# Light-Induced Structural Evolutions in Electrostatic Nanoassemblies

## TL;DR

This paper shows how light can control the self-assembly of nanostructures, enabling dynamic and tunable materials.

## Contribution

The study introduces light-induced electrostatic self-assembly with real-time monitoring using SANS.

## Key findings

- Light-induced isomerization of azobenzene dyes controls self-assembly kinetics and morphology.
- Two assembly pathways (A and B) yield different morphologies and stability based on irradiation timing.
- Structural transitions from spherical to ellipsoidal shapes are driven by electrostatic and dipole interactions.

## Abstract

Studying nanoscale self-assembly in real time using external stimuli unlocks new opportunities for dynamic and adaptive materials. While electrostatic self-assembly is well-established, real-time monitoring of its structural evolution under light irradiation remains largely unexploited. In this study, we employ light-responsive azobenzene dyes (Acid Yellow 38, AY38) and pH-sensitive polyamidoamine (PAMAM) dendrimers to investigate the kinetics of electrostatic self-assembly under UV irradiation. Using a custom in situ small-angle neutron scattering (SANS) setup, we track the real-time morphological transformations of self-assembled structures with sub-minute resolution. We introduce two distinct pathways: method A (pre-irradiated cis-AY38 for controlled, slow kinetics) and method B (direct UV-induced self-assembly, fast kinetics). The results reveal that trans-cis isomerization kinetics dictate the rate of self-assembly, influencing aggregate stability, ζ-potential evolution, and final morphology. Structural analysis using dynamic and static light scattering (DLS and SLS) and SANS elucidates a transition from spherical to ellipsoidal morphologies governed by electrostatic and dipole-dipole interactions. These findings establish photoisomerization-driven self-assembly as a robust mechanism for tunable nanoscale architectures, paving the way for adaptive photonic materials, targeted drug delivery, and reconfigurable nanostructures.