Surface weakly charged

In an ideal SEC separation, the mechanism is purely sieving, with no chemical interaction between the column matrix and the sample molecules. In practice, however, a small number of weakly charged groups on the surface of all TSK-GEL PW type packings can cause changes in elution order from that of an ideal system. Fortunately, the eluent composition can be varied greatly with TSK-GEL PW columns to be compatible with a wide range of neutral, polar, anionic, and cationic samples. Table 4.8 lists appropriate eluents for GFC of all polymer types on TSK-GEL PW type columns (11). 

At low electrolyte concentrations, the experimental results can be explained within the DLVO theory. A well-known approximation for the double layer interaction between weakly charged spheres, at constant surface charge, is1... 

Furthermore, adsorption at basic pH, where the surface is weakly charged, was found to be low but not negligible. To explain this adsorption, Van der Waals... 

Figure 13.4 shows that when Zi, Zj > 0, there is a potential minimum for large h and the surface potentials y(0) and y h) increase with decreasing membrane separation h. This potential minimum disappears ath = h, where the surface potential of the weakly charged membrane, y(h), coincides with its Donnan potential 3 don2- The value of he can be obtained from Eq. (13.16), namely. 

For a weakly charged surface such consideration of q(z) reduces to the MSA-M AL description in the framework of which the MSA theory for double layer [49] should be modified by correcting the ion density using the density of free ions, api, obtained from Eq. (2). However, for the activity coefficients in the form (35) and (36), we should change T to I defined by Eq. (24),... 

With high particle charges and low ionic concentrations, electrostatic repulsion (39,4C) alone should be capable of stabilizing, the colloid. This Typically occurs when surface potentials are around lOOmV. Steric stabilization (41,42) in nonaq-ueous media is important to achieve stability in weakly charged systems. Direct experimental measurements of particle-particle forces or potentials in nonaqueous media are not yet available. 

The band at 1338 cm was identified in Ref [16] to be a Bjg band based on its frequency and intensity in the crystal spectra, while a band at 1292 cm is likely to be a shifted variant of the C-H deformation Ag mode at 1303 cm in the single crystal [17]. The other bands correspond to modes which normally show infrared activity (see Figure 13.4). Considering that all the modes occurring upon In and Ag deposition are normal modes of the PTCDA molecule, the observed break-down of the Raman-infrared selection rules was proposed to originate from a weak charge transfer between the molecules and the metal surface mediated by molecular vibrations [9]. 

In combination with adsorption measurements, electro-optics is proved to be a powerful technique for studying the structure of adsorbed polyelectrolyte layers. Our data show flat conformation of the adsorbed macromolecules, which slightly depends on the polyelectrolyte charge density in accordance with the theory for weak poly electrolytes. Counterion condensation is also suggested on the surface of weakly charged poly electrolytes, which has not been predicted from the theory. 

Copper phthalocyanine (CuPc) is one of the most important blue organic pigments that are widely used in the varnish-, paint- and printing industries. Its surface is hydrophobic and weakly charged. The particles of CuPc during contact with water without a stabilizer are not wetted and float on the water surface. 

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