# Molding Process Retaining Gold Nanoparticle Assembly Structures during Transfer to a Polycarbonate Surface

## TL;DR

This paper shows how gold nanoparticle structures can be preserved on a polycarbonate surface during molding, enabling plasmonic devices.

## Contribution

A molding process that retains gold nanoparticle assembly structures on polycarbonate surfaces is demonstrated.

## Key findings

- Gold nanoparticle line assemblies on polycarbonate retain their order during molding with an orientational order parameter of ~0.98.
- The assemblies show plasmonic coupling and dichroic properties with dichroic ratios of 0.28 and 0.52.
- The structures withstand injection molding, detachment, and boiling ethanol extraction.

## Abstract

The immobilization of gold nanoparticle (AuNP) linear surface assemblies on polycarbonate (PC) melt surface via molding is investigated. The order of the particle assemblies is preserved during the molding process. The assemblies on PC exhibit plasmonic coupling features and dichroic properties. The structure of the assemblies is quantified based on Scanning Electron Microscopy (SEM) and image analysis data using an orientational order parameter. The transfer process from mold to melt shows high structural fidelity. The order parameter of around 0.98 reflects the orientation of the lines and remains unaffected, independent of the injection direction of the melt relative to the particle lines. This is discussed in the frame of fountain flow during injection molding. The particles were permanently fixed and withstood the injection molding process, detachment of the substrate, and extraction in boiling ethanol. The plasmonic particles coupled strongly within the dense nanoparticle lines to produce anisotropic optical properties, as quantified by dichroic ratios of 0.28 and 0.52 using ultraviolet–visible–near-infrared (UV–Vis–NIR) spectroscopy. AuNP line assemblies on a polymer surface may be a basis for plasmonic devices like surface-enhanced Raman scattering (SERS) sensors or a precursor for nanowires. Their embedding via injection molding constitutes an important link between particle-self-assembly approaches for optically functional surfaces and polymer processing techniques.