Thesis

Monitoring the gelation mechanism of resorcinal-formaldehyde xerogels

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Awarding institution
  • University of Strathclyde
Date of award
  • 2014
Thesis identifier
  • T13975
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Abstract
  • Resorcinol-Formaldehyde (RF) xerogels are a type of porous material used in many applications, such as gas storage. These applications often require fine control of the material's porosity, and while it is known that the porosity of a xerogel can be changed through altering synthesis variables, it is not clear why these changes have such an impact. To understand this effect, the gelation process was studied using dynamic light scattering (DLS), with the xerogel products undergoing low temperature nitrogen adsorption measurements to determine textural properties. RF gels are composed of cross-linked clusters and DLS was used to study changes in how these clusters grow. It was found that cluster growth was a thermodynamically controlled process, and for a given catalyst, how the cluster size grows with time was independent of the catalyst concentration. However, the catalyst did kinetically control the number concentration of clusters initially formed, and in turn, the size to which they, therefore, had to grow to reach a critical volume fraction to form the gel, such that higher catalyst concentrations led to smaller clusters making up the gel. This resulted in smaller intercluster voids, hence, smaller pores. The catalysts used also demonstrated a range of different abilities to stabilise the colloidal suspension of clusters. This also affected cluster size, with less stabilising catalysts resulting in larger clusters. This knowledge led to the ability to further tailor the porosity by introducing a secondary catalyst, in various forms, into a separate gelling mixture. The different catalysts, with their varied abilities to stabilise the growing clusters, and the range of concentrations used, resulted in a variety of cluster sizes within the final gel, which changed the porosity of the xerogel products formed.
Resource Type
DOI
Date Created
  • 2014
Former identifier
  • 1218768

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