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Dumas, Rebecca; Tejedor-Tejedor, Isabel; Anderson, Marc A.

doi:10.1023/a:1009682117946

Cited by 13 publications

(4 citation statements)

References 5 publications

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“…The gel texture of sample A3 is much finer than those of samples A1 and A2 according to the FE-SEM images shown above. This result is consistent with the work of Dumas et al (6), who noted that slow evaporation of solvents leads to xerogels with looser structures. Finer textures with finer pores facilitate further condensation reactions.…”

Section: Influence On Porositysupporting

confidence: 93%

Influence of Calcination Procedure on Porosity and Surface Fractal Dimensions of Silica Xerogels Prepared under Different Evaporation Conditions

Huang

Liang

Cui³

et al. 2000

Journal of Colloid and Interface Science

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Section: Influence On Porositysupporting

confidence: 93%

Influence of Calcination Procedure on Porosity and Surface Fractal Dimensions of Silica Xerogels Prepared under Different Evaporation Conditions

Huang

Liang

Cui³

et al. 2000

Journal of Colloid and Interface Science

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“…These results show that while the pumping rate did not affect the molecular connectivity of the xerogel, it did affect the degree of pore collapse upon drying (Table ). Faster evaporation resulted in loss of porosity, an effect also reported by other researchers. , The marked effect of the drying rate on the samples' porosity was observed with the other samples too. Control sample E was heated to 50 °C during drying and, therefore, dried more quickly than sample D which dried at ambient temperature.…”

Section: Resultssupporting

confidence: 82%

Effect of Gravity on the Gelation of Silica Sols

et al. 2007

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Acid-catalyzed silica polymerization was carried out under gravity conditions varied from 0.01g aboard a reduced gravity aircraft to 70g in a centrifuge. The silicate connectivity of the final xerogels was analyzed using solid state 29 Si NMR and the porosity using nitrogen adsorption. Gravity was found to have an important influence on the occurrence of intra-and intermolecular condensation reactions. Under reduced gravity buoyancy driven-free convection is limited and silica polymerization occurs in a diffusion-limited regime. Intramolecular condensations and densifications prevail and extended coils of cages are formed through cyclization reactions in the sol particles. In terrestrial and high-gravity conditions, bimolecular reactions compete more favorably with internal condensations. More open structures composed of chains and rings are formed. These flexible species delay the onset of gelation, leading to an increase in gelation time as the gravity level is increased. During the subsequent drying procedure, pore collapse changes the structure from meso-to microporous. The porosity of the finally obtained xerogels is mostly defined by the drying conditions of the gel, irrespective of the silicate connectivity.

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“…As seen in Figure , there is no apparent enantioselectivity: 0.243 ± 0.002 nmol of ( R )- 2 vs 0.237 ± 0.007 nmol of ( S )- 2 . Calcination is also known to close off sol−gel-generated pores, − which is reflected in the lower adsorption levels, seen in Figure . Thus, we believe that chiral induction in the thin film by templating creates in our case (cf., ref ) a very delicate enantio-discriminative structure that can easily be destroyed by the calcination process, which causes a collapse of the fine arrangement of molecular moieties within the cage.…”

Section: Results and Preliminary Discussionmentioning

confidence: 99%

Enantioselective, Chirally Templated Sol−Gel Thin Films

et al. 2005

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Enantioselective surfactant-templated thin films were fabricated through the sol-gel (SG) process. The enantioselectivity is general in the sense that it discriminates between pairs of enantiomers not used for the imprinting process. The chiral cationic surfactant (-)-N-dodecyl-N-methylephedrinium bromide (1) was used as the surfactant template, and after its extraction chiral domains were created. The chiral discriminative feature of these films was examined by challenging with pure enantiomer solutions for rebinding. Selective adsorption was shown using (R)- and (S)-propranolol, (R)-2 and (S)-2, respectively, and (R)- and (S)-2,2,2-trifluoro-1-(9-anthryl)ethanol, (R)-3 and (S)-3, respectively, as the chiral probes. The selective adsorption was measured by fluorescence analysis, and the chiral selectivity factors were found to be 1.6 for 2 and 2.25 for 3. In both cases, (R)-enantiomer was adsorbed preferably. The resulting material was characterized by transmission electron microscopy, by diffraction, and by surface area measurements, and was found to be semicrystalline with short-range ordered domains (50 A) of hexagonal symmetry.

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Untitled

Cited by 13 publications

References 5 publications

Influence of Calcination Procedure on Porosity and Surface Fractal Dimensions of Silica Xerogels Prepared under Different Evaporation Conditions

Influence of Calcination Procedure on Porosity and Surface Fractal Dimensions of Silica Xerogels Prepared under Different Evaporation Conditions

Effect of Gravity on the Gelation of Silica Sols

Enantioselective, Chirally Templated Sol−Gel Thin Films

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