Interfacing Mercury Porosimetry with Nitrogen Sorption

Combinations of gas sorption and mercury porosimetry experiments have been run in series on the same sample. This has been achieved by freezing entrapped mercury in place before a subsequent gas sorption experiment was carried out. Several different bidisperse materials with similarly shaped mercury intrusion curves and similar levels of mercury entrapment have been studied. The entrapment of mercury within certain pores in the porous medium can often lead to marked changes in the shape of the gas sorption hysteresis loop between the data obtained prior and subsequent to porosimetry. It was found that the degree of the change of shape of the sorption hysteresis loops differed markedly between different materials. The analysis of the gas sorption hysteresis loops using percolation theory has allowed information to be obtained on the pore length distribution, and/or the distribution of pore co‐ordination number and the spatial arrangement of pores within the sample, in addition to the pore connectivity and lattice size usually obtained. The interfaced experiments have also allowed the internal consistency of analysis methods based on percolation theory to be tested, semi‐empirical alternatives to the Washburn Equation for the analysis of raw mercury porosimetry data to be independently validated, and the mechanisms of mercury entrapment in various samples to be determined.     

The development and influence of gas bubbles in phreatic aquifers under natural flow conditions

In a phreatic aquifer, bubbles may result from the entrapment of air during groundwater recharge and/or bacterial metabolism. The calculated critical depth of about 1 m at which bubbles are most likely to be found in a granular aquifer, coincides with the depth of 0.60 m of an almost stagnant water layer (specific discharge 1 × 10^-6 cm sec^-1) found at the water table region under natural flow conditions. Bubbles clog pores and therefore reduce the hydraulic conductivity without significantly reducing the volumetric water content. Stagnation at the water table region results since prevailing pressures (in the order of 10^-1 atmospheres) are not sufficiently large to move bubbles through porous media in a water environment.     

Immobilization of a recombinant cutinase by entrapment and by covalent binding

Fusarium solani pisi recombinant cutinase, immobilized by entrapment in calcium alginate and by covalent binding on porous silica, was used to catalyze the hydrolysis of tricaprylin. The influence of relevant parameters on the catalytic activity such as pH, temperature, and the substrate concentration were studied. Cutinase immobilized by entrapment presented a Michaelis-Menten kinetics for tricaprylin concentrations up to 200 mM. At higher concentrations of substrate, inhibition was observed. For covalent binding immobilization, diffusional limitations were observed at low substrate concentrations and substrate inhibition occurred for concentrations higher than 150 mM. The stability of immobilized cutinase was also evaluated. The enzyme immobilized by entrapment showed a high stability, in contrast to the immobilization on porous silica.