Porosity Development in Silica Particles during Polymerization: Effect of Solvent Reactivity and Precursor Concentration

Abstract

The porous morphology drives the application of nano-and mesoporous materials in a variety of areas. However, limited information is available on the porosity development during their synthesis at various times due to challenges in experimental and simulation techniques. In this work, we have probed the porosity development in silica particles using Monte Carlo simulation techniques. We have developed an algorithm to measure the porosity of small, irregular shaped, finite-size particles formed during the polymerization process. We observed that smaller and denser clusters are formed initially, which later aggregate to form porous clusters in the range of 500−1000 h for the system having a concentration of silica precursor = 104 mg/cm 3 in a reactive solvent. In the case of nonreactive solvents, the porosity development is significantly different and occurs from initial stages of polymerization and lasts until the aggregation stage, in the range of 2−2000 h for similar concentrations. This significant change is due to faster kinetics of polymerization. Further polymerization leads to the formation of denser clusters due to aging in both cases. The mechanism of porosity formation in reactive solvent systems is due to random aggregation of denser clusters, whereas in a nonreactive solvent, it occurs by merging of smaller porous clusters. We also prepared a phase diagram of porosity evolution at various concentrations and observed that it has a tremendous effect on porosity development. We find three concentration ranges where silica cluster transforms from small denser to large denser particles in multiple stages. For a nonreactive solvent, the porosity evolution phase diagram shifts and stretches toward lower concentration ranges. We believe that this detailed understanding of porosity development will be useful to control the porous morphology of nano-and mesoporous materials during their synthesis.

Understanding the mechanism and kinetics of the formation and breaking of ring structures during silica polymerization: a computational study

“…To understand the effect of the initial concentration of silica precursor (C SiP ) on the ring formation behavior, we have probed two systems with R = 20 and R = 2, which correspond to C SiP = 104 and 155 mg cm À3 (henceforth referred to as dilute silica (DS) and concentrated silica (CS) systems), respectively. In our recent work, 68 we observed that the silica system with C SiP lower than 104 mg cm À3 does not result in larger silica clusters within the simulation timescales, whereas, at C SiP = 155 mg cm À3 , all of the silica precursors react to form one giant cluster and the rate of silica polymerization is faster compared to the other systems studied.…”

“…However, the development of the algorithms for silica polymerization and their verification are discussed in detail in our previous work. 65,68 The developed algorithms successfully capture the kinetics of silica polymerization and the evolution of rings, clusters, and porosity during polymerization. 65,68 To report our observations with respect to real-time, we scaled the simulation time (i.e., MC steps) with appropriate scaling factors calculated from the kinetic model of silica polymerization (discussed in detail in our recent work 68 ).…”

“…65,68 The developed algorithms successfully capture the kinetics of silica polymerization and the evolution of rings, clusters, and porosity during polymerization. 65,68 To report our observations with respect to real-time, we scaled the simulation time (i.e., MC steps) with appropriate scaling factors calculated from the kinetic model of silica polymerization (discussed in detail in our recent work 68 ). Hence, all results in this work are discussed in real-time (of hours).…”

“…All the properties are discussed in detail in our earlier work, 63,65,68 hence we only briefly describe them here.…”

“…Polymerization of silica precursors in these systems has also been studied in earlier works, [63][64][65]68 where various polymerization and structural evolution stages were investigated. For the sake of completeness and quick reference, we describe the essential aspects of the polymerization details in brief here, which will also be helpful in the latter part of this work.…”