PH-responsive behavior

More recendy, two different types of nonglass pH electrodes have been described which have shown excellent pH-response behavior. In the neutral-carrier, ion-selective electrode type of potentiometric sensor, synthetic organic ionophores, selective for hydrogen ions, are immobilized in polymeric membranes (see Membrane technology) (9). These membranes are then used in more-or-less classical glass pH electrode configurations. 

Although the bulk of PDA sensors involve vesicles and Langmuir monolayers, a few examples of responsive PDA assemblies based on bolaamphiphiles and diyne silica nanocomposites have been reported (Lu et al. 2001 Song et al. 2001, 2004 Yang et al. 2003 Peng et al. 2006). Although these materials have not been broadly utilized for analyte sensing, they do exhibit the thermochromic, solvatochro-mic, and pH responsive behavior seen with monolayers and liposomes and hold promise for future development. 

Similarly, pH can be used to control the permeability of the capsule wall in hydrogen-bonded LbL systems. Kozlovskaya et al. [32] have demonstrated in a number of studies the pH-responsive behavior of single-component polyacid... 

Figure 4S By using dual pH-responsive block copolymers, adjustment of the aqueous solution pH leads to triggering of multimolecular micellar assembly, which is then followed by covalent cross-linking by a pH-unresponsive fluorescent cross-linker, to obtain a pH-responsive behavior for the resulting nano-object. Reproduced with permission from Lee, N. S. Sun, G. Neumann, W. L. etal. Adv. Mater. 2009,21,1344-1348. ...

The observed pH-responsive behavior may originate from the electrostatic interaction between the amine end-groups of the poly(L-alanine) bmsh and the residual amines on the silica surface in a manner similar to that described earlier for other types of surface-immobilized polymer brushes [21, 68]. It is possible that at low pH, both types of amine groups become protonated and their mutual repulsion leads to the polymer extension, as described above. Thus, at low pH, the polymer brush blocks a larger portion of the nanopore volume. As the pH is increased, the eleetrostatic... 

J. Zhang, K. Yuan, Y.-R Wang, and S.-T. Zhang, Preparation and pH responsive behavior of poly( vinyl alcohol)-chitosan-poly(acrylic acid) fuU-IPN hydrogels. Journal of Bioactive and Compatible Polymers, 22 (2), 207-218, 2007. 

Other types of bilayer sheet made from DMAEMA and BMA can be prepared by using the same method and changing the two layer compositions. The pH-responsive behavior of one kind of bilayer sheet (Layer A DMABMA BMA=1/1 Layer B DMABMA BMA=l/4, both are in molar ratio) was examined in detail by placing the sheets in deionized water as shown in Figure 6. It can be seen that the bilayer began to curl very quickly. Since Layer A is more hydrophilic than Layer B, the sheet bent gradually until a circle was formed. The curling time, the time when... 

After the development of thermoresponsive polymers, oiu interest was directed towards pH-responsive behavior in polymer aqueous solutions, and... 

Colloidal photonic crystals are often synthesized from monodisperse microspheres of PMMA, PS, and silica. The use of functionalized microspheres can increase the performance of certain photonic devices and CCTP has been successful in the synthesis of NC-loaded photonic crystals with a polymerizable macromonomer. Monodisperse microspheres composed of a PS core with a poly(methacrylic acid) (PMAA) shell were synthesized through an emulsion copolymerization of PMAA macromonomers synthesized by CCTP with PS. It was found that the CdZnS NCs capped with PMAA macromonomers could be anchored to the microsphere surface as the PMAA acts as a ligand. These colloidal crystals are then formed into a film, yielding well-ordered, hexagonal close packed structures that show pH-responsive behavior. All films with different hydrodynamic diameters simultaneously exhibit brilliant colors from red to blue, providing a promising avenue for the next generation of photonic devices. 

Fig. 9.15 Liquid Jimction potentials fiw a 10 mM KCl solutirai with added appropriate concentrations of HCl or KOH to arrive at the indicated pH values. This potmtial arises at the reference electrode and results, on the basis of the practical definition of pH, in a deviation from the Nemstian pH response behavior and is often erroneously associated with measurement error (alkaline and acid error)...

These redox reactions exhibit the two oxidation states of iridium oxide by which it is able to create an electrochemical potential as a pH sensor being similar to the conventional glass electrode. If there is any variation in the stoichiometry of the metal oxide then its pH response behavior will also be changed. If the metal oxide contains hydroxyl (OH ) groups at its surface the pH response will also be generated due to ion exchange ... 

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