Pore structure of gels

Finally, the surface and pore structure of gels obtained after dehydrating sols may be affected by the presence of oligomeric silica. This effect will be particularly evident with sols of small particle size in which partial particle coalescence may occur, together with the generation of small micropores (<2 nm), as has been previously observed (18). 

Krajeswska, B. (1996). Pore structure of gel chitosan membranes.III.Pressure driven mass transport measurements. Polymer Gels Networks 4, 55. 

The large pore structure of the TSK-GEL G6000PW allows it to separate large molecules such as pBR322 plasmid from contaminating RNAs and proteins in a much shorter time frame than other methods (23). A two column system of G6000PW (7.5 mm i.d. X 60 cm) was used to separate the cleared lysate and phenol extract of the plasmid as shown in Fig. 4.34 (page 130). The plasmid... 

In a further study, Rill et al. [325] developed a model of gel permeation chromatography that included a bimodal pore stracture. The smallest mode in the pore-size distribution represents the basic background polyacrylamide pore structure of about 1-mn mean radius, and the second mode was around 5 nm, i.e., in the range of size of the molecular templates. The introduction of this second pore structure was found to substantially improve the peak resolution for molecules with molecular sizes in the range of the pore size. 

This sol-gel procedure is an elaboration on well established entrapment methods [29], but with the added advantage of stability and better flow properties. Interestingly, none of the examples presented thus far demonstrate competitive behavior between multiple ligands (i.e. displacement) in the FAC analysis of trimethoprim and pyrimethamine a reversed order of elution based on is described, but this could simply be due to the shift towards an on-rate limited situation for higher affinity compounds, as described earlier. Erosion of dynamic competition between ligands could occur if the sol-gel allows convective mixing of the entrapped protein however the bimodal pore structure of these materials would... 

Determination of Pore Size Distributions. The shape and range of a GPC calibration curve are, in part, a reflection of the pore size distribution (PSD) of the column packing material. A consideration of the nature of PSDs for the ULTRASTYRAGEL columns to be used in this work is therefore appropriate. The classical techniques for the measurement of PSDs are mercury porisimetry and capillary condensation. The equipment required to perform these measurements is expensive to own and maintain and the experiments are tedious. In addition, it is not clear that these methods can be effectively applied to swellable gels such as the styrene-divinylbenzene copolymer used in ULTRASTYRAGEL columns. Both of the classical techniques are applied to dry solids, but a significant portion of the pore structure of the gel is collapsed in this state. For this reason, it would be desirable to find a way to determine the PSD from measurements taken on gels in the swollen state in which they are normally used, e.g. a conventional packed GPC column. 

The pore volume and specific surface area of carbosils decrease with Cc values independent of pyrocarbon origin (Table 2, Figure 2).16 However, the precursor type as well as the initial pore structure of silica gels, e.g. Si-40 (Table 1) and Si-60 (Table 2), affect the pore characteristics of carbosils (Figures 1 and 2). The narrower the pores of the pristine silica gel, the larger the specific surface area reduction under the same pyrolysis conditions. 

The pore structure of two types of catalyst support material were studied 7-alumina and silica aerogel. The alumina samples were commercial catalyst supports made in 1/8 inch diameter pellet form by Harshaw Chemical. Silica aerogels were prepared from silica gels synthesized by a two step acid/base catalyzed procedure employing TE0S with a water to silicon ratio equal to 3.7 [17] and ammonium hydroxide concentration of 0.005 M (sample A) or 0.01 M... 

Molecules larger than the pore size do not enter the pores and elute together as the first peak in the chromatogram and this is called total exclusion volume which defines the exclusion limit for a particular column. Molecules that can enter the pores diffuse into the internal pore structure of the gel to an extent depending on their size and the pore size distribution of the... 

To obtain the desired oxide phase, solvent remaining entrapped within the pore structure of the film and the organic moieties associated with the gel network must be removed. This is typically achieved via low-temperature heat treatment, which results in a rearrangement of the gel network through a variety of bond... 

Kusakabe K, Sakamoto S, Saie T, and Morooka S. Pore structure of silica membranes formed by a sol-gel technique using tetraethoxysilane and alkyltriethoxysilanes. Sep. Purif. Technol. 1999 16 139-146. 

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