Prostredny Martin, Fletcher Ashleigh, Mulheran Paul
Department of Chemical and Process Engineering, University of Strathclyde Glasgow G1 1XJ UK
RSC Adv. 2019 Jun 27;9(35):20065-20074. doi: 10.1039/c9ra01979k. eCollection 2019 Jun 25.
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.
由于多孔有机材料的广泛应用，人们对其形成和性质的研究投入了大量的研究兴趣。然而，文献中的现有模型并未完全解释这些体系的观测结果，因此，本研究提出了一个模型，该模型旨在充分描述从凝胶组成初始阶段存在的单体物种开始的生长过程。在本研究中，我们采用基于二维晶格的动力学蒙特卡罗模型来研究生长过程如何影响模型凝胶的结构性质。在实验中，凝胶生长主要通过催化剂浓度（它决定了被激活以快速生长的物种的密度）和固体浓度来控制；我们的模型捕捉了这两种依赖性。增加固体含量和活化单体的百分比会导致闭孔率更高，并且随着活化水平的提高，可及表面积的值也会更高。使用关联维数分析生成结构的分形性质。增加固体含量和活化物种的百分比会导致关联维数增加，该维数在2处趋于平稳，与催化剂浓度无关，这表明在高固体负载量（超过50%）时结构变化很小。在可及孔隙中扩散的随机漫步者的赫斯特指数呈现相反的趋势，从不受限扩散时的1/2变化到在渗流阈值处通过孔网络扩散时的1/3。这些特征支持了对模型簇结构中孔结构复杂性和曲折度增加的直观观察。讨论了这些结果对针对特定应用定制的多孔结构设计的意义。
