Pore volume, determination

The adsorption of 3,3-dimethyl-1-butene at 303 K on the heat-treated sample is shown in Fig. 3. The 3,3-dimethyl-l-butene adsorption yielded a Type 1 isotherm. The BET sur ce area value of 161 m g obtained, fi om 3,3-dimethyl-l-butene is lower than those derived fi om nitrogen and 1-hexene (Table 1). The pore volume determined fi-om this sorptive was also lower (0.13 cm g ) than that for 1-hexene on the heat-treated sample. This suggests that adsorption of 3,3-dimethyl-l-butene, which approximates to a spherical shape, is sterically hindered, whereas in 1-hexene, which is a straight chain molecule, is less sterically hindered to interact with the surface. 

The isotherm model is compared directly to the experimental adsorption data in Figures 2 and 3. The plots show that there is good agreement between model predictions and the experimental data for all of the adsorbates. Furthermore, the regressed value of ft s is in excellent agreement with the total pore volume determined from N 2 adsorption at 77 K. It is also somewhat surprising to observe that most of the TBM measurements were in the nonlinear range of the isotherms even at the low concentrations considered in this study. 

Nitrogen isotherms were measured by using an ASAP (Micromeritics) at 77K. Prior to each analysis, the samples were outgassed at S73K for 10 - 12 h to obtain a residual pressure of less than 10 torr. The amount on nitrogen adsorbed was used to calculate specific surface area, and the micro pore volumes determined from the BET equation [14] and t-plot method [15], respectively. Also, the Horvath-Kawazoe model [16] was applied to the experimental nitrogen isotherms for pore size distribution. 

DVB were valid in this system as well. These concern the dependence of surface area and pore volume on the amount of diluent and cross-linker. The surface area increases with the amount of EDMA and goes through a maximum with increasing amount of diluent. Using cyclohexanol-dodecanol as a solvent-non-solvent pair, the factors of importance for the structure and morphology of the polymers were studied by experimental design [34]. In these experiments the concentration of the diluent mixture was varied between 20 and 77% (volume/total volume), the concentration of EDMA between 25 and 100% (volume/monomer volume), the concentration of initiator (AIBN) between 0.2 and 4% (w/w), the concentration of non-solvent (dodecanol), between 0 and 15% (v/v) and the polymerisation temperature between 70° and 90°C. The surface area (determined by nitrogen sorption), pore volume (determined by mercury porosimetry) (see Section 2.11.6.) and the mechanical properties were chosen as responses. 

Vp is a pore volume determined from Nj isotherms at P/P =0.6 using the bulk liquid nitrogen density. 

Two mesoporous silica molecular sieves synthesized by using n-octadecyl-ammonium bromide and n-dodecylammonium bromide as a templates were characterized for their pore size distribution by temperature programmed desorption method and low temperature nitrogen adsorption method. The pore size distributions and total pore volumes determined by the two methods agree quite well and are within experimental error. 

The morphologic characterization of the immobilized enzyme is important to correlate the biocatalyst performance with porous structure parameters. BET analysis, which is usually based on N2 isothermal adsorption at 77 K, allows determining the solid-specific surface area, total pore volume, pore size distribution, and mean pore diameter. It is not recommended for solids with a low specific surface area (<5 m g ). Table 2 shows the specific smface area, mean pore diameter, and total pore volume determined by BET for the pure sol-gel silica matrix having TEOS as the precursor and the same matrix with the encapsulated CGTase. 

Capillary pores are those characterized by capillary forces, so that in them, water moves in the direction of elevation forces and not of gravitational forces. The capillary pore volume determines the soil water retention capacity. The motion of air in capillary pores is strongly restricted. 

Wp (cm /g) is the total pore volume calculated from the true (1.12 cm /g) and apparent densities, (cm /g) is the total pore volume determined by mercury intrusion. 

Specific Surface Area and Pore Volume Determination... 

Another method frequently used for the determination of pore volume of chromatographic media is based on the solvent regain. In this method, the gel slurry is centrifuged to remove the ectra-particle liquid. The solvent regain is then determined gravimetrically after evaporation of the interparticle liquid (38). Discrepancies tietween the pore volume determined by solvent regain and Isy SEC may indicate sorption effects. In this case another solute-solvent system should be used in the chrcmatographic method. 

An electron microscopic study of fine-pored silica gel by Sugar and Guba (119) revealed that the structure indeed was made up of a threadlike or fiberlike network, but the fibers were made up of chains of spheres. The pore volume determined by adsorption could be correlated with the observed size and spacing of the chains of particles on the assumption that these were on the average cylindrical and that the pore space was the complementary space of a skeleton built up of the network of cylindrical elements. 

Pore size distributions of carbon molecular sieve determined by this method are shown in Fig 2 18, where IF., is the maximum pore volume determined from the amount adsorbed at plp,=0 9... 

On dry gels, standard characterization techniques for porous media are used, several of which have been described in Volume 2 of this series helium pycnometry for pore volume determination (Section 6.3.1.2) as well as nitrogen adsorption at 77 K for surface area (Section 6.3.2.2, BET method), for microporosity (Section 6.3.3.2, Dubinin-Radushkevich method), for pore size distribution (Section 6.3.3.3, BJFl method), and for total pore volume (Section 6.3.3.4). When characterizing gels by nitrogen adsorption, other methods are also used for data interpretation, for example, the t-plot method for microporosity (Lippens and de Boer, 1965) and the Dollimore-Heal method (Dollimore and Heal, 1964) or Broekhoff-de Boer theory for mesoporosity (Lecloux, 1981). 

Comparison of Pore Volumes Determined by Mercury Porosimetry and loss of Polymer. 

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