Modelling the formation of porous organic gels – how structural properties depend on growth conditions

Abstract

We explore how structural properties depend on the growth conditions in a model of gel nucleation, growth and aggregation.

Modelling Organic Gel Growth in Three Dimensions: Textural and Fractal Properties of Resorcinol–Formaldehyde Gels

“…When the random walker size is increased from one to three, the value obtained decreases far more rapidly as its ability to move around the lattice is restricted by its width. In this case, values range from 0.4904(2) at 10% and 0.5% to 0.356(1) at 50% and 4% , close to the limit of 1/3 that is expected at the percolation threshold [ 12 ]. As with the analysis of the inaccessible sites for a particle of three sites in size, assessing the motion of such a particle through a porous material in this manner provides valuable insight for their use in applications involving diffusion of larger particles.…”

“…The percentage of sites inaccessible to a particle of Size 1 remains consistently low, ranging from 0.028(2)% at 10% and 0.5% to 4.47(7)% at 60% and 4% . These values are considerably lower than those obtained for the 2D version of the code, which reached up to 25% inaccessible sites for structures formed with 50% and 3% [ 12 ]. Simulating the porous structure in three dimensions opens new accessible pathways for connectivity, which would otherwise be limited by the two-dimensional structure, explaining the significant decrease in the percentage of inaccessible sites within the lattice, and providing a more accurate representation of the porous materials synthesised in reality.…”

“…The 3D model presented here builds on the work published by Prostredny et al [ 12 ]—a 2D simulation which operates under the same principles—where a detailed description of the simulation process can be found. Here, a cubic lattice of Size 100 × 100 × 100 sites, totalling 1,000,000 sites, was initially populated at random with monomers according to the desired percentage solids content ( ), an important parameter in the synthesis of RF gels in laboratory experiments.…”

“…The simulation begins with the random diffusion (nearest-neighbour hopping) of monomers on the lattice, with periodic boundary conditions, during which free monomers attach to activated monomers when they come into contact, forming larger primary clusters of monomers. These monomers attach in an approximately spherical sequence, as described in the work by Prostredny et al [ 12 ], producing primary clusters that also diffuse on the lattice following the same basic scaling laws for diffusion. Two diffusing clusters irreversibly attach when they meet, retaining the primary clusters intact.…”

“…This growth pathway forms the basis for the computational work presented here, a three-dimensional (3D) simulation that models the formation and growth of porous materials, such as RF gels, using a kinetic Monte Carlo methodology. This software has been developed in-house and builds upon a previous 2D simulation from within our group [ 12 ].…”