# High Resolution Imaging of Nonequilibrium Colloidal Self-Assembly via Photofixation

## TL;DR

This paper introduces a new method called FRAME to study and preserve dynamic colloidal nanoparticle structures for detailed imaging and analysis.

## Contribution

The FRAME method enables high-resolution imaging of nonequilibrium colloidal assemblies without altering their structure.

## Key findings

- FRAME uses UV photopolymerization and advanced imaging to fix and analyze out-of-equilibrium colloidal structures.
- The method was validated on Optical Matter structures with nanoparticles ranging from 200 nm to 1 μm.
- Fixation does not alter the structural properties of the assemblies, ensuring accurate analysis.

## Abstract

The self-organization
of colloidal nanoparticles into
complex structures,
both in equilibrium and out-of-equilibrium, is a growing area in colloidal
science with potential for creating functional materials. While equilibrium
assemblies form stable and periodic structures, out-of-equilibrium
(or active) assemblies exhibit dynamic, reconfigurable behavior under
external stimuli. Therefore, understanding the structure–function
relationships in these assemblies remains challenging due to their
transient nature and limitations of current characterization methods.
In this work, we present a methodology termed Fixation and Resolving
of Colloidal Active Matter Ensembles (FRAME). FRAME combines UV photopolymerization
to fix nonequilibrium colloidal assemblies with high-resolution imaging
techniques, including 3D confocal microscopy, SEM and 3D STED super-resolution
imaging, for subsequent structural characterization. We applied this
method to Optical Matter (OM) structures formed within an optical
trap at the glass/water interface. Using FRAME, we conducted a detailed
analysis of OM structures composed of colloidal nanoparticles ranging
from 200 nm to 1 μm. We demonstrate the robustness of this method
by validating that the fixation process does not alter structural
properties, allowing for accurate structural analysis. FRAME offers
a distinct approach for investigating nonequilibrium colloidal assemblies,
enabling the way for their rational design and application across
a broad range of colloidal systems.