Hydroxyl group concentration determination

In order to clarify the nature of hydroxylic cover and to determine the hydroxyl group concentration on silica... 

Considering the absorption maximum of [OH] vibrations, presence of HAp and its thermal stability can be determined, as well as hydroxyl group concentration in the sample. 

The photooxidative degradation of anhydride-cured epoxies was studied. The degradation was heterogeneous, the surface being much more affected than the bulk. The disappearance rate of aromatic groups was dependent only upon their initial concentration, while the formation kinetics of hydroxyl groups was determined by the diffusion of oxygen into the material. The formation of hydrophilic products. 

The relationship between the BET monolayer capacity of physically adsorbed water and the hydroxyl content of the surface of silica has been examined by Naono and his co-workers in a systematic study, following the earlier work by Morimoto. Samples of the starting material—a silica gel—were heated for 4 hours in vacuum at a succession of temperatures ranging from 25 to 1000°C, and the surface concentration of hydroxyl groups of each sample was obtained from the further loss on ignition at 1100°C combined with the BET-nitrogen area. Two complete water isotherms were determined at 20°C on each sample, and to ensure complete... 

In Table 5.3, is compared with the total hydroxyl concentration (Ni, + N ) of the corresponding fully hydroxylated, sample. The results clearly demonstrate that the physical adsorption is determined by the total hydroxyl content of the surface, showing the adsorption to be localized. It is useful to note that the BET monolayer capacity n JH2O) (= N ) of the water calculated from the water isotherm by the BET procedure corresponds to approximately 1 molecule of water per hydroxyl group, and so provides a convenient means of estimating the hydroxyl concentration on the surface. Since the adsorption is localized, n.(H20) does not, of course, denote a close-packed layer of water molecules. Indeed, the area occupied per molecule of water is determined by the structure of the silica, and is uJH2O) 20A ... 

The BET monolayer capacity N, calculated from the first water isotherm included both physisorbed and chemisorbed water, whereas that from the second isotherm iV, included only the physisorbed water. Thus the difference (iV, - N,) gave the amount of chemisorbed water taken up as hydroxyl groups during the isotherm determination. N, + iV ) was therefore the total concentration of hydroxyl groups on the surface when the second water isotherm was being measured. 

Several assumptions were made in order to analyze kinetic data in terms of this expression (2). First it was assumed that k 2 m kj, k2 k 3, and kj/k j k /k ( - If). Second it was assumed that the rate constants were independent of the extent of reaction i.e., that all six functional groups were equally reactive and that the reaction was not diffusion controlled. The concentration of polymer hydroxyl functionality was determined experimentally using infrared spectroscopy as described elsewhere (7). A major unknown is the instantaneous concentration of methanol. Fits to the kinetic data were made with a variety of assumptions concerning the methanol concentration. The best fit was achieved by assuming that the concentration of methanol was initally constant but decreased at a rate proportional to the concentration of residual polymer hydroxy groups towards the end of the reaction. As... 

The CL enhancement of the lucigenin reaction with catecholamines in the presence of HTAH micelles was used for determination of dopamine, norepinephrine, and epinephrine [42], However, the presence of an anionic surfactant, SDS, inhibits the CL of the system. The aforementioned CL enhancement in the presence of HTAH can be explained in the following way the deprotonated forms of the catecholamines are expected to be the principal species present in aqueous alkaline solution due to the dissociation of the catechol hydroxyl groups, and to react with lucigenin to produce CL. The anionic form of the catecholamines and the hydroxide ion interact electrostatically with and bond to the cationic micelle, to which the lucigenin also bonds. Therefore, the effective concentration of the... 

We have examined very carefully reaction mixtures of (I) in methylene dichloride with perchloric acid. Under our best anhydrous conditions, when the reaction mixtures were neutralised with anhydrous triethylamine, the concentration of hydroxyl groups was between 2 x 10"3 and 10"2 M, which corresponds to between 2 and 5% of the perchloric acid concentration [18]. These small concentrations of hydroxyl groups are difficult to determine accurately, and they probably correspond to the residual water concentration. Thus this line of evidence favours the Keele mechanism. 

The objective of this work is to determine the surface concentration of the hydroxyl groups of cellulose and PVA films utilizing their chemical modification. We chose these polymers mainly because the hydroxyl group is their sole functional group. Recently we have reported that a cellulose film is more excellent in wettability towards water than PVA, though cellulose is insoluble in water, in contrast to PVA(4). Since only the chemical composition of the surface must be responsible for water... 

The ion that determines the p>otential of the compact layer is called the potential-determining ion. In cases in which the potentied of compact layer is determined by the dissociation reaction of adsorbed hydroxyl groups, the potential -determining ions are hydrated protons or hydroxide ions. For cadmium sulfide electrodes, the potential-determining ions are not hydrated protons but hydrated sulfide ions the iso-electric point is at the sulfide ion concentration of 4 x 10 M [Ginley-Butler, 1978]. 

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