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

There has been significant research interest invested into the study of the formation and properties of porous organic materials, due to their widespread applications. However, present models in the literature do not fully explain the observations made for these systems, therefore, this work presents a model developed to fully capture growth from the monomeric species present in the initial stages of the gelation composition. In this work, we employ a two-dimensional lattice-based kinetic Monte Carlo model to investigate how growth processes impact the structural properties of model gels. Experimentally, gel growth is primarily controlled through catalyst concentration, which determines the density of species that are activated for rapid growth, and solids concentration; our model captures both of these dependencies. Increasing both solids content and percentage of activated monomers leads to a higher ratio of closed porosity, and higher values of accessible surface area with increasing level of activation. The generated structures are analysed for their fractal properties using a correlation dimension. Increasing both solids content and percentage of activated species leads to an increase in correlation dimension, which plateaus at a value of 2, independent of catalyst concentration, suggesting little structural change at high solid loadings, over 50%. The Hurst exponent of a random walker diffusing in the accessible pores shows the opposite trend, varying from ½ for unconstrained diffusion and reducing to ⅓ for diffusion through the pore network at the threshold of percolation. These characteristics support visual observations of increasing complexity and tortuosity of pore structures in the model cluster structures. The implications of these results, for the design of porous structures tailored to particular applications, are discussed.