# Tailormade PMMA Spheres: Synthesis and Growth Mechanism

## TL;DR

This paper describes a new method to synthesize PMMA spheres with controlled sizes and a two-step growth mechanism.

## Contribution

The study introduces an improved synthesis method for PMMA spheres with tunable diameters and reveals a two-step growth mechanism.

## Key findings

- PMMA spheres with diameters from 170 to 800 nm can be synthesized by adjusting temperature and ionic strength.
- A two-step growth process occurs below ∼400 K, with initial particle formation followed by coalescence.
- At higher temperatures, the two growth phases overlap into a single process.

## Abstract

Inverse opal structures
are of interest for various applications,
as they exhibit high surface areas in conjunction with unique structure-specific
properties such as the possibility to create photonic band gaps, e.g.,
for photocatalytic applications. An established synthetic pathway
to prepare these nanostructures is to infiltrate the voids of a template
comprised of close-packed spheres with a metal oxide and to remove
the template subsequently by pyrolysis. To this end, polymer spheres
are typically used which are produced by a water-based emulsion polymerization
process. In this work, we present an improved and extended approach
of that kind in case of PMMA spheresfeaturing narrow size
distributions and mean diameters that can be varied over a large range
between 170 up to 800 nm by properly adjusting the synthesis temperature
and the ionic-strength of the water phase. By using reflux conditions,
advanced experimental techniques requiring protective gas atmospheres
are dispensable and comparatively short synthesis times can be realized.
Time-resolved experiments reveal a two-step growth process occurring
at temperatures below ∼400 K. It consists of a first phase,
during which initial particles are formed, followed by a time-delayed
second phase, where their diameter increases by roughly a factor of
2, most likely due to coalescence processes. At higher temperatures,
both processes increasingly overlap so that only a single growth phase
is observed.