Adsorption hydroxy group effect

Essentially nonionic soil-release agents comprise polyesters, polyamides, polyurethanes, polyepoxides and polyacetals. These have been used mainly on polyester and polyester/ cellulosic fabrics, either crosslinked to effect insolubilisation (if necessary) or by surface adsorption at relatively low temperature. Polyester soil-release finishes have been most important, particularly for polyester fibres and their blends with cellulosic fibres. These finishes, however, have much lower relative molecular mass (1000 to 100 000) than polyester fibres and hence contain a greater proportion of hydrophilic hydroxy groups. They have been particularly useful for application in laundering processes. These essentially nonionic polymers may be given anionic character by copolymerising with, for example, the carboxylated polymers mentioned earlier these hybrid types are generally applied with durable press finishes. 

Heats of adsorption measurements do not lead to very specific interpretation since the isosteric heat of adsorption (AH) arises from both nonspecific interactions, which occur in all cases of adsorption, and from specific interactions with the hydroxy groups nevertheless, valuable conclusions about the binding forces can be deduced. Saturated hydrocarbons, e.g., n-pentane, have a value of — AH of 8.0 kcal/mole, while saturated ethers have values of around 16 kcal/mole.14 Probably dispersion forces only are involved in the former case and additional specific interaction with the silanol-OH occurs in the second case. On graphite, where there is no specific interaction, the heats of adsorption of hydrocarbons and ethers are very similar.17 The heat of adsorption of furan (11 kcal/mole) is 5 kcal/mole less than that of tetrahydrofuran this again indicates the effect that delocalization of electrons by the double bonds has on the binding forces.14... 

The highest reactivity and adsorptivity were exhibited by substrates with a mono- and disubstituted double bond. The high adsorption coefficient of l-propene-3-ol and 2-butene-l-ol was attributed (700) to the presence of the hydroxy group in the molecule of these substrates on the contrary, the phenyl group had a negative effect on the adsorption coefficient of the phenyl-substituted olefin. 

Jacobs et al. [724] introduced the FTIR measurement of the shift of the OH stretching band upon benzene adsorption as a measure of the acid strength of the hydroxy groups. Jacobs [725] also provided a theoretical reasoning for this effect. Similarly, O Malley [794] developed an electrostatic model for predicting the shift of typical IR bands upon adsorption of aromatics on the respective zeolitic OH groups. 

Surface science and calculation also provide new elements of understanding on the effect of water depicted in Section 15.3.4. The influence of water vapor on the adsorption of O2 on anion gold clusters has been studied both experimentally and theoretically [177]. The presence of an hydroxy group on Au " clusters (N=2 to 5) leads to a reversed O2 adsorption activity with respect to bare clusters (Section 15.4.3) Non-reactive bare gold clusters, with odd-N atoms, become active when OH is bound (Auj OH ), whereas active bare clusters, with even-N atoms, become inactive. DFT calculation provides evidence that electron-transfer induced by the binding of an OH group enhances the reactivity toward O2 for odd anionic gold clusters and suppresses it for the even ones. 

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