Reproducibility and Reversibility

The question of reproducibility of titrations has been addressed in a few publications (e.g., the results of repeated titrations are reported in [570]) but are ignored in many others. Poor reproducibility of silica titration curves at low ionic strength and good reproducibility at high ionic strength are reported in [591]. Poor reproducibility of charging curves of amorphous HFO is reported in [592]. 

In principle, the course of charging curves and the CIP should be independent of the solid-to-liquid ratio, and systematic studies in this direction are rare. The CIP in a yttria-NaC104 system was found to shift to a high pH as the solid load increased [597], 

Lyklema and co-workers [599,600] demonstrated the similarity of charging curves of various metal oxides at a certain ionic strength and temperature when Gg was plotted against pH-PZC, and the only difference between the different materials was in the positions of their PZCs. The similarity of the shapes of the charging curves demonstrated for selected samples of hematite, rutile, and RUO2 was impressive, but the charging curves of other samples of oxides are not that similar. 

FIGURE 2.11 A set of charging curves at three electrolyte concentrations (Cj Cj C3) with high absolute value of the slope near the PZC. 

---

In view of the complications which may be produced by surface hydration, hydroxylation and ageing, it is essential to check the reproducibility and reversibility of water isotherms if sound conclusions are to be... 

The bis-dioxolone azine 28 failed to give reproducible and reversible electrochemical behavior upon anodic oxidation. 

Other spectroscopic techniques that have been used with electrochemistry to probe nanoparticles include electronic and vibrational spectroscopies. The spec-troelectrochemistry of nanosized silver particles based on their interaction with planar electrodes has been studied recently [146] using optically transparent thin layer electrodes (OTTLE). Colloidal silver shows a surface plasmon resonance absorption at 400 nm corresponding to 0.15 V vs. Ag/AgCl. This value blue shifts to 392 nm when an Au mesh electrode in the presence of Ag colloid is polarized to —0.6 V (figure 20.12). The absorption spectrum is reported to be quite reproducible and reversible. This indicates that the electron transfer occurs between the colloidal particles and a macroelectrode and vice versa. The kinetics of electron transfer is followed by monitoring the absorbance as a function of time. The use of an OTTLE cell ensures that the absorbance is due to all the particles in the cell between the cell walls and the electrode. The distance over which the silver particles will diffuse has been calculated to be 80 pm in 150 s, using a diffusion coef-... 

The Pt film is at ground potential and Na Is photoemission from the Pt should of course appear at fixed kinetic energy, independent of Vwr. Thus our XP spectra clearly reveal the location of relationship between the two types of Na sampled by photoemission. For intermediate values of Vwr the amount of Na on Pt varies monotonically with catalyst potential and the (constant intensity) Na Is emission from the p"-Al203 shifts with Vwr. This spectral behaviour was reproducible and reversible as a function of Vwr. 

The use of materials having known reproducible (and reversible) temperature transitions and direct measurement of temperature. 

Figure 6.17 shows what happens when a constant value of pressure is repeatedly applied and removed over time. The drain current variation is reproducible and reversible, despite the presence of a hysteresis. The sensor... 

The force curves. The forces measured by Klein for the higher molecular weight polystyrene sample as a function of the distance of separation are shown in Fig. 13.10. These forces were stable, reproducible and reversible over... 

The strain-indueed orientation is analyzed with the help of birefringence measurements [107, 115, 120, 123] (realized in the isotropic state, close to the transition), measurements of the IR dichroism [124, 126], and X-ray experiments [93, 108,120, 122, 125]. It was observed that the orientational order parameter, labeled P2 on Fig. 32, obtained from X-ray experiments [122], quiekly inereases with strain at the beginning, then saturates at a P2 value of about 0.4-0.6 for a sample synthesized in an isotropic state [99, 107, 121, 122]. On condition that they were realized above the gel point [122], the networks display reproducible and reversible behavior independent of the sample history. 

BLAKELY Pretreatment with CI2 was necessary to achieve reproducible and reversible results. It probably removes any excess Ag produced during specimen preparation. The sample thickness was of the order of a few mm. 

Polymers that respond to an external field in a controlled, reproducible, and reversible manner have tremendous application potential. As we have highlighted in the preceding examples, the diverse utility of such polymers spans the gamut from biological to stealth to electro-optic systems. This highly interdisciplinary area includes research in chemical synthesis, property characterization, device... 

Sol-gel optical sensors were developed for many different applications the determination of pH [160], measuring the absorbance of common pH indicators immobilized in thin-film silica matrices [161,162] or as a coating in fiber-optics, where the evanescent wave absorption is measured [163,164], and sensors based on fluorescent pH indicators in hybrid matrices [165,166] were also developed, showing excellent reproducibility and reversibility. Zirconia in hybrid films doped with methyl-red showed reversible response to acid and base vapors [167]. Silica-titania thin films with entrapped sensing molecules have been developed as pH sensors [168]. 

---