Nitrogen distribution at 77.7 K in mesoporous Gelsil 50 generated via evolutionary minimization with statistical descriptors derived from adsorption and in situ SANS.

Digitized periodic material models of size 100(3) nm3 of mesoporous xerogel Gelsil 50 are reconstructed by use of an evolutionary minimization technique, with two-point probability S2(r) and volume-based pore size distribution Psi(D) as a hybrid target function. S2(r) and Psi(D) are derived from small-angle neutron scattering (SANS) and adsorption data, respectively. The nitrogen distribution in Gelsil 50 is characterized in the multilayer adsorption and capillary-condensation regimes by S2(r) and statistical parameters obtained from in situ SANS data. The fraction of liquid-free pore space varphi is calculated from nitrogen adsorption data, and the distribution Psicorr(D) of the diameter of the liquid-free pore space at certain relative pressures is derived from Psi(D). The evolutionary algorithm is also used to generate the spatial nitrogen distribution by means of the descriptors varphi, S2(r), and Psicorr(D). The morphological parameters obtained from the reconstructs are compared to the respective SANS results.

Knowledge-based reconstruction of random porous media.

An evolutionary optimization technique is used to reconstruct digitized material models of 300(3) nm3 size for mesoporous two-phase systems. The models are adapted to the two-point probability (TPP) and to a volume-based pore-size distribution (PSD) which were derived from SANS and adsorption experiments and which carry statistical information about morphology and topology of the pore system. To avoid extreme update-costs, the bulk of mutations are assessed by means of a suitable approximation of the PSD; it is demonstrated that a sporadic insertion of the PSD suffices to drive the algorithm towards satisfactory models in acceptable time. Our approach is knowledge-based in the sense that (i) the mutations are restricted to expedient exchanges of phase-voxels by a heuristic rule, and (ii) the sporadic calculation of the PSD from the current state of the model, in essence, provides an efficient self-control for the evolutionary process. We applied the method to reconstruct periodic models of the xerogel Gelsil 200. Such reconstructs of real mesoporous solids could be utilized, for instance, to verify theories of adsorption and capillary condensation.