Structural models of dense gels

Abstract

Abstract. The structural models of gels typically reported concentrate either on the "solid space" or the "pore space" of the system. The models described in this paper present a connection between grain and pore spaces, applicable to dense gels with uniform particulate microstructure. The gel structure is depicted as a hierarchy at several levels by means of models built up using the Monte-Carlo technique, on the basis of random close packing (RCP) premises. The pore volume distributions are calculated from the largest sphere radius inscribed within the interstices. These distributions are compared to the pore volume distributions of various RCP classic models and to the pore volume distributions of a series of xerogels measured by means of the Brunauer-Emmett-Teller method. Data on the pore volumes associated with different hierarchical levels (e.g., micro-, meso-, or macropores), the local density of the i-th aggregation level and packing of the successive levels are obtained.

The cluster model: A hierarchically-ordered assemblage of random-packing spheres for modelling microstructure of porous materials

“…The starting point for this algorithm is the previous structural model for gels proposed by Rodríguez-Ortega and Esquivias [26,34]. These authors developed an algorithm for randomly-packed spheres and they characterise systems by geometrical considerations.…”

Structure of bioactive mixed polymer/colloid aerogels

“…Applying RCP structural models the existence of several typical sizes is manifested, whereas the USAXS (ultra small X-ray scattering) tests [15] shows a hierarchy-ordered structure. In this paper this structural approach, thoroughly described in former papers [2,16,17], has been applied.…”

Structure of Hybrid Colloid−Polymer Xerogels

“…The goal of this paper is to describe the gel structure, as a prior step to establishing a relationship between texture and mechanical behavior. The xerogel structure has been depicted as a hierarchy of several levels by means of models built up using the Monte Carlo calculations, on the basis of random close packing (RCP) premises. − Here we expect to find two structures sharing the same space but that can be studied separately, under these hypotheses.…”

“…C depends on the definition of the closeness of the contact (distance between the centers of two particles/particle diameter, L / d ) and is almost linearly related by N CM ≈ 12.7 C , presenting a maximum at N CM ≈ 8. Here we considered it interesting to obtain systematic data on the pore size distribution Ψ( K ). , In this respect, a network created from randomly distributed nucleation spots harmonizes better with the intrinsic nature of the gelling kinetics and gel consolidation. Thus, the models are not purely geometric but were submitted to a series of different processes of relaxation and “hollowing out”.…”

“…We showed, in a preceding paper, that the most appropriate model can be selected from our catalog with the help of an estimate of the K value at which the model pore volume distribution must have its maximum, K max . This is calculated from the position of the maximum of the pore distribution of the i th level, r max i , and that of the tail of the preceding level, r t i -1 , by the expression This value is only a standard, bearing in mind other plausible hypotheses would give a deviation no higher than 10%.…”