Electrostatic, adsorption surface

The most frequent type of interaction between solid and species in solution would be electrostatic adsorption (ion exchange), due to the action of attractive coulomb forces between charged particles in solution and the solid surfaces. This process would also be concentration dependent. 

Surfactants greatly improve the performance of trans-cinnamaldehyde as a corrosion inhibitor for steel in HCl [741,1590,1591]. They act by enhancing the adsorption at the surface. Increased solubility or dispersibility of the inhibitor is an incidental effect. N-dodecylpyridinium bromide is effective in this aspect far below its critical micelle concentration, probably as a result of electrostatic adsorption of the monomeric form of N-dodecylpyridinium bromide. This leads to the formation of a hydrophobic monolayer, which attracts the inhibitor. On the other hand, an ethoxylated nonylphenol, a nonionic surfactant, acts by incorporating the inhibitor into micelles, which themselves adsorb on the steel surface and facilitate the adsorption of trans-cinnamaldehyde. 

Depending on the size of the probe, either covalent (Figures 10 and 11) or electrostatic immobilization (Figure 12) may be preferred. In general, oligonucleotides and DNA fragments of approximately 20 to 70 bases are amino-modified and bound covalently to the chip surface. Complete or partially complementary DNA of up to 5000 nucleotide bases is bound to the chip by electrostatic adsorption. 

Since immunosensors usually measure the signals resulting from the specific immu-noreactions between the analytes and the antibodies or antigens immobilized, it is clear that the immobilization procedures of the antibodies (antigens) on the surfaces of base transducers should play an important role in the construction of immunosensors. Numerous immobilization procedures have been employed for diverse immunosensors, such as electrostatic adsorption, entrapment, cross-linking, and covalent bonding procedures. They may be appropriately divided into two kinds of non-covalent interaction-based and covalent interaction-based immobilization procedures. 

Figure 6.1 A simple electrostatic adsorption mechanism illustrating the protonation-deprotonation chemistry of surface hydroxyl groups on oxide surfaces (which are neutral at the PZC) and the corresponding uptake of anionic or cationic complexes. Proton transfer to or from the surface can significantly affect the solution pH.

Figure 6.2 Electrostatic adsorption mechanism of Brunelle [1] (a) surface polarization as a function of pH (b) measurement of PZC of some oxides (equivalent to isoelectric point) by electrophoresis.

If one considers now different options to generate interaction in solution between Ag+ and the PdO surface. Pig. 13.32 shows that in the pH = 5 to 10 range electrostatic adsorption is expected to take place. In this pH range, deprotonated hydroxyl groups of the PdO surface have a negative charge and can interact with the Ag+ cations. 

Electrode surfaces can be modified by redox polyelectrolytes via a sol-gel process, yielding random redox hydrogels or by layer-by-layer self-assembly of different redox and nonredox polyelectrolytes by alternate electrostatic adsorption from solutions containing the polyelectrolytes to produce highly organized redox-active ultrathin multilayers. 

Thus, one approach to the liberation of electrostatically-bound ions from soil particle surfaces involves the use of partial leaches containing complexing ligands (such as halide salt solutions). These liberate the adsorbed metals by forming complexes, thereby out-competing the adsorption surfaces for these metals. 

A chitosan-modified CP (ChiCP) material was prepared for the electrostatic adsorption of dsDNA, ssDNA and ODNs [92]. The immobilized ODN could selectively hybridize with the target DNA to form a hybrid on the ChiCP surface. 

Besides DNA adsorption driven by a positive potential (electrostatic adsorption) DNA was also wet-adsorbed at an open circuit on a home-made polystyrene-based carbon ink [110]. This ink was prepared by a 2 3 mixture of polystyrene and graphite particles in mesitylene, and then printed on a polyester film. DNA was wef-adsorbed over the ink at 37 °C overnight. The nature of the electrode surface (graphite particles embedded in a polystyrene... 

Figure2. Electrostatic adsorption of colloidal hydrogels to functionalized surfaces.

Fig. 4 Schematic illustration of living anionic surface-initiated polymerization (LASIP) from clay surfaces showing initiator design and electrostatic adsorption to the surface of clay [28,29]...

The mechanism of particle capture by depth filtration is more complex than for screen filtration. Simple capture of particles by sieving at pore constructions in the interior of the membrane occurs, but adsorption of particles on the interior surface of the membrane is usually at least as important. Figure 2.34 shows four mechanisms that contribute to particle capture in depth membrane filters. The most obvious mechanism, simple sieving and capture of particles at constrictions in the membrane, is often a minor contributor to the total separation. The three other mechanisms, which capture particles by adsorption, are inertial capture, Brownian diffusion and electrostatic adsorption [53,54], In all cases, particles smaller than the diameter of the pore are captured by adsorption onto the internal surface of the membrane. 

With the application of protein microarrays in mind, Spencer and coworkers immobilized poly(lysine) with grafted PEG side chains on various metal or semiconductor oxide surfaces via electrostatic adsorption [200], Part of the PEG side chain was functionalized with biotin at the distal end. Streptavidin was bound to the surface-tethered biotin in a subsequent step, and the remaining unoccupied binding pockets of streptavidin were then used to immobilize biotinylated capture antibodies. As an example of an immunoassay, biotinylated goat anti-rabbit IgG was immobilized, which then specifically bound rabbit IgG. 

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