Structure of the Bonded Layer

Bonded alkyl ligands are flexible, although their flexibility is significantly restricted by immobilization on the surface also, the higher the ligand bonding density, the less flexibility these chains have. 

The main goal of chemical modification of the surface is to create a preferably uniform surface with a selected type of interactions. Energetic uniformity of the surface is dependent on the ligand s bonding density, distribution, and conformations. An additional desirable feature is hydrolytic stability, which in most cases is achieved by proper shielding of anchoring bonds. 

Shielding of the base material, leading to the elimination of the influence of residual sUanols, is essentially the main focus in the development of most recent packing materials. 

Type of bonding distribution is significantly dependent on the conditions under which the bonding reaction is performed. Type of catalyst (usually amine), reagent concentration, temperature, and presence of residual adsorbed water on the substrate surface affect this process. Detailed discussion of this could be found in reference 61. 

A similar study was performed on packed columns at HPLC conditions, and it was found that at any composition of the mobile phase, regardless of the type of organic modifier (THF, methanol or acetonitrile), the volume of the bonded layer corresponds to the densest arrangement of bonded ligands [60]. 

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The FTIR spectrum of magnetite with aminopropylsiloxane coating is shown in Figure 10.9. The intensive doublet at 1037 and 1135 cm is caused by formation of polymer structure with a high degree of polymerization, that is, on the surface of magnetite occurs hydrolytic polycondensation of molecules of modifier with formation of polymer structure of the bonded layer of modifier. 

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