Surface topology silica

Golub A, Matyshevska O, Prylutska S et al. (2003) Fullerenes immobilized at silica surface topology, structure and bioactivity. J Mol Fiq. 105 141-147. 

Fig. 15. Schematic representation of the surface topology of the fumed silica primary particles, depending on the flame temperature.

The hydrophobicity of several highly fluorinated surfaces was found to increase with the number of layers, and their water-repellent abilities were directly correlated to the surface topologies (number of layers of silica nanoparticles and their organization on the glass support). 

Anhydrous, fumed, silicas have a higher li than hydrated, precipitated silicas and, moreover, the lower the specific surface area, the lower the dispersive component, irrespective of the production process. According to Wang et al., the difference in the dispersive component between both types of synthetic silica might depend on the surface topology of their particles, and less on the concentration of hydroxyl groups. 

Fig. 3. Schematic representation of the topological space of hydration water in silica fine-particle cluster (45). The processes responsible for the water spin-lattice relaxation behavior are restricted rotational diffusion about an axis normal to the local surface (y process), reorientations mediated by translational displacements on the length scale of a monomer (P process), reorientations mediated by translational displacements in the length scale of the clusters (a process), and exchange with free water as a cutoff limit.

In addition, chiral dendrimers (see Section 4.2) can be resolved with the aid of HPLC into their enantiomers, if the silica gel material used as stationary phase has optically active substances bound to its surface [9]. Since the chiral stationary phase (CSP) [10] undergoes different intensities of interaction with the enantiomeric dendrimers, they are retained to different degrees, and in the ideal case two completely separated (baseline separated) peaks are obtained. This separation technique was successfully applied inter alia to racemic mixtures of planar-chiral dendro[2.2]paracyclophanes, cycloenantiomeric dendro[2] rotaxanes, topologically chiral dendro[2]catenanes [11] as well as topologically chiral, dendritically substituted molecular knots (knotanes) [12] (Section 4.2.3). 

As in carbon-black-filled EPDM and NR rubbers, the physical network in silica-filled PDMS has a bimodal structure [61]. A loosely bound PDMS fraction has a high density of adsorption junctions and topological constraints. Extractable or free rubber does virtually not interact with the silica particles. It was found that the density of adsorption junctions and the strength of the adsorption interaction, which depends largely on the temperature and the type of silica surface, largely determine the modulus of elasticity and ultimate stress-strain properties of filled silicon rubbers [113]. 

The most commonly used model for pore topology is to represent the material as composed of independent, non-interconnected pores of some simple geometry usually these are of slit shape for activated carbons, and of cylindrical geometry for glasses, oxides, silicas, etc. Usually, the heterogeneity is approximated by a distribution of pore sizes, it being implicitly assumed that all pores are of the same geometry and surface chemistry. In this case the excess adsorption, f(P), at a pressure P can be represented by... 

The strained two-member silicon rings, which are the most peculiar topological defects on the surface of amorphous silica, proved the most reactive [55]. Thus, hydratation occurs preferentially with these rings - they are cleaved through the processes shown schematically in Fig. 5.18. This is in agreement with the most abundant spectroscopic evidence collected in real hydratation and dehydratation experiments and reported in literature. 

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