# In Situ Coherent X‑Ray Scattering Investigation of Macropore Formation in Porous Silica

## TL;DR

Scientists used X-ray techniques to study how macropores form in silica materials during gelation and phase separation.

## Contribution

The study reveals how gelation and phase separation interact to control pore size in hierarchically porous silica.

## Key findings

- Silica-rich domains initially form as ramified clusters and evolve into compact structures during gelation.
- Arrest of phase separation occurs when the gel network forms, limiting further domain growth.
- Higher PEO content leads to earlier gelation and smaller macropores in the final material.

## Abstract

Hierarchically porous silica was prepared via a sol–gel
route accompanied by phase separation, using low-molecular-weight
poly­(ethylene oxide) (PEO) as a phase separation inducer. The interplay
between gelation and spinodal decomposition was investigated in situ
through the combined use of ultra-small-angle X-ray scattering (USAXS)
and X-ray photon correlation spectroscopy (XPCS), enabling simultaneous
characterization of structural and dynamic evolution. The silica-rich
domains are initially formed by ramified cluster aggregates, which
progressively grow and reorganize into more compact structures as
gelation proceeds. Arrest of the transient phase-separated state occurs
when the gel network structure becomes established, dominated by superdiffusive
dynamics, and constrains further growth of the separated domains.
Increasing PEO content induces earlier gelation and earlier arrest
of the phase-separated transient state, leading to thinner silica
skeletons and smaller macropores in the final material. The results
establish how the initial composition modulates the sol–gel
transition and the arrest of separated domains, which control the
pore size. The insights obtained in this work contribute to a deeper
understanding of how gelation and phase separation govern the development
of hierarchical porosity in silica materials, which is critical for
designing materials with tailored structural and functional properties.