various materials have been employed as the supports for dye immobilization including cellulose membrane [18,33,50,55], silica sol-gels [56,57] and synthetic organic polymers [32,53] with cellulose and sol-gels being more commonly used than the other due to the optical transparency of their matrices and in many cases, the convenience of attachment process. However, cellulose degrades easily in highly alkaline media [32,58] and sol-gels are completely deteriorated at pH higher than 10 within relatively short time.…”

Development of optical pH sensors based on derivatives of hydroxyazobenzene, and the extended linear dynamic range using mixture of dyes

“…The resulting transparent TAC films were placed in the selected dye solutions and stirred for 3 h at room temperature. To remove the loosely immobilized dye molecules, films were finally washed by detergent solution and stored in water for further use [16,17].…”

Full-range optical pH sensor based on imaging techniques

“…Different types of immobilization techniques for pH indicating dyes have been used [9], including (a) dye entrapment in different materials such as cellulose acetate [10,11], sol-gel [12], PVC [7], methacrylic-acrylic copolymers [13] and different composites like SiO 2 /ZrO 2 -organic polymer (styrene/methyl methacrylate copolymer or Nafion) [14], (b) retention of dye by ion-exchange materials such as Amberlite XAD-2 resin [15] or Dowex l-X10 resin [16], in some instances including the ionexchanger containing dyes in polymeric encapsulated membranes using PVC [17], (c) adsorption of the dye on materials such as non-ionic styrene/divinylbenzene copolymer [18], polyester/lycra blends textile [19], cellulose [20], cellulose acetate [21], or polymer track membranes combining retention in surface and bulk [22], (d) covalent binding of dye by different synthetic strategies to form microparticles or membranes, in some cases formed on glass fibre, using different polymers such as polyacrylamide [8,23], triacetylcellulose [24], cellulose acetate [25,26], agarose [27] or polyamide [28], among others, (e) polymerization of monomers to prepare both membrane and dye, as with aniline [29] or pyrrole [30].…”