Plasmonic complex fluids of nematiclike and helicoidal self-assemblies of gold nanorods with a negative order parameter

TL;DR

This paper reports on a novel soft matter system where gold nanorods self-assemble with micelles to form complex fluids exhibiting negative orientational order, tunable by additives and mechanical stress, with optical properties matching theoretical models.

Contribution

It introduces a new plasmonic complex fluid system with negative order parameter and demonstrates control over nanorod alignment and structure.

Findings

Nanorods align perpendicular to micelle normals due to surface anchoring.

Helicoidal nanorod structures are achieved with chiral additives.

Optical properties agree with simple anisotropic surface interaction models.

Abstract

We describe a soft matter system of self-organized oblate micelles and plasmonic gold nanorods that exhibit a negative orientational order parameter. Because of anisotropic surface anchoring interactions, colloidal gold nanorods tend to align perpendicular to the director describing the average orientation of normals to the discoidal micelles. Helicoidal structures of highly concentrated nanorods with a negative order parameter are realized by adding a chiral additive and are further controlled by means of confinement and mechanical stress. Polarization-sensitive absorption, scattering, and two-photon luminescence are used to characterize orientations and spatial distributions of nanorods. Self-alignment and effective-medium optical properties of these hybrid inorganic-organic complex fluids match predictions of a simple model based on anisotropic surface anchoring interactions of nanorods with the structured host medium.