Hydrophilic silica layers

Yang et al. [139] reported the sulfuric acid functionalization of a phenylene-silica PMO involving the attachment of propyl sulfuric acid groups to the hydrophilic silica layers. In this material, as the catalytic acid sites and the hydrophobic benzene sites were apart from each other on the mesoporous surfece, a dimensionally designed surface structure with better catalytic environment resulted. The sulfuric acid-functionalized PMO was derived from a phenylene-silica... 

The frequency of PDMS chain mobility in the interfacial layer is largely dependent on the type of silica surface. Water adsorption by the hydrophilic silicas causes the degree of chain immobilisation in the interface to decrease [107]. Sililation of the silica surface results in a significant decrease in the strength of adsorption interactions at the silica... 

A PDMS layer chemically attached at both chain ends to the surface of hydrophilic silica has been studied by means of H T2 relaxation experiments [112]. The average length of the grafted chains in samples studied was varied from about 4 to 8 Si-O bonds. These experiments showed that the T2 relaxation method is very sensitive to the heterogeneous... 

Fig. 2. Specular reflectivity for bare hydrophilic silica surface, ( ) Si/D20, (A) Si/ H20, and ( ) Si/cmSi. The solid lines are calculated curves for a thin oxide layer of 15 A and a scattering length density of 3.5 x 10-6A-2.

Figure 2.30 is the first example we consider. Here, the adsorbent Is hydrophilic silica (TK 900, Degussa), containing sllanol and siloxane groups on the surface. The pH was not checked It could have exerted some influence because an electrical double layer will develop at the silica-water Interface the state of hydration of the Interface Is also pH-dependent. The Isotherm clearly exhibits different regimes, with almost vertical parts and shorter or longer plateaus. So much fine structure Is not always found for instance with C Eg instead of C12E5 the short first plateau Is absent (not shown in fig. 2.30). 

In the case of NH2 and CN plates, the functional groups are bonded through a trimethylene chain to the silica gel. The hydrophilic-modilied layers are wetted by all solvents, including water, and are useful for the separation of polar substances which can cause problems with silica or alumina (see Table 2). The NH2 ready-to-use plates can act as a weak basic ion exchanger. 

The globular molecule C6o (diameter 1003 pm) is itself a nonpolar molecule and dispersion forces predominate in its interaction with the environment. For the subsequent reactions of PVFA-co-PVAm/silica hybrids with C6o> carefully dried samples were suspended in dry toluene. However, traces of water which are incorporated in the hydrophilic polyelectrolyte layer or adsorbed on bare silica cannot be excluded completely. 

Hydrophobic solid particles. Typically hydrophobic, amorphous silica or hydrophobic polymers are used with 0.2—30-/ m particle size. Hydrophobic silica is produced by covering the surface of hydrophilic silica with a nonpolar, molecular layer from silicone oil or paraffinic hydrocarbon (83). 

If in a hydrophilic—hydrophobic silicas—water mixture (prepared at >10,000 rpm), the inner layer is composed of hydrophobic silica and the outer layer is of hydrophilic silica that air bubbles can be entrapped in the microspheres. The bulk density of this fresh gel-like mixture can be relatively low, 0.5-0.6 g/cm due to entrapped air (Mironyuk et al. 1994,1999). In the case of the opposite structure of the composition, water is located inside microparticles with the hydrophobic outer shell that give the dry water material mentioned earlier. In the dry water materials, instead of hydrophilic silica, starch or other superhydrophilic polymers or other hydrophilic compounds can be used to provide stronger and longer retention of water inside microparticles. 

Fig. 7 Schematic representation of the adsorbed layer of CiiEe adsorbed at the hydrophilic silica/water interface [17]...

Data on catalytic activity of adsorbed proteins give the information of great importance about conformational state in adsorbed states. Proteolytic enzymes show the ability to autholysis, that can proceed in the solution and in adsorption layers. We observed inhibition of autholysis of protein molecules in adsorption layers [22]. Sometimes the addition of suspensions with hydrophibic or hydrophilic particles leads to change in the rate of autholysis [101]. For savinase the half-life of enzymatic activity in solution is 3.5 hours, and this period is strongly reduced in the presence of particles with hydrophobic surfaces. On the contrary, hydrophilic silica particles stabilize the adsorbed enzyme against autholysis. 

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