Prediction and control of organic xerogel microstructure, experiments and modelling

Resorcinol-formaldehyde (RF) gels are a fairly new addition to the variety of porous materials used by current industry. However, a better understanding of their formation processes is crucial for efficient structure tailoring, leading to high-performance materials for a range of applications. The usual RF gel manufacture process involves gelation of an RF sol at elevated temperatures, followed by exchanging water within the structure for another liquid, in order to limit shrinkage during the final drying step. Yet, despite significant research efforts, the RF growth processes are still not fully understood and there is no accepted model describing these processes. Therefore, this study combines experimental and simulation approaches to better understand the gel growth process, and how the resulting structure depends on the growth conditions. The experimentally investigated areas include the influence of sodium carbonate catalyst concentration, processing temperature, solvent exchange and drying methods, as well as the presence of different anions within the reaction solution. Discussion on optimal processing parametersis included, in order to preserve the majority of the porous structure of RF xerogel materials, taking process economics into account, and the diversity of textural properties for obtained materials is examined. In order to model the growth processes in RF gels, and investigate how they impact the structural properties of final materials, a two-dimensional lattice-based computational model, using kinetic Monte Carlo, was developed in this work. The presented model is developed to capture growth from monomeric species present in the initial stages of the gelation composition. Experimentally, gel growth is primarily controlled through catalyst concentration, which determines the density of species that are activated for rapid growth, and solids concentration; the model captures both of these dependencies.;Generated cluster structures were analysed for textural properties, such as accessible porosity and accessible surface area, as well as fractal properties, in the form of the correlation dimension and the Hurst exponent. Increasing both solids content and percentage of activated monomers led to an observed increase in complexity of cluster arrangement and tortuosity of pore structure, both reflected in the values of evaluated fractal properties. In order to allow comparison of generated cluster structures with trends observed for experimental samples, gas sorption was modelled here using a lattice gas in a mean field approximation. The observations for model pores with varying dimensions agree with the background theory and the trends observed for the cluster structures were in line with those obtained experimentally. This helps to close the loop from growth processes to textural properties, providing the possibility to tailor materials for specific application.Resorcinol-formaldehyde (RF) gels are a fairly new addition to the variety of porous materials used by current industry. However, a better understanding of their formation processes is crucial for efficient structure tailoring, leading to high-performance materials for a range of applications. The usual RF gel manufacture process involves gelation of an RF sol at elevated temperatures, followed by exchanging water within the structure for another liquid, in order to limit shrinkage during the final drying step. Yet, despite significant research efforts, the RF growth processes are still not fully understood and there is no accepted model describing these processes. Therefore, this study combines experimental and simulation approaches to better understand the gel growth process, and how the resulting structure depends on the growth conditions. The experimentally investigated areas include the influence of sodium carbonate catalyst concentration, processing temperature, solvent exchange and drying methods, as well as the presence of different anions within the reaction solution. Discussion on optimal processing parametersis included, in order to preserve the majority of the porous structure of RF xerogel materials, taking process economics into account, and the diversity of textural properties for obtained materials is examined. In order to model the growth processes in RF gels, and investigate how they impact the structural properties of final materials, a two-dimensional lattice-based computational model, using kinetic Monte Carlo, was developed in this work. The presented model is developed to capture growth from monomeric species present in the initial stages of the gelation composition. Experimentally, gel growth is primarily controlled through catalyst concentration, which determines the density of species that are activated for rapid growth, and solids concentration; the model captures both of these dependencies.;Generated cluster structures were analysed for textural properties, such as accessible porosity and accessible surface area, as well as fractal properties, in the form of the correlation dimension and the Hurst exponent. Increasing both solids content and percentage of activated monomers led to an observed increase in complexity of cluster arrangement and tortuosity of pore structure, both reflected in the values of evaluated fractal properties. In order to allow comparison of generated cluster structures with trends observed for experimental samples, gas sorption was modelled here using a lattice gas in a mean field approximation. The observations for model pores with varying dimensions agree with the background theory and the trends observed for the cluster structures were in line with those obtained experimentally. This helps to close the loop from growth processes to textural properties, providing the possibility to tailor materials for specific application

Modelling organic gel growth in three-dimensions : textural and fractal properties of resorcinol-formaldehyde gels

Tailoring the properties of porous organic materials, such as resorcinol–formaldehyde gels, for use in various applications has been a central focus for many studies in recent years. In order to achieve effective optimisation for each application, this work aims to assess the impact of the various synthesis parameters on the final textural properties of the gel. Here, the formation of porous organic gels is modelled using a three-dimensional lattice-based Monte Carlo simulation. We model growth from monomer species into the interconnected primary clusters of a gel, and account for varying catalyst concentration and solids content, two parameters proven to control gel properties in experimental work. In addition to analysing the textural properties of the simulated materials, we also explore their fractal properties through correlation dimension and Hurst exponent calculations. The correlation dimension shows that while fractal properties are not typically observed in scattering experiments, they are possible to achieve with sufficiently low solids content and catalyst concentration. Furthermore, fractal properties are also apparent from the analysis of the diffusion path of guest species through the gel’s porous network. This model, therefore, provides insight into how porous organic gels can be manufactured with their textural and fractal properties computationally tailored according to the intended application

Investigating the role of the catalyst within resorcinol-formaldehyde gel synthesis

Resorcinol–formaldehyde (RF) gels are porous materials synthesized via a sol–gel reaction and subsequently dried, producing structures with high surface areas and low densities—properties that are highly attractive for use in various applications. The RF gel reaction takes place in the presence of a catalyst, either acidic or basic in nature, the concentration of which significantly impacts final gel properties. The full extent of the catalyst’s role, however, has been subject to debate, with the general consensus within the field being that it is simply a pH-adjuster. The work presented here explores this theory, in addition to other theories postulated in the literature, through the synthesis and analysis of RF gels catalysed by mixtures of relevant compounds with varying concentrations. The relationship between catalyst concentration and initial solution pH is decoupled, and the individual roles of both the cation and the anion within the catalyst are investigated. The results presented here point towards the significance of the metal cation within the RF gel reaction, with similar structural properties observed for gels synthesized at constant Na+ concentrations, regardless of the initial solution pH. Furthermore, through the use of alternative cations and anions within catalyst compounds, the potential effects of ions on the stabilization of macromolecules in solution are explored, the results of which suggest a ‘Hofmeister-like’ series could be applicable within the catalysis of RF gel reactions

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 1/2 for unconstrained diffusion and reducing to 1/3; 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

The impact of deuterium oxide on the properties of resorcinol-formaldehyde gels

Resorcinol-formaldehyde gels offer a range of properties that can be exploited in a variety of applications, but better understanding of gel formation mechanisms is needed to enable rational control and optimisation of the physico-chemical characteristics of these materials. Our previous studies have focussed on investigating the formation pathways of these gels, using nuclear magnetic resonance and dynamic light-scattering techniques, as well as evaluating their final physical and chemical properties, via sorption and spectroscopic methods. Nuclear magnetic resonance has been used over the years to probe the chemical species formed during resorcinol-formaldehyde gel polymerisation, but the technique typically involves the prior addition of deuterium oxide to provide a deuterium lock for NMR measurements. However, the effect of deuterium oxide to resorcinol-formaldehyde systems is currently unknown, although the substitution of water by deuterium oxide has been previously reported to alter the chemical and physical properties of reacting systems. In this work we examine the effect of adding deuterium oxide to resorcinol-formaldehyde sol-gel synthesis at different dilution levels and the impact that this addition has on the final characteristics of the synthesised gels, in order to assess the validity of using NMR with a deuterium lock for the investigation of polymerisation mechanism in resorcinol-formaldehyde sol-gel processes

Process activities to develop a Digital Twin MMIC GC1 : introduction and activities

The Medicines-Manufacturing-Innovation Centre (MMIC) is a joint industry-governmentacademic venture to create state of the art, pharmaceutical manufacturing facilities to enable new process technologies to be developed and deployed for commercial end use. The founding consortium comprises CPI, University of Strathclyde, Astra Zeneca and GlaxoSmithKline. Companies such as Pfizer, Gericke, PEL, and Perceptive have joined as the program expands and grows. In addition to the underpinning infrastructure, the initial investment is focused upon two key processing technologies – Continuous Direct Compression and Just in time automated pharmacy. Also known as MMIC grand challenge 1 and 2. University of Strathclyde is leading the technical delivery of grand challenge 1 - development of a state of the art digital twin of continuous direct compression. Developing a digital twin comprises the understanding of the various unit operations in isolation as well as operation in the range of configurations to obtain a complete picture of the system. In the current phase, the bulk materials transfer, feeding and blending units can be operated in a range of modes as well as integrated. In the next phase the current system will be integrated with additional compression technologies in the new MMIC facility

Medicines Manufacturing Innovation Centre (MMIC) : the use of a Digital Twin

Current State of Pharmaceutical Industry • Pharma R&D costs significantly increasing. • Increasing globalised competition from generic pharma manufacturers. • High solvent waste: reactions + separations. • Technological innovation required to maintain profitability & sustainability

Advancing computational analysis of porous materials – modelling three-dimensional gas adsorption in organic gels

Assessing the efficacy of specific porous materials for use in various applications has been a central focus for many experimental studies over the years, with a view to altering the material properties according to the desired characteristics. The application potential for one such class of nanoporous materials - organic resorcinol-formaldehyde (RF) gels - is of particular interest, due to their attractive and adjustable properties. In this work, we simulate adsorption analysis using lattice-based mean field theory, both in individual pores and within three-dimensional porous materials generated from a kinetic Monte Carlo cluster aggregation model. We investigate the impacts of varying pore size and geometry on the adsorptive behavior, with results agreeing with those previously postulated in the literature. The adsorption analysis is carried out for porous materials simulated with varying catalyst concentrations and solids contents, allowing their structural properties to be assessed from resulting isotherms and the adsorption and desorption processes visualized using density color maps. Isotherm analysis indicated that both low catalyst concentrations and low solids contents resulted in structures with open transport pores that were larger in width, while high catalyst concentrations and solids contents resulted in structures with bottleneck pores that were narrower. We present results from both the simulated isotherms and pore size analysis distributions, in addition to results from RF gels synthesized in the lab and analyzed experimentally, with significant similarities observed between the two. Not only do the results of this comparison validate the kinetic Monte Carlo model's ability to successfully capture the formation of RF gels under varying synthesis parameters, but they also show significant promise for the tailoring of material properties in an efficient and computationally inexpensive manner - something which would be pivotal in realizing their full application potential, and could be applied to other porous materials whose formation mechanism operates under similar principles

Electrically conductive composites based on an elastomeric matrix filled with expanded graphite as a potential oil sensing material

The preparation and properties of electrically conductive polymeric composites based on an elastomer matrix (styrene-isoprene styrene block copolymer) filled with expanded graphite are reported in this paper. The developed materials were tested as oil sensors in various modes. The operation of this sensor is based on changes in the electrical resistance R of the composites when exposed to oil. This phenomenon involves both simple geometrical changes and changes in inherent material characteristics such as the specific electrical conductivity (resistivity). An original method for the improvement of the sensors' response rate based on the application of stretched sensing films was developed. Slightly stretched films (by 4% of the original length) showed a response that was 12.5 times faster with respect to oil absorption than an un-stretched film. The specific electrical conductivity of a material strongly depends on the extent to which it is stretched. For a composite filled with 10 wt.% of the filler, it was found that the electrical conductivity remained constant up to 11% of the sample extension before sharply decreasing. It was also found that an increase in the filler content reduced the response rate of the sensors.Scopu