Untreated silica

The dried polyoxazoline-modified silica gel was immersed into distilled water. The adsorption property of the resulting gel was estimated by the water content. The water uptake was calculated from an expression of (W -W)jW, where Wis the weight of dried gel and W is the weight of water-absorbed gel. The modified gel showed a higher water-adsorption property than that of untreated silica gel, which absorbed 10.8 multiples of water. The water uptake of modified gel was up to 13.7 multiples of the weight of dried gel. Thus, silica gel has been made more hydrophilic by a polyoxazoline segment. 

Untreated silica column can be advantageously used for HPLC preseparation of PAHs from triglycerides. The capacity of a silica column to retain fat (for columns of the same particle size) depends on the column size, the mobile phase composition, as well as the type and by-products (free acids and polymerized material) of the fat injected [706,713]. Off-line HPLC-HPLC, employing silica column (250 X 4.6 mm i.d., 5 pm of particle size) for sample preparation before RP-HPLC and spec-trofluorometric detection, was successfully applied for PAH determination in edible oils [659,691] and fish [714]. After PAH elution, the silica column needs to be backflushed with dichloromethane to remove the fat. The entire sample preparation step can be automated by using a backflush valve and a programmable switching valve box [691]. 

Hydrophobicity - Before plasma treatment, silica powder is highly hydrophilic and immediately sinks in water. After plasma film deposition, the material floats on water for several hours. A significant reduction in polarity and in surface energy compared to untreated silica is found, down to the range of 28.4-47.7 mJ/m2. The water penetration into powder beds of untreated and plasma-treated silica is shown in Fig. 7. The untreated silica absorbs water very fast, whereas the plasma-treated silicas show a significantly decreased water penetration rate. The lowest rate is found for the polythiophene-coated silica (PTh-silica). 

Amount of deposited material - The difference in weight loss between coated and untreated silica corresponds to the weight of the plasma-polymerized film deposited on the surface. For the plasma-treated silicas, decomposition of the coating starts at 265°C for poly acetylene, 200°C for polypyrrole, and 225°C for poly thiophene, and is complete at 600°C. Between 265 and 600°C, PA-silica shows 6 wt% weight loss, and PPy- and PTh-silicas show 4.5 wt% and 5 wt% loss, respectively. 

Functionalities on the silica surface - The ToF-SIMS spectra were recorded of the untreated and treated silicas. Figure 8 represents an untreated silica sample, and Fig. 9 an acetylene-treated one. They show a complex structure of a plasma-polymerized acetylene film on the silica surface. 

In the spectra of the untreated silica sample, no specific peaks in the low mass region up to 150 amu (atomic mass units) such as from 3+, 10+, and no cluster peaks in the higher mass region are found. The spectra of the acetylene-treated sample do show these specific plasma-polymerized acetylene peaks in the... 

Fig. 7 Water penetration into powder beds of untreated silica and plasma-polymerized acetylene-, pyrrole-, and thiophene-coated silica...

The spectra of the negative ions of the untreated silica powders (Fig. 8b) have no specific peaks such as from C , CH in the mass range of 0-40 amu, in contrast to the spectra of the acetylene-treated sample (Fig. 9b), which do show these C and CH- peaks again in this mass region. This is another proof of the surface coating on the silica powders. 

Morphology - SEM images of untreated and plasma acetylene-treated silica samples are shown in Fig. 10. The PA-silica shows a clear difference in dimensions in comparison to the untreated silica powder The film deposition occurs onto small-sized aggregates, resulting in larger spherical particles connected into an open structure. 

Fig. 8 ToF-SIMS spectra of untreated silica (a) positive and (b) negative...

Fig. 10 SEM images (magnification 100,000 x) of untreated silica (a) and PA-silica filler (b)...

Sample codes SU S-SBR reinforced with untreated silica SPA S-SBR with PA-silica SPPy S-SBR with PPy-silica SPTh S-SBR with PTh-silica ST S-SBR with silanized silica... 

The Payne effect of S-SBR compounds filled with untreated silica, PA-, PPy-, and PTh-silicas, and silane-modified silica are shown Fig. 17. 

Figure 18 shows the bound rubber content of samples filled with untreated silica, plasma-treated silicas, and silane-modified silica, as representative of the filler-polymer interactions. Samples SPTh and SPA show the highest bound rubber contents, and the ST the lowest value. The SPPy sample shows a bound rubber content slightly lower than that of SU. 

The Payne effects of S-SBR/EPDM blend filled with untreated silica, plasma-modified silicas, and silane-treated silica are shown in Fig. 22. 

Sample codes SEU SBR/EDPM reinforced with untreated silica SEPA SBR/EDPM with PA-silica SEPPy SBR/EDPM with PPy-silica SEPTh SBR/EDPM with PTh-silica SET SBR/EDPM with silanized silica... 

Rhodium(I) complexes immobilized on silica using 3-(3-silylpropyl)-2,4-pentanedio-nato ligands (38) show good activity in the hydrosilylation of 1-octene with HSi(OEt)3 at 100°C60. The immobilized Rh catalysts are prepared by (i) reaction of (EtO)3Si(CH2)3C(COMe)2Rh(CO)2 with untreated silica (Catalyst A), (ii) reaction of Rh(acac)(CO)2 (acac = acetylacetonato = 2,4-pentanedionato) with silica modified by [(EtO)3Si(CH2)3C(COMe)2] prior to the complexation (Catalyst B), (iii) reaction of [Rh(CO)2Cl]2 with a polycondensate of [(EtO)3Si(CH2)3C(COMe)2] , Si(OEt)4 and water (Catalyst C) and (iv) sol-gel processing of (EtO)3Si(CH2)3C(COMe)2Rh(CO)2 and Si(OEt)4 (Catalyst D). The Catalysts A and B show ca three times better activity than their homogeneous counterparts, while the Catalyst D exhibits only low activity and the Catalyst C is inactive60. 

Figure 4. Spectrum obtained after adsorption of 10BFa on dehydrated Cab-O-Sil (A) untreated silica (B) 18O-exchanged silica (---) indicates the back-...

Figure 10.3 Infra-red. spectrum obtained after chemisorption ofwBF3 on dehydrated Cab-O-Sil (a) untreated silica, (b) lsO exchanged silica. The dotted line represents the background spectrum of silica before the BF3 chemisorption.

The first studies of the modification reaction of silica with diborane were performed by Weiss and Shapiro.34,35,36,49 Their studies were focused on the nature and localization of the hydroxylic species in the silica. Reaction of untreated silica gel with at room temperature gave a hydrolysis ratio of six, indicating total hydrolysis of the B2H6 molecules. The same situation is found when reacting diborane with excess water,34 according to the reaction ... 

Figure 11.2. Low frequency Raman spectra of (A) liquid TiCl4, (B) untreated silica and (C) TiCl4 or (D) GeCl4 on silica.

Fink610 has studied the conversion of Si-NH, functions towards silazane ( = Si-NH-Sis) groups for the reaction of ammonia with untreated silica. 

Upon degassing in vacuo, the CSC precursor converts gradually towards nitrides. After degassing at 973 K, already 20% of the available N species are nitrides. More than 60% nitrides can be achieved by degassing the precursor at 1113 K. The positive effect of the enormous ammonia uptake enhancement, compared to untreated silica, remains besides NH4C1, only a small fraction of the N-species is lost upon degassing. 

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