Modified silicate surfaces

D. Adsorption of n-Butanol from Water on Modified Silicate Surfaces... 

Morrall2 used a HPLC system with two columns. The first column was loaded with the controlled pore glass (CPG) to be modified. The second column was used for separation of the reaction effluents. This column was coupled to a refractive index detector, allowing for quantitative detection of the effluents. The reaction was initiated by injecting an APTS/toluene mixture and stopped by injection of pure toluene. With this so-called stop-flow mechanism reaction times down to 18 seconds could be used. From these analyses it became evident that upon mixing of the aminosilane with the silica, a very rapid physisorption occurs. The initial adsorption of the APTS (from toluene solution on dried CPG) occurred before the 18 second minimum time delay of the stop-flow apparatus. For non-aminated silanes the adsorption proved to be much slower. This study also revealed the pivotal role of surface water in the modification of siliceous surfaces with alkoxysilanes, as discussed in the previous chapter. 

By the use of other reagents certain oxidized ores may be floated. For the oxides and carbonates of basic metals, fatty acids such as oleic, and soaps, are frequently useful. These no doubt form an oriented thin film of the soap of the heavy metal present in the mineral, by double decomposition with the surface layer the long hydrocarbon chain is probably oriented outwards. By special activation it is said that even quartz may be floated by the judicious use of soaps, if its surface is contaminated naturally or artificially with small amounts of heavy metals. There would appear to be a vast range of possibilities in the separation of complex minerals, by proper selection of reagents capable of modifying their surfaces. A detailed study of the flotation of various silicate minerals, with oleic acid, has been given by Patek.4... 

The alkenyl ethoxysilane monomers and silylester functionalized copolymers were used for the silanization of hydroxyl groups on silicate surfaces, thus producing silylester modified silicates or covalently fixed polymer films as demonstrated in Eq. 2 and Fig. 1. 

Figure 6.12 The mobility of deuterated silane monolayers on silical gel can be studied by solid state deuterium NMR spectroscopy. The degree of coating as well as the environment can be modified. The above models summarize the results. These modified silica surfaces are the most simple models for receptors of apolar molecules. The unique advantage of these probes is the large quantity of monolayer in a small volume.

It is not yet known with certainty if this occurs through surface dissolution of the silica support (eventually promoted by Ni I adsorption, cf. IV.B) followed by copredpitation of a mixed phase, or through an interface reaction between Ni complexes in the solution and the modified silica surface. The neoformed silicate layers are observed to be in narrow assodation with the silica partides, which would rather suggest an interface... 

The effects of the influence of NS at their interaction into liquid medium depend on the type of NS, their content in the medium and medium nature. Depending on the material modified, FS of NS based on different media are used. Water and water solutions of surface-active substances, plasticizers, foaming agents (when modifying foam concretes) are applied as such media to modify silicate, gypsum, cement and concrete compositions. To modify epoxy compounds and glues based on ERs the media based on polyethylene polyamine, isomethyltetrahydrophthalic anhydride, toluene and alcohol—acetone solutions are applied. 

K.G. Proctor and D.E. Leyden, Surface Acidity Characterization of Siliceous Materials by Variable Temperature Diffuse Reflectance FTIR, Chemically Modified Oxide Surfaces, Vol. 3, D.E. Leyden and W.T. Collins Eds., Gordon and Breach Science Publishers, New York, pp. 137-149, 1990. 

PMMA is slightly affected by the addition of layered silicates in a wide temperature range below and above Tg. On the other hand, copolymers of methyl methacrylate (MMA) with small amounts of polar monomer show a significant increase in the storage shear modulus, G [Okamoto et al 2001]. It could be assumed that the increased polymer polarity results in better interaction with the silicate surface. This view is supported by a study performed on the effect of sulfonation of PS chains on their ability to interact with silicate. The need to provide polar functionality for PS originates in the observation that the Tg value of PS-based CPNC increases with the degree of sulfonation at a constant silicate content [Mauritz et al., 2004]. As suggested by Kawasumi et al. [1997], silicate layers, even those modified by nonpolar alkyl chains, are polar and thus immiscible with nonpolar polymers such as polyolefins (POs). 

Recently we found (Sakurai, Urabe, and Izumi 1988 1989) that interlayer La cations were irreversibly fixed by heating onto the exchange sites of silicate layer in TSM, and the fixed La ions gave the pillared TSM a strong acidity. The resultant La -modified pillared TSM possesses, in principle, all of the La ions, or acid sites only on the silicate surfaces but not on the pillars. Here, we have extended the type of modifying cation and host layered clay, respectively, to various cations and clays other than TSM, and report on their chemical and structural characteristics with respect to catalytic performances (Sakurai, Urabe, and Izumi 1990 1991). 

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